Significance: Cancer is the leading cause of death worldwide, although studies revealed that dysregulation of the Hippo pathway contributes to tumorigenesis, whereas its roles in tumor invasion and cell migration remain paradoxical and largely elusive. Using Drosophila as a model, we herein find cross-talk between the Hippo and JNK pathways in regulating cell migration and invasion. Mechanistically, we identify bantam -Rox8 modules as essential components downstream of Yorkie in mediating JNK-dependent cell invasion. Our finding is particularly important as it offers a wake-up call for therapeutic interventions of Hippo-related cancers, because simply increasing Hippo signal activity may paradoxically accelerate cell invasion and metastasis.

Phosphoinositides, a family of phosphorylated derivatives of phosphatidylinositol (PtdIns), are tightly regulated both temporally and spatially by PtdIns phosphatases and kinases. Mutations in inositol polyphosphate 5-phosphatase E (INPP5E) cause Joubert syndrome, a human disorder associated with numerous ciliopathic defects, including renal cyst formation, linking phosphoinositides to ciliopathies. However, the molecular mechanism by which INPP5E-mediated PtdIns signaling regulates ciliogenesis and cystogenesis is unclear. Here, we utilized an in vivo vertebrate model of renal cystogenesis to show that Inpp5e enzymatic activity at the apical membrane directs apical docking of basal bodies in renal epithelia. Knockdown or knockout of inpp5e led to ciliogenesis defects and cystic kidneys in zebrafish. Furthermore, knockdown of inpp5e in embryos led to defects in cell polarity, cortical organization of F-actin, and apical segregation of PtdIns(4,5)P₂ and PtdIns(3,4,5)P₃. Knockdown of the ezrin gene, which encodes an ezrin/radixin/moesin (ERM) protein that crosslinks PtdIns(4,5)P₂ and F-actin, phenocopied inpp5e knockdowns. Notably, overexpression of the ezrin gene rescued inpp5e morphants. Finally, treatment with the PI 3-kinase inhibitor LY294002, which decreases PtdIns(3,4,5)P₃ levels, rescued the cellular, phenotypic, and renal functional defects in inpp5e-knockdown embryos. Together, our data indicate that Inpp5e functions as a key regulator of cell polarity in the renal epithelia, by inhibiting PtdIns(3,4,5)P₃ and subsequently stabilizing PtdIns(4,5)P₂ and recruiting Ezrin, F-actin, and basal bodies to the apical membrane, and suggest a possible novel approach for treating human ciliopathies.

Significance: Both Hippo and c-Jun N-terminal kinase (JNK) signaling have well-established roles in promoting tissue growth, while it remains elusive whether and how the two pathways interact or coordinate in growth control. We report in the present study that the Hpo–Yki pathway modulates Rho1–JNK signaling-mediated growth in Drosophila wing development. We show that the impaired Hpo pathway activates JNK through transcriptional up-regulation of Rho1. These findings expands our understanding about the cross-talk between two important signaling pathways, namely Hippo–Yki and Rho1–JNK, in regulating growth.

The Hippo signaling pathway and its transcriptional co-activator Yap are known as essential regulators for cell proliferation and organ size. However, little is known about their roles in kidney development and ciliogenesis. We examined expression of Yap during zebrafish embryogenesis, and its transcripts were detected in pronephric duct, while Yap protein was found to be localized in the cytoplasm and apical membrane in kidney epithelium cells. By morpholino (MO) knockdown of yap expression in zebrafish, the injected larve exhibits pronephic cysts and many aspects of ciliopathy, which can be rescued by full-length yap mRNA, but not yap^S127A mRNA. With transgenic Tg(Na⁺/K⁺ ATPase:EGFP), we found that lacking Yap led to expansion and discontinuities of pronephric duct, as well as disorganization of cloaca during pronephros morphogenesis. Mis-located Na⁺/K⁺ ATPase and ciliary abnormalities are also detected in pronephric duct of yap morphants. In addition, genetic analysis suggests that yap interacts with ift20, ift88 and arl13b in pronephric cyst formation. Taken together, our data reveals that Yap is required for pronephric duct integrity, maintenance of baso-lateral cell polarity, and ciliogenesis during zebrafish kidney development.

Hormone therapy resistance and the ensuing aggressive tumor progression present a significant clinical challenge. However, the mechanisms underlying the induction of tumor malignancy upon inhibition of steroid hormone signaling remain poorly understood. Here, we demonstrate that Drosophila malignant epithelial tumors show a similar reduction in ecdysone signaling, the main steroid hormone pathway. Our analysis of ecdysone-induced downstream targets reveals that overexpression of the nuclear receptor E75, particularly facilitates the malignant transformation of benign tumors. Genome-wide DNA binding profiles and biochemistry data reveal that E75 not only binds to the transcription factors of both Hippo and Notch pathways, but also exhibits widespread co-binding to their target genes, thus contributing to tumor malignancy. We further validated these findings by demonstrating that depletion of NR1D2 , the mammalian homolog of E75, inhibits the activation of Hippo and Notch target genes, impeding glioblastoma progression. Together, our study unveils a novel mechanism by which hormone inhibition promotes tumor malignancy, and describes an evolutionarily conserved role of the oncogene E75/NR1D2 in integration of Hippo and Notch pathway activity during tumor progression.

Cilia are hair‐like structures that function like antennae to detect chemical and mechanical signals in the environment. Recently, phosphoinositides were shown to play an important role in cilia assembly and disassembly. However, the precise molecular and cellular mechanisms underlying this process remain unknown. Here, we report that suppression of apical phosphatidylinositol 4,5‐ bis phosphate [PtdIns(4,5)P ₂ ], by overexpressing apically targeted PtdIns(4,5)P ₂ phosphatase or by knocking down type I phosphatidylinositol 4‐phosphate 5‐kinase (Pip5k1), leads to ciliogenesis defects and polycystic kidney disease (PKD) in zebrafish embryos that phenocopied inpp5e mutant, a Joubert syndrome model. We further demonstrate that decreased expression of apical PtdIns(4,5)P ₂ disrupted apical ezrin recruitment, F‐actin organization, and basal body docking. Moreover, the ciliogenesis and polycystic kidney defects in PtdIns(4,5)P ₂ ‐depleted embryos can be rescued by overexpression of ezrin. Finally, Pip5k1a overexpression rescued the ciliogenesis defects and PKD phenotypes in Inpp5e‐depleted embryos. Taken together, our results reveal that apical PtdIns(4,5)P ₂ is essential for ciliogenesis and the prevention of PKD and suggest a novel possibility for treating PKD and other human ciliopathies.—Xu, W., Jin, M., Huang, W., Wang, H., Hu, R., Li, J., Cao, Y. Apical PtdIns(4,5)P ₂ is required for ciliogenesis and suppression of polycystic kidney disease. FASEB J. 33, 2848–2857 (2019). www.fasebj.org