Background:
Mir-143 and mir-145 are believed to function as colon cancer tumor suppressors, as they inhibit colon cancer cell growth and are downregulated in sporadic colonic tumors. we speculated that mir-143 and mir-145 might also be downregulated and contribute to malignant transformation of colonic epithelium in longstanding ulcerative colitis (uc).
Methods:
Biopsies were obtained 20 cm proximal to the anus from individuals with quiescent uc and from normal controls. rna and proteins were extracted and measured. mir-143 and mir-145 were quantified by real-time polymerase chain reaction (pcr) and mir-145 was also assessed by in situ hybridization. putative targets of these mirnas, k-ras, api5, mek-2 (mir-143), and irs-1 (mir-145) were determined by western blotting. to assess the effects of mir-143 and mir-145 on these predicted targets, hct116 and hca-7 colorectal cancer cells were transfected with mir-143 and mir-145 and expression levels of these proteins were measured.
Results:
In uc, mir-143 and mir-145 were significantly downregulated 8.3-fold (3.4-20.1) (p < 0.0001) and 4.3-fold (2.3-7.8) (p < 0.0001), respectively, compared to normal colon. in contrast, irs-1, k-ras, api5, and mek-2 were upregulated in uc, consistent with their assignments as targets of these mirnas. furthermore, transfected mir-143 and mir-145 significantly downregulated these proteins in hct116 or hca-7 cells.
Conclusions:
Compared to normal colonic mucosa, in chronic uc mir-143 and mir-145 were significantly downregulated and their predicted targets, irs-1, k-ras, api5, and mek-2 were upregulated. we postulate that loss of these tumor suppressor mirnas predispose to chronic inflammation and neoplastic progression in ibd.