Mutational and nonmutational activation of p21ras 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 mutations, including those in the K-ras gene and CTNNB1, that codes for beta-catenin. Prior in vitro studies have also demonstrated that wild type p21(K-ras) 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 single 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 p21ras activation levels. All tumors assayed possessing K-ras mutations had significantly higher p21ras 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%; n = 70; P < 0.05). Among tumors with wild-type K-ras, there was a subset of tumors (18 of 70) that had significantly higher p21ras activation levels (8.0 +/- 0.9%; n = 18) compared with control colons. In three of four tumors examined with activated wild-type p21ras, we observed increased c-erbB-2 receptor expression and decreased Ras-GAP expression. In contrast, only one of eight tumors examined with wild-type ras and nonactivated p21ras demonstrated these alterations. Mitogen-activated protein kinase (MAPK) activation and cyclooxygenase-2 (COX-2) expression were increased in tumors with mutated or activated wild-type p21ras, compared with their nonactivated counterparts. Although beta-catenin mutations did not alter COX-2 expression or MAPK activity, mutations in either K-ras or beta-catenin significantly increased cyclin D1 expression. In contrast, in tumors with wild-type but activated p21-ras, cyclin D1 expression was not enhanced. Thus, the spectrum of changes in MAPK, COX-2, and cyclin D1 is distinct among tumors with ras or beta-catenin mutations or nonmutational activation of p21ras.
Bissonnette
M
M
University of California, San Diego 92093, USA.
Khare
S
S
von Lintig
F C
FC
Wali
R K
RK
Nguyen
L
L
Zhang
Y
Y
Hart
J
J
Skarosi
S
S
Varki
N
N
Boss
G R
GR
Brasitus
T A
TA
D000818:Animals; D001397:Azoxymethane; D002273:Carcinogens; D003110:Colonic Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism; D019938:Cyclin D1 / Q000096:biosynthesis*; D051546:Cyclooxygenase 2; D003598:Cytoskeletal Proteins / Q000235:genetics; D004789:Enzyme Activation; D011905:Genes, ras / Q000235:genetics; D007527:Isoenzymes / Q000096:biosynthesis*; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D009154:Mutation / Q000502:physiology*; D012150:Polymorphism, Restriction Fragment Length; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D015534:Trans-Activators; D051176:beta Catenin
D002273:Carcinogens; C495268:Ctnnb1 protein, rat; D003598:Cytoskeletal Proteins; D007527:Isoenzymes; D015534:Trans-Activators; D051176:beta Catenin; D019938:Cyclin D1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D020929:Mitogen-Activated Protein Kinase Kinases; D016283:Proto-Oncogene Proteins p21(ras); D001397:Azoxymethane