Hu antigen R and Tristetraprolin: Regulates Claudin 1 mRNA Stability in Colon Cancer

RNA binding proteins (RBPs) play a crucial role in Posttranscriptional gene regulation but the mechanism of most RBPs is stil unknown. The human RBP HuR/ELAVL1 is a conserved mRNA stability regulator. ELAV like RNA‐binding proteins Hu antigen R (HuR) and tristetraprolin (TTP) associate with labile mRNAs bearing AU‐rich elements located in the 3′ untranslated regions (3′‐UTRs) and modulate their stability. We have identified putative HUR–binding sites in the proximal region of the claudin‐1, 3′‐UTR and demonstrate that HuR and TTP interacts with these AU‐rich elements. Claudin‐1, a tight junction protein, expression is dysregulated in the majority of human colorectal carcinomas. We used a ribonomic and site‐directed mutagenesis approach to test the binding of HuR and TTP to claudin‐1, 3′UTR and their role in stabilization/destabilization of claudin‐1 mRNA in the presence of HDAC inhibitor. We found that Claudin‐1 mRNA was stabilized by activated HUR in both SW480 and SW620 cells, whereas overexpression of TTP inhibited it; limited TTP expression antagonized HuR‐mediated claudin 1 mRNA stabilization. On treatment with TSA the binding of HuR to claudin‐1 3′UTR decreases while the binding of TTP increases correlating well with the rapid decay of claudin‐1 mRNA in presence of TSA in colon cancer only. Thus, our data suggest that claudin‐1 is regulated via mRNA stability and a novel regulatory feedback loop between HuR and TTP in colon specific tumorigenesis.