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Ursodeoxycholic acid inhibits Ras mutations, wild-type Ras activation, and cyclooxygenase-2 expression in colon
Sharad Khare1, Sonia Cerda, Ramesh K Wali
1Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA. skhare@medicine.bsd.uchicago.edu
Abstract:
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.
Insights
Ursodeoxycholic acid (UDCA) prevents colon cancer by suppressing Ras mutations and blocking wild-type Ras activation. UDCA also inhibits cyclooxygenase-2 (Cox-2) expression, offering a potential therapeutic strategy for colon cancer.
Area of Science:
- Oncology
- Gastroenterology
- Molecular Biology
Background:
- K-ras mutations are common in colon cancer, driving tumor growth.
- Wild-type Ras can be activated by upstream pathways like ErbB signaling.
- Increased cyclooxygenase-2 (Cox-2) expression is observed in tumors with mutant or activated Ras.
Purpose of the Study:
- To investigate the role of Ras in ursodeoxycholic acid (UDCA)-mediated inhibition of cyclooxygenase-2 (Cox-2).
- To determine if UDCA affects K-ras mutations or wild-type Ras activation in a colon cancer model.
Main Methods:
- Azoxymethane (AOM)-induced rat colon cancer model.
- Assessment of K-ras mutations and Ras activation (GTP-bound Ras).
- Quantification of Cox-2 mRNA and protein levels.
Main Results:
- UDCA significantly suppressed the incidence of tumors with K-ras mutations (3.2% vs. 27%).
- UDCA completely abolished the development of tumors with activated wild-type Ras (0% vs. 23%).
- UDCA inhibited Cox-2 up-regulation in tumors, irrespective of Ras mutational status.
Conclusions:
- UDCA suppresses colon tumor development by inhibiting both K-ras mutations and wild-type Ras activation.
- UDCA effectively reduces Cox-2 expression through Ras-dependent and -independent mechanisms.
- UDCA demonstrates potential as a therapeutic agent for colon cancer prevention and treatment.