YAP Tyrosine Phosphorylation and Nuclear Localization in Cholangiocarcinoma Cells Are Regulated by LCK and Independent of LATS Activity

GPCR-mediated YAP/TAZ inactivation in fibroblasts via EPAC1/2, RAP2C, and MAP4K7

Yes-associated protein (YAP) and PDZ-binding motif (TAZ) have emerged as important regulators of pathologic fibroblast activation in fibrotic diseases. Agonism of Gαs-coupled G protein coupled receptors (GPCRs) provides an attractive approach to inhibit the nuclear localization and function of YAP and TAZ in fibroblasts that inhibits or reverses their pathological activation. Agonism of the dopamine D1 GPCR has proven effective in preclinical models of lung and liver fibrosis. However, the molecular mechanisms coupling GPCR agonism to YAP and TAZ inactivation in fibroblasts remain incompletely understood. Here, using human lung fibroblasts, we identify critical roles for the cAMP effectors EPAC1/2, the small GTPase RAP2c, and the serine/threonine kinase MAP4K7 as the essential elements in the downstream signaling cascade linking GPCR agonism to LATS1/2-mediated YAP and TAZ phosphorylation and nuclear exclusion in fibroblasts. We further show that this EPAC/RAP2c/MAP4K7 signaling cascade is essential to the effects of dopamine D1 receptor agonism on reducing fibroblast proliferation, contraction, and extracellular matrix production. Targeted modulation of this cascade in fibroblasts may prove a useful strategy to regulate YAP and TAZ signaling and fibroblast activities central to tissue repair and fibrosis.

The effect of melatonin on Hippo signaling pathway in dental pulp stem cells

Dental pulp stem cells (DPSCs) have a high capacity to differentiate into the neuronal cell lineage. Meanwhile, both Hippo signaling and melatonin are key regulators in neuronal differentiation of neuronal progenitor cells. Recently emerging evidences suggest the possible interaction between melatonin and Hippo signaling in different cell lines. But underlying mechanisms involved in the initiation or progression of neurogenic differentiation in DPSCs through this connection need to be explored. Therefore, the scope of this study is to investigate the effect of melatonin on Hippo signaling pathway through the expression of its downstream effector (YAP/p-YAP^Y357) after the neuronal differentiation of DPSCs. In regard with this, DPSCs were incubated with growth and dopaminergic neuronal differentiation medium with or without melatonin (10 μM) for 21 days. The morphological changes were followed by phase contrast microscopy and differentiation of DPSCs was evaluated by immunofluorescence labelling with NeuN, GFAP, and tyrosine hydroxylase. Furthermore, we evaluated the presence of neural progenitor cells by nestin immunoreactivity. Hippo signaling pathway was investigated by evaluating the immunoreactivity of YAP and p-YAP^Y357. Our results were also supported by western-blot analysis and SOX2, PCNA and caspase-3 were also evaluated. The positive immunoreactivity for NeuN, tyrosine hydroxylase and negative immunoreactivity for GFAP showed the successful differentiation of DPSCs to neurons, not glial cells. Melatonin addition to dopaminergic media induced tyrosine hydroxylase and decreased significantly nestin expression. The expressions of PCNA and caspase-3 were also decreased significantly with melatonin addition into growth media. Melatonin treatment induced phosphorylation of YAP^Y357 and reduced YAP expression. In conclusion, melatonin has potential to induce neuronal differentiation and reduce the proliferation of DPSCs by increasing phosphorylation of YAP^Y357 and eliminating the activity of YAP, which indicates the active state of Hippo signaling pathway.

