Loss Of Heterozygosity Of P16 Gene And Expression Of HMSH2 MRNA In Gastric Cancer

Microsatellite instability ( MI) frequently occurs near the sites of tumor suppressor genes, pi6 gene can specificly inhibit the phosphatlatekinase activaty of CDK4/CDK6 complex. High frequent loss of homozygosity occurs in various kinds of tumor.Human mismactch repair genes may detect and correct mismatched or non-matched base pairs during the process of DNA duplication or damage, and then contribute to the normal processions of duplication and recombinant. The normal function of DNA repair plays an important role in inhibiting mutations of onco-genes and tumor - suppressor genes. hMSH2 is one of the human mismatch repair genes. Up to date, few reports about MI of p16 gene related to hMSH2 gene inactivation in gastric carcinoma have been seen.The polymerase chain reaction - polyacrylamide gel clectrophoresis - silver staining was used to analyze the loss of heterozygosity ( LOH ) frequency of micro-satellite siles D9sl748, D9sl26 adjacent to of p16 gene. Meanwhile, in situ hybridization (ISH) was used to analyize the expression of the mismatch repair gene, hMSH2. Further investigation was made to analyse the mechanisms between these abnormalities during the turmorgenesis and development of gastric cancer. The study aim was to explore the relations and mechanisms in the levels of DNA and mRNA, then to apply important materials and theoretic evidences to the genetic diagnosis and treatment of gastric cancer.Results1. LOH frequency of microsatellite sites D9sl748, D9sl26 in gastric cancer; in 4 and 1 of 20 cases of gastric cancer tissues and 20 cases of adjacent tissues, LOH in D9sl748 was detected, while in D9sl26 site was 7 cases and 3 cases, respectively. In frequencies of LOH between two sites there was no significant difference ( P > 0. 05 ). The rate of LOH was higher in gastric cancers than that in adjacent cancer tissues ( P < 0. 05). No significant difference was noted between well differentiated gastric cancers and moderate and poorly differentiated gastric cancers ( P > 0. 05 ). The frequencies of LOH in early and advanced gastric cancer were 44. 4% (4/9) and 63.6% (7/11), respectively. Statistically, the LOH frequencies of the two microsatellite sites were closely correlated (P<0.005).2. ISH: 31 cases of gastric cancer tissues, 31 cases of adjacent tissues and 31 casses of normal gastric mucosa were examined by using ISH for the expressionof HMSH2 mRNA. The positive rates were 73. 2% , 58. l%and 67. 7% , respectively. ISH positive cells were enumerated from 5 regions under microscope randomly and the data were presented as mean ?standard deviation. The significantly reduced expression of hMSH2 mRNA were displayed in gastric cancer tissues (41. 6 ?1. 6) and adjacent cancer tissues (98. 7 ?18. 6) , in comparision with normal gastric mucosa ( 174. 0 ?20. 1) , and there was significant difference between cancers and adjacent tissues ( P < 0. 01) . The positive cells were significantly reduced in poorly differentiated carcinomas ( 21. 6 ?20. 5 ) than those in well and moderately differentiated carcinomas (50. 4 ?19. 1 and 71. 8 ?23. 1 respectively) (P <0. 05). No significant difference was noted among various clinical stage of gastric carcinomas ( P > 0. 05 ) . The positive signal cells in LOH ( + ) tissues (24. 9 ?10. 5) were obviously decreased than those in LOH (-) tissues (60.0 ?1. 3) (P<0.05). Conclusion;1. The frequencies of LOH in the two microsatellite sites, D9sl748 and D9sl26, are high in gastric cancer. There are relations between the rates of LOH in both sites.2. The number of ISH positive signal cells of the mismatch repair gene hMSH2 mRNA in gastric cancer is significantly less than those in normal gastric mucosa, the poorer the differentiated carcinomas, the less is expressed.3. The down regulation of the mismatch repair gene hMSH2 mRNA may cause the genetic instability in gastric cancer.