Expression of oncofetal RNA‐binding protein CRD‐BP/IMP1 predicts clinical outcome in colon cancer

The oncofetal CRD‐BP/IMP1 RNA binding protein regulates posttranscriptionally a handful of RNA transcripts, implicated in cell adhesion and invadopodia formation and was recently identified as a target of the β‐catenin/Tcf transcription factor that is constitutively activated in colorectal carcinomas (CRCs). The expression of CRD‐BP/IMP1 was studied in normal adult intestines and CRCs. In normal mucosa, CRD‐BP/IMP1 immunoreactivity was observed in few scattered cells located predominantly at or near the bottom of the crypts, whereas in CRCs the protein was detectable in tumor cells of 50% of the specimens analyzed. CRD‐BP/IMP1 mRNA expression was measured by qRT‐PCR in 78 CRCs. Thirty‐two (41%) of the specimens were negative or had negligible expression, whereas the remaining forty‐six (59%) expressed a wide range of CRD‐BP/IMP1 mRNA levels. CRD‐BP/IMP1 mRNA expression correlated with that of the putative stem/progenitor cell marker Musashi‐1 mRNA ( p = 0. 035). CRD‐BP/IMP1 positive tumors metastasized and/or recurred more frequently ( p = 0.001) and its expression defined a group of patients with shorter survival ( p = 0.014). Furthermore, in a multivariate analysis CRD‐BP/IMP1 expression was found to be an independent predictor of survival ( p = 0.015). For stage I & II patients, the differences in metastasis/recurrence and survival rates remained significant ( p = 0.001 and 0.033, respectively). These findings indicate that CRD‐BP/IMP1 positive tumors exhibit early disease dissemination and unfavorable prognosis. © 2007 Wiley‐Liss, Inc.