Search Results (10)

The Drosophila midgut serves as a powerful model system for studying the mechanisms underlying stem cell hyperproliferation induced by gut damage and Yorkie (Yki) activation. Homeodomain-interacting protein kinase (Hipk) has recently been shown to regulate intestinal stem cell (ISC) proliferation and differentiation during normal homeostasis. Here, we show that Hipk is cell-autonomously required for ISC hyperproliferation stimulated by both gut damage and Yki activation. Progenitor-specific hipk knockdown abolished the ISC hyperproliferation and gut hyperplasia induced by dextran sulfate sodium (DSS)-mediated injury and Yki overexpression. Mechanistically, Hipk promotes Yki protein stability and nuclear accumulation in progenitors. This regulation is specific to wild-type Yki, as the constitutively active Yki^S168A mutant, which escapes Warts-mediated inhibition, is insensitive to Hipk depletion. These findings identify Hipk as a critical regulator of Yki activation during ISC hyperproliferation. Full article

The Hippo–Yorkie (Yki) signaling pathway is a conserved regulator of tissue growth, and its dysregulation leads to excessive growth and tumorigenesis. Although several microRNAs (miRNAs) have been implicated in Hippo pathway regulation, how they modulate Yki activity in vivo remains incompletely understood. Here, we identify miR-137 as a suppressor of Yki-driven overgrowth in a Drosophila model. A functional miRNA screen revealed that miR-137 overexpression markedly suppresses Yki-induced eye overgrowth, whereas inhibition of miR-137 enhances eye overgrowth phenotypes. Through bioinformatic prediction and genetic screening, we identified Drep1 as a candidate downstream factor associated with miR-137 function. RNAi-mediated depletion of Drep1 phenocopies the suppressive effects of miR-137, whereas Drep1 overexpression enhances Yki-driven tissue overgrowth and proliferation. Consistent with these phenotypes, miR-137 overexpression or Drep1 depletion reduces the expression of canonical Yki target genes, including Diap1 and Expanded, indicating decreased Yki transcriptional output. Importantly, Drep1 knockdown was associated with reduced Yki immunostaining in a complementary wing-disk context, suggesting a potential link between Drep1 and Yki-associated signaling. Consistent with this, miR-137 also reduced the expression of ICAD, the mammalian homolog of Drep1, providing preliminary evidence that miR-137 may regulate ICAD expression in mammalian cells. Together, these findings support a potential regulatory relationship between miR-137 and Drep1 that modulates Yki-driven eye overgrowth and reveal an additional layer of Hippo pathway regulation in vivo. Full article

Cancer cells expand rapidly in response to altered intercellular and signaling interactions to achieve the hallmarks of cancer. Impaired cell polarity combined with activated oncogenes is known to promote several hallmarks of cancer, e.g., activating invasion by increased activity of Jun N-terminal kinase (JNK) and sustained proliferative signaling by increased activity of Hippo effector Yorkie (Yki). Thus, JNK, Yki, and their downstream transcription factors have emerged as synergistic drivers of tumor growth through pro-tumor signaling and intercellular interactions like cell competition. However, little is known about the signals that converge onto JNK and Yki in tumor cells and enable tumor cells to achieve the hallmarks of cancer. Here, using mosaic models of cooperative oncogenesis (Ras^V12,scrib⁻) in Drosophila, we show that Ras^V12,scrib⁻ tumor cells grow through the activation of a previously unidentified network comprising Wingless (Wg), Dronc, JNK, and Yki. We show that Ras^V12,scrib⁻ cells show increased Wg, Dronc, JNK, and Yki signaling, and all these signals are required for the growth of Ras^V12,scrib⁻ tumors. We report that Wg and Dronc converge onto a JNK–Yki self-reinforcing positive feedback signal-amplification loop that promotes tumor growth. We found that the Wg–Dronc–Yki–JNK molecular network is specifically activated in polarity-impaired tumor cells and not in normal cells, in which apical-basal polarity remains intact. Our findings suggest that the identification of molecular networks may provide significant insights into the key biologically meaningful changes in signaling pathways and paradoxical signals that promote tumorigenesis. Full article

