MLIP and Its Potential Influence on Key Oncogenic Pathways

Muscle-enriched A-type lamin-interacting protein (MLIP) is an emerging protein involved in cellular homeostasis and stress adaptation. Eukaryotic cells regulate various cellular processes, including metabolism, DNA repair, and cell cycle progression, to maintain cellular homeostasis. Disruptions in this homeostasis can lead to diseases such as cancer, characterized by uncontrolled cell growth and division. This review aims to explore for the first time the unique role MLIP may play in cancer development and progression, given its interactions with the PI3K/Akt/mTOR pathway, p53, MAPK9, and FOXO transcription factors, all critical regulators of cellular homeostasis and tumor suppression. We discuss the current understanding of MLIP’s involvement in pro-survival pathways and its potential implications in cancer cells’ metabolic remodeling and dysregulated homeostasis. Additionally, we examine the potential of MLIP as a novel therapeutic target for cancer treatment. This review aims to shed light on MLIP’s potential impact on cancer biology and contribute to developing innovative therapeutic strategies.


Introduction
Eukaryotic cells maintain cellular homeostasis through an extensive array of sensory mechanisms to respond and adapt to both intrinsic and extrinsic stimuli and insults.This involves the regulation of various cellular processes, including metabolism, DNA repair, and cell cycle progression.Disruptions to cellular homeostasis can lead to the development of various diseases, including cancer.Cancer is a devasting disease with metabolic remodeling and dysregulated homeostasis as distinctive features [1] and is characterized by uncontrolled cell growth and division, leading to the formation of tumors [2].This process is the result of a disruption in the delicate balance between cell proliferation and cell death [3], which is normally maintained by cellular homeostasis.Several signaling molecules and pathways have been identified as pro-oncogenic and have therefore been targeted for the therapeutic treatment of cancer [4].
The integrated actions of the tumor suppressors p53 (p53), FOXO, and the PI3K/Akt/mTOR pathway enable cells to respond to a wide range of stresses, including oxidative stress, nutrient deprivation, and DNA damage.This integrated stress response is crucial for maintaining cellular and organismal homeostasis.In cancer cells, however, mutations or changes in the genes encoding proteins in this pathway can cause hyperactivation, resulting in uncontrolled cell growth and resistance to apoptosis (programmed cell death).For example, the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt)/mammalian target of rapamycin (mTOR) pathway is tightly regulated in normal cells, ensuring a balance between cell growth and death.However, p53 and forkhead box O family (FOXO), downstream of Cells 2024, 13, 1109 2 of 16 the PI3K/Akt/mTOR pathway, respectively, are critical integrators of genomic and metabolic stresses [5][6][7][8].Both p53 and FOXO are stress-activated transcription factors that promote an adaptive pro-survival response to insult [9][10][11].Specifically, p53 stimulates DNA repair in response to DNA damage [12,13] and FOXO regulates metabolic remodeling to maintain metabolic homeostasis [14][15][16].
Cancer metabolism modifies cellular metabolic pathways to facilitate rapid cell growth and proliferation [17][18][19].Cancer cells undergo metabolic reprogramming to meet the high energy and biosynthetic demands associated with their fast growth.This reprogramming promotes glycolysis at the expense of oxidative phosphorylation, a phenomenon known as the "Warburg effect", which occurs even in the presence of oxygen.The "Warburg effect" is the preference of cancer cells to utilize aerobic glycolysis instead of oxidative phosphorylation for energy generation [20,21].Tumor cells derive advantages from this alteration in metabolism.Initially, glycolysis generates energy at a quicker rate compared to oxidative phosphorylation, although producing a lower amount of ATP.Additionally, glycolysis generates intermediary compounds that are crucial for the synthesis of nucleotides, amino acids, and lipids, all of which play vital roles in the growth and multiplication of cells.Furthermore, cancer cells reduce the production of reactive oxygen species (ROS) and mitigate oxidative stress and apoptosis by minimizing mitochondrial respiration.P53, the PI3K/Akt/mTOR pathway and the FOXO transcription factor have all been implicated in the metabolic remodeling that cancer cells undergo during tumorigenesis [20,[22][23][24][25].
Muscle enriched A-type lamin-interacting protein (MLIP) is a novel protein of unknown structure and function that is required for the proper cardiac and skeletal muscle adaptation to stress [26][27][28][29][30][31].MLIP is a crucial mediator of cardiac adaptation through its interaction with the Akt/mTOR pro-survival pathway [28], FOXO1 [31] and p53 [28].A detailed comparative pathway analysis based on global gene expression differences between normal and MLIP-deficient hearts has now revealed MLIP as a modulator of both p53 and FOXO activity.Given MLIP's interactions with the PI3K/Akt pathway, p53, and FOXO [28,32], this review explores the roles MLIP may play in tumor formation and progression and the potential of MLIP as a new therapeutic target.The focus of this review is to explore the relationship of MLIP with well characterized factors that are associated with the development and progression of cancer.

