Expression, Mutation And LOH Of Gene ING1 In Sporadic Colorectal Carcinoma

Expression, Mutation and LOH of Gene ING1 in Sporadic Colorectal Carcinoma BACKGROUND & OBJECTIVE: ING1 has been identified as a novel tumor suppressor gene, and proved to be involved in the modulation of cell cycle. Its expression can inhibit cell growth, control cellular aging, and induce cell apoptosis. It has more than 3 different splices at transcription, and becomes three subtypes at least. P33^ING1 is 'molecular partner'of wild type p53; they both depend and cooperate with each other in cell growth control. The abnormal alterations of gene ING1, such as low expression, loss and mutation, have been found in some human tumors. These findings demonstrate that ING1 may play a role in the genesis and progression of human tumors. There are seldom reports about ING1 in colorectal cancer, and no report about p47^ING1 by now. Our study was to explore the effect and significance of ING1 gene in the genesis and progression of sporadic colorectal cancer by detecting mRNA expression of p33^ING1 and p47^ING1, LOH and mutation of gene ING1. METHODS: mRNA expression, mutation and LOH of gene ING1 in 46 specimens of sporadic colorectal cancer tissues and matched normal tissues were detected by semi-quantitative RT-PCR, PCR-SSCP and PCR-SSLP,respectively. RESULTS: (1) All the 46 samples of tumor tissues and their normal counterparts express both p33^ING1 mRNA and p47_ING1 mRNA. The average ratios of light density of p33^ING1 mRNA, and p47/ING1 mRNA in the cancerous tissues were significantly lower than those in their normal counterparts, respectively (0.52 vs 1.28, P<0.01; 0.51 vs 1.21, P<0.01). Difference between the 2 mRNA splices was not significant in the matched tissues (P>0.05). (2) The average ratios of light density of p33^ING1 mRNA and p47^ING1 mRNA in the cancerous tissues of Dukes C/D stage were significantly lower than those in the cancerous tissues of Dukes A/B stage, respectively (0.38 vs 0.65, P<0.01; 0.40 vs 0.63, P<0.01). But there are no statistical differences between the groups of different age, gender, location of tumor, tumor invasive scope, and differentiation, respectively. (3) To investigate whether the ING1 gene is the target of functional loss in tumors, we searched for mutation in the encoding regions of the gene in all 46 samples of colorectal cancer by PCR-SSCP, but no mutation was found. (4) To investigate whether allelic imbalance of terminal regions of chromosome 13q is reserved, we examined DNA from 46 pairs of matched tumor tissues and normal tissues for LOH at 5 microsatellite markers by PCR-SSLP, but only 5 cases of LOH (10.9%) were found. CONCLUSIONS: (1) Sporadic colorectal cancerous tissues and their normal counterpartsexpressed both different intensities of p33^ING1 mRNA and p47^ING1 mRNA. Their expressions in the cancerous tissues were significantly lower than those in the normal counterparts. The more advanced clinical stage they were at, the less mRNA expression of p33^ING1 and p47^ING1 they presented. Their down-regulation relate tightly with the genesis and progression of sporadic colorectal cancers. (2) No mutation of gene ING1 was found in sporadic colorectal cancer. Only a few of LOH were found at chromosome 13q^33-34. These were not the main reason for the decreased expressions of p33^ING1 mRNA and p47^ING1 mRNA. Their down-regulations maybe happen in the level of transcription or post-transcription.