Abstract
Inhibitor of growth 5, a tumor suppressor protein, can interact with p53, thereby inhibiting cell growth and inducing apoptosis. Inhibitor of growth 5 overexpression results in a reduction in colony-forming efficiency and cell population in S phase. To clarify the roles of inhibitor of growth 5 in tumorigenesis and progression of colorectal carcinomas, we examined inhibitor of growth 5 expression by immunohistochemistry on a tissue microarray containing colorectal carcinomas (n = 306), adenomas (n = 69), and nonneoplastic mucosa (n = 288) and compared this with clinicopathologic parameters of the carcinomas. In addition, inhibitor of growth 5 expression in colorectal carcinoma tissues and cell lines (DLD-1, HCT-15, SW480, and WiDr) was analyzed by Western blot and reverse transcriptase-polymerase chain reaction. It was found that the inhibitor of growth 5 protein was localized to the nuclei of colon carcinoma cells with no differences at mRNA levels. Among 18 frozen samples of colorectal carcinoma, significantly increased expression of inhibitor of growth 5 protein was observed in the carcinoma in comparison with adjacent mucosa in 14 cases (77.8%; P < .05), and 71.4% (10/14) of carcinoma cases exhibited up-regulated inhibitor of growth 5 mRNA expression. Decreased inhibitor of growth 5 expression was detected by immunohistochemistry in colorectal carcinoma, compared with non-neoplastic mucosa and adenoma (P < .05). Nuclear inhibitor of growth 5 expression was negatively correlated with tumor size, depth of invasion, degree of dedifferentiation, and Union Internationale Contre le Cancer staging (P < .05). In contrast, cytoplasmic inhibitor of growth 5 expression was positively correlated with depth of invasion, lymphatic invasion, and Union Internationale Contre le Cancer staging (P < .05). It was suggested that aberrant inhibitor of growth 5 expression may contribute to pathogenesis, growth, and invasion of colorectal carcinomas and could be considered as a promising marker to gauge aggressiveness of colorectal carcinomas.