Parallel genome-wide RNAi screens identify lymphocyte-specific protein tyrosine kinase (LCK) as a targetable vulnerability of cell proliferation and chemoresistance in nasopharyngeal carcinoma

Despite recent in advances in the management of nasopharyngeal carcinoma (NPC), development of targeted therapy remains challenging particularly in patients with recurrent or metastatic disease. To search for clinically relevant targets for the treatment of NPC, we carried out parallel genome-wide functional screens to identified essential genes that are required for NPC cells proliferation and cisplatin resistance. We identified lymphocyte-specific protein tyrosine kinase (LCK) as a key vulnerability of both proliferation and cisplatin resistance. Depletion of endogenous LCK or treatment of cells with LCK inhibitor induced tumor-specific cell death and synergized cisplatin sensitivity in EBV-positive C666-1 and EBV-negative SUNE1 cells. Further analyses demonstrated that LCK is regulating the proliferation and cisplatin resistance through activation of signal transducer and activator of transcription 5 (STAT5). Taken together, our study provides a molecular basis for targeting LCK and STAT5 signaling as potential druggable targets for the management of NPC.

Scribble sub-cellular localization modulates recruitment of YES1 to regulate YAP1 phosphorylation

The multi-domain scaffolding protein Scribble (Scrib) regulates cell polarity and growth signaling at cell-cell junctions. In epithelial cancers, Scrib mislocalization and overexpression paradoxically transform Scrib from a basolateral tumor suppressor to a cytosolic driver of tumorigenicity. To address the function of Scrib (mis)localization, a Scrib-HaloTag fusion was genome engineered in polarized epithelial cells. Expression of the epithelial to mesenchymal transcription factor Snail displaced Scrib-HaloTag from cell junctions, mirroring the mislocalization observed in cancers. Interestingly, Snail expression promotes Yes-associated protein-1 (YAP1) nuclear localization independent of hippo pathway-regulated YAP-S127 phosphorylation. Furthermore, Scrib HaloPROTAC degradation attenuates YAP1-Y357 phosphorylation. Halo-ligand affinity purification mass spectrometry analysis identified the Src family kinase YES1 as a mislocalized Scrib interaction partner, preferentially recruiting the kinase active and open global conformation (αC helix in). Altogether, mislocalized Scrib enhances YAP1 phosphorylation by scaffolding active YES1.

The nuclear export protein XPO1 - from biology to targeted therapy

Exportin 1 (XPO1), also known as chromosome region maintenance protein 1, plays a crucial role in maintaining cellular homeostasis via the regulated export of a range of cargoes, including proteins and several classes of RNAs, from the nucleus to the cytoplasm. Dysregulation of this protein plays a pivotal role in the development of various solid and haematological malignancies. Furthermore, XPO1 is associated with resistance to several standard-of-care therapies, including chemotherapies and targeted therapies, making it an attractive target of novel cancer therapies. Over the years, a number of selective inhibitors of nuclear export have been developed. However, only selinexor has been clinically validated. The novel mechanism of action of XPO1 inhibitors implies a different toxicity profile to that of other agents and has proved challenging in certain settings. Nonetheless, data from clinical trials have led to the approval of the XPO1 inhibitor selinexor (plus dexamethasone) as a fifth-line therapy for patients with multiple myeloma and as a monotherapy for patients with relapsed and/or refractory diffuse large B cell lymphoma. In this Review, we summarize the progress and challenges in the development of nuclear export inhibitors and discuss the potential of emerging combination therapies and biomarkers of response.

Piezo 1 activation facilitates cholangiocarcinoma metastasis via Hippo/YAP signaling axis

Tumor metastasis is one of the major factors for the high mortality in cholangiocarcinoma (CCA), but its underlying mechanisms are not fully understood. Here, we report that Piezo-type mechanosensitive ion channel component 1 (Piezo 1) is detected to be significantly upregulated in CCA tissues, which is linked to a poor prognosis in patients, suggesting that Piezo 1 may act in a pro-metastatic role in CCA development. Piezo 1 is activated through 20% simulated physiological stretch, and deleting Piezo 1 impedes epithelial-to-mesenchymal transition (EMT) of CCA cells, as well as impairing their metastatic capacity in vitro and in vivo. Mechanistically, the activation of Piezo 1 results in large amounts of Yes-associated protein 1 (YAP) translocated into the nucleus from the cytoplasm, and thus the motility of CCA cells is significantly increased. These findings indicate that mechanical stimulation induces Piezo 1 activation, which might be involved in CCA metastasis via the Hippo/YAP signaling axis. Therefore, Piezo 1 and its downstream effectors may be a novel therapeutic target for CCA treatment.

