Increased Musashi-2 and Decreased NUMB Protein Levels Observed in Human Colorectal Cancer are reverted to Normal Levels by ATRA-Induced Cell Differentiation

Abstract

Background: Musashi stem cell (SC) proteins (MSI-1 & MSI-2) are known to become over expressed during colorectal tumorigenesis in humans and mice. MSI-1 overexpression induces tumorigenesis through Notch activation via inactivation of NUMB. Previous studies also show that MSI-2 overexpression in mice induces intestinal tumorigenesis but the mechanism is independent of NUMB. However, whether the MSI-2/NUMB pathway contributes to colorectal cancer (CRC) development in humans is still undetermined. Methods: We evaluated expression of MSI-2 and NUMB proteins in matched normal and CRC patient samples, as well as in human CRC cell lines. We also determined whether induction of cellular differentiation by all-trans retinoic acid (ATRA) influences MSI-2 and NUMB expression. Results: Analysis of matched patient tissue samples and CRC cell lines showed that MSI-2 protein expression is significantly increased and NUMB expression is decreased in CRCs compared to the normal colonic tissue. Immunostaining of normal and adenomatous colonic epithelium revealed that MSI-1+ and MSI-2+ SCs reside in the SC niche and they become overpopulated during colon tumorigenesis. Moreover, promoting cellular differentiation by ATRA reduces MSI-2 protein levels, while increasing NUMB protein levels in human CRC cell lines. Conclusions: MSI-2/NUMB protein expression is altered during colon tumorigenesis, and indicates that MSI-2/ NUMB signaling in human colonic stem cells is closely linked to normal colonic epithelial homeostasis. Implications: The ability to normalize MSI-2/NUMB signaling by inducing differentiation of cancer SCs suggests a novel therapeutic approach for CRC treatment.

HOXA9 Overexpression Contributes to Stem Cell Overpopulation That Drives Development and Growth of Colorectal Cancer

“…First, IC50 concentrations were determined for ATRA and DEAB in HT29 and SW480 cells ( Figure 1 A,B). We found that the IC50 concentration for ATRA was 10 µM for both cell lines, which is consistent with prior studies [ 7 , 23 , 25 ]. The IC50 concentrations for DEAB were 100 µM for SW480 and 1 mM for HT29.…”