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  • Title: Glutathione S-transferase-pi overexpression is closely associated with K-ras mutation during human colon carcinogenesis.
    Author: Miyanishi K, Takayama T, Ohi M, Hayashi T, Nobuoka A, Nakajima T, Takimoto R, Kogawa K, Kato J, Sakamaki S, Niitsu Y.
    Journal: Gastroenterology; 2001 Oct; 121(4):865-74. PubMed ID: 11606500.
    Abstract:
    BACKGROUND & AIMS: In colorectal adenoma and carcinoma, glutathione S-transferase-pi (GSTP1-1) is highly expressed. K-ras mutation is also known to occur frequently in colorectal adenoma and carcinoma, as well as in the putative precursor of adenoma, aberrant crypt foci (ACF). Further, forced expression of v-H-ras in rat liver epithelial cells has been shown to enhance rat pi-class GST expression. The aim of the present study is, therefore, to investigate the causative relationship between GSTP1-1 overexpression and K-ras mutation in these lesions. METHODS: Twenty-seven specimens of colorectal carcinoma, 24 of adenoma, and 28 of ACF were examined in this study. The expression of GSTP1-1 or p21(K-ras) was examined by immunohistochemistry. The GSTP1-1 messenger RNA levels were measured by TaqMan reverse-transcription polymerase chain reaction (PCR). K-ras mutation was detected by two-step PCR restriction fragment length polymorphism. v-K-ras transfection to RPMI-4788 colon carcinoma cells was carried out by the lipofection method. Activities of GSTP1-1 promoters containing AP-1 and Sp1 responsive elements in the v-K-ras transfectants were measured by a secreted form of human placental alkaline phosphatase (SEAP) assay. Nuclear protein from these transfectants bound to the GSTP1-1 promoter was analyzed by electrophoretic mobility shift assay (EMSA). RESULTS: In human colorectal carcinoma, adenoma, and ACF, close association of increased expression of GSTP1-1 with K-ras mutation was observed. v-K-ras transfectants showed significantly higher SEAP activity than that of mock-transfectant activity. EMSA showed specific interaction of AP-1 with promoter of GSTP1-1. CONCLUSIONS: It is highly plausible that GSTP1-1 overexpression in ACF, colorectal adenoma, and carcinoma is induced by K-ras mutation via AP-1 activation.
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