YAP1-LATS2 feedback loop dictates senescent or malignant cell fate to maintain tissue homeostasis.

Dysfunction of the homeostasis-maintaining systems in specific cell types or tissues renders the organism susceptible to a range of diseases, including cancers. One of the emerging mechanisms for maintaining tissue homeostasis is cellular senescence. Here, we report that the Hippo pathway plays a critical role in controlling the fate of ovarian cells. Hyperactivation of Yes-associated protein 1 (YAP1), the major effector of the Hippo pathway, induces senescence in cultured primary human ovarian surface epithelial cells (hOSEs). Large tumor suppressor 2 (LATS2), the primary upstream negative regulator of YAP1, is elevated in both YAP1-induced and natural replicative-triggered senescence. Deletion of LATS2 in hOSEs prevents these cells from natural replicative and YAP1-induced senescence. Most importantly, loss of LATS2 switches ovarian cells from YAP-induced senescence to malignant transformation. Our results demonstrate that LATS2 and YAP1, two major components of the Hippo/YAP signaling pathway, form a negative feedback loop to control YAP1 activity and prevent ovarian cells from malignant transformation. Human cancer genomic data extracted from TCGA datasets further confirm the clinical relevance of our finding.

Zyxin promotes colon cancer tumorigenesis in a mitotic phosphorylation-dependent manner and through CDK8-mediated YAP activation.

Zyxin is a member of the focal adhesion complex and plays a critical role in actin filament polymerization and cell motility. Several recent studies showed that Zyxin is a positive regulator of Yki/YAP (Yes-associated protein) signaling. However, little is known about the mechanisms by which Zyxin itself is regulated and how Zyxin affects Hippo-YAP activity. We first showed that Zyxin is phosphorylated by CDK1 during mitosis. Depletion of Zyxin resulted in significantly impaired colon cancer cell proliferation, migration, anchorage-independent growth, and tumor formation in xenograft animal models. Mitotic phosphorylation is required for Zyxin activity in promoting growth. Zyxin regulates YAP activity through the colon cancer oncogene CDK8. CDK8 knockout phenocopied Zyxin knockdown in colon cancer cells, while ectopic expression of CDK8 substantially restored the tumorigenic defects of Zyxin-depletion cells. Mechanistically, we showed that CDK8 directly phosphorylated YAP and promoted its activation. Fully activated YAP is required to support the growth in CDK8-knockout colon cancer cells in vitro and in vivo. Together, these observations suggest that Zyxin promotes colon cancer tumorigenesis in a mitotic-phosphorylation-dependent manner and through CDK8-mediated YAP activation.

Timely expression and activation of YAP1 in granulosa cells is essential for ovarian follicle development.

Although the role of the Hippo signaling pathway in development and tumorigenesis has been extensively studied in multiple organs, its role in ovarian follicle development remains largely unknown. Here, we report that Yes-Associated Protein 1 (YAP1), the major effector of Hippo signaling, is spatiotemporally expressed in ovarian granulosa cells and plays a critical role in the regulation of follicle development. We found that the active form of YAP1 (nuclear YAP1) was predominantly expressed in proliferative granulosa cells, whereas the inactive form of YAP1 (cytoplasmic YAP1) was mainly detected in luteal cells (terminally differentiated granulosa cells). Pharmacological inhibition of YAP1 activity disrupted mouse ovarian follicle development in vitro and in vivo. Foxl2 promoter-driven knockout of Yap1 in ovarian granulosa cells resulted in increased apoptosis of granulosa cells, decreased number of corpora lutea, reduced ovarian size, and subfertility in transgenic mice. However, Cyp19a1 promoter-driven knockout of Yap1 in differentiated granulosa cells of preovulatory follicles and luteal cells of corpora lutea had no effect on ovarian morphology and fertility. Mechanistic studies demonstrated that YAP1 interacted with epidermal growth factor receptor and TGF-ß signaling pathways to regulate granulosa cell proliferation, differentiation, and survival. Results from this study identify YAP1 as a critical regulator of granulosa cell proliferation and differentiation. Balanced expression and activation of YAP1 is essential for follicle development and successful reproduction. YAP1 is a promising target for treatment of subfertility associated with abnormal granulosa cell function.-Lv, X., He, C., Huang, C., Wang, H., Hua, G., Wang, Z., Zhou, J., Chen, X., Ma, B., Timm, B. K., Maclin, V., Dong, J., Rueda, B. R., Davis, J. S., Wang, C. Timely expression and activation of YAP1 in granulosa cells is essential for ovarian follicle development.