MLIP Discovery and Cellular Role
The discovery of muscle-enriched A-type lamin-interacting protein (MLIP) [27] marks a significant advancement in understanding the molecular intricacies associated with laminopathies-degenerative disorders tied to mutations in the LMNA gene.This discovery sheds light on MLIP's evolution, as it is uniquely found in amniotes [27], suggesting its emergence as an evolutionary novelty in these organisms.MLIP is characterized by alternatively spliced variants [27,29], showing a broad expression spectrum with a predominance in muscular tissues.Its interaction with lamin A/C and co-localization with promyelocytic leukemia (PML) bodies [27] suggest a vital role in cellular organization and differentiation, hinting at its contribution to the mesenchymal phenotypes observed in laminopathies.
Parallel to the original discovery of MLIP, the identification of cardiac Isl1-interacting protein (CIP, an alias of MLIP) [33] provided insights into cardiac hypertrophy's regulatory mechanisms [34], underscoring its repressive role in cardiomyocyte hypertrophy and downregulation in hypertrophic conditions.CIP's interaction with Isl1, essential for cardiac progenitor specification [34], emphasizes its regulatory capacity in cardiac development and hypertrophy.Further studies elucidated MLIP's essential roles in cardiac and skeletal muscle function.For instance, MLIP deletion or overexpression significantly impacted the Akt/mTOR pathways [28], highlighting its potential as a cardiac stress sensor.This insight and genome-wide association studies linking MLIP to the cardiac stress response [28] underscores its therapeutic potential in cardiac diseases.
The exploration into MLIP's function revealed its interaction with chromatin [26], suggesting a role in regulating muscle-specific gene networks and highlighting its im-Cells 2024, 13, 1109 3 of 16 portance in muscle differentiation and maintenance.This chromatin association and its ability to influence myoblast differentiation [26] positions MLIP as a critical factor in muscle physiology [30].Moreover, studies revealed MLIP's potential link to cancer through its involvement in gene networks related to cellular stress responses, including those mediated by p53 [28] and FOXO [31].Such connections suggest a broader role for MLIP in cellular homeostasis and disease, including potential implications in cancer biology.

MLIP Expression in Cancer
Limited research has focused on elucidating the role of MLIP in the initiation and/or progression of cancer.Our investigation identified two primary types of cancers where MLIP's role was emphasized: breast cancer and esophageal cancer (Table 1).

Cancer Status Reference
Breast cancer 1 out of 6 genes associated with breast cancer risk and recurrence-free survival [35] Triple-negative breast cancer Upregulated in and associated with patient survival in triple-negative breast cancer [36] Esophageal cancer One of seven risk RNAs for esophageal cancer [37] Breast cancer and esophageal cancer represent significant global health challenges, with the former being one of the most prevalent cancers among women and the latter noted for its particularly low survival rates [38,39].The genetic underpinnings of these cancers are complex, and though substantial progress has been made in identifying key genetic risk factors, a significant proportion of the genetic risk remains unexplained.Recent research has begun to shed light on this gap, with a particular focus on the role of copy number variants (CNVs) and differentially expressed genes.One gene that has emerged as a potential key player in both breast and esophageal cancer is the MLIP gene.

Expression of MLIP in Different Types of Cancer
Breast cancer stands as one of the prevalent malignancies affecting women, with around one million new cases and over 400,000 reported deaths annually worldwide.In the year 2023, an estimated 297,790 women and 2800 men were projected to be diagnosed with breast cancer [40].While single nucleotide polymorphisms and mutations contribute to approximately 49% of the genetic risk associated with breast cancer [41,42], Kumaran and colleagues (2017) sought to uncover the remaining 51% by identifying germline copy number variants (CNVs) linked to breast cancer [39].Whole genome CNV genotyping was performed on 422 cases and 348 controls.Two hundred CNVs were identified to be associated with breast cancer of which 21 CNV regions overlapped with 22 genes.MLIP was identified as one of six genes associated with the breast cancer risk and recurrence-free survival [39].Specifically, Kumaran and colleagues reported that a loss in MLIP CNVs was associated with significant reduction in the breast cancer risk and recurrence-free survival, with a reported hazard ratio of 0.62 [0.4-0.94][39].
Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that is defined by the absence of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 expression.These receptors are commonly used as targets for breast cancer treatment, and the absence of these receptors in TNBC makes it more difficult to treat.Zhang and colleagues performed RNA-seq on 30 TNBC patient tumors, 15 of which had lymph node metastasis while the other 15 showed no lymph node metastasis [32].Differential gene expression analysis was performed in order to determine the key genes involved in the progression and oncogenesis of TNBC [32].The analysis revealed 2953 genes with differential expression in breast tumors compared to normal control tissues and 975 genes with differential expression between 15 patients with lymph node metastasis and 15 patients without.A subset of 117 genes exhibited differential expression in both sets among those with and without lymph node metastasis in triple-negative breast cancer (TNBC), implying their involvement in TNBC oncogenesis and progression.Among the 117 genes of interest, MLIP was found to be upregulated in TNBC and exhibited a negative association with the cytotoxicity of CD8+ T cells [32].
Esophageal cancer is one of the most common malignancies, ranking seventh in global morbidity and sixth in cancer-related mortality.The 5-year overall survival rate is only about 15-20%, although progress has been made in diagnosis and treatment [38].To further define prognostic mRNAs of esophageal cancer, functional enrichment analyses of lncRNA, mRNA, and miRNA in 81 tumors and 11 normal control tissues was performed.MLIP was identified as one of seven risk RNAs for esophageal cancer with a hazard ratio of 1.67 (1.22-2.29,p < 0.001) [38].
Finally, according to the recently found role of MLIP in cancer (Table 1), it has been suggested as a potential biomarker for triple-negative breast cancer and esophageal cancer.However, more research is needed to fully understand MLIP's role in these cancers and its potential as a therapeutic target or diagnostic tool.

