OBJECTIVETo study the expression of p53 protein, incidence of p53 gene mutation and microsatellite instability in ulcerative colitis, dysplasia of colonic mucosa and ulcerative colitis-associated colorectal cancer.

METHODSP53 protein expression was detected by immunohistochemistry in 70 specimens from 21 cases of ulcerative colitis and 25 colonic mucosa specimens from normal subjects. The specimens of ulcerative colitis were examined for the mutation in exon 5, 6, 7, 8 of p53 gene with microdissection-PCR-SSCP/HA-clone-sequencing technique and the alterations in 10 microsatellite loci with microdissection-PCR-SSLP-clone- sequencing technique.

RESULTNone of 25 normal specimens was p53-positive immunohistochemically, while 4/21 of ulcerative colitis specimens were p53-positive. P53- positive rate in inflammatory mucosa of ulcerative colitis specimens was 0/5, while that was 1/7, 2/7 and 1/2 in low-grade displasia (LGD), high-grade displasia (HGD) and carcinoma, respectively. The abnormal exons were detected by SSCP and confirmed by sequencing in 2 out of 21 cases: one was exon 6 in a case with carcinoma and the other was exon 8 in a HGD case; both had positive P53 expression. Two cases showed positive in Bat26 locus by SSLP: one was a LGD case, the other was a case of carcinoma, who also had abnormal exon 6 of p53 gene. Other 9 microsatellite loci, (TGF beta RII(A)(10), IGFIIR(G)(8), IGFIIR(CT)(5), TGF beta RII(GT)(3), BAX(G)(8), hMSH3(A)8, hMSH6(C)(8), TCF4(A)(9) and DPC4 (CA)(17)) were showed negative in all cases.

CONCLUSIONP53 gene mutations and microsatellite instability may be one of the mechanisms for higher risk of carcinogenesis in ulcerative colitis.