ABSTRACT
The RASSF family proteins have been implicated in the development of human cancers. To date, the expression pattern and biological significance of RASSF4 in colorectal cancers (CRC) have not been fully investigated. In the current study, we explored expression pattern of RASSF4 in 118 CRC specimens and 30 adjacent 'normal' colon tissues by immunohistochemistry. The results showed that RASSF4 was downregulated in CRC tissues compared with adjacent 'normal' tissues. RASSF4 downregulation significantly associated with advanced tumour-node-metastasis (TNM) stage, T status, positive node status and high Ki-67 index. Analysis of TCGA dataset also supported RASSF4 downregulation in CRC tissues. Ectopically expressed RASSF4 in LoVo cells inhibited cell growth, colony formation, cell cycle progression and increased the sensitivity to 5-FU treatment. Annexin V/PI apoptosis assay showed that RASSF4 overexpression increased 5-FU-induced apoptosis and downregulated the mitochondrial membrane potential. In addition, Western blot demonstrated that RASSF4 overexpression repressed YAP and Bcl-2 while upregulating p21 expression. YAP knockdown abolished the role of RASSF4 on Bcl-2. ChIP assay showed that TEAD4, a major YAP binding transcription factor, could bind to the promoter regions of Bcl-2. In conclusion, our data showed that RASSF4 was downregulated in human CRC. RASSF4 regulated malignant behaviour through YAP/Bcl-2 signalling in CRC cells.