Molecular Relationship of MLIP with Pro-Survival/Oncogenic Pathways and Tumor Suppressors
The intricate network of cellular signaling pathways that govern cell growth, proliferation, survival, and metabolism is often dysregulated in various cancer types, contributing to tumorigenesis and disease progression.Central to this network are the PI3K/Akt/mTOR, FOXO, AMPK, p53, and lamin A/C pathways, each playing critical roles in maintaining cellular homeostasis and responding to stress signals.Recently, MLIP has emerged as a key interactor/regulator of the PI3K/Akt/mTOR, FOXO, AMPK, p53, and lamin A/C pathways (Figure 1), influencing a variety of cellular processes and potentially playing roles in both cancer pathogenesis and cardiac disorders.
expression in both sets among those with and without lymph node metastasis in trip negative breast cancer (TNBC), implying their involvement in TNBC oncogenesis and p gression.Among the 117 genes of interest, MLIP was found to be upregulated in TN and exhibited a negative association with the cytotoxicity of CD8+ T cells [32].
Esophageal cancer is one of the most common malignancies, ranking seventh global morbidity and sixth in cancer-related mortality.The 5-year overall survival rate only about 15-20%, although progress has been made in diagnosis and treatment [38].further define prognostic mRNAs of esophageal cancer, functional enrichment analy of lncRNA, mRNA, and miRNA in 81 tumors and 11 normal control tissues was p formed.MLIP was identified as one of seven risk RNAs for esophageal cancer with a h ard ratio of 1.67 (1.22-2.29,p < 0.001) [38].
Finally, according to the recently found role of MLIP in cancer (Table 1), it has be suggested as a potential biomarker for triple-negative breast cancer and esophageal ca cer.However, more research is needed to fully understand MLIP's role in these canc and its potential as a therapeutic target or diagnostic tool.

Molecular Relationship of MLIP with Pro-Survival/Oncogenic Pathways and Tumor Suppressors
The intricate network of cellular signaling pathways that govern cell growth, pro eration, survival, and metabolism is often dysregulated in various cancer types, contr uting to tumorigenesis and disease progression.Central to this network are t PI3K/Akt/mTOR, FOXO, AMPK, p53, and lamin A/C pathways, each playing critical ro in maintaining cellular homeostasis and responding to stress signals.Recently, MLIP h emerged as a key interactor/regulator of the PI3K/Akt/mTOR, FOXO, AMPK, p53, a lamin A/C pathways (Figure 1), influencing a variety of cellular processes and potentia playing roles in both cancer pathogenesis and cardiac disorders.

