RNA helicase p68 deploys β-catenin in regulating RelA/p65 gene expression: implications in colon cancer

Abstract

BACKGROUND: RelA/p65 a crucial member of NF-κB signaling pathway plays diverse role in mediating oncogenesis. Limited knowledge prevails on the mechanistic insights of RelA gene regulation. RNA helicase p68 apart from being a vital player of RNA metabolism acts as a transcriptional coactivator of several oncogenic transcription factors including β-catenin and is highly implicated in cancer progression. In this study, we aim to discern the molecular mechanism of how an RNA helicase, p68 deploys a major oncogenic signaling pathway, Wnt/ β-catenin to regulate the expression of RelA, an indispensable component of NF-κB signaling pathway towards driving colon carcinogenesis. METHODS: Immunoblotting and quantitative RT-PCR was performed for determining the protein and mRNA expressions of the concerned genes respectively. Luciferase assay was employed for studying the promoter activity of RelA. Chromatin immunoprecipitation was used to evaluate the occupancy of transcription factors on the RelA promoter. Immunohistochemical analysis was conducted using FFPE sections derived from normal human colon and colon cancer patient samples. Finally, a syngeneic colorectal allograft mouse model was used to assess physiological significance of the in vitro findings. RESULTS: p68, β-catenin and RelA proteins were found to bear strong positive correlation in normal and colon carcinoma patient samples. Both p68 and β-catenin increased RelA mRNA and protein expression. p68, β-catenin and Wnt3a elevated RelA promoter activity. Conversely, p68 and β-catenin knockdown diminished RelA promoter activity and led to reduced RelA mRNA and protein expression. p68 was perceived to occupy RelA promoter with β-catenin at the TCF4/LEF (TBE) sites thereby potentiating RelA transcription. p68 and β-catenin alliance positively modulated the expression of signature NF-κB target genes. Enhanced NF-κB target gene expression by p68 was corroborated by findings in clinical samples. Tumors generated in mice colorectal allograft model, stably expressing p68 further reinforced our in vitro findings. CONCLUSIONS: We report for the first time a novel mechanism of alliance between p68 and β-catenin in regulating the expression of RelA and stimulating the NF-κB signaling axis towards driving colon carcinogenesis. This study unravels novel modes of p68-mediated colon carcinogenesis, marking it a potential target for therapy.