Search Results (16)

Hypertension is a leading risk factor for cardiovascular disease and is associated with maladaptive cardiac remodeling, including hypertrophy and fibrosis. The roles of the receptor for advanced glycation end-products (RAGE) and the small GTPase Rap1a in angiotensin II (AngII)-induced remodeling remain unclear. This study examined how RAGE and Rap1a influence cardiac responses to AngII using wild-type (WT), RAGE knockout (RAGE KO), and Rap1a knockout (RapKO) mice. Cardiac structure and function were evaluated following AngII infusion. RapKO mice were protected from AngII-induced hypertrophy, whereas RAGE KO mice exhibited altered remodeling patterns. AngII consistently increased left ventricular wall thickness across all genotypes, indicating that structural remodeling is primarily treatment-driven. Measures of cardiac output and stroke volume also changed significantly with AngII, suggesting hemodynamic load as a key driver of functional adaptation. In contrast, diastolic functional parameters were genotype-dependent and remained stable with AngII exposure, demonstrating an intrinsic influence of RAGE and Rap1a on myocardial relaxation. These findings highlight distinct roles for RAGE and Rap1a in modulating hypertensive cardiac remodeling and may parallel human hypertensive heart disease, where increased RAGE and Rap1a expression associate with fibrosis and impaired relaxation. Targeting the crosstalk between the RAGE-AT1R axis and the cAMP-EPAC-Rap1a pathway may offer therapeutic potential to reduce adverse cardiac remodeling in hypertension. Full article

Rap1A and Rap1B are closely related small GTPases that regulate endothelial adhesion, vascular integrity, and signaling pathways via effector domain interactions, with downstream effectors controlling integrins and cadherins. Although both isoforms are essential for vascular development, recent studies using endothelial-specific knockout models have uncovered distinct, non-redundant functions. Rap1B is a key regulator of VEGFR2 signaling, promoting angiogenesis, nitric oxide production, and immune evasion in tumors while restraining proinflammatory signaling in atherosclerosis. In contrast, Rap1A unexpectedly functions as a modulator of endothelial calcium homeostasis by restricting Orai1-mediated store-operated calcium entry, thereby limiting inflammatory responses and vascular permeability. New insights into Rap1 regulation highlight the roles of context-specific guanine nucleotide exchange factors, such as RasGRP3, and non-degradative ubiquitination in effector selection. Emerging data suggest that isoform-specific interactions between the Rap1 hypervariable regions and plasma membrane lipids govern their localization to distinct nanodomains, potentially influencing downstream signaling specificity. Together, these findings redefine the roles of Rap1A and Rap1B in endothelial biology and highlight their relevance in diseases such as tumor angiogenesis, atherosclerosis, and inflammatory lung injury. We discuss the therapeutic implications of targeting Rap1 isoforms in vascular pathologies and cancer, emphasizing the need for isoform-specific strategies that preserve endothelial homeostasis. Full article

Huntingtin-interacting protein 1-related (HIP1R) shares some function similarities with HIP1, and HIP1 regulates arthritis and RA fibroblast-like synoviocytes (FLS) invasiveness. Therefore, we hypothesized that HIP1R might be involved in the regulation of FLS phenotypes and molecular processes relevant to RA. siRNA was used to knockdown HIP1R, HIP1 or control in RA FLS, followed by cell studies for invasion in Matrigel, migration, proliferation, and adhesion. RNA was sequenced and analyzed. HIP1R knockdown significantly reduced RA FLS invasiveness and migration (p < 0.05). The DEGs in siRNA HIP1R had an enrichment for GO processes “astrocyte and glial cell projection”, “small GTPase signaling”, and “PDGFR signaling”. The most significantly DEGs had decreased expression in siRNA HIP1R and included AKT1S1, GABBR2, GPR56, and TXNDC12. siRNA HIP1 RA FLS had an enrichment for the “Rap1 signaling pathway” and “Growth factor receptor binding”. The most significantly DEGs in HIP1 siRNA included FGF2, PGF, and SLC39A8. HIP1R and HIP1 DEG lists had a greater than expected number of similar genes (p = 0.0015), suggesting that, despite the major differences detected, both have partially overlapping functions in RA FLS. The most significantly DEGs in both HIP1R and HIP1 analyses are involved in cancer cell behaviors and outcomes. HIP1R is a new gene implicated in RA FLS invasiveness and migration, and regulates unique pathways and cell processes relevant to both RA as well as cancer biology. Our study provides new insight into processes implicated in FLS invasiveness, which is relevant for joint damage in RA, and identify new potential gene targets for FLS-specific treatments. Full article