MLIP: AMPK Function and Dysfunction in Cancer
The study by Cattin et al. in 2015 sheds light on the molecular mechanisms underlying the reduced glucose uptake observed in MLIP-deficient cardiac tissues [28].In MLIP-deficient hearts, adenosine monophosphate-activated protein kinase (AMPK) was reported to undergo dephosphorylation at AMPK alpha-Thr-172, a crucial step leading to the deactivation of the AMPK complex and subsequently resulting in decreased glucose uptake compared to normal cardiac tissues [28].Remarkably, this deactivation of AMPK occurred despite similar activity of liver kinase B1 (LKB1), the kinase responsible for AMPK activation [43], indicating an LKB1-independent inactivation of AMPK in MLIP-deficient hearts.
AMPK serves as a pivotal enzyme governing the cellular energy balance.Its primary function involves detecting shifts in the cellular energy status, particularly reductions in ATP, and initiating processes that generate ATP while concurrently inhibiting ATPconsuming processes.AMPK functions as a heterotrimeric complex, comprising catalytic α subunits and regulatory β and γ subunits.The γ subunit accommodates binding sites for AMP and ATP, enabling AMPK to sense alterations in the AMP/ATP ratio and selfactivate during energy depletion.AMPK activation triggers diverse downstream effects, including heightened glucose uptake, fatty acid oxidation, and mitochondrial biogenesis, along with diminished protein synthesis, lipogenesis, and gluconeogenesis.AMPK also influences autophagy, cell growth, proliferation, and inflammation [44,45].In response to stressors causing ATP depletion, such as hypoxia and glucose deprivation, AMPK activity is heightened [44,45].Additionally, stimulating AMPK in skeletal muscle enhances glucose uptake and fatty acid oxidation while reducing lipid accumulation and inflammation [46].These findings, combined with other research, collectively underscore the crucial role of AMPK in governing energy metabolism and cellular function.
The precise function of AMPK in cancer cells is complicated and relies on the specific context of AMPK activation.In certain instances, AMPK activation can serve as a tumor suppressor by restraining cell growth, curbing proliferation, and encouraging apoptosis.However, in other scenarios, AMPK activation might support the survival of tumor cells by facilitating metabolic adaptation to the unique conditions of the tumor microenvironment.Hence, targeting AMPK activation could be a problematic or promising approach for cancer treatment (Figure 2) [47].Additionally, research indicates that combining AMPK activation with other anticancer therapies like chemotherapy or radiation has the potential to augment their effectiveness [47,48].
Cells 2024, 13, x FOR PEER REVIEW 5 of 16 hearts, adenosine monophosphate-activated protein kinase (AMPK) was reported to undergo dephosphorylation at AMPK alpha-Thr-172, a crucial step leading to the deactivation of the AMPK complex and subsequently resulting in decreased glucose uptake compared to normal cardiac tissues [28].Remarkably, this deactivation of AMPK occurred despite similar activity of liver kinase B1 (LKB1), the kinase responsible for AMPK activation [43], indicating an LKB1independent inactivation of AMPK in MLIP-deficient hearts.AMPK serves as a pivotal enzyme governing the cellular energy balance.Its primary function involves detecting shifts in the cellular energy status, particularly reductions in ATP, and initiating processes that generate ATP while concurrently inhibiting ATP-consuming processes.AMPK functions as a heterotrimeric complex, comprising catalytic α subunits and regulatory β and γ subunits.The γ subunit accommodates binding sites for AMP and ATP, enabling AMPK to sense alterations in the AMP/ATP ratio and self-activate during energy depletion.AMPK activation triggers diverse downstream effects, including heightened glucose uptake, fatty acid oxidation, and mitochondrial biogenesis, along with diminished protein synthesis, lipogenesis, and gluconeogenesis.AMPK also influences autophagy, cell growth, proliferation, and inflammation [44,45].In response to stressors causing ATP depletion, such as hypoxia and glucose deprivation, AMPK activity is heightened [44,45].Additionally, stimulating AMPK in skeletal muscle enhances glucose uptake and fatty acid oxidation while reducing lipid accumulation and inflammation [46].These findings, combined with other research, collectively underscore the crucial role of AMPK in governing energy metabolism and cellular function.
The precise function of AMPK in cancer cells is complicated and relies on the specific context of AMPK activation.In certain instances, AMPK activation can serve as a tumor suppressor by restraining cell growth, curbing proliferation, and encouraging apoptosis.However, in other scenarios, AMPK activation might support the survival of tumor cells by facilitating metabolic adaptation to the unique conditions of the tumor microenvironment.Hence, targeting AMPK activation could be a problematic or promising approach for cancer treatment (Figure 2) [47].Additionally, research indicates that combining AMPK activation with other anticancer therapies like chemotherapy or radiation has the potential to augment their effectiveness [47,48].Interactions between MLIP and AMPK may hold implications for cancer biology.AMPK, recognized as a metabolic tumor suppressor, hampers cell growth and proliferation during low energy conditions, thereby impeding the uncontrolled cell growth characteristic of cancer [49].Consequently, the observed reduction in AMPK activation in the absence of MLIP might potentially elevate the risk of unregulated cell growth and proliferation, contributing to oncogenesis.Furthermore, the decline in AMPK levels in MLIPdeficient cardiac tissues led to the heightened activation of the Akt/mTOR pathway [28,50].This pathway significantly influences cell growth, proliferation, and survival, and its Interactions between MLIP and AMPK may hold implications for cancer biology.AMPK, recognized as a metabolic tumor suppressor, hampers cell growth and proliferation during low energy conditions, thereby impeding the uncontrolled cell growth characteristic of cancer [49].Consequently, the observed reduction in AMPK activation in the absence of MLIP might potentially elevate the risk of unregulated cell growth and proliferation, contributing to oncogenesis.Furthermore, the decline in AMPK levels in MLIP-deficient cardiac tissues led to the heightened activation of the Akt/mTOR pathway [28,50].This pathway significantly influences cell growth, proliferation, and survival, and its dysregulation is commonly observed in various types of cancers.These findings suggest that MLIP could potentially modulate these crucial pathways, thereby influencing cancer biology [28,49,50].However, it is crucial to acknowledge that these observations were made specifically in cardiac tissue, and it remains uncertain whether similar mechanisms would apply to other tissues or cancer cells.Additional research is required to directly investigate the involvement of MLIP in cancer biology.

