Ursodeoxycholic acid inhibits Ras mutations, wild-type Ras activation, and cyclooxygenase-2 expression in colon cancer.
K-ras mutations occur frequently in colon cancer and contribute to autonomous growth. In the azoxymethane (AOM) model of colon cancer, in addition to K-ras mutations, we have shown that wild-type (WT) Ras can be activated by upstream pathways, including, e.g., signaling by ErbB receptors. Tumors with mutant or activated WT Ras had increased cyclooxygenase-2 (Cox-2) expression. We have also shown that ursodeoxycholic acid (UDCA) prevented AOM-induced colon cancer and suppressed Cox-2 induction. In this study, we examined the role of Ras in Cox-2 inhibition by UDCA. Rats were fed AIN-76A chow alone, or supplemented with 0.4% UDCA, and received 20 mg/kg AOM i.p. weekly x 2 weeks. At 40 weeks, rats were sacrificed, and tumors were harvested. K-ras mutations were assessed by primer-mediated RFLP, allele-specific oligonucleotide hybridization, and direct DNA sequencing. Ras was immunoprecipitated and defined as activated if [Ras - GTP/(Ras - GTP + Ras - GDP)] was >3 SD above normal colonocytes. Cox-2 mRNA was determined by reverse transcription-PCR, and protein expression was assessed by Western blotting and immunostaining. In the AOM alone group, Ras was activated by mutations in 8 of 30 (27%) tumors, and WT Ras was activated in 7 of 30 (23%) tumors. UDCA significantly suppressed the incidence of tumors with mutant Ras (1 of 31, 3.2%; P < 0.05) and totally abolished the development of tumors with activated WT Ras (0 of 10; P < 0.05). In the AOM alone group, Cox-2 was up-regulated >50-fold in tumors with normal Ras activity and further enhanced in tumors with mutant or signaling-activated Ras. UDCA significantly inhibited Cox-2 protein and mRNA levels in tumors with normal Ras activity. In summary, we have shown for the first time that UDCA suppressed the development of tumors with Ras mutations and blocked activation of WT Ras. Furthermore, UDCA inhibited Cox-2 induction by Ras-dependent and -independent mechanisms.
Khare
Sharad
S
Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA. skhare@medicine.bsd.uchicago.edu
Cerda
Sonia
S
Wali
Ramesh K
RK
von Lintig
Friederike C
FC
Tretiakova
Maria
M
Joseph
Loren
L
Stoiber
Debra
D
Cohen
Greg
G
Nimmagadda
Kiran
K
Hart
John
J
Sitrin
Michael D
MD
Boss
Gerry R
GR
Bissonnette
Marc
M
D000818:Animals; D001397:Azoxymethane; D003110:Colonic Neoplasms / Q000139:chemically induced / Q000201:enzymology / Q000235:genetics*; D051546:Cyclooxygenase 2; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D011905:Genes, ras / Q000187:drug effects; D007527:Isoenzymes / Q000235:genetics*; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000187:drug effects*; D014580:Ursodeoxycholic Acid / Q000494:pharmacology*
D007527:Isoenzymes; D012333:RNA, Messenger; D014580:Ursodeoxycholic Acid; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D001397:Azoxymethane