The vascular endothelium, a specialized monolayer of endothelial cells (ECs), is crucial for maintaining vascular homeostasis by controlling the passage of substances and cells. In the tumor microenvironment, Vascular Endothelial Growth Factor A (VEGF-A) drives tumor angiogenesis, leading to endothelial anergy and vascular immunosuppression—a state where ECs resist cytotoxic CD8⁺ T cell infiltration, hindering immune surveillance. Immunotherapies have shown clinical promise. However, their effectiveness is significantly reduced by tumor EC anergy. Anti-angiogenic treatments aim to normalize tumor vessels and improve immune cell infiltration. Despite their potential, these therapies often cause significant systemic toxicities, necessitating new treatments. The small GTPase Rap1B emerges as a critical regulator of Vascular Endothelial Growth Factor Receptor 2 (VEGFR2) signaling in ECs. Our studies using EC-specific Rap1B knockout mice show that the absence of Rap1B impairs tumor growth, alters vessel morphology, and increases CD8⁺ T cell infiltration and activation. This indicates that Rap1B mediates VEGF-A’s immunosuppressive effects, making it a promising target for overcoming vascular immunosuppression in cancer. Rap1B shares structural and functional similarities with RAS oncogenes. We propose that targeting Rap1B could enhance therapies’ efficacy while minimizing adverse effects by reversing endothelial anergy. We briefly discuss strategies successfully developed for targeting RAS as a model for developing anti-Rap1 therapies. Full article

Four Ras guanine nucleotide-releasing proteins (RasGRP1 through 4) belong to the family of guanine nucleotide exchange factors (GEFs). RasGRPs catalyze the release of GDP from small GTPases Ras and Rap and facilitate their transition from an inactive GDP-bound to an active GTP-bound state. Thus, they regulate critical cellular responses via many downstream GTPase effectors. Similar to other RasGRPs, the catalytic module of RasGRP1 is composed of the Ras exchange motif (REM) and Cdc25 domain, and the EF hands and C1 domain contribute to its cellular localization and regulation. RasGRP1 can be activated by a diacylglycerol (DAG)-mediated membrane recruitment and protein kinase C (PKC)-mediated phosphorylation. RasGRP1 acts downstream of the T cell receptor (TCR), B cell receptors (BCR), and pre-TCR, and plays an important role in the thymocyte maturation and function of peripheral T cells, B cells, NK cells, mast cells, and neutrophils. The dysregulation of RasGRP1 is known to contribute to numerous disorders that range from autoimmune and inflammatory diseases and schizophrenia to neoplasia. Given its position at the crossroad of cell development, inflammation, and cancer, RASGRP1 has garnered interest from numerous disciplines. In this review, we outline the structure, function, and regulation of RasGRP1 and focus on the existing knowledge of the role of RasGRP1 in leukemia and other cancers. Full article

Integrin LFA1 is a cell adhesion receptor expressed exclusively in leukocytes, and plays crucial roles in lymphocyte trafficking, antigen recognition, and effector functions. Since the discovery that the adhesiveness of LFA1 can be dynamically changed upon stimulation, one challenge has been understanding how integrins are regulated by inside-out signaling coupled with macromolecular conformational changes, as well as ligand bindings that transduce signals from the extracellular domain to the cytoplasm in outside-in signaling. The small GTPase Rap1 and integrin adaptor proteins talin1 and kindlin-3 have been recognized as critical molecules for integrin activation. However, their cooperative regulation of integrin adhesiveness in lymphocytes requires further research. Recent advances in single-molecule imaging techniques have revealed dynamic molecular processes in real-time and provided insight into integrin activation in cellular environments. This review summarizes integrin regulation and discusses new findings regarding the bidirectionality of LFA1 activation and signaling processes in lymphocytes. Full article