MLIP and the PI3K/Akt/mTOR Pathway
The documented association between MLIP and the PI3K/AKT/mTOR signaling pathway is evident in research findings that highlight MLIP's direct impact on this pathway [28].Specifically, the absence of MLIP leads to the selective hyperactivation of the Akt/mTOR signaling pathway in cardiac cells (Figure 3) [28].Conversely, MLIP overexpression results in the inhibition of this pathway.The study demonstrates that the hyperactivation of Akt/mTOR occurs in cardiac cells when MLIP is absent [28].These results suggest that a deficiency in MLIP may potentially contribute to an accelerated aging phenomenon within cardiac cells, heightening susceptibility to tumor development.
Cells 2024, 13, x FOR PEER REVIEW 6 of 16 dysregulation is commonly observed in various types of cancers.These findings suggest that MLIP could potentially modulate these crucial pathways, thereby influencing cancer biology [28,49,50].However, it is crucial to acknowledge that these observations were made specifically in cardiac tissue, and it remains uncertain whether similar mechanisms would apply to other tissues or cancer cells.Additional research is required to directly investigate the involvement of MLIP in cancer biology.

MLIP and the PI3K/Akt/mTOR Pathway
The documented association between MLIP and the PI3K/AKT/mTOR signaling pathway is evident in research findings that highlight MLIP's direct impact on this pathway [28].Specifically, the absence of MLIP leads to the selective hyperactivation of the Akt/mTOR signaling pathway in cardiac cells (Figure 3) [28].Conversely, MLIP overexpression results in the inhibition of this pathway.The study demonstrates that the hyperactivation of Akt/mTOR occurs in cardiac cells when MLIP is absent [28].These results suggest that a deficiency in MLIP may potentially contribute to an accelerated aging phenomenon within cardiac cells, heightening susceptibility to tumor development.The regulatory link between MLIP and the PI3K/AKT/mTOR pathway is underscored by research indicating MLIP's direct influence on this critical signaling pathway [28].The absence of MLIP leads to the selective hyperactivation of the Akt/mTOR pathway in cardiac cells, as evidenced by the significant increase in pathway activity in MLIP-deficient cells.Conversely, MLIP overexpression results in the inhibition of this pathway, highlighting MLIP's role as a negative regulator [28,31].This hyperactivation of the Akt/mTOR pathway in the absence of MLIP suggests that MLIP deficiency may accelerate aging in cells and may heighten their susceptibility to tumor development, potentially implicating MLIP in cancer biology.The PI3K/Akt/mTOR pathway is crucial for regulating cellular processes such as growth, proliferation, survival, and metabolism, and its dysregulation is frequently observed in various cancers.Activation of this pathway in cancer cells can occur through multiple mechanisms, including genetic mutations, activation of upstream growth factor receptors, and loss of negative regulators.This activation promotes increased cell proliferation, survival, and resistance to cell death, contributing to tumor growth and progression (Figure 4) [51][52][53][54].Thus, MLIP deficiency could facilitate these oncogenic processes, suggesting that MLIP might be a novel target for cancer therapy.Targeting the PI3K/Akt/mTOR pathway (Table 2) has become a promising cancer treatment strategy [53,54], with several drugs in development and testing showing potential in preclinical and clinical studies.However, these therapies must balance effectiveness with minimizing toxicity, necessitating ongoing research to improve their selectivity and efficacy [51,53,54].Understanding MLIP's regulatory role may offer new insights into cancer treatment strategies, potentially leading to more effective interventions.The regulatory link between MLIP and the PI3K/AKT/mTOR pathway is underscored by research indicating MLIP's direct influence on this critical signaling pathway [28].The absence of MLIP leads to the selective hyperactivation of the Akt/mTOR pathway in cardiac cells, as evidenced by the significant increase in pathway activity in MLIP-deficient cells.Conversely, MLIP overexpression results in the inhibition of this pathway, highlighting MLIP's role as a negative regulator [28,31].This hyperactivation of the Akt/mTOR pathway in the absence of MLIP suggests that MLIP deficiency may accelerate aging in cells and may heighten their susceptibility to tumor development, potentially implicating MLIP in cancer biology.The PI3K/Akt/mTOR pathway is crucial for regulating cellular processes such as growth, proliferation, survival, and metabolism, and its dysregulation is frequently observed in various cancers.Activation of this pathway in cancer cells can occur through multiple mechanisms, including genetic mutations, activation of upstream growth factor receptors, and loss of negative regulators.This activation promotes increased cell proliferation, survival, and resistance to cell death, contributing to tumor growth and progression (Figure 4) [51][52][53][54].Thus, MLIP deficiency could facilitate these oncogenic processes, suggesting that MLIP might be a novel target for cancer therapy.Targeting the PI3K/Akt/mTOR pathway (Table 2) has become a promising cancer treatment strategy [53,54], with several drugs in development and testing showing potential in preclinical and clinical studies.However, these therapies must balance effectiveness with minimizing toxicity, necessitating ongoing research to improve their selectivity and efficacy [51,53,54].Understanding MLIP's regulatory role may offer new insights into cancer treatment strategies, potentially leading to more effective interventions.
Dysregulation of FOXO gene expression or activity has been reported to be associated with the development and progression of cancer [90].There are four members of the FOXO family in mammals: FOXO1, FOXO3, FOXO4, and FOXO6.Among these, FOXO1 and FOXO3 are the most well-studied in the context of cancer (Table 3).In normal cells, FOXO1 and FOXO3 are often activated in response to cellular stress, leading to the expression of target genes that promote cell cycle arrest, DNA repair, and apoptosis.This helps to prevent the development of cancer by eliminating cells with damaged DNA [91].However, in cancer cells, the activity of FOXO1 and FOXO3 is often dysregulated [92][93][94].In tumors, FOXO expression or activity is often suppressed to promote cell proliferation and survival, or alternatively, FOXO may be activated to promote cell migration and invasion [92][93][94].

