Expression of second class of KIP protein p57KIP2 in human colorectal carcinoma

p57KIP2, the second class of KIP family protein, is one of the negative regulators of the cell cycle. To elucidate the role of p57KIP2 in colorectal normal mucosa and cancer, we examined the expression of p57KIP2 protein in 110 pairs of colorectal non-tumor and cancer tissues. Immunohistochemical analysis showed that p57KIP2 was weakly detected in the normal colonic epithelium and lymph follicles. A unique expression pattern of p57KIP2 was exclusively noted in the elastic fibers within the walls of relatively large blood vessels (diameter >100 μm). In cancer tissues, p57KIP2 protein was localized mainly in nuclei. Using the mean percentage of nuclear p57KIP2 expression (25%) as the cut-off value, we divided our cases into those with high expression (n=44, 40%) and low expression (n=66, 60%) of p57KIP2 among 110 colorectal cancer cases tested. The clinical and pathological survey showed a significant correlation between low expression of p57KIP2 and large tumor size (p<0.05) or the presence of tumors in females (p<0.01). Survival analysis showed that p57KIP2 expression did not influence prognosis. RT-PCR analysis was also performed using RNA extracts from 6 colorectal cancer tissues. When the levels of p57KIP2 mRNAs were compared with expression of p57KIP2 protein, a clear correlation was found, suggesting that expression of the p57KIP2 protein may be regulated at the transcription level. The present study revealed p57KIP2 expression in colorectal cancer and suggests that p57KIP2 may not play a central role in the progression of colorectal cancer.