Emerging evidence indicates that the TRPM8 channel plays an important role in prostate cancer (PCa) progression, by impairing the motility of these cancer cells. Here, we reveal a novel facet of PCa motility control via direct protein-protein interaction (PPI) of the channel with the small GTPase Rap1A. The functional interaction of the two proteins was assessed by active Rap1 pull-down assays and live-cell imaging experiments. Molecular modeling analysis allowed the identification of four putative residues involved in TRPM8-Rap1A interaction. Point mutations of these sites impaired PPI as shown by GST-pull-down, co-immunoprecipitation, and PLA experiments and revealed their key functional role in the adhesion and migration of PC3 prostate cancer cells. More precisely, TRPM8 inhibits cell migration and adhesion by trapping Rap1A in its GDP-bound inactive form, thus preventing its activation at the plasma membrane. In particular, residues E207 and Y240 in the sequence of TRPM8 and Y32 in that of Rap1A are critical for the interaction between the two proteins not only in PC3 cells but also in cervical (HeLa) and breast (MCF-7) cancer cells. This study deepens our knowledge of the mechanism through which TRPM8 would exert a protective role in cancer progression and provides new insights into the possible use of TRPM8 as a new therapeutic target in cancer treatment. Full article

Diabetics have an increased risk for heart failure due to cardiac fibroblast functional changes occurring as a result of AGE/RAGE signaling. Advanced glycation end products (AGEs) levels are higher in diabetics and stimulate elevated RAGE (receptor for AGE) signaling. AGE/RAGE signaling can alter the expression of proteins linked to extracellular matrix (ECM) remodeling and oxidative stressors. Our lab has identified a small GTPase, Rap1a, that may overlap the AGE/RAGE signaling pathway. We sought to determine the role Rap1a plays in mediating AGE/RAGE changes and to assess the impact of isolated collagen on further altering these changes. Primary cardiac fibroblasts from non-diabetic and diabetic mice with and without RAGE expression and from mice lacking Rap1a were cultured on tail collagen extracted from non-diabetic or diabetic mice, and in addition, cells were treated with Rap1a activator, EPAC. Protein analyses were performed for changes in RAGE-associated signaling proteins (RAGE, PKC-ζ, ERK1/2) and downstream RAGE signaling outcomes (α-SMA, NF-κB, SOD-2). Increased levels of endogenous AGEs within the diabetic collagen and increased Rap1a activity promoted myofibroblast transition and oxidative stress, suggesting Rap1a activity elevated the impact of AGEs in the diabetic ECM to stimulate myofibroblast transition and oxidative stress. Full article

RAS guanyl nucleotide-releasing proteins (RASGRPs) are important proteins that act as guanine nucleotide exchange factors, which activate small GTPases and function as molecular switches for intracellular signals. The RASGRP family is composed of RASGRP1–4 proteins and activates the small GTPases, RAS and RAP. Among them, RASGRP2 has different characteristics from other RASGRPs in that it targets small GTPases and its localizations are different. Many studies related to RASGRP2 have been reported in cells of the blood cell lineage. Furthermore, RASGRP2 has also been reported to be associated with Huntington’s disease, tumors, and rheumatoid arthritis. In addition, we also recently reported RASGRP2 expression in vascular endothelial cells, and clarified the involvement of xenopus Rasgrp2 in the vasculogenesis process and multiple signaling pathways of RASGRP2 in human vascular endothelial cells with stable expression of RASGRP2. Therefore, this article outlines the existing knowledge of RASGRP2 and focuses on its expression and role in vascular endothelial cells, and suggests that RASGRP2 functions as a protective factor for maintaining healthy blood vessels. Full article