FOXO4
Required for stem cell function in multiple tissues, including the maintenance of hematopoietic, neural, and muscle stem cell pools.

Tumor suppressor, regulation of cell cycle arrest and apoptosis
Not specified [90] FOXO1 has been found to play a role in the regulation of estrogen receptor (ER) signaling.In breast cancer, the loss of FOXO1 activity is associated with resistance to endocrine therapy, while overexpression of FOXO1 has been shown to sensitize breast cancer cells to endocrine therapy [35].Likewise, in prostate cancer, FOXO3 has been identified as a partiCIPant in the control of androgen receptor signaling [94].Reduced FOXO3 activity has been linked to resistance to androgen deprivation therapy, whereas increased FOXO3 expression has demonstrated the ability to enhance the sensitivity of prostate cancer cells to this therapy.
Although the precise mechanism through which MLIP increases FOXO-1 expression remains unknown, FOXO-1 is acknowledged for its involvement in cell cycle arrest, apoptosis, and tumor suppression, implying a potential role for MLIP in cancer pathogenesis.The activation of FOXO1 prompts the transcription of the cyclin-dependent kinase inhibitor p27 KIP1 while suppressing the transcription of cyclin D1 and D2.Both effects result in cell cycle arrest at G1 phase.The loss of one allele of FOXO may render cells susceptible to dysregulated cell cycle events, triggering tumor formation.Activation of MLIP may mitigate the impact of FOXO haploinsufficiency on tumorigenesis.

MLIP and P53
MLIP-deficient hearts were found to have increased activation of p53 [28], indicating that MLIP-deficient hearts may be experiencing genotoxic and/or metabolic stress.The p53 gene functions as a crucial tumor suppressor, actively preventing cancer development by regulating various cellular processes, including DNA repair, cell cycle arrest, apoptosis, and senescence [7,8,37,[95][96][97].In response to DNA damage, p53 is activated, enabling it to pause the cell cycle for DNA repair or initiate apoptosis to eliminate damaged cells.In cancer, the p53 gene is frequently mutated or deleted, resulting in the loss of its tumor suppressor function [12,98].Mutations in p53 represent one of the most prevalent genetic alterations in cancer, with up to 50% of all human cancers exhibiting p53 mutations [99,100].The functional loss of p53 contributes to cancer development and progression by allowing the proliferation of damaged cells, facilitating the accumulation of additional genetic changes that can lead to cancer formation.
Beyond its role in the DNA damage response, p53 also partiCIPates in the regulation of cellular metabolism [101][102][103].P53 has been demonstrated to influence the expression of genes involved in glycolysis, oxidative phosphorylation [104,105], and fatty acid metabolism [101,106].P53 loss or mutation can contribute to the metabolic rewiring commonly observed in cancer cells [107].However, the activation of p53 is triggered by other genes and is crucial for its role as a tumor suppressor [8].This implies a potential alternative function of MLIP, wherein it may promote tumor formation by inhibiting p53, a critical tumor suppressor gene.Alternatively, MLIP inhibition might impact p53 function by influencing other genes associated with p53 activation.
Based on the findings of increased activation of p53 in MLIP-deficient hearts, one can speculate that MLIP may play a role in modulating p53 function in cancer.This potential role could involve MLIP influencing p53 activation and its associated pathways, either through direct interaction or by impacting other genes involved in p53 regulation.Understanding this relationship may provide novel insights into how MLIP contributes to cancer development and progression, particularly through its interaction with the crucial tumor suppressor gene p53.