NEK1 Phosphorylation of YAP Promotes Its Stabilization and Transcriptional Output

Simple Summary

We earlier described the involvement of the TLK1>NEK1>ATR>Chk1 axis as a key determinant of cell cycle arrest in androgen-dependent prostate cancer (PCa) cells after androgen deprivation. We now report that the TLK1>NEK1 axis is also involved in stabilization of yes-associated protein 1 (YAP1), the transcriptional co-activator in the Hippo pathway, presumably facilitating reprogramming of the cells toward castration-resistant PCa (CRPC). NEK1 interacts with YAP1 physically resulting in its phosphorylation of 6 residues, which enhance its stability and activity. Analyses of cancer Protein Atlas and TCGA expression panels revealed a link between activated NEK1 and YAP1 expression and several YAP transcription targets.

Abstract

Most prostate cancer (PCa) deaths result from progressive failure in standard androgen deprivation therapy (ADT), leading to metastatic castration-resistant PCa (mCRPC); however, the mechanism and key players leading to this are not fully understood. While studying the role of tousled-like kinase 1 (TLK1) and never in mitosis gene A (NIMA)-related kinase 1 (NEK1) in a DNA damage response (DDR)-mediated cell cycle arrest in LNCaP cells treated with bicalutamide, we uncovered that overexpression of wt-NEK1 resulted in a rapid conversion to androgen-independent (AI) growth, analogous to what has been observed when YAP1 is overexpressed. We now report that overexpression of wt-NEK1 results in accumulation of YAP1, suggesting the existence of a TLK1>NEK1>YAP1 axis that leads to adaptation to AI growth. Further, YAP1 is co-immunoprecipitated with NEK1. Importantly, NEK1 was able to phosphorylate YAP1 on six residues in vitro, which we believe are important for stabilization of the protein, possibly by increasing its interaction with transcriptional partners. In fact, knockout (KO) of NEK1 in NT1 PCa cells resulted in a parallel decrease of YAP1 level and reduced expression of typical YAP-regulated target genes. In terms of cancer potential implications, the expression of NEK1 and YAP1 proteins was found to be increased and correlated in several cancers. These include PCa stages according to Gleason score, head and neck squamous cell carcinoma, and glioblastoma, suggesting that this co-regulation is imparted by increased YAP1 stability when NEK1 is overexpressed or activated by TLK1, and not through transcriptional co-expression. We propose that the TLK1>NEK1>YAP1 axis is a key determinant for cancer progression, particularly during the process of androgen-sensitive to -independent conversion during progression to mCRPC.

Functional characterization of uveal melanoma oncogenes

Uveal melanoma (UM) is a currently untreatable form of melanoma with a 50% mortality rate. Characterization of the essential signaling pathways driving this cancer is critical to develop target therapies. Activating mutations in the Gαq signaling pathway at the level of GNAQ, GNA11, or rarely CYSLTR2 or PLCβ4 are considered alterations driving proliferation in UM and several other neoplastic disorders. Here, we systematically examined the oncogenic signaling output of various mutations recurrently identified in human tumors. We demonstrate that CYSLTR2 → GNAQ/11 → PLCβ act in a linear signaling cascade that, via protein kinase C (PKC), activates in parallel the MAP-kinase and FAK/Yes-associated protein pathways. Using genetic ablation and pharmacological inhibition, we show that the PKC/RasGRP3/MAPK signaling branch is the essential component that drives the proliferation of UM. Only inhibition of the MAPK branch but not the FAK branch synergizes with inhibition of the proximal cascade, providing a blueprint for combination therapy. All oncogenic signaling could be extinguished by the novel GNAQ/11 inhibitor YM-254890, in all UM cells with driver mutation in the Gαq subunit or the upstream receptor. Our findings highlight the GNAQ/11 → PLCβ → PKC → MAPK pathway as the central signaling axis to be suppressed pharmacologically to treat for neoplastic disorders with Gαq pathway mutations.

