Alternate RASSF1 Transcripts Control SRC Activity, E-Cadherin Contacts, and YAP-Mediated Invasion.

Abstract

Tumor progression to invasive carcinoma is associated with activation of SRC family kinase (SRC, YES, FYN) activity and loss of cellular cohesion. The hippo pathway-regulated cofactor YAP1 supports the tumorigenicity of RAS mutations but requires both inactivation of hippo signaling and YES-mediated phosphorylation of YAP1 for oncogenic activity. Exactly how SRC kinases are activated and hippo signaling is lost in sporadic human malignancies remains unknown. Here, we provide evidence that hippo-mediated inhibition of YAP1 is lost upon promoter methylation of the RAS effector and hippo kinase scaffold RASSF1A. We find that RASSF1A promoter methylation reduces YAP phospho-S127, which derepresses YAP1, and actively supports YAP1 activation by switching RASSF1 transcription to the independently transcribed RASSF1C isoform that promotes Tyr kinase activity. Using affinity proteomics, proximity ligation, and real-time molecular visualization, we find that RASSF1C targets SRC/YES to epithelial cell-cell junctions and promotes tyrosine phosphorylation of E-cadherin, β-catenin, and YAP1. RASSF1A restricts SRC activity, preventing motility, invasion, and tumorigenesis in vitro and in vivo, with epigenetic inactivation correlating with increased inhibitory pY527-SRC in breast tumors. These data imply that distinct RASSF1 isoforms have opposing functions, which provide a biomarker for YAP1 activation and explain correlations of RASSF1 methylation with advanced invasive disease in humans. The ablation of epithelial integrity together with subsequent YAP1 nuclear localization allows transcriptional activation of β-catenin/TBX-YAP/TEAD target genes, including Myc, and an invasive phenotype. These findings define gene transcript switching as a tumor suppressor mechanism under epigenetic control.

• Authors: Nikola Vlahov, Simon Scrace, Manuel Sarmiento Soto, Anna M Grawenda, Leanne Bradley, Daniela Pankova, Angelos Papaspyropoulos, Karen S Yee, Francesca Buffa, Colin R Goding, Paul Timpson, Nicola Sibson, Eric O'Neill
• Journal: Current biology : CB (Curr Biol) Vol. 25 Issue 23 Pg. 3019-34 (Dec 07 2015) ISSN: 1879-0445 [Electronic] England
• PMID: 26549256 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

Chemical References

• Adaptor Proteins, Signal Transducing
• Cadherins
• Phosphoproteins
• RASSF1 protein, human
• Transcription Factors
• Tumor Suppressor Proteins
• YAP-Signaling Proteins
• YAP1 protein, human
• Protein Kinases

Topics

• Adaptor Proteins, Signal Transducing (genetics, metabolism)
• Cadherins (genetics, metabolism)
• Cell Line, Tumor
• Cell Proliferation
• Cell Transformation, Neoplastic
• Gene Expression Regulation, Neoplastic
• Humans
• Phosphoproteins (genetics, metabolism)
• Protein Kinases (genetics, metabolism)
• Signal Transduction
• Transcription Factors
• Transcriptional Activation
• Tumor Suppressor Proteins (genetics, metabolism)
• YAP-Signaling Proteins