The MST/YAP (mammalian Ste20-like kinase/Yes-associated protein 2) pathway plays an important role in hepatocellular carcinoma (HCC). Although post-translational modification-especially MST/Lats (large tumor suppressor)-mediated phosphorylation and PP1 (protein phosphatase-1)-mediated dephosphorylation-has been found to regulate the activity of YAP2, very little is known about its acetylation. In our experiments, we observed that the expression of SIRT1 is significantly upregulated in the tumor samples of the hepatocarcinoma patients, and SIRT1 mRNA level positively correlates with connective tissue growth factor (CTGF) mRNA level. We then found that SIRT1 deacetylates YAP2 protein in HCC cells and SIRT1-mediated deacetylation increases the YAP2/TEAD4 association, leading to YAP2/TEAD4 transcriptional activation and upregulated cell growth in HCC cells. Moreover, knockdown of SIRT1 blocks the cisplatin (CDDP)-induced nuclear translocation of YAP2 and enhances the chemosensitivity of HCC cells to CDDP treatment. Together, our findings reveal a new regulatory mechanism of YAP2 by the SIRT1-mediated deacetylation that may be involved in HCC tumorigenesis and drug resistance.

Introduction To depict the genomic landscape of Chinese early-stage lung squamous cell carcinoma (LUSC) and investigate its correlation with tumor mutation burden (TMB), PD-L1 expression, and immune infiltrates. Methods Whole-exome sequencing was performed on 189 surgically resected LUSC. TMB was defined as the sum of nonsynonymous single nucleotide and indel variants. CD8 + tumor-infiltrating lymphocyte (TIL) density and PD-L1 expression were evaluated by immunohistochemistry. Six immune infiltrates were estimated using an online database. Results The median TMB was 9.43 mutations per megabase. Positive PD-L1 expression and CD8 + TILs density were identified in 24.3% and 78.8%. PIK3CA amplification was associated with significantly higher TMB ( P = 0.036). Frequent genetic alterations had no impact on PD-L1 expression but PIK3CA amplification and KEAP1 mutation were independently associated with significantly lower CD8 + TIL density ( P < 0.001, P = 0.005, respectively). Low TMB and high CD8 + TIL density were independently associated with longer disease-free survival (DFS) while none of them could individually predict the overall survival (OS). Combination of TMB and PD-L1 expression or TMB and CD8 + TIL density could stratify total populations into two groups with distinct prognosis. Classifying tumor-immune microenvironment based on PD-L1 expression and CD8 + TIL density showed discrepant genomic alterations but similar TMB, clinical features, and OS. Notably, patients with different smoking status had distinct prognostic factors. Conclusion The combination of TMB, PD-L1 expression, immune infiltrates, and smoking status showed the feasibility to subgroup stratification in Chinese patients with early-stage LUSC, which might be helpful for future design of personalized immunotherapy trials in LUSC. Electronic supplementary material The online version of this article (10.1186/s13045-019-0762-1) contains supplementary material, which is available to authorized users.

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Mammalian Sterile 20-like kinase 1 (MST1) protein kinase plays an important role in the apoptosis induced by a variety of stresses. The MST1 is a serine/threonine kinase that is activated upon apoptotic stimulation, which in turn activates its downstream targets, JNK/p38, histone H2B and FOXO. It has been reported that overexpression of MST1 initiates apoptosis by activating p53. However, the molecular mechanisms underlying MST1-p53 signaling during apoptosis are unclear. Here, we report that MST1 promotes genotoxic agent-induced apoptosis in a p53-dependent manner. We found that MST1 increases p53 acetylation and transactivation by inhibiting the deacetylation of Sirtuin 1 (Sirt1) and its interaction with p53 and that Sirt1 can be phosphorylated by MST1 leading to the inhibition of Sirt1 activity. Collectively, these findings define a novel regulatory mechanism involving the phosphorylation of Sirt1 by MST1 kinase which leads to p53 activation, with implications for our understanding of signaling mechanisms during DNA damageinduced apoptosis.The protein kinase mammalian Sterile 20-like kinase 1 (MST1) 4 contains a Ste20-related kinase catalytic domain in the amino-terminal segment followed by a regulatory domain at the COOH terminus (1). It has been implicated in diverse biological functions, including cell proliferation, differentiation, morphogenesis, and cytoskeletal rearrangements. Previous studies have indicated that the noncatalytic tail of MST1 is cleaved by caspase-3 in response to a number of apoptotic stimuli such as death receptor triggering by CD95/FasL, staurosporine or ceramide, and heat shock and arsenite. The amino-terminal fragment of cleaved MST1 translocates into the nucleus where it contributes to chromatin condensation and then apoptosis (2-4). Furthermore, when MST1 is overexpressed, cleavage and subsequent induced apoptosis can also be observed (5). It has been reported that the two major cleavage sites are Asp-326 and Asp-349, and kinase activation, nuclear translocation, and the ability of MST1 to induce cell death are apparently attenuated by mutating these cleavage sites (4, 6). Recently threonine 183 has been identified as a crucial phosphoactivation site in subdomain VIII of MST1, and it is essential for kinase activation. Autophosphorylation of threonine 183 within the MST1 kinase domain is required for its activation (7). Hippo, a mammalian homolog of MST1/2 in Drosophila, has been extensively shown to restrain cell growth and proliferation through inhibition of the transcription and/or degradation of cyclin E and Drosophila Inhibitor of Apoptosis proteins (8, 9) or the phosphorylation and inhibition of Yorkie (10). In mammals, it has been shown that MST1 can activate c-Jun amino-terminal kinase (JNK) and p38 MAPK kinase signaling pathways through MKK4/MKK7 and MKK3/MKK6, respectively (3). Recently, it has been suggested that JNK is essential and sufficient for MST1 activation and MST1-mediated apoptosis via phosphorylation of serine 82 in MST1 (11,12). In addition, MST1-induced c...