Emerging Kinase Therapeutic Targets in Pancreatic Ductal Adenocarcinoma and Pancreatic Cancer Desmoplasia

Kinase drug discovery represents an active area of therapeutic research, with previous pharmaceutical success improving patient outcomes across a wide variety of human diseases. In pancreatic ductal adenocarcinoma (PDAC), innovative pharmaceutical strategies such as kinase targeting have been unable to appreciably increase patient survival. This may be due, in part, to unchecked desmoplastic reactions to pancreatic tumors. Desmoplastic stroma enhances tumor development and progression while simultaneously restricting drug delivery to the tumor cells it protects. Emerging evidence indicates that many of the pathologic fibrotic processes directly or indirectly supporting desmoplasia may be driven by targetable protein tyrosine kinases such as Fyn-related kinase (FRK); B lymphoid kinase (BLK); hemopoietic cell kinase (HCK); ABL proto-oncogene 2 kinase (ABL2); discoidin domain receptor 1 kinase (DDR1); Lck/Yes-related novel kinase (LYN); ephrin receptor A8 kinase (EPHA8); FYN proto-oncogene kinase (FYN); lymphocyte cell-specific kinase (LCK); tec protein kinase (TEC). Herein, we review literature related to these kinases and posit signaling networks, mechanisms, and biochemical relationships by which this group may contribute to PDAC tumor growth and desmoplasia.

Comprehensively investigating the expression levels and the prognostic role of transforming growth factor beta-induced (TGFBI) in glioblastoma multiforme

BACKGROUND

Transforming growth factor beta-induced (TGFBI) protein has been found expressed in several cancer types, and expression levels of TGFBI can affect the cancer patients' outcomes, but the role of TGFBI in glioblastoma multiforme (GBM) remains obscure.

METHODS

The TGFBI expression levels in GBM were performed via Gene Expression Profiling Interactive Analysis (GEPIA) and UALCAN databases. Further, the mutations types of TGFBI were analyzed by using the cBioportal dataset. LinkedOmics selected correlated genes, kinases, and microRNA (miRNA) targets of TGFBI. GEPIA conducted the prognostic value of TGFBI and correlated genes. Then, the relationship between TGFBI and immune infiltrates was performed by Tumor Immune Estimation Resource (Timer). We compared the TGFBI protein expression levels in GBM and control samples through the Human Protein Atlas (HPA). Finally, the GSCAlite was used to achieve the drugs, and molecules target the TGFBI and significantly correlated genes.

RESULTS

TGFBI is significantly overexpressed in GBM, but the clinical features do not have considerable influence on TGFBI expression levels. Overexpression of TGFBI acts as an adverse biomarker of GBM. The enrichment function of TGFBI showed that the main biological functions, including extracellular matrix (ECM) organization, angiogenesis, leukocyte migration, T cell activation, cell cycle G2/M phase transition, and growth factor binding. About the significant correlated genes, overexpression of mitogen-activated protein kinase 13 (MAPK13) [Log-rank P=0.08 HR (high) =1.4], myosin IG (MYO1G) [Log-rank P=0.06 HR (high) =1.4], plasminogen activator urokinase receptor (PLAUR) [Log-rank P=0.03 HR (high) =1.5], thrombomodulin (THBD) [Log-rank P=0.028 HR (high) =1.5] indicated the poor prognosis of GBM. Further, TGFBI had a significant association with dendritic cell (DC) infiltrates (cor =0.516, P=9.00e-30). The higher the DC infiltration, the shorter survival of GBM. TGFBI protein expression levels were not significantly different in GBM and normal tissue. Finally, TGFBI is associated with resistance to belinostat, LAQ824, CAY10603, CUDC-101, methotrexate, 5-fluorouracil, and navitoclax.

CONCLUSIONS

In the present study, we showed TGFBI was overexpressed in GBM, and TGFBI is associated with DC cell infiltrates. Overexpression of TGFBI and high DC infiltration might be an adverse biomarker of GBM. Finally, TGFBI is associated with tumor multi-drug resistance.