Cyclin-dependent kinase 1 (CDK1)-mediated mitotic phosphorylation of the transcriptional co-repressor Vgll4 inhibits its tumor-suppressing activity.

The Hippo pathway is an evolutionarily conserved signaling pathway that plays important roles in stem cell biology, tissue homeostasis, and cancer development. Vestigial-like 4 (Vgll4) functions as a transcriptional co-repressor in the Hippo-Yes-associated protein (YAP) pathway. Vgll4 inhibits cell proliferation and tumor growth by competing with YAP for binding to TEA-domain proteins (TEADs). However, the mechanisms by which Vgll4 itself is regulated are unclear. Here we identified a mechanism that regulates Vgll4's tumor-suppressing function. We found that Vgll4 is phosphorylated in vitro and in vivo by cyclin-dependent kinase 1 (CDK1) during antimitotic drug-induced mitotic arrest and also in normal mitosis. We further identified Ser-58, Ser-155, Thr-159, and Ser-280 as the main mitotic phosphorylation sites in Vgll4. We also noted that the nonphosphorylatable mutant Vgll4-4A (S58A/S155A/T159A/S280A) suppressed tumorigenesis in pancreatic cancer cells in vitro and in vivo to a greater extent than did wild-type Vgll4, suggesting that mitotic phosphorylation inhibits Vgll4's tumor-suppressive activity. Consistent with these observations, the Vgll4-4A mutant possessed higher-binding affinity to TEAD1 than wild-type Vgll4. Interestingly, Vgll4 and Vgll4-4A markedly suppressed YAP and ß-catenin signaling activity. Together, these findings reveal a previously unrecognized mechanism for Vgll4 regulation in mitosis and its role in tumorigenesis.

Ajuba Phosphorylation by CDK1 Promotes Cell Proliferation and Tumorigenesis.

Recent studies identified the adaptor protein Ajuba as a positive regulator of Yes-associated protein (YAP) oncogenic activity through inhibiting large tumor suppressor (Lats1/2) core kinases of the Hippo pathway, a signaling pathway that plays important roles in cancer. In this study, we define a novel mechanism for phospho-regulation of Ajuba in mitosis and its biological significance in cancer. We found that Ajuba is phosphorylated in vitro and in vivo by cyclin-dependent kinase 1 (CDK1) at Ser(119) and Ser(175) during the G2/M phase of the cell cycle. Mitotic phosphorylation of Ajuba controls the expression of multiple cell cycle regulators; however, it does not affect Hippo signaling activity, nor does it induce epithelial-mesenchymal transition. We further showed that mitotic phosphorylation of Ajuba is sufficient to promote cell proliferation and anchorage-independent growth in vitro and tumorigenesis in vivo Collectively, our discoveries reveal a previously unrecognized mechanism for Ajuba regulation in mitosis and its role in tumorigenesis.

Oncoprotein YAP regulates the spindle checkpoint activation in a mitotic phosphorylation-dependent manner through up-regulation of BubR1.

The transcriptional co-activator YAP (Yes-associated protein) functions as an oncogene; however, it is largely unclear how YAP exerts its oncogenic role. In this study, we further explored the functional significance of YAP and its mitotic phosphorylation in the spindle checkpoint. We found that the dynamic mitotic phosphorylation of YAP was CDC14-dependent. We also showed that YAP was required for the spindle checkpoint activation induced by spindle poisons. Mitotic phosphorylation of YAP was required for activation of the spindle checkpoint. Furthermore, enhanced expression of active YAP hyperactivated the spindle checkpoint and induced mitotic defects in a mitotic phosphorylation-dependent manner. Mechanistically, we documented that mitotic phosphorylation of YAP controlled transcription of genes associated with the spindle checkpoint. YAP constitutively associated with BubR1 (BUB1-related protein kinase), and knockdown of BubR1 relieved YAP-driven hyperactivation of the spindle checkpoint. Finally, we demonstrated that YAP promoted epithelial cell invasion via both mitotic phosphorylation and BubR1-dependent mechanisms. Together, our results reveal a novel link between YAP and the spindle checkpoint and indicate a potential mechanism underlying the oncogenic function of YAP through dysregulation of the spindle checkpoint.