Cardiovascular disease is a common diabetic complication that can arise when cardiac fibroblasts transition into myofibroblasts. Myofibroblast transition can be induced by advanced glycated end products (AGEs) present in the extracellular matrix (ECM) activating RAGE (receptor for advanced glycated end products) to elicit intracellular signaling. The levels of AGEs are higher under diabetic conditions due to the hyperglycemic conditions present in diabetics. AGE/RAGE signaling has been shown to alter protein expression and ROS production in cardiac fibroblasts, resulting in changes in cellular function, such as migration and contraction. Recently, a small GTPase, Rap1a, has been identified to overlap the AGE/RAGE signaling cascade and mediate changes in protein expression. While Rap1a has been shown to impact AGE/RAGE-induced protein expression, there are currently no data examining the impact Rap1a has on AGE/RAGE-induced cardiac fibroblast function. Therefore, we aimed to determine the impact of Rap1a on AGE/RAGE-mediated cardiac fibroblast contraction, as well as the influence isolated diabetic ECM has on facilitating these effects. In order to address this idea, genetically different cardiac fibroblasts were embedded in 3D collagen matrices consisting of collagen isolated from either non-diabetic of diabetic mice. Fibroblasts were treated with EPAC and/or exogenous AGEs, which was followed by assessment of matrix contraction, protein expression (α-SMA, SOD-1, and SOD-2), and hydrogen peroxide production. The results showed Rap1a overlaps the AGE/RAGE cascade to increase the myofibroblast population and generation of ROS production. The increase in myofibroblasts and oxidative stress appeared to contribute to increased matrix contraction, which was further exacerbated by diabetic conditions. Based off these results, we determined that Rap1a was essential in mediating the response of cardiac fibroblasts to AGEs within diabetic collagen. Full article

Cardiovascular disease, specifically heart failure, is a common complication for individuals with type 2 diabetes mellitus. Heart failure can arise with stiffening of the left ventricle, which can be caused by “active” cardiac fibroblasts (i.e., myofibroblasts) remodeling the extracellular matrix (ECM). Differentiation of fibroblasts to myofibroblasts has been demonstrated to be an outcome of AGE/RAGE signaling. Hyperglycemia causes advanced glycated end products (AGEs) to accumulate within the body, and this process is greatly accelerated under chronic diabetic conditions. AGEs can bind and activate their receptor (RAGE) to trigger multiple downstream outcomes, such as altering ECM remodeling, inflammation, and oxidative stress. Previously, our lab has identified a small GTPase, Rap1a, that possibly overlaps the AGE/RAGE signaling cascade to affect the downstream outcomes. Rap1a acts as a molecular switch connecting extracellular signals to intracellular responses. Therefore, we hypothesized that Rap1a crosses the AGE/RAGE cascade to alter the expression of AGE/RAGE associated signaling proteins in cardiac fibroblasts in type 2 diabetic mice. To delineate this cascade, we used genetically different cardiac fibroblasts from non-diabetic, diabetic, non-diabetic RAGE knockout, diabetic RAGE knockout, and Rap1a knockout mice and treated them with pharmacological modifiers (exogenous AGEs, EPAC, Rap1a siRNA, and pseudosubstrate PKC-ζ). We examined changes in expression of proteins implicated as markers for myofibroblasts (α-SMA) and inflammation/oxidative stress (NF-κB and SOD-1). In addition, oxidative stress was also assessed by measuring hydrogen peroxide concentration. Our results indicated that Rap1a connects to the AGE/RAGE cascade to promote and maintain α-SMA expression in cardiac fibroblasts. Moreover, Rap1a, in conjunction with activation of the AGE/RAGE cascade, increased NF-κB expression as well as hydrogen peroxide concentration, indicating a possible oxidative stress response. Additionally, knocking down Rap1a expression resulted in an increase in SOD-1 expression suggesting that Rap1a can affect oxidative stress markers independently of the AGE/RAGE signaling cascade. These results demonstrated that Rap1a contributes to the myofibroblast population within the heart via AGE/RAGE signaling as well as promotes possible oxidative stress. This study offers a new potential therapeutic target that could possibly reduce the risk for developing diabetic cardiovascular complications attributed to AGE/RAGE signaling. Full article