The YAP-Interacting Phosphatase SHP2 Can Regulate Transcriptional Coactivity and Modulate Sensitivity to Chemotherapy in Cholangiocarcinoma

The Hippo pathway effector Yes-associated protein (YAP) is localized to the nucleus and transcriptionally active in a number of tumor types, including a majority of human cholangiocarcinomas. YAP activity has been linked to chemotherapy resistance and has been shown to rescue KRAS and BRAF inhibition in RAS/RAF-driven cancers; however, the underlying mechanisms of YAP-mediated chemoresistance have yet to be elucidated. Herein, we report that the tyrosine phosphatase SHP2 directly regulates the activity of YAP by dephosphorylating pYAPY357 even in the setting of RAS/RAF mutations, and that diminished SHP2 phosphatase activity is associated with chemoresistance in cholangiocarcinomas. A screen for YAP-interacting tyrosine phosphatases identified SHP2, and characterization of cholangiocarcinomas cell lines demonstrated an inverse relationship between SHP2 levels and pYAPY357. Human sequencing data demonstrated lower SHP2 levels in cholangiocarcinomas tumors as compared with normal liver. Cell lines with low SHP2 expression and higher levels of pYAPY357 were resistant to gemcitabine and cisplatin. In cholangiocarcinomas cells with high levels of SHP2, pharmacologic inhibition or genetic deletion of SHP2 increased YAPY357 phosphorylation and expression of YAP target genes, including the antiapoptotic regulator MCL1, imparting resistance to gemcitabine and cisplatin. In vivo evaluation of chemotherapy sensitivity demonstrated significant resistance in xenografts with genetic deletion of SHP2, which could be overcome by utilizing an MCL1 inhibitor. IMPLICATIONS: These findings demonstrate a role for SHP2 in regulating YAP activity and chemosensitivity, and suggest that decreased phosphatase activity may be a mechanism of chemoresistance in cholangiocarcinoma via a MCL1-mediated mechanism.

Mechano-modulatory synthetic niches for liver organoid derivation

The recent demonstration that primary cells from the liver can be expanded in vitro as organoids holds enormous promise for regenerative medicine and disease modelling. The use of three-dimensional (3D) cultures based on ill-defined and potentially immunogenic matrices, however, hampers the translation of liver organoid technology into real-life applications. We here use chemically defined hydrogels for the efficient derivation of both mouse and human hepatic organoids. Organoid growth is found to be highly stiffness-sensitive, a mechanism independent of acto-myosin contractility and requiring instead activation of the Src family of kinases (SFKs) and yes-associated protein 1 (YAP). Aberrant matrix stiffness, on the other hand, results in compromised proliferative capacity. Finally, we demonstrate the establishment of biopsy-derived human liver organoids without the use of animal components at any step of the process. Our approach thus opens up exciting perspectives for the establishment of protocols for liver organoid-based regenerative medicine.

3D liver organoids hold great promise for regenerative medicine but the use of ill-defined matrices limits their potential. Here, the authors generate human and mouse liver organoids using a chemically defined matrix, and reveal a link between matrix stiffness and organoid growth that does not require acto-myosin contraction.

Core Hippo pathway components act as a brake on Yap and Taz in the development and maintenance of the biliary network

The development of the biliary system is a complex yet poorly understood process, with relevance to multiple diseases, including biliary atresia, choledochal cysts and gallbladder agenesis. We present here a crucial role for Hippo-Yap/Taz signaling in this context. Analysis of sav1 mutant zebrafish revealed dysplastic morphology and expansion of both intrahepatic and extrahepatic biliary cells, and ultimately larval lethality. Biliary dysgenesis, but not larval lethality, is driven primarily by Yap signaling. Re-expression of Sav1 protein in sav1-/- hepatocytes is able to overcome these initial deficits and allows sav1-/- fish to survive, suggesting cell non-autonomous signaling from hepatocytes. Examination of sav1-/- rescued adults reveals loss of gallbladder and formation of dysplastic cell masses expressing biliary markers, suggesting roles for Hippo signaling in extrahepatic biliary carcinomas. Deletion of stk3 revealed that the phenotypes observed in sav1 mutant fish function primarily through canonical Hippo signaling and supports a role for phosphatase PP2A, but also suggests Sav1 has functions in addition to facilitating Stk3 activity. Overall, this study defines a role for Hippo-Yap signaling in the maintenance of both intra- and extrahepatic biliary ducts.

