The DEAD box protein p68: a novel coactivator of Stat3 in mediating oncogenesis.

DEAD box RNA helicase p68 acts as a transcriptional coactivator of several oncogenic transcription factors apart from being a vital player of RNA metabolism. Signal transducer and activator of transcription 3 (Stat3) is a major oncogenic contributor of diverse cancers, including that of colon. Deciphering the mechanistic insights of coactivation of Stat3 transcriptional activity may aid in improved therapeutic strategies. Here we report for the first time a novel mechanism of alliance between p68 and Stat3 in stimulating transcriptional activity of Stat3. Interestingly, we observed that the expression of p68 and Stat3 bears strong positive correlation and significant colocalization in normal and colon carcinoma patient samples. We demonstrated that p68 directly interacts with Stat3 in HEK293 cells as well as multiple colon cancer cell lines. Additionally, p68 positively modulated both mRNA and protein expression levels of Stat3 target genes; promoter activity of Stat3 target gene Mcl-1 in multiple colon cancer cell lines. Also, p68 occupied the promoters of multiple Stat3 target genes in enhancing Stat3-dependent transcription. Moreover, the strong positive correlation between the abundance of p68 and Stat3 target genes in the same set of colon carcinoma samples further supported our observations. Enhanced expression levels of Stat3 target genes observed in primary tumors and metastatic lung nodules, generated in mice colorectal allograft model using syngeneic cells stably expressing p68, further reinforced our in vitro findings. Hence, this study unravels novel modes of p68-mediated oncogenesis through coactivation of Stat3 and enhancing Stat3 signaling.