The transcriptional coactivators Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are the main downstream effectors of the evolutionarily conserved Hippo signaling pathway. YAP/TAZ are implicated in the transcriptional regulation of target genes that are involved in a wide range of key biological processes affecting tissue homeostasis and play dual roles in the aging process, depending on the cellular and tissue context. The aim of the present study was to investigate whether pharmacological inhibitors of Yap/Taz increase the lifespan of Drosophila melanogaster. Real-time qRT-PCR was performed to measure the changes in the expression of Yki (Yorkie, the Drosophila homolog of YAP/TAZ) target genes. We have revealed a lifespan-increasing effect of YAP/TAZ inhibitors that was mostly associated with decreased expression levels of the wg and E2f1 genes. However, further analysis is required to understand the link between the YAP/TAZ pathway and aging. Full article

In the Hippo pathway, activation of Hippo and Warts (Wts) kinases results in the phosphorylation of Yorkie (Yki), to prevent its nuclear translocation. Shrimp aquaculture is threatened by Vibrio genus bacteria. In this study, we examine the role of the Hippo pathway in immune defense against Vibrio parahaemolyticus in Pacific white shrimp Penaeus vannamei. We show that V. parahaemolyticus infection promotes the expression of Yki and facilitates the dephosphorylation and nuclear translocation of Yki, indicating the inhibition of Hippo signaling upon bacterial infection. There is a complex regulatory relationship between the Hippo pathway components Hippo, Wts, and Yki and the immune-related transcription factors Dorsal, Relish, and STAT. Silencing of Hippo and Wts weakened hemocyte phagocytosis, while the silencing of Yki enhanced it, suggesting a positive regulation of shrimp cellular immunity by Hippo signaling activation. In vivo silencing of Hippo and Wts decreased the survival rates of V. parahaemolyticus-infected shrimp and elevated the bacterial content in tissues, while the silencing of Yki showed the opposite results. This suggests that the activation of Hippo signaling and the inhibition of Yki enhance antibacterial immunity in shrimp. Full article

Cancer and heart diseases are the two leading causes of mortality and morbidity worldwide. Many cancer patients undergo heart-related complications resulting in high incidences of mortality. It is generally hypothesized that cardiac dysfunction in cancer patients occurs due to cardiotoxicity induced by therapeutic agents, used to treat cancers and/or cancer-induced cachexia. However, it is not known if localized tumors or unregulated cell growth systemically affect heart function before treatment, and/or prior to the onset of cachexia, hence, making the heart vulnerable to structural or functional abnormalities in later stages of the disease. We incorporated complementary mouse and Drosophila models to establish if tumor induction indeed causes cardiac defects even before intervention with chemotherapy or onset of cachexia. We focused on one of the key pathways involved in irregular cell growth, the Hippo–Yorkie (Yki), pathway. We used overexpression of the transcriptional co-activator of the Yki signaling pathway to induce cellular overgrowth, and show that Yki overexpression in the eye tissue of Drosophila results in compromised cardiac function. We rescue these cardiac phenotypes using antioxidant treatment, with which we conclude that the Yki induced tumorigenesis causes a systemic increase in ROS affecting cardiac function. Our results show that systemic cardiac dysfunction occurs due to abnormal cellular overgrowth or cancer elsewhere in the body; identification of specific cardiac defects associated with oncogenic pathways can facilitate the possible early diagnosis of cardiac dysfunction. Full article

Developmental growth and patterning are regulated by an interconnected signalling network of several pathways. In Drosophila, the Warts (Wts) kinase, a component of the Hippo signalling pathway, plays an essential role in regulating transcription and growth by phosphorylating its substrate Yorkie (Yki). The phosphorylation of Yki critically influences its localisation and activity as a transcriptional coactivator. In this study, we identified the homeodomain-interacting protein kinase (Hipk) as another kinase that phosphorylates Yki and mapped several sites of Yki phosphorylated by Hipk, using in vitro analysis: Ser168, Ser169/Ser172 and Ser255. These sites might provide auxiliary input for Yki regulation in vivo, as transgenic flies with mutations in these show prominent phenotypes; Hipk, therefore, represents an additional upstream regulator of Yki that works in concert with Wts. Full article