The Hippo Pathway and YAP Signaling: Emerging Concepts in Regulation, Signaling, and Experimental Targeting Strategies With Implications for Hepatobiliary Malignancies

The Hippo pathway and its effector protein YAP (a transcriptional coactivator) have been identified as important in the biology of both hepatocellular carcinoma and cholangiocarcinoma. First identified as a tumor suppressor pathway in Drosophila, the understanding of the mammalian YAP signaling and its regulation continues to expand. In its "on" function, the canonical regulatory Hippo pathway, a well-described serine/threonine kinase module, regulates YAP function by restricting its subcellular localization to the cytoplasm. In contrast, when the Hippo pathway is "off," YAP translocates to the nucleus and drives cotranscriptional activity. Given the role of Hippo/YAP signaling in hepatic malignancies, investigators have sought to target these molecules; however, standard approaches have not been successful based on the pathways' negative regulatory role. More recently, additional regulatory mechanisms, such as tyrosine phosphorylation, of YAP have been described. These represent positive regulatory events that may be targetable. Additionally, several groups have identified potentiating feed-forward signaling for YAP in multiple contexts, suggesting other experimental therapeutic approaches to interrupt these signaling loops. Herein we explore the current data supporting alternative YAP regulatory pathways, review the described feed-forward signaling cascades that are YAP dependent, and explore targeting strategies that have been employed in preclinical models of hepatic malignancies.

The YAP/TAZ Pathway in Osteogenesis and Bone Sarcoma Pathogenesis

YAP and TAZ are intracellular messengers communicating multiple interacting extracellular biophysical and biochemical cues to the transcription apparatus in the nucleus and back to the cell/tissue microenvironment interface through the regulation of cytoskeletal and extracellular matrix components. Their activity is negatively and positively controlled by multiple phosphorylation events. Phenotypically, they serve an important role in cellular plasticity and lineage determination during development. As they regulate self-renewal, proliferation, migration, invasion and differentiation of stem cells, perturbed expression of YAP/TAZ signaling components play important roles in tumorigenesis and metastasis. Despite their high structural similarity, YAP and TAZ are functionally not identical and may play distinct cell type and differentiation stage-specific roles mediated by a diversity of downstream effectors and upstream regulatory molecules. However, YAP and TAZ are frequently looked at as functionally redundant and are not sufficiently discriminated in the scientific literature. As the extracellular matrix composition and mechanosignaling are of particular relevance in bone formation during embryogenesis, post-natal bone elongation and bone regeneration, YAP/TAZ are believed to have critical functions in these processes. Depending on the differentiation stage of mesenchymal stem cells during endochondral bone development, YAP and TAZ serve distinct roles, which are also reflected in bone tumors arising from the mesenchymal lineage at different developmental stages. Efforts to clinically translate the wealth of available knowledge of the pathway for cancer diagnostic and therapeutic purposes focus mainly on YAP and TAZ expression and their role as transcriptional co-activators of TEAD transcription factors but rarely consider the expression and activity of pathway modulatory components and other transcriptional partners of YAP and TAZ. As there is a growing body of evidence for YAP and TAZ as potential therapeutic targets in several cancers, we here interrogate the applicability of this concept to bone tumors. To this end, this review aims to summarize our current knowledge of YAP and TAZ in cell plasticity, normal bone development and bone cancer.

