Overexpression of an mRNA-binding protein in human colorectal cancer

A Coding Region instability Determinant-Binding Protein (CRD-BP) binds in vitro to c-myc mRNA and appears to stabilize the mRNA. The CRD-BP gene is amplified in one-third of human breast cancer cases, and the CRD-BP appears to be an oncofetal protein. To analyse CRD-BP expression in human cancer tissue, paired extracts of cancer and normal colon specimens from 21 patients were analysed by immunoblotting and/or reverse transcriptase-polymerase chain reaction. Seventeen cancer specimens out of 21 (81%) were positive for CRD-BP expression by one or both assays. With one exception, normal colon specimens were negative for CRD-BP expression; specimens of inflammatory bowel and a villous adenoma also had no detectable CRD-BP. The lack of CRD-BP expression in normal colon did not result from indiscriminate protein or RNA degradation. c-myc mRNA levels appeared to be elevated in tumor specimens. We conclude that the CRD-BP is scarce or absent from normal colon but is overexpressed in colorectal cancer. The CRD-BP might be a novel human tumor marker.