Mutational and nonmutational activation of p21(ras) in rat colonic azoxymethane-induced tumors: Effects on mitogen-activated protein kinase, cyclooxygenase-2, and cyclin D1

Azoxymethane (AOM)-induced colonic carcinogenesis involves a number of muta tions, including those in the R-ras gene and CTNNB1, that codes for beta-ca tenin Prior in vitro studies have also demonstrated that wild type p21(K-ra s) can be activated by epigenetic events. We identified 15 K-ras mutations in 14 of 84 AOM-induced colonic tumors by three independent methods. By sin gle strand conformational polymorphism, we also observed mutations in 22 of 68 tumors in exon 3 of CTNNB1. A highly sensitive method was then used to measure p21(ras) activation Levels. All tumors assayed possessing R-ms muta tions had significantly higher p21(ras) activation levels (8.8 +/- 1.5%; n = 13) compared with that of control colon (3.7 +/- 0.4; n = 6; P < 0.05) or tumors without such mutations (4.2 +/- 0.4%; Ir = 70; P < 0.05). Among tum ors with wild-type K-ras, there was a subset of tumors (18 of 70) that had significantly higher p21(ras) activation levels (8.0 +/- 0.9%; n = 18) comp ared with control colons. In three of four tumors examined with activated w ild-type p21(ras) we observed increased c-erbB-2 receptor expression and de creased Ras-GAP expression. In contrast, only one of eight tumors examined with wild-type ras and nonactivated p21(ras) demonstrated these alterations . Mitogen-activated protein kinase (MAPK) activation and cyclooxygenase-2, (COX-2 expression Here increased in tumors with mutated or activated wild-t ype p21(ras), compared with their nonactivated counterparts. Although beta- catenin mutations did not alter COX-2, expression or MAPK activity, mutatio ns in either R-ras or beta-catenin significantly increased cyclin D1 expres sion. In contrast, in tumors with wild-type but activated D21(ras). cyclin DI expression was not enhanced. Thus, the spectrum of changes in MAPK, COX- 2, and cyclin DI is distinct among tumors with ras of beta-catenin mutation s or nonmutational activation of p21(ras).