Case report: Significant relief of linezolid-induced peripheral neuropathy in a pre-XDR-TB case after acupuncture treatment.

The revised WHO guidelines on multidrug- or rifampicin-resistant tuberculosis (MDR/RR-TB) include linezolid in the core drug group. Common adverse events of prolonged linezolid use are bone marrow suppression and peripheral neuropathy (PN). Available measures against linezolid-induced PN (LIPN) often have insignificant effects, leading to linezolid discontinuation and a decline in the success rate of MDR/RR-TB treatment. Acupuncture treatment is a symptomatic treatment measure from traditional Chinese medicine (TCM) to relieve pain with overall very low evidence and has never been reported in LIPN. The pilot use of acupuncture in a pre-extensively drug-resistant (XDR)-TB (a more severe form of MDR/RR-TB) patient exhibited significant improvements in LIPN and thus maintained linezolid in the regimen for a longer period.

Reprogramming of Ovarian Granulosa Cells by YAP1 Leads to Development of High-Grade Cancer with Mesenchymal Lineage and Serous Features.

Understanding the cell-of-origin of ovarian high grade serous cancer (HGSC) is the prerequisite for efficient prevention and early diagnosis of this most lethal gynecological cancer. Recently, a mesenchymal type of ovarian HGSC with the poorest prognosis among ovarian cancers was identified by both TCGA and AOCS studies. The cell-of-origin of this subtype of ovarian cancer is unknown. While pursuing studies to understand the role of the Hippo pathway in ovarian granulosa cell physiology and pathology, we unexpectedly found that the Yes-associated protein 1 (YAP1), the major effector of the Hippo signaling pathway, induced dedifferentiation and reprogramming of the ovarian granulosa cells, a unique type of ovarian follicular cells with mesenchymal lineage and high plasticity, leading to the development of high grade ovarian cancer with serous features. Our research results unveil a potential cell-of-origin for a subtype of HGSC with mesenchymal features.

A Human Papillomavirus-Independent Cervical Cancer Animal Model Reveals Unconventional Mechanisms of Cervical Carcinogenesis.

HPV infections are common in healthy women and only rarely cause cervical cancer, suggesting that individual genetic susceptibility may play a critical role in the establishment of persistent HPV infection and the development of cervical cancer. Here, we provide convincing in vitro and in vivo evidence showing that differential expression and activation of YAP1 oncogene determine individual susceptibility to HPV infection and cervical carcinogenesis. We found that hyperactivation of YAP1 in mouse cervical epithelium was sufficient to induce invasive cervical cancer. Cervical epithelial cell-specific HPV16 E6/E7 and YAP1 double-knockin mouse model demonstrated that high-risk HPV synergized with hyperactivated YAP1 to promote the initiation and progression of cervical cancer. Our mechanistic studies indicated that hyperactivation of YAP1 in cervical epithelial cells facilitated HPV infection by increasing the putative HPV receptor molecules and disrupting host cell innate immunity. Our finding reveals an unconventional mechanism for cervical carcinogenesis.

Cyclin-dependent kinase 1-mediated phosphorylation of YES links mitotic arrest and apoptosis during antitubulin chemotherapy.

YES is a member of the SRC family kinase (SFK) group of non-receptor tyrosine kinases, which are implicated in multiple key cellular processes involved in oncogenesis. Antitubulin agents have been widely used as chemotherapeutics for cancer patients and these drugs arrest cells in mitosis, leading to subsequent cell death. In the present study, we define a mechanism for phospho-regulation of YES that is critical for its role in response to antitubulin agents. Specifically, we found that YES is phosphorylated at multiple sites on its N-terminal unique domain by the cell cycle kinase CDK1 during antitubulin drug-induced mitotic arrest. Phosphorylation of YES occurs during normal mitosis. Deletion of YES causes arrest in prometaphase and polyploidy in a p53-independent manner. We further show that YES regulates antitubulin chemosensitivity. Importantly, mitotic phosphorylation is essential for these effects. In support of our findings, we found that YES expression is high in recurrent ovarian cancer patients. Finally, through expression profiling, we documented that YES phosphorylation affects expression of multiple cell cycle regulators. Collectively, our results reveal a previously unrecognized mechanism for controlling the activity of YES during antitubulin chemotherapeutic treatment and suggest YES as a potential target for the treatment of antitubulin-resistant cancer.