A gain-of-functional screen identifies the Hippo pathway as a central mediator of receptor tyrosine kinases during tumorigenesis

The Hippo pathway has emerged as a key signaling pathway that regulates various biological functions. Dysregulation of the Hippo pathway has been implicated in a broad range of human cancer types. While a number of stimuli affecting the Hippo pathway have been reported, its upstream kinase and extracellular regulators remain largely unknown. Here we performed the first comprehensive gain-of-functional screen for receptor tyrosine kinases (RTKs) regulating the Hippo pathway using an RTK overexpression library and a Hippo signaling activity biosensor. Surprisingly, we found that the majority of RTKs could regulate the Hippo signaling activity. We further characterized several of these novel relationships [TAM family members (TYRO3, AXL, METRK), RET, and FGFR family members (FGFR1 and FGFR2)] and found that the Hippo effectors YAP/TAZ are central mediators of the tumorigenic phenotypes (e.g., increased cell proliferation, transformation, increased cell motility, and angiogenesis) induced by these RTKs and their extracellular ligands (Gas6, GDNF, and FGF) through either PI3K or MAPK signaling pathway. Significantly, we identify FGFR, RET, and MERTK as the first RTKs that can directly interact with and phosphorylate YAP/TAZ at multiple tyrosine residues independent of upstream Hippo signaling, thereby activating their functions in tumorigenesis. In conclusion, we have identified several novel kinases and extracellular stimuli regulating the Hippo pathway. Our findings also highlight the pivotal role of the Hippo pathway in mediating Gas6/GDNF/FGF-TAM/RET/FGFR-MAPK/PI3K signaling during tumorigenesis and provide a compelling rationale for targeting YAP/TAZ in RTK-driven cancers.

BCR-ABL induces tyrosine phosphorylation of YAP leading to expression of Survivin and Cyclin D1 in chronic myeloid leukemia cells

In the present study, we studied downstream signals of BCR-ABL with regard to Src family kinases and YAP, a transcription cofactor and an effector of the Hippo pathway. We first checked the phosphorylation status of YAP and found that it was constitutively phosphorylated at tyrosine 357 in CML-derived cell lines (TCC-S and K562) but not in AML-derived cell lines (HL-60 and KG-1a). Treatment with imatinib or RK-20449 inhibited cell growth and decreased tyrosine phosphorylation of YAP in both CML lines. Expression of Survivin or Cyclin D1 was decreased in TCC-S, but not in either HL-60 or KG-1a. Furthermore, we established BCR-ABL stable transfectant and control empty vector transfectant from TF-1, a factor-dependent human erythroleukemia cell line, to verify our results obtained with CML cell lines. YAP was phosphorylated at Y357 constitutively in BCR-ABL stable transfectant but not in control transfectant, and treatment with imatinib or RK-20449, a Src family kinase-specific inhibitor, inhibited cell growth, YAP tyrosine phosphorylation, and expression of Cyclin D1 in BCR-ABL stable transfectant. These results suggest that BCR-ABL induces tyrosine phosphorylation of YAP presumably through Src family kinases, which results in expression of Survivin and Cyclin D leading to leukemogenesis in CML cells.

YES1 Is a Targetable Oncogene in Cancers Harboring YES1 Gene Amplification

Targeting genetic alterations of oncogenes by molecular-targeted agents (MTA) is an effective approach for treating cancer. However, there are still no clinical MTA options for many cancers, including esophageal cancer. We used a short hairpin RNA library to screen for a new oncogene in the esophageal cancer cell line KYSE70 and identified YES proto-oncogene 1 (YES1) as having a significant impact on tumor growth. An analysis of clinical samples showed that YES1 gene amplification existed not only in esophageal cancer but also in lung, head and neck, bladder, and other cancers, indicating that YES1 would be an attractive target for a cancer drug. Because there is no effective YES1 inhibitor so far, we generated a YES1 kinase inhibitor, CH6953755. YES1 kinase inhibition by CH6953755 led to antitumor activity against YES1-amplified cancers in vitro and in vivo. Yes-associated protein 1 (YAP1) played a role downstream of YES1 and contributed to the growth of YES1-amplified cancers. YES1 regulated YAP1 transcription activity by controlling its nuclear translocation and serine phosphorylation. These findings indicate that the regulation of YAP1 by YES1 plays an important role in YES1-amplified cancers and that CH6953755 has therapeutic potential in such cancers. SIGNIFICANCE: These findings identify the SRC family kinase YES1 as a targetable oncogene in esophageal cancer and describe a new inhibitor for YES1 that has potential for clinical utility.See related commentary by Rai, p. 5702.