Clinical and experimental evidence indicates that macrophages could promote solid-tumor progression and metastasis. However, the mechanisms underlying this process remain unclear. Here we show that yes-associated protein 1 (YAP1), a transcriptional regulator that controls tissue growth and regeneration, has an important role in tumor necrosis factor α (TNF α)-induced breast cancer migration. Mechanistically, macrophage conditioned medium (CM) or TNFα triggers IκB kinases (IKKs)-mediated YAP phosphorylation and activation in breast cancer cells. We further found that TNFα or macrophage CM treatment increases the interaction between p65 and YAP. Chromatin immunoprecipitation (ChIP) assay shows that YAP/TEAD (TEA domain family member) and p65 proteins synergistically regulate the transcription of hexokinase 2 (HK2), a speed-limiting enzyme in glycolysis, and promotes TNFα-induced or macrophage CM-induced cell migration. Together, our findings indicate an important role of TNFα-IKK-YAP/p65-HK2 signaling axis in the process of inflammation-driven migration in breast cancer cells, which reveals a new molecular link between inflammation and breast cancer metastasis.

The Yes-associated protein (YAP), a transcriptional coactivator inactivated by the Hippo tumor suppressor pathway, functions as an oncoprotein in a variety of cancers. However, its contribution to breast cancer remains controversial. This study investigated the role of YAP in breast cancer cells under nutrient deprivation (ND). Here, we show that YAP knockdown sensitized MCF7 breast cancer cells to nutrient deprivation-induced apoptosis. Furthermore, in response to ND, YAP increased the autolysosome degradation, thereby enhancing the cellular autophagic flux in breast cancer cells. Of note, autophagy is crucial for YAP to protect MCF7 cells from apoptosis under ND conditions. In addition, the TEA domain (TEAD) family of growth-promoting transcription factors was indispensable for YAP-mediated regulation of autophagy. Collectively, our data reveal a role for YAP in promoting breast cancer cell survival upon ND stress and uncover an unappreciated function of YAP/TEAD in the regulation of autophagy.

BackgroundOsteosarcoma is the most common bone malignancy in children and adolescents, and 20%–30% of the patients suffer from poor prognosis because of individual chemoresistance. The Hippo/yes-associated protein (YAP) signaling pathway has been shown to play a role in tumor chemoresistance, but no previous report has focused on its involvement in osteosarcoma chemoresistance. This study aimed to investigate the role of the Hippo/YAP signaling pathway in osteosarcoma chemoresistance and to determine potential treatment targets.MethodsUsing the Cell Titer-Glo Luminescent cell viability assay and flow cytometry analysis, we determined the proliferation and chemosensitivity of YAP-overexpressing and YAP-knockdown osteosarcoma cells. In addition, using western blotting and the real-time polymerase chain reaction technique, we investigated the alteration of the Hippo/YAP signaling pathway in osteosarcoma cells treated with chemotherapeutic agents.ResultsMammalian sterile 20-like kinase 1 (MST1) degradation was increased, and large tumor suppressor kinase 1/2 (LATS1/2) total protein levels were decreased by methotrexate and doxorubicin, which increased activation and nuclear translocation of YAP. Moreover, YAP increased the proliferation and chemoresistance of MG63 cells.ConclusionsThe Hippo/YAP signaling pathway plays a role in osteosarcoma chemoresistance, and YAP is a potential target for reducing chemoresistance.

Shp2 is a tumor suppressor, and the decrease in Shp2 expression was a new prognostic marker in HCC. The oncogenic role of Shp2 was tissue specific, and the therapeutic target of human gene PTPN11 should be reconsidered.