Implication of USP22 in the regulation of BMI-1, c-Myc, p16INK4a, p14ARF, and cyclin D2 expression in primary colorectal carcinomas.

BACKGROUND

Increasing experimental evidence suggests that USP22 plays a crucial role in the pathologic processes of epithelial malignancies and other solid tumors. BMI-1, p16INK4a, p14ARF, cyclin D2, and c-Myc have been implicated in the regulation of the cell cycle mediated by USP22 in cell culture experiments. In this study, we examined whether these in vitro findings can be extrapolated to the in vivo situation.

METHODS

We measured the expression of USP22 and the candidate targets such as BMI-1, c-Myc, cyclin D2, p16INK4a, p14ARF by quantitative real time-polymerase chain reaction, Western blotting, and immunostaining in a series of 43 colorectal carcinomas (CRCs) and correlated the data with several clinicopathologic variables.

RESULTS

The frequency of overexpression (4-fold expression analysis) was 37.0% for USP22, 48.9% for BMI-1, 48.9% for c-Myc, and 58.0% for cyclinD2, respectively. Statistical correlation analysis at the mRNA level showed USP22 to be significantly correlated with BMI-1 (r=0.889, P<0.0001), c_Myc (r=0.573, P<0.0001), and cyclin D2 (r=0.872, P<0.0001), but not p16IN K4a (r=0.222, P=0.153) or p14Are (r=-0.154, P=0.325) by quantitative real time-polymerase chain reaction. These findings were confirmed by the Western blotting assay. Furthermore, the k-means cluster analysis showed that CRCs with high mRNA expression of USP22, BMI-1, c-Myc, and cyclin D2 were significantly correlated with the advanced AJCC stage (P=0.01) associated with poor prognosis.

CONCLUSIONS

The findings of this study supported dysregulation of a proposed functional pathway by upregulation of gene products in primary CRC.