Beyond TCR Signaling: Emerging Functions of Lck in Cancer and Immunotherapy

In recent years, the lymphocyte-specific protein tyrosine kinase (Lck) has emerged as one of the key molecules regulating T-cell functions. Studies using Lck knock-out mice or Lck-deficient T-cell lines have shown that Lck regulates the initiation of TCR signaling, T-cell development, and T-cell homeostasis. Because of the crucial role of Lck in T-cell responses, strategies have been employed to redirect Lck activity to improve the efficacy of chimeric antigen receptors (CARs) and to potentiate T-cell responses in cancer immunotherapy. In addition to the well-studied role of Lck in T cells, evidence has been accumulated suggesting that Lck is also expressed in the brain and in tumor cells, where it actively takes part in signaling processes regulating cellular functions like proliferation, survival and memory. Therefore, Lck has emerged as a novel druggable target molecule for the treatment of cancer and neuronal diseases. In this review, we will focus on these new functions of Lck.

YAP and the Hippo pathway in cholangiocarcinoma

Cholangiocarcinoma (CCA) has an increasing incidence and remains a difficult to treat malignancy. In a search for more effective treatment options, progress has been made in identifying molecular drivers of oncogenic signaling including IDH mutations and FGFR2 fusions. In addition, multiple investigators have identified increased activity of YAP, the effector protein of the Hippo pathway, in CCA. The Hippo pathway regulates organ size, cellular proliferation, and apoptosis via YAP, a transcriptional co-activator. Targeting of the pathway has been difficult due the lack of a dedicated cell-surface receptor. However, more recently, additional cross-regulatory pathways have been identified that are potentially targetable. In this review, we address the current treatment landscape for CCA, the Hippo pathway broadly, animal models of CCA with attention to Hippo-related models, and the current strategies for targeting YAP.

Emerging roles of YAP/TAZ in lung physiology and diseases

The YAP and TAZ, as the downstream effectors of Hippo pathway, have emerged as important translational co-activators of a wide variety of biological processes. YAP/TAZ plays a crucial role in the lung development and physiology. Dysregulation of YAP/TAZ signaling pathway contributes to the development and progression of chronic lung diseases, including lung cancer, pulmonary fibrosis, pulmonary hypertension, COPD, asthma, and lung infection. Therefore, owing to its critical functions, delineation of the signaling mechanisms of YAP/TAZ in pathological conditions will shed light on developing strategies for its therapeutic targeting. Currently, the complex regulation of this pathway is under extensive investigation. In this review, we summarize and present recent findings of molecular mechanisms of YAP/TAZ in the lung physiological and pathological conditions, as well as the implications of YAP/TAZ for lung diseases treatment and regeneration.

Enigma proteins regulate YAP mechanotransduction

Human cells can sense mechanical stress acting upon integrin adhesions and respond by sending the YAP (also known as YAP1) and TAZ (also known as WWTR1) transcriptional co-activators to the nucleus to drive TEAD-dependent transcription of target genes. How integrin signaling activates YAP remains unclear. Here, we show that integrin-mediated mechanotransduction requires the Enigma and Enigma-like proteins (PDLIM7 and PDLIM5, respectively; denoted for the family of PDZ and LIM domain-containing proteins). YAP binds to PDLIM5 and PDLIM7 (hereafter PDLIM5/7) via its C-terminal PDZ-binding motif (PBM), which is essential for full nuclear localization and activity of YAP. Accordingly, silencing of PDLIM5/7 expression reduces YAP nuclear localization, tyrosine phosphorylation and transcriptional activity. The PDLIM5/7 proteins are recruited from the cytoplasm to integrin adhesions and F-actin stress fibers in response to force by binding directly to the key stress fiber component α-actinin. Thus, forces acting on integrins recruit Enigma family proteins to trigger YAP activation during mechanotransduction.This article has an associated First Person interview with the first author of the paper.