RNPC1, an RNA-binding protein and a target of the p53 family, regulates p63 expression through mRNA stability.

P63, a p53 family tumor suppressor, is involved in many cellular processes, including growth suppression and differentiation. Thus, p63 activity needs to be tightly controlled. Here, we found that RNPC1, a RNA-binding protein and a target of the p53 family, regulates p63 mRNA stability and consequently p63 activity. Specifically, we showed that overexpression of RNPC1 decreases, whereas knockdown of RNPC1 increases, the half-life of p63 transcript, which leads to altered p63 expression. Consistent with this, we showed that RNPC1 binds the AU-/U-rich elements in p63 3' UTR in vitro and in vivo and the RRM domain in RNPC1 is required for binding, and regulating the stability of, p63 transcript. Furthermore, we showed that RNPC1 promotes keratinocyte differentiation by repressing p63 expression. Together, we uncovered a previously undetected mechanism by which p63 expression is regulated via mRNA stability and a novel regulatory feedback loop between RNPC1 and p63.