Bam32 (B cell adaptor molecule of 32 kDa) functions in the immune responses of various leukocytes. However, the role of neutrophil Bam32 in inflammation is entirely unknown. Here, we determined the role of Bam32 in chemokine CXCL2-induced neutrophil chemotaxis in three mouse models of neutrophil recruitment. By using intravital microscopy in the mouse cremaster muscle, we found that transmigrated neutrophil number, neutrophil chemotaxis velocity, and total neutrophil chemotaxis distance were increased in Bam32^−/− mice when compared with wild-type (WT) mice. In CXCL2-induced mouse peritonitis, the total emigrated neutrophils were increased in Bam32^−/− mice at 2 but not 4 h. The CXCL2-induced chemotaxis distance and migration velocity of isolated Bam32^−/− neutrophils in vitro were increased. We examined the activation of small GTPases Rac1, Rac2, and Rap1; the levels of phospho-Akt2 and total Akt2; and their crosstalk with Bam32 in neutrophils. The deficiency of Bam32 suppressed Rap1 activation without changing the activation of Rac1 and Rac2. The pharmacological inhibition of Rap1 by geranylgeranyltransferase I inhibitor (GGTI298) increased WT neutrophil chemotaxis. In addition, the deficiency of Bam32, as well as the inhibition of Rap1 activation, increased the levels of CXCL2-induced Akt1/2 phosphorylation at Thr308/309 in neutrophils. The inhibition of Akt by SH-5 attenuated CXCL2-induced adhesion and emigration in Bam32^−/− mice. Together, our results reveal that Bam32 has a suppressive role in chemokine-induced neutrophil chemotaxis by regulating Rap1 activation and that this role of Bam32 in chemokine-induced neutrophil recruitment relies on the activation of PI3K effector Akt. Full article

Angiopoietin-1 (Ang-1) is an important proangiogenic factor also involved in the maintenance of endothelial-barrier integrity. The small GTPase Rap1 is involved in the regulation of adherens junctions through VE-cadherin-mediated adhesion, and in endothelial permeability. While many studies established that Rap1 activation is critical for endothelial cell–cell adhesions, its roles in the antipermeability effects of Ang-1 are ill-defined. Thus, we determined the contribution of Rap1 to Ang-1-stimulated angiogenic effects on endothelial cells (ECs). We found that Rap1 is activated following Ang-1 stimulation and is required for the antipermeability effects of Ang-1 on EC monolayers. Our results also revealed that Rap1 is necessary for EC sprouting stimulated by Ang-1 but had no significant effect on Ang-1-induced EC migration and adhesion. In contrast, downregulation of VE-cadherin markedly increased the adhesiveness of ECs to the substratum, which resulted in inhibition of Ang-1-stimulated migration. These results revealed that Rap1 is central to the effects of Ang-1 at intercellular junctions of ECs, whereas VE-cadherin is also involved in the adhesion of ECs to the extracellular matrix. Full article

Few papers have focused on small guanosine triphosphate (GTP)-binding proteins and their regulation during spermatogenesis. TBC1D21 genes (also known as male germ cell RAB GTPase-activating protein MGCRABGAP) are related to sterility, as determined through cDNA microarray testing of human testicular tissues exhibiting spermatogenic defects. TBC1D21 is a protein specifically expressed in the testes that exhibits specific localizations of elongating and elongated spermatids during mammalian spermiogenesis. Furthermore, through co-immunoprecipitation (co-IP) and nano liquid chromatography–tandem mass spectrometry (nano LC–MS/MS), Rap1 has been recognized as a potential TBC1D21 interactor. This study determined the possible roles of Rap1 and TBC1D21 during mammalian spermiogenesis. First, the binding ability between Rap1 and TBC1D21 was verified using co-IP. Second, the stronger signals of Rap1 expressed in elongating and elongated murine spermatids extracted from testicular sections, namely spermatogonia, spermatocytes, and round spermatids, were compared. Third, Rap1 and TBC1D21 exhibited similar localizations at postacrosomal regions of spermatids and at the midpieces of mature sperms, through isolated male germ cells. Fourth, the results of an activating Rap1 pull-down assay indicated that TBC1D21 overexpression inactivates Rap1 activity in cell models. In conclusion, TBC1D21 may interact with and potentially regulate Rap1 during murine spermatogenesis. Full article

This review addresses the issue of the numerous roles played by Rap1 GTPase (guanosine triphosphatase) in different cell types, in terms of both physiology and pathology. It is one among a myriad of small G proteins with endogenous GTP-hydrolyzing activity that is considerably stimulated by posttranslational modifications (geranylgeranylation) or guanine nucleotide exchange factors (GEFs), and inhibited by GTPase-activating proteins (GAPs). Rap1 is a ubiquitous protein that plays an essential role in the control of metabolic processes, such as signal transduction from plasma membrane receptors, cytoskeleton rearrangements necessary for cell division, intracellular and substratum adhesion, as well as cell motility, which is needed for extravasation or fusion. We present several examples of how Rap1 affects cells and organs, pointing to possible molecular manipulations that could have application in the therapy of several diseases. Full article