CDK1-mediated mitotic phosphorylation of PBK is involved in cytokinesis and inhibits its oncogenic activity.

PDZ-binding kinase (PBK) plays a major role in proliferation and in safeguarding mitotic fidelity in cancer cells. Frequently upregulated in many cancers, PBK drives tumorigenesis and metastasis. PBK has been shown to be phosphorylated in mitosis by cyclin-dependent kinase 1 (CDK1)/cyclin B, however, no studies have been done examining PBK mitotic phosphorylation in oncogenesis. Additionally to the previously identified Threonine-9 phosphorylation, we found that Threonine-24, Serine-32, and Serine-59 of PBK are also phosphorylated. PBK is phosphorylated in vitro and in cells by CDK1 during antimitotic drug-induced mitotic arrest and in normal mitosis. We demonstrated that mitotic phosphorylation of Threonine-9 is involved in cytokinesis. The non-phosphorylatable mutant PBK-T9A augments tumorigenesis to a greater extent than wild type PBK in breast cancer cells, suggesting that PBK mitotic phosphorylation inhibits its tumor promoting activity. The PBK-T9A mutant also transforms and increases the proliferation of immortalized breast epithelial cells. Collectively, this study reveals that CDK1-mediated mitotic phosphorylation of PBK is involved in cytokinesis and inhibits its oncogenic activity.

MST2 phosphorylation at serine 385 in mitosis inhibits its tumor suppressing activity.

Mammalian sterile 20-like kinase 1/2 (MST1/2) are core tumor suppressors in the Hippo signaling pathway. MST1/2 have been shown to regulate mitotic progression. Here, we report a novel mechanism for phospho-regulation of MST2 in mitosis and its biological significance in cancer. We found that the mitotic kinase cyclin-dependent kinase 1 (CDK1) phosphorylates MST2 in vitro and in vivo at serine 385 during antimitotic drug-induced G2/M phase arrest. This phosphorylation occurs transiently during unperturbed mitosis. Mitotic phosphorylation of MST2 does not affect its kinase activity or Hippo-YAP signaling. We further showed that mitotic phosphorylation-deficient mutant MST2-S385A possesses higher activity in suppressing cell proliferation and anchorage-independent growth in vitro and tumorigenesis in vivo. Together, our findings reveal a novel layer of regulation for MST2 in mitosis and its role in tumorigenesis.

KIBRA promotes prostate cancer cell proliferation and motility.

KIBRA is a regulator of the Hippo-yes-associated protein (YAP) pathway, which plays a critical role in tumorigenesis. In the present study, we show that KIBRA is a positive regulator in prostate cancer cell proliferation and motility. We found that KIBRA is transcriptionally upregulated in androgen-insensitive LNCaPC4-2 and LNCaP-C81 cells compared to parental androgen-sensitive LNCaP cells. Ectopic expression of KIBRA enhances cell proliferation, migration and invasion in both immortalized and cancerous prostate epithelial cells. Accordingly, knockdown of KIBRA reduces migration, invasion and anchorage-independent growth in LNCaP-C4-2/C81 cells. Moreover, KIBRA expression is induced by androgen signaling and KIBRA is partially required for androgen receptor signaling activation in prostate cancer cells. In line with these findings, we further show that KIBRA is overexpressed in human prostate tumors. Our studies uncover unexpected results and identify KIBRA as a tumor promoter in prostate cancer.

CDK1 phosphorylation of TAZ in mitosis inhibits its oncogenic activity.

The transcriptional co-activator with PDZ-binding motif (TAZ) is a downstream effector of the Hippo tumor suppressor pathway, which plays important roles in cancer and stem cell biology. Hippo signaling inactivates TAZ through phosphorylation (mainly at S89). In the current study, we define a new layer of regulation of TAZ activity that is critical for its oncogenic function. We found that TAZ is phosphorylated in vitro and in vivo by the mitotic kinase CDK1 at S90, S105, T326, and T346 during the G2/M phase of the cell cycle. Interestingly, mitotic phosphorylation inactivates TAZ oncogenic activity, as the non-phosphorylatable mutant (TAZ-S89A/S90A/S105A/T326A/T346A, TAZ-5A) possesses higher activity in epithelial-mesenchymal transition, anchorage-independent growth, cell migration, and invasion when compared to the TAZ-S89A mutant. Accordingly, TAZ-5A has higher transcriptional activity compared to the TAZ-S89A mutant. Finally, we show that TAZ-S89A or TAZ-5A (to a greater extent) was sufficient to induce spindle and centrosome defects, and chromosome misalignment/missegregation in immortalized epithelial cells. Together, our results reveal a previously unrecognized connection between TAZ oncogenicity and mitotic phospho-regulation.

