Research On Clinical-pathological Analysis And The Mutation-expression Of β-catenin Gene In Peutz-Jeghers Syndrome

BackgroundPeutz-Jeghers syndrome(PJS) is a rare autosomal dominant hereditary disease characterized by gastrointestinal hamartomatous polyps and mucocutaneous melanin deposition.In earlier studies,PJS polyps were thought to be hamartomatous or hyperplastic polyps which had rare risk of canceration.Along with the research on PJS,it is found that some PJS polyps are adenomatoid polyps which have higher risk of canceration.And hamartoma may change to adenomatoid polyps and cancer which is known as hamartoma - adenoma - carcinoma sequence.PJS patients have obviously higer risk to develop into cancer both in digestive tissues and parenteral organs than health people.The incidence of tumor is almost 20%in China.And the PJS families also have higer incidence of tumor than general population.So it is necessary to make further study on the development and canceration of PJS.There are 4 different signal pathways:WnT/wingless,K-ras,β-TGF and p53 whose disfunction may result in tumor formation.Latest research indicate that p53,APC,K-ras12 are not the key molecular basis in the generation,development and caceration of PJS polyps.So we focus on WnT/wingless pathway which may have some relation with PJS.β-catenin is the key element of the pathway.Theβ-catenin gene(CTNNB1) is located in human chromosome 3P21.3- P22, which often generate malignancy change.The gene contains 23.2kb nucleotide and 16 exons.It's mRNA contains 3362 nucleotide residues.The mutation of exon 3 can reduceβ-catenin degration,which can make ectopic cytoplasmic accumulation of this protein,and then transfer into nuclear.By binding with the transcription factor,the transcription of downstream gene,such as c-myc and cyclin D1,make cell proliferation and differentiation out of control.Many tumors refer to the mutation ofβ-catenin gene and alteration or transposition ofβ-catenin protein expression. The latest studies indicate that the change ofβ-catenin gene play a significant role in the generation of adenoma,especially in the canceration of colon adenoma. Nowadays,there is few of research onβ-catenin gene mutation and protein expression in PJS.Objective:To detect gene mutation and protein expression ofβ-catenin in PJS,and make some research on the role ofβ-catenin in the generation,development and canceration of PJS polyps,in order to provide further experimental basis for the clinical diagnosis and prognosis.Materials and Methods:1,Study on clinical pathological characteristics of Peutz-Jeghers syndrome:the clinical pathological data of 71 patients with PJS admitted in Nanfang Hospital from 2001 to 2007 were analyzed retrospectively.And by reviewing literature,explored a more perfect scheme of clinical diagnosis-treatment and follow-up.2,Detection ofβ-catenin gene mutation:12 PJS polyps,14 colon adenoma,14 colon cancer and 12 normal tissues were collected to extract RNA.RT-PCR and sequencing were made,in order to study the mutation ofβ-catenin gene exon 3 in PJS.3,Detection ofβ-catenin protein expression:expression ofβ-catenin was examined immunohistochemically in 20 cases of PJS polyps,20 cases of colorectal adenoma,20 cases of colorectal carcinoma and 20 cases of colorectal normal tissues.Results:1,Twenty-six PJS patients(36.6%) had positive family history.The pathology of the PJS polyps was not only hamartomas,but also adenoma,hyperplastic polyps,et al. The incidence of malignancy was 7.0%in the PJS patients and 12.7%in the PJS families.2,The ratio ofβ-catenin IOD and GAPDH IOD in PJS tissues was 1.044±0.331,which had no significant difference between colon adenoma (0.917±0.207),colon cancer(1.109±0.283 ) and normal tissues(1.000±0.386 ) (Oneway Anova,F=0.972,P=0.414＞0.05).There was no significant difference ofβ-catenin mRNA level between these four groups.3,Gene deletion and insertion mutation were detected in PJS polyps.There was an A deletion mutation at nucleotide 431 in 70%PJS patients which might resulte in frameshifting and stop-codon appearing in advance.There was a T insertion at nucleotide 184 in 80%PJS patients which might result in abnormal of protein synthesis regulation region.Similar mutations were also detected in the blood and nomal colonic mucosa of PJS patients and health PJS family members.4,In normal colonic mucosa,β-catenin was detected in the cell membranes of epithelial cells.Cytoplasmic,nuclear expression and Reduced membranous expression were found in the PJS polyps,colorectal adenoma and carcinoma tissues.The reduced membranousβ-catenin expression rate was 30.0%in PJS polyps,which was significantly different from that in colorectal adenoma(45.0%),carcinoma(75.0%) and normal mucosa(5.0%)(R×Cχ~2 test,χ_p~2 =21.646,P=0.000＜0.05 ).The cytoplasmicβ-catenin expression rate and intension in PJS were significantly different from that in colorectal adenoma,carcinoma and normal mucosa (Kruskal-Wallis H test,χ~2 =30.584,P=0.003＜0.05 ).The nuclearβ-catenin expression rate was 60.0%in PJS polyps,which was significantly different from that in colorectal adenoma(30.0%),carcinoma(80.0%) and normal mucosa(5.0%) (R×Cχ~2 test,χ_p~2=26.565,P=0.001＜0.05).The whole ectopic expression rate was 60.0%in PJS,which was significantly different from that in colorectal adenoma(50.0%),carcinoma(90.0%) and normal mucosa(5.0%)(R×Cχ~2 test, χ_p~2=29.769,P=0.000＜0.05 ).Conclusion:1,The pathology of the PJS polyps was not only hamartomas,but also adenoma,hyperplastic polyps,et al.PJS was a cancer-susceptibility syndrome.Both PJS patients and his families had high cancer incidence and should be followed up closely.2,Cytoplasmic,nuclear expression and Reduced membranous expression were found in the PJS polyps,which indicated that the abnomal ofβ-catenin protein expression might be one characteristics of PJS polyps.3,There was no significant difference ofβ-catenin mRNA expression between PJS tissue,colon adenoma,colon cancer and normal colonic tissues,which indicated that the abnomal cytoplasmicβ-catenin accumulation was not related with the elevation ofβ-catenin mRNA expression in PJS polyps.4,The mutation ofβ-catenin gene exon 3 was common in PJS tissues,especial A deletion mutation at nucleotide 431 and T insertion mutation at nucleotide 184.These mutation may result in protein synthesis abnormal.And the same mutation was also detected in blood and nomal colonic mucosa of PJS patients and health PJS family members,which indicated thatβ-catenin gene mutation was not only somatic mutation but also germ-line mutation.