MLIP and MAPK9 (Jak2)
The global mapping of the human binary protein interactome revealed and confirmed the interaction between MLIP and MAPK9 [108].MAPK9, also known as JNK2, interacts intricately with several key signaling pathways, significantly impacting cellular processes and cancer biology [109,110].One of its crucial interactions is with the PI3K/Akt/mTOR pathway, a major regulator of cell growth, proliferation, and survival [3,111,112].MAPK9 modulates this pathway through phosphorylation events, often inhibiting PI3K/Akt activity under stress conditions and thus promoting apoptosis over cell survival [111].This interaction can form a negative feedback loop that counterbalances the pro-survival signals from PI3K/Akt/mTOR, maintaining cellular equilibrium.
In relation to the tumor suppressor p53, MAPK9 plays a pivotal role in enhancing p53 activity through phosphorylation [113,114].This phosphorylation stabilizes p53, particularly in response to cellular stress and DNA damage, leading to the activation of p53-dependent apoptotic genes [113,115].Through this mechanism, MAPK9 contributes to the elimination of cells with damaged DNA, acting as a barrier against malignant transformation.
MAPK9 also interacts with FOXO transcription factors, which are key regulators of apoptosis, cell cycle arrest, and oxidative stress resistance.MAPK9 phosphorylates FOXO proteins, promoting their nuclear translocation and subsequent activation of stress response genes [111].This regulation by MAPK9 is crucial for cellular responses to oxidative damage, helping to maintain cellular integrity and prevent uncontrolled proliferation.Overall, MAPK9 ′ s interactions with MLIP, the PI3K/Akt/mTOR pathway, p53, and FOXO transcription factors create a complex network (Figure 1) that governs cell survival, apoptosis, and stress responses.These molecular relationships underscore how MLIP may have a multifaceted role in maintaining cellular homeostasis and its possible role in cancer progression.

Conclusions and MLIP as a Potential Therapeutic Target
MLIP is an emerging factor implicated in the regulation of key signaling pathways that govern cell growth, proliferation, survival, and metabolism, which are often dysregulated in cancer.Through its interactions with the PI3K/Akt/mTOR pathway, MLIP appears to exert an inhibitory effect [28].Overexpression of MLIP leads to the downregulation of this pathway, while its loss results in the pathway's overactivation [28,31,34,116].This implies that MLIP might act as a suppressor of cell growth and proliferation, two key processes that are often hyperactivated in cancer.Therefore, therapies aimed at enhancing MLIP expression or its regulatory effect on the PI3K/Akt/mTOR pathway might be beneficial for inhibiting cancer progression.
Moreover, MLIP appears to be involved in the regulation of FOXO1 signaling [31], a pathway that plays critical roles in cell cycle control, apoptosis, and DNA repair-processes that are crucial for maintaining genomic integrity and preventing tumorigenesis.Dysregulation of FOXO1 signaling is often associated with cancer progression.Given that the deletion of MLIP leads to a downregulation of the FOXO1 pathway, and overexpression of MLIP is likely to have the opposite effect, therapeutics aimed at enhancing MLIP function or expression could potentially restore the normal function of FOXO1 signaling, thereby inhibiting cancer development and progression.
Additionally, MLIP's interactions with p53 [28], a well-known tumor suppressor gene, further underscore its potential as a therapeutic target.Given that MLIP-deficient cardiomyocytes showed an increased expression of p53, it is plausible to hypothesize that MLIP could play a role in the regulation of p53, and by extension, cell cycle control and apoptosis.
However, it is essential to remember that the exact mechanisms of MLIP in these signaling pathways are not fully understood, and further research is necessary to establish MLIP as a therapeutic target.Furthermore, it is crucial to understand the potential offtarget effects and safety profile of any MLIP-targeting therapies due to MLIP's role in noncancerous cells and processes, especially within the context of cardiac tissue where MLIP deficiency increase the susceptibility to developing heart failure [28,31] In summary, the modulation of MLIP's function or its interactions with key signaling pathways represents a promising approach for the development of novel cancer therapeutics.

Figure 1 .
Figure 1.Schematic representation of MLIP-associated stress response pathways in cellular hom stasis and disease.The central role of MLIP (muscle-enriched A-type lamin-interacting protein coordinating cellular responses to genotoxic and metabolic stress is shown, highlighting its poten implications in cancer.

Figure 1 .
Figure 1.Schematic representation of MLIP-associated stress response pathways in cellular homeostasis and disease.The central role of MLIP (muscle-enriched A-type lamin-interacting protein) in coordinating cellular responses to genotoxic and metabolic stress is shown, highlighting its potential implications in cancer.

