<p>RASSF6 Is Downregulated In Human Bladder Cancers And Regulates Doxorubicin Sensitivity And Mitochondrial Membrane Potential Via The Hippo Signaling Pathway</p>

Abstract

BackgroundThe present study aimed to investigate the clinicopathological significance and biological roles of RASSF6 in human bladder cancers.Materials and methodsImmunohistochemistry and Western blots were used to examine the protein expression of RASSF6 in bladder cancer tissues. Biological roles of RASSF6 were examined using MTT, colony formation assay, Matrigel invasion assay, cell cycle analysis, AnnexinV/PI staining and JC-1 staining. Western blot analysis was used to examine the potential mechanism.ResultsWe found that RASSF6 was downregulated in 73 of 138 bladder cancer specimens, which correlated with advanced stages. RASSF6 overexpression decreased the cell growth rate and inhibited invasion ability in T24 cell line. Downregulation of RASSF6 using siRNA increased the cell proliferation rate and promoted invasion in 5637 cell line. Cell cycle studies showed that RASSF6 overexpression suppressed the process of cell cycle progression. RASSF6 overexpression also increased the cellular response to doxorubicin (DOX) treatment. AnnexinV/PI staining showed that RASSF6 overexpression promoted DOX-induced apoptosis with increased cytochrome c and cleavage of caspase-3 and caspase-9. We also showed that RASSF6 overexpression downregulated the mitochondrial membrane potential, while RASSF6 depletion showed the opposite effect. Western blot analysis demonstrated that RASSF6 overexpression repressed p-Rb and Bcl-xL while upregulating p21 expression. In addition, we found that RASSF6 overexpression affected the Hippo signaling pathway by downregulating YAP. Depletion of YAP downregulated Bcl-xL expression and abolished the effect of RASSF6 on Bcl-xL. Depletion of YAP also upregulated the level of apoptosis and downregulated mitochondrial membrane potential. YAP siRNA abolished the effects of RASSF6 on DOX-induced apoptosis and loss of mitochondrial membrane potential.ConclusionTaken together, our results showed that RASSF6 was downregulated in bladder cancers. RASSF6 inhibited cell proliferation and invasion, as well as the progression of cancer, by regulating DOX sensitivity and mitochondrial membrane potential, possibly via the Hippo signaling pathway.

Context-dependent roles of YAP/TAZ in stem cell fates and cancer

“…In senescent tumor cells, YAP sustains expression of the anti-apoptotic factor survivin [ 159 ]. YAP activates expression of BCL-xL in bladder cancer, and depletion of YAP increases apoptosis [ 160 ]. Using a hybrid spheroid model of cell competition, Liu et al showed that glioblastoma cells express YAP heterogeneously, and YAP-low cells experience more apoptosis, reminiscent of the E4.5 mouse epiblast, though it is not specified what downstream targets are involved [ 161 ].…”

The Hippo Signaling Pathway in Drug Resistance in Cancer

“…The tumor suppressor RASSF6 (another member in the RASSF family, along with RASSF1A), which is frequently downregulated in bladder cancer, regulates doxorubicin sensitivity via the Hippo pathway [ 95 ]. RASSF6 overexpression augments doxorubicin-triggered cell apoptosis by negatively regulating YAP and the pro-apoptosis protein Bcl-xL.…”

Characterization of mouse embryonic fibroblasts derived from Rassf6 knockout mice shows the implication of Rassf6 in the regulation of NF‐κB signaling

“…Allen et al identified RASSF6 based on the homology with RASSF1 and reported it as a putative tumor suppressor (Allen et al, 2007). The studies of cancer patients support its tumor suppressive role in human cancers (Djos et al, 2012;Guo et al, 2016;Hesson et al, 2009;Liang et al, 2014;Mezzanotte et al, 2014;Richter et al, 2009;Tan et al, 2019;Wen et al, 2011;Ye et al, 2015;Younesian et al, 2019). The experiments using human cancer cell lines show that RASSF6 is involved in the regulation of p53, RB1 and the tumor suppressor Hippo pathway (Hossain et al, 2018;Ikeda et al, 2009;Iwasa et al, 2013).…”