The Relationship Of LKB1 Gene Promoter And The Pathogenesis Of Peutz-Jeghers Syndrome Polyps

Peutz-Jeghers syndrome(PJS)is a rare inherited disease and also an autosomal dominant genetic disorder characterized by mucocutancous pigmentation,gastrointestinal hamartomatous polyps and elevated cancer risk.Gremline mutation of LKB1 which is a tumor suppressor gene is the main cause of familial PJS.Various types of mutations in LKB1 are associated with the incidence of PJS,but the specific molecular mechanisms involved are not yet fully defined.Some PJS patients did not detect LKB1 mutation in some reports,suggesting that if there any alternative ways involved in the pathogenesis of PJS.Germline mutation of the LKB1 gene was detected in 66%~94% fami-lial PJS patients,including missing,point mutation,insertion and so on.However,the LKB1 gene mutation rate of sporadic PJS patients is 16.7%.Previous studies have found that hypermethylation mediated transcriptional silence in the LKB1 promoter region may be involved in the pathogenesis of PJS.DNA methylation is belonging to epigenetic modification.Epigenetics is a mechanism or phenomenon that changes the expression of the gene in the condition that the DNA sequence is not involved.As one of the important mechanisms of epigenetic,DNA methylation plays an important role in maintaining the stability of genome and chromosome conformation,X chromosome inactivation,gene imprinting and gene silencing,and is closely related to the pathogenesis of tumors.We found that methylation specific PCR(MSP)was used in previous studies.This method has fewer detection sites,relatively low sensitivity and specificity.The bisulfite PCR sequencing method is used in this study,which can detect methylation status across the whole Cp G island.It cannot only make qualitative and accurate quantification,but also overcome the disadvantages of MSP method.In this study,we collected 50 cases of PJS polyps(including 3 cases of PJS polyps with digestive tract gastroinstinal tumors)and 20 cases of normal intestinal mucosa(including 12 cases of effective data)and to sequence and compare with them.This study is aimed to explore the relationship between methylation of LKB1 gene promoter region and Peutz-Jeghers syndrome polyps.The result of BSP shows that there are 4701 methylated clones in 50 PJS polyps,and average methylation rate is 44.78%,standard error is 0.61412.There are 148 methylated clones in 12 normal mucosa,and average methylation rate is 5.87%,standard error is 0.481812.There are 128 methylated clones in 3 cases of Peutz-Jerghers syndrome with gastrointestinal tumors and average methylation rate is 20.32%.Compared to the average methylation rate of polyps with normal mucosa groups of T test,there is significant difference(P=6.09371×10-60,P<0.05).In conclusion,firstly,the hypermethylation of LKB1 gene promoter is common in PJS polyps.Therefore,the pathogenesis of PJS polyps is closely related to the methylation of LKB1 promoter region.Secondly,there are three patterns of methylation of LKB1 promoter region in PJS polyps.The first pattern is the hypermethylation,the average methylation rate is above 70% in 9 cases,suggesting that most of the Cp G sites of both alleles are methylated.The second pattern is the hemimethylation,the average methylation rate is between 30% and 70% in 37 cases,suggesting that only one allele is methylated.The third pattern is the hypomethylation,the average methylation rate is below 30% in 14 cases,suggesting that almost none of the two alleles are methylated.Thirdly,the promoter status of LKB1 gene in the PJS polyps malignant transformation group was hypomethylated.The mechanism of the hypomethylation was not clear,and there was no relevant report.The mechanism of malignant transformation and methylation of PJS polyps remains to be further studied.Lastly,the promoter region of LKB1 gene in normal mucosa showed unmethylation status.