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Summary 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. [ABSTRACT FROM AUTHOR]

The RASSF family of proteins has been extensively studied in terms of their genetics, structure and function. One of the functions that has been increasingly studied is the role of the RASSF proteins in the DNA damage response. Surprisingly, this research, which encompasses both the classical and N-terminal RASSF proteins, has revealed an involvement of the RASSFs in oncogenic pathways as well as the more familiar tumour suppressor pathways usually associated with the RASSF family members. The most studied protein with respect to DNA damage is RASSF1A, which has been shown, not only to be activated by ATM, a major regulator of the DNA damage response, but also to bind to and activate a number of different pathways which all lead to and feedback from the guardian of the genome, p53. In this review we discuss the latest research linking the RASSF proteins to DNA damage signalling and maintenance of genomic integrity and look at how this knowledge is being utilised in the clinic to enhance the effectiveness of traditional cancer therapies such as radiotherapy. [ABSTRACT FROM AUTHOR]

Summary: Hypermethylation of CpG islands in the RASSF1 promoter is one of the most frequent events identified in human cancer . The epigenetic-driven loss of RASSF1A protein expression is observed more often in tumors of higher grade and correlates with a decreased responsiveness to DNA-damaging therapy . Ras association domain-containing family 1A (RASSF1A) promotes apoptosis by signaling through the MST2 and LATS1 kinases, leading to stabilization of the YAP1/p73 transcriptional complex . Here we provide evidence for a new pathway linking DNA damage signaling to RASSF1A via the main sensor of double-strand breaks in cells, ataxia telangiectasia mutated (ATM). We show that, upon DNA damage, RASSF1A is phosphorylated by ATM on Ser131 and is involved in the activation of both MST2 and LATS1, leading to the stabilization of p73. Furthermore, lung and ovarian tumor cell lines that retain RASSF1A expression commonly harbor polymorphisms in the region of Ser131 , and our analysis shows that the S131F polymorphism conveys resistance to DNA-damaging agents. Thus, we present a novel DNA damage pathway emanating from ATM that is frequently disabled in tumors via epigenetic silencing of RASSF1 or mutation of an ATM phosphorylation site. [Copyright &y& Elsevier]

Summary Epigenetic inactivation of the Hippo pathway scaffold RASSF1A is associated with poor prognosis in a wide range of sporadic human cancers. Loss of expression reduces tumor suppressor activity and promotes genomic instability, but how this pleiotropic biomarker is regulated at the protein level is unknown. Here we show that TGF-β is the physiological signal that stimulates RASSF1A degradation by the ubiquitin-proteasome pathway. In response to TGF-β, RASSF1A is recruited to TGF-β receptor I and targeted for degradation by the co-recruited E3 ubiquitin ligase ITCH. RASSF1A degradation is necessary to permit Hippo pathway effector YAP1 association with SMADs and subsequent nuclear translocation of receptor-activated SMAD2. We find that RASSF1A expression regulates TGF-β-induced YAP1/SMAD2 interaction and leads to SMAD2 cytoplasmic retention and inefficient transcription of TGF-β targets genes. Moreover, RASSF1A limits TGF-β induced invasion, offering a new framework on how RASSF1A affects YAP1 transcriptional output and elicits its tumor-suppressive function. [ABSTRACT FROM AUTHOR]

Abstract: Pin1 is an emerging oncology target strongly implicated in Ras and ErbB2-mediated tumourigenesis. Pin1 isomerizes bonds linking phospho-serine/threonine moieties to proline enabling it to play a key role in proline-directed kinase signalling. Here we report a novel series of Pin1 inhibitors based on a phenyl imidazole acid core that contains sub-μM inhibitors. Compounds have been identified that block prostate cancer cell growth under conditions where Pin1 is essential. [ABSTRACT FROM AUTHOR]

Abstract: The peptidyl prolyl cis/trans isomerase Pin1 is a promising molecular target for anti-cancer therapeutics. Here we report the structure-guided evolution of an indole 2-carboxylic acid fragment hit into a series of α-benzimidazolyl-substituted amino acids. Examples inhibited Pin1 activity with IC50 <100nM, but were inactive on cells. Replacement of the benzimidazole ring with a naphthyl group resulted in a 10–50-fold loss in ligand potency, but these examples downregulated biomarkers of Pin1 activity and blocked proliferation of PC3 cells. [Copyright &y& Elsevier]