Novel APC gene mutations associated with protein alteration in diffuse type gastric cancer

Souvik Ghatak,Arup Bhaumik,Nachimuthu Senthil Kumar,Payel Chakraborty,Biswajit Chowdhury,Sandeep Roy Sarkar

doi:10.1186/s12881-017-0427-2

Souvik Ghatak, Arup Bhaumik + Show 4 more

Open Access

https://doi.org/10.1186/s12881-017-0427-2

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Abstract

BackgroundThe role of adenomatous polyposis coli (APC) gene in mitosis might be critical for regulation of genomic stability and chromosome segregation. APC gene mutations have been associated to have a role in colon