Figure 2 .
Figure 2. Regulatory interactions between MLIP and AMPK in cancer metabolism.This schematic illustrates the bidirectional regulatory relationship between muscle-enriched A-type lamin-interacting protein (MLIP) and AMP-activated protein kinase (AMPK).MLIP is depicted as acting on the fulcrum of AMPK action as an oncogene or tumor suppressor.

Figure 2 .
Figure 2. Regulatory interactions between MLIP and AMPK in cancer metabolism.This schematic illustrates the bidirectional regulatory relationship between muscle-enriched A-type lamin-interacting protein (MLIP) and AMP-activated protein kinase (AMPK).MLIP is depicted as acting on the fulcrum of AMPK action as an oncogene or tumor suppressor.

Figure 3 .
Figure 3. Comparative schematic of MLIP signaling pathways in physiological and pathological states.A comparative overview of the intracellular signaling pathways involving muscle-enriched A-type lamin-interacting protein (MLIP) in two states: physiological (left panel) and pathological (right panel).In the physiological state, MLIP negatively regulates AKT, leading to reduced mTOR activity and an increase in AMPK activity, depicted by solid black lines.These interactions suggest a role for MLIP in maintaining the cellular energy balance and potentially inhibiting cancer cell growth.In the pathological state (right panel), the loss of MLIP leads to increased AKT-mTOR activity, potentially promoting cell growth and proliferation.The altered signaling dynamics of MLIP in the pathological state underscore its potential as a regulatory switch in cancer metabolism and a target for therapeutic intervention.Figure created with BioRender.com.Reprinted with permission from Ref. [28].Copyright 2015 Creative Commons CC-BY license.

Figure 3 .
Figure 3. Comparative schematic of MLIP signaling pathways in physiological and pathological states.A comparative overview of the intracellular signaling pathways involving muscle-enriched A-type lamin-interacting protein (MLIP) in two states: physiological (left panel) and pathological (right panel).In the physiological state, MLIP negatively regulates AKT, leading to reduced mTOR activity and an increase in AMPK activity, depicted by solid black lines.These interactions suggest a role for MLIP in maintaining the cellular energy balance and potentially inhibiting cancer cell growth.In the pathological state (right panel), the loss of MLIP leads to increased AKT-mTOR activity, potentially promoting cell growth and proliferation.The altered signaling dynamics of MLIP in the pathological state underscore its potential as a regulatory switch in cancer metabolism and a target for therapeutic intervention.Figure created with BioRender.com.Reprinted with permission from Ref. [28].Copyright 2015 Creative Commons CC-BY license.

Figure 4 .
Figure 4. Influence of MLIP on key signaling pathways and therapeutic interventions in cancer.This figure delineates the role of muscle-enriched A-type lamin-interacting protein (MLIP) in modulating critical signaling cascades involved in cancer pathophysiology.In the left panel, the MLIP interaction with the PI3K/AKT/mTOR pathway is illustrated, depicting potential points of therapeutic intervention with the listed drugs.The dashed lines represent indirect effects on downstream processes such as cell cycle arrest, DNA repair, senescence, and apoptosis, which are key cellular responses in cancer therapy.In the right panel, the absence of MLIP's regulatory influence is shown to result in enhanced cell growth and division, as well as angiogenesis, contributing to tumor progression.The drugs targeting these pathways are grouped according to their mechanism of action, highlighting the potential for MLIP to serve as a pivotal point for therapeutic targeting in cancer treatment.Figure created with BioRender.com.

Figure 4 .
Figure 4. Influence of MLIP on key signaling pathways and therapeutic interventions in cancer.This figure delineates the role of muscle-enriched A-type lamin-interacting protein (MLIP) in modulating critical signaling cascades involved in cancer pathophysiology.In the left panel, the MLIP interaction with the PI3K/AKT/mTOR pathway is illustrated, depicting potential points of therapeutic intervention with the listed drugs.The dashed lines represent indirect effects on downstream processes such as cell cycle arrest, DNA repair, senescence, and apoptosis, which are key cellular responses in cancer therapy.In the right panel, the absence of MLIP's regulatory influence is shown to result in enhanced cell growth and division, as well as angiogenesis, contributing to tumor progression.The drugs targeting these pathways are grouped according to their mechanism of action, highlighting the potential for MLIP to serve as a pivotal point for therapeutic targeting in cancer treatment.Figure created with BioRender.com.

Table 1 .
Association of MLIP with various cancer types and clinical outcomes.

Table 2 .
Overview of targeted therapies acting on the PI3K/AKT/mTOR pathway in cancer.
[86][87][88]re a subgroup of the forkhead family of transcription factors that play a critical role in regulating various cellular processes, including cell cycle control, DNA repair, apoptosis, and the oxidative stress response[86][87][88][89].Notably, the deletion of MLIP

Table 3 .
Functional roles of FOXO transcription factors in cell Biology and cancer.