Aberration of p53 and DCC in gastric and colorectal cancer

Tumor suppress genes screening analysis on 4q in sporadic colorectal carcinoma

AIM: To search candidate tumor suppressor genes (TSGs) on chromosome 4q through detecting high loss of heterozygosity (LOH) regions in sporadic colorectal carcinoma in Chinese patients.

METHODS: Thirteen fluorescent labeled polymorphic microsatellite markers were analyzed in 83 cases of colorectal carcinoma and matched normal tissue DNA by polymerase chain reaction (PCR). PCR products were electrophoresed on an ABI 377 DNA sequencer. Genescan 3.7 and Genotype 3.7 software were used for LOH scanning and analysis. Comparison between LOH frequency and clinicopathological factors were performed by χ² test.

RESULTS: Data were collected on all informative loci. The average LOH frequency on 4q was 28.56%. The D4S2915 locus showed highest LOH frequency (36.17%). Two obvious deletion regions were detected: one between D4S3000 and D4S2915 locus (4q12-21.1), another flanked by D4S407 and D4S2939 locus (4q25-31.1). None case showed complete deletion of 4q, most cases displayed interstitial deletion pattern solely. Furthermore, compared with clinicopathological features, a significant relationship was observed between LOH frequencies on D4S3018 locus. In tumors larger than 5 cm in diameter, LOH frequency was significantly higher than tumors that were less than 5 cm (56% vs 13.79%, P = 0.01). On D4S1534 locus, LOH was significantly associated with liver metastasis (80% vs 17.25%, P = 0.012). No relationship was detected on other locus compared with clinicopathological features.

CONCLUSION: By high resolution deletion mapping, two high frequency regions of LOH (4q12-21.1 and 4q25-31.1) were detected, which may contribute to locate TSGs on chromosome 4q involved in carcinogenesis and progression of sporadic colorectal carcinoma.

Are there tumor suppressor genes on chromosome 4p in sporadic colorectal carcinoma?

AIM: To study the candidate tumor suppressor genes (TSG) on chromosome 4p by detecting the high frequency of loss of heterozygosity (LOH) in sporadic colorectal carcinoma in Chinese patients.

METHODS: Seven fluorescent labeled polymorphic microsatellite markers were analyzed in 83 cases of colorectal carcinoma and matched normal tissue DNA by PCR. PCR products were eletrophoresed on an ABI 377 DNA sequencer. Genescan 3.7 and Genotype 3.7 software were used for LOH scanning and analysis. The same procedure was performed by the other six microsatellite markers spanning D4S3013 locus to make further detailed deletion mapping. Comparison between LOH frequency and clinicopathological factors was performed by χ² test.

RESULTS: Data were collected from all informative loci. The average LOH frequency on 4p was 24.25%, and 42.3% and 35.62% on D4S405 and D4S3013 locus, respectively. Adjacent markers of D4S3013 displayed a low LOH frequency (< 30%) by detailed deletion mapping. Significant opposite difference was observed between LOH frequency and tumor diameter on D4S412 and D4S1546 locus (0% vs 16.67%, P = 0.041; 54.55% vs 11.11%, P = 0.034, respectively). On D4S403 locus, LOH was significantly associated with tumor gross pattern (11.11%, 0, 33.33%, P = 0.030). No relationship was detected on other loci compared with clinicopathological features.

CONCLUSION: By deletion mapping, two obvious high frequency LOH regions spanning D4S3013 (4p15.2) and D4S405 (4p14) locus are detected. Candidate TSG, which is involved in carcinogenesis and progression of sporadic colorectal carcinoma on chromosome 4p, may be located between D4S3017 and D4S2933 (about 1.7 cm).

Loss of heterozygosity on hromosome 1 in sporadic colorectal carcinoma

AIM: Loss of heterozygosity (LOH) on tumor suppressor genes is believed to play a key role in carcinogenesis of colorectal cancer. When it occurs at a tumor suppressor gene locus with abnormal allele, neoplastic transformation happens. In this study, we analyzed the LOH at 21 loci on chromosome 1 in sporadic colorectal cancer to identify additional loci involved in colorectal tumorigenesis.

METHODS: Twenty-one polymorphic micro-satellite DNA markers were analyzed with PCR both in 83 cases of colorectal cancer and in normal tissues. 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. χ² test was used to compare LOH frequency with clinicopathological data. P < 0.05 was considered as statistically significant.

RESULTS: The average LOH frequency of chromosome 1, short arm and long arm was 19.83%, 18.00% and 21.66%, respectively. The 2 highest LOH loci with a frequency of 36.54% and 32.50% were identified on D1S468 (1p36.33-p36.31) and D1S413 (1q31.3), respectively. On D1S2726 locus, LOH frequency of rectal cancer was 28.57% (6/21), which was higher than that of colon cancer (0.00%, 0/33) (P = 0.002), suggesting that the mechanism of carcinogenisis was different in both groups.

CONCLUSION: Putative tumor suppressor genes on chromosome 1 may relate to sporadic colorectal carcinomas. Tumor-suppressor-genes might locate on 1p36.33-36.31 and/or 1q31.3.

Refinement of heterozygosity loss on chromosome 5p15 in sporadic colorectal cancer

AIM: To refine the loss of heterozygosity on chromosome 5p15 and to identify the new tumor suppressor gene (s) in colorectal tumorigenesis.

METHODS: Sixteen polymorphic microsatellite markers were analyzed on chromosome 5 and another 6 markers were applied on chromosome 5p15 in 83 cases of colorectal and normal DNA by PCR. PCR products were electrophoresed on an ABI 377 DNA sequencer. Genescan 3.1 and Genotype 2.1 software were used for LOH scanning and analysis.

RESULTS: We observed 2 distinct regions of frequent allelic deletions on Chromosome 5, at D5S416 on 5p15 and D5S428-D5S410 on 5q. Another 6 polymorphric microsatellite markers were applied to 5p15 and the minimal region of frequent loss of heterozygosity was established on 5p15 spanning the D5S416 locus.

CONCLUSION: Through our detailed deletion mapping studies, we have found a critical and precise location of 5p deletions, 5p15.2-5p15.3, which must contain one or more unknown tumor suppressor gene (s) of colorectal cancer.

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

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 colorectal 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 χ² 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 putative 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.