Loss of heterozygosity on long arm of chromosome 22 in sporadic colorectal carcinoma

AIM: The loss of heterozygosity (LOH) on tumorsuppressor genes is believed to play a key role incarcinogenesis of colorectal cancer, In this study, weanalyzed the LOH at 5 loci on the long arm ofchromosome 22 in sporadic colorectal cancer to identifyadditional loci involved in colorectal tumorigenesis.METHODS: Five polymorphic microsatellite markerswere analyzed in 83 cases of colorectal and normal DNAby PCR. PCR products were eletrophoresed on an ABI377 DNA sequencer; Genescan 3.1 and Genotype 2.1software were used for LOH scanning and analysisComparison between LOH frequency andclinicopathological data were performed by x2 test. P＜0.05 was considered as statistically significant.RESULTS: The average LOH frequency on chromosome22q was 28.38 %. The region between markersD22S280 and D22S274 (22q12.2-q13.33) exhibitedrelatively high LOH frequency. The two highest LOH lociwith frequencies of 35.09 % and 34.04 % wasidentified on D22S280 (22q12.2-12.3) and D22S274(22q13.32-13.33). 8 cases showed LOH at allinformative loci, suggesting that one chromosome 22qhad been completely lost. On D22S274 locus, LOHfrequency of rectal cancer was 50 % (9/18), which washigher than that of proximal colon cancer (12 %, 2/17) (P=0.018). The frequency of distal colon cancer was42 % (5/12), also higher than that of proximal coloncancer. But there was no statistical significance. Puttingboth the tumors in distal colon and rectum togetherinto consideration, the frequency, 47 % (14/30), washigher than that of proximal colon cancer (P=0.015),suggesting the mechanism of carcinogenisis wasdifferent in both groups.CONCLUSIONS: This study provided evidence for theinvolvement of putative tumor suppressor genes relatedto the sporadic colorectal carcinoma on chromosome22q. The tumor-suppressor-gene(s) might locate on the22q12.2-12.3 and/or 22q13.32-13.33.

AIM:The loss of heterozygosity(LOH)on tumor suppressor genes is believed to play a key role in carcinogenesis of colorectal cancer.In this study,we analyzed the LOH at 5 loci on the long arm of chromosome 22 in sporadic colorectal cancer to identify additional loci involved in colorectal tumorigenesis. METHODS:Five polymorphic microsatellite markers were analyzed in 83 cases of celorectal and normal DNA by PCR.PCR products were eletrophoresed on an ABI 377 DNA sequencer;Genescan 3.1 and Genotype 2.1 software were used for LOH scanning and analysis. Comparison between LOH frequency and clinicopathological data were performed by x^2 test.P <0,05 was considered as statistically significant. RESULTS:The average LOH frequency on chromosome 22q was 28.38 %.The region between markers D22S280 and D22S274(22q12.2-q13.33)exhibited relatively high LOH frequency.The two highest LOH loci with frequencies of 35.09 % and 34.04 % was identified on D22S280(22q12.2-12.3)and D22S274 (22q13.32-13.33).8 cases showed LOH at all informative loci,suggesting that one chromosome 22q had been completely lost.On D22S274 locus,LOH frequency of rectal cancer was 50 %(9/18),which was higher than that of proximal colon cancer(12 %,2/ 17)(P=0.018).The frequency of distal colon cancer was 42 %(5/12),also higher than that of proximal colon cancer.But there was no statistical significance.Putting both the tumors in distal colon and rectum together into consideration,the frequency,47 %(14/30),was higher than that of proximal colon cancer(P=0.015), suggesting the mechanism of carcinogenisis was different in both groups. CONCLUSIONS:This study provided evidence for the involvement of putaUve tumor suppressor genes related to the sporadic colorectal carcinoma on chromosome 22q.The tumor-suppressor-gene(s)might locate on the 22q12.2-12.3 and/or 22q13.32-13.33.