Cloning and Characterization of a p53 and DNA Damage Down-regulated Gene PIQ that Codes for a Novel Calmodulin-Binding IQ Motif Protein and Is Up-regulated in Gastrointestinal Cancers

Abstract

We have identified a p53 and DNA damage–regulated gene that encodes a novel IQ motif protein, which we have named p53 and DNA damage–regulated IQ motif protein (PIQ). PIQ has two isoforms, long (PIQ-_L) and short (PIQ-_S), and both bind to calmodulin in the presence and absence of calcium. PIQ expression is down-regulated by p53 and DNA damage–inducing agents, whereas PIQ itself represses the expression of p53 up-regulated modulator of apoptosis that is a key mediator of p53-induced apoptosis. Thus, PIQ is a novel protein that may function to bridge a crosstalk between p53 and calmodulin-regulated cellular processes. We further show that PIQ expression is up-regulated in a number of primary colorectal and gastric tumors when compared with matching normal tissues, suggesting that PIQ may be involved in tumorigenesis and could serve as a valuable diagnostic/prognostic marker for gastrointestinal tumors.