Tissue development demands precise control of cell proliferation and organization, which is achieved through multiple conserved signaling pathways and protein complexes in multicellular animals. Epithelia are a ubiquitous tissue type that provide diverse functions including physical protection, barrier formation, chemical exchange, and secretory activity. However, epithelial cells are also a common driver of tumorigenesis; thus, understanding the molecular mechanisms that control their growth dynamics is important in understanding not only developmental mechanisms but also disease. One prominent pathway that regulates epithelial growth is the conserved Hippo/Warts/Yorkie network. Hippo/Warts inactivation, or activating mutations in Yorkie that prevent its phosphorylation (e.g., Yki^S168A), drive hyperplastic tissue growth. We recently reported that loss of Mushroom body defect (Mud), a microtubule-associated protein that contributes to mitotic spindle function, restricts Yki^S168A-mediated growth in Drosophila imaginal wing disc epithelia. Here we show that Mud loss alters cell cycle progression and triggers apoptosis with accompanying Jun kinase (JNK) activation in Yki^S168A-expressing discs. To identify additional molecular insights, we performed RNAseq and differential gene expression profiling. This analysis revealed that Mud knockdown in Yki^S168A-expressing discs resulted in a significant downregulation in expression of core basement membrane (BM) and extracellular matrix (ECM) genes, including the type IV collagen gene viking. Furthermore, we found that Yki^S168A-expressing discs accumulated increased collagen protein, which was reduced following Mud knockdown. Our results suggest that ECM/BM remodeling can limit untoward growth initiated by an important driver of tumor growth and highlight a potential regulatory link with cytoskeleton-associated genes. Full article

During development, the precise control of tissue morphogenesis requires changes in the cell number, size, shape, position, and gene expression, which are driven by both chemical and mechanical cues from the surrounding microenvironment. Such physical and architectural features inform cells about their proliferative and migratory capacity, enabling the formation and maintenance of complex tissue architecture. In polarised epithelia, the apical cell cortex, a thin actomyosin network that lies directly underneath the apical plasma membrane, functions as a platform to facilitate signal transmission between the external environment and downstream signalling pathways. One such signalling pathway culminates in the regulation of YES-associated protein (YAP) and TAZ transcriptional co-activators and their sole Drosophila homolog, Yorkie, to drive proliferation and differentiation. Recent studies have demonstrated that YAP/Yorkie exhibit a distinct function at the apical cell cortex. Here, we review recent efforts to understand the mechanisms that regulate YAP/Yki at the apical cell cortex of epithelial cells and how normal and disturbed YAP–actomyosin networks are involved in eye development and disease. Full article

The Hippo signaling pathway is an evolutionarily conserved regulator that plays important roles in organ size control, homeostasis, and tumorigenesis. As the key effector of the Hippo pathway, Yorkie (Yki) binds to transcription factor Scalloped (Sd) and promotes the expression of target genes, leading to cell proliferation and inhibition of apoptosis. Thus, it is of great significance to understand the regulatory mechanism for Yki protein turnover. Here, we provide evidence that the deubiquitinating enzyme ubiquitin-specific protease 10 (Usp10) binds Yki to counteract Yki ubiquitination and stabilize Yki protein in Drosophila S2 cells. The results in Drosophila wing discs indicate that silence of Usp10 decreases the transcription of target genes of the Hippo pathway by reducing Yki protein. In vivo functional analysis ulteriorly showed that Usp10 upregulates the Yki activity in Drosophila eyes. These findings uncover Usp10 as a novel Hippo pathway modulator and provide a new insight into the regulation of Yki protein stability and activity. Full article