Role of interleukin-6/signal transduction and activator of transcription 3 signalling in cholic acid-induced intestinal carcinogenesis in Apcmin/+ mice

Abstract

Objective To investigate the effect of cholic acid on intestinal carcinogenesis and its possible mechanisms in Apcmin/+ mice. Methods Twenty Apcmin/+ mice were divided into control group and cholic acid group, 10 mice in each group. The mice of control group were fed with regular diet, and the mice of cholic acid group were fed with regular diet and 0.4% cholic acid. All mice were sacrificed after treated for 12 weeks. The number, size and location of intestinal adenomas were observed in two groups. The pathological type was assessed by hematcxylin-eosin (HE) staining. The level of tumor cell proliferation was detected by Ki-67 immunohistochemistry staining. The expression level of intestinal inflammatory cytokines interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α were measured by real-time polymerase chain reaction (PCR). The impact of cholic acid on the activation of IL-6/signal transduction and activator of transcription3 (STAT3) signalling was determined by immunohistochemistry. The role of cholic acid on IL-6/STAT3 activation and its downstream gene cyclin D1 was further confirmed by Western blot. Independent sample t test was performed for mean comparison between two samples. Results Compard with that of control group, cholic acid significantly increased the total number of intestinal adenomas in Apcmin/+ mice (22.80±0.93 vs 33.40±1.17) and percentage of Ki-67 positive cells ((31.60±2.14)% vs (71.20±3.19)%), and the differences were statistically significant (t=7.11 and 10.31, both P<0.01). There was no obvious inflammatory cells infiltration in cholic acid group according to HE staining. The relative expression levels of inflammatory cytokines IL-1β, IL-6 and TNF-α were higher than those of control group (7.09±1.03 vs 1.09±0.11, 2.27±0.19 vs 0.99±0.09 and 14.70±2.29 vs 1.13±0.10, respectively), and the differences were statistically significant (t=5.81, 6.11 and 5.92, all P<0.01). In mice intestinal tissues, cholic acid could significantly increase the expression of IL-6 and phospho-STAT3 at protein level. And the expression of phospho-STAT3 (Tyr705) was five times as much as that in control group (5 517.00±81.50 vs 863.50±9.13) in immorto-min colonic epithelial cell line (IMCE) stimulated by cholic acid, and the expression of cyclin D1 was seven times as much as that in control group (11 165.00±78.53 vs 2 443.00±45.85), and the differences were statistically significant (t=56.74 and 95.91, both P<0.01). Conclusion Cholic acid may induce low-grade inflammation in intestine, active IL-6/STAT3 signalling pathway, promote tumor cell proliferation and then cause intestinal adenoma carcinogenesis in Apcmin/+ mice. Key words: Cholic acid; Intestinal adenoma; Carcinogenesis; IL-6; STAT3; Apcmin/+ mice