Spatiotemporal model of cellular mechanotransduction via Rho and YAP

How cells sense and respond to mechanical stimuli remains an open question. Recent advances have identified the translocation of Yes-associated protein (YAP) between nucleus and cytoplasm as a central mechanism for sensing mechanical forces and regulating mechanotransduction. We formulate a spatiotemporal model of the mechanotransduction signalling pathway that includes coupling of YAP with the cell force-generation machinery through the Rho family of GTPases. Considering the active and inactive forms of a single Rho protein (GTP/GDP-bound) and of YAP (non-phosphorylated/phosphorylated), we study the cross-talk between cell polarization due to active Rho and YAP activation through its nuclear localization. For fixed mechanical stimuli, our model predicts stationary nuclear-to-cytoplasmic YAP ratios consistent with experimental data at varying adhesive cell area. We further predict damped and even sustained oscillations in the YAP nuclear-to-cytoplasmic ratio by accounting for recently reported positive and negative YAP-Rho feedback. Extending the framework to time-varying mechanical stimuli that simulate cyclic stretching and compression, we show that the YAP nuclear-to-cytoplasmic ratio's time dependence follows that of the cyclic mechanical stimulus. The model presents one of the first frameworks for understanding spatiotemporal YAP mechanotransduction, providing several predictions of possible YAP localization dynamics, and suggesting new directions for experimental and theoretical studies.

Targeting cholesterol biosynthesis promotes anti-tumor immunity by inhibiting long noncoding RNA SNHG29-mediated YAP activation

Anti-tumor immunity through checkpoint inhibitors, specifically anti-programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) interaction, is a promising approach for cancer therapy. However, as early clinical trials indicate that colorectal cancers (CRCs) do not respond well to immune-checkpoint therapies, new effective immunotherapy approaches to CRC warrant further study. Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (CoA) reductase (HMGCR), the rate-limiting enzyme of the mevalonate (MVA) pathway for the cholesterol biosynthesis. However, little is known about the functions of simvastatin in the regulation of immune checkpoints or long noncoding RNA (lncRNA)-mediated immunoregulation in cancer. Here, we found that simvastatin inhibited PD-L1 expression and promoted anti-tumor immunity via suppressing the expression of lncRNA SNHG29. Interestingly, SNHG29 interacted with YAP and inhibited phosphorylation and ubiquitination-mediated protein degradation of YAP, thereby facilitating downregulation of PD-L1 transcriptionally. Patient-derived tumor xenograft (PDX) models and the clinicopathological analysis in samples from CRC patients further supported the role of the lncRNA SNHG29-mediated PD-L1 signaling axis in tumor microenvironment reprogramming. Collectively, our study uncovers simvastatin as a potential therapeutic drug for immunotherapy in CRC, which suppresses lncRNA SNHG29-mediated YAP activation and promotes anti-tumor immunity by inhibiting PD-L1 expression.

YAP Activation Drives Liver Regeneration after Cholestatic Damage Induced by Rbpj Deletion

Liver cholestasis is a chronic liver disease and a major health problem worldwide. Cholestasis is characterised by a decrease in bile flow due to impaired secretion by hepatocytes or by obstruction of bile flow through intra- or extrahepatic bile ducts. Thereby cholestasis can induce ductal proliferation, hepatocyte injury and liver fibrosis. Notch signalling promotes the formation and maturation of bile duct structures. Here we investigated the liver regeneration process in the context of cholestasis induced by disruption of the Notch signalling pathway. Liver-specific deletion of recombination signal binding protein for immunoglobulin kappa j region (Rbpj), which represents a key regulator of Notch signalling, induces severe cholestasis through impaired intra-hepatic bile duct (IHBD) maturation, severe necrosis and increased lethality. Deregulation of the biliary compartment and cholestasis are associated with the change of several signalling pathways including a Kyoto Encyclopedia of Genes and Genomes (KEGG) gene set representing the Hippo pathway, further yes-associated protein (YAP) activation and upregulation of SRY (sex determining region Y)-box 9 (SOX9), which is associated with transdifferentiation of hepatocytes. SOX9 upregulation in cholestatic liver injury in vitro is independent of Notch signalling. We could comprehensively address that in vivo Rbpj depletion is followed by YAP activation, which influences the transdifferentiation of hepatocytes and thereby contributing to liver regeneration.