Active YAP promotes pancreatic cancer cell motility, invasion and tumorigenesis in a mitotic phosphorylation-dependent manner through LPAR3.

The transcriptional co-activator Yes-associated protein, YAP, is a main effector in the Hippo tumor suppressor pathway. We recently defined a mechanism for positive regulation of YAP through CDK1-mediated mitotic phosphorylation. Here, we show that active YAP promotes pancreatic cancer cell migration, invasion and anchorage-independent growth in a mitotic phosphorylation-dependent manner. Mitotic phosphorylation is essential for YAP-driven tumorigenesis in animals. YAP reduction significantly impairs cell migration and invasion. Immunohistochemistry shows significant upregulation and nuclear localization of YAP in metastases when compared with primary tumors and normal tissue in human. Mitotic phosphorylation of YAP controls a unique transcriptional program in pancreatic cells. Expression profiles reveal LPAR3 (lysophosphatidic acid receptor 3) as a mediator for mitotic phosphorylation-driven pancreatic cell motility and invasion. Together, this work identifies YAP as a novel regulator of pancreatic cancer cell motility, invasion and metastasis, and as a potential therapeutic target for invasive pancreatic cancer.

The hippo pathway effector YAP regulates motility, invasion, and castration-resistant growth of prostate cancer cells.

Yes-associated protein (YAP) is an effector of the Hippo tumor suppressor pathway. The functional significance of YAP in prostate cancer has remained elusive. In this study, we first show that enhanced expression of YAP is able to transform immortalized prostate epithelial cells and promote migration and invasion in both immortalized and cancerous prostate cells. We found that YAP mRNA was upregulated in androgen-insensitive prostate cancer cells (LNCaP-C81 and LNCaP-C4-2 cells) compared to the level in androgen-sensitive LNCaP cells. Importantly, ectopic expression of YAP activated androgen receptor signaling and was sufficient to promote LNCaP cells from an androgen-sensitive state to an androgen-insensitive state in vitro, and YAP conferred castration resistance in vivo. Accordingly, YAP knockdown greatly reduced the rates of migration and invasion of LNCaP-C4-2 cells and under androgen deprivation conditions largely blocked cell division in LNCaP-C4-2 cells. Mechanistically, we found that extracellular signal-regulated kinase-ribosomal s6 kinase signaling was downstream of YAP for cell survival, migration, and invasion in androgen-insensitive cells. Finally, immunohistochemistry showed significant upregulation and hyperactivation of YAP in castration-resistant prostate tumors compared to their levels in hormone-responsive prostate tumors. Together, our results identify YAP to be a novel regulator in prostate cancer cell motility, invasion, and castration-resistant growth and as a potential therapeutic target for metastatic castration-resistant prostate cancer (CRPC).

The Hippo/YAP pathway interacts with EGFR signaling and HPV oncoproteins to regulate cervical cancer progression.

The Hippo signaling pathway controls organ size and tumorigenesis through a kinase cascade that inactivates Yes-associated protein (YAP). Here, we show that YAP plays a central role in controlling the progression of cervical cancer. Our results suggest that YAP expression is associated with a poor prognosis for cervical cancer. TGF-α and amphiregulin (AREG), via EGFR, inhibit the Hippo signaling pathway and activate YAP to induce cervical cancer cell proliferation and migration. Activated YAP allows for up-regulation of TGF-α, AREG, and EGFR, forming a positive signaling loop to drive cervical cancer cell proliferation. HPV E6 protein, a major etiological molecule of cervical cancer, maintains high YAP protein levels in cervical cancer cells by preventing proteasome-dependent YAP degradation to drive cervical cancer cell proliferation. Results from human cervical cancer genomic databases and an accepted transgenic mouse model strongly support the clinical relevance of the discovered feed-forward signaling loop. Our study indicates that combined targeting of the Hippo and the ERBB signaling pathways represents a novel therapeutic strategy for prevention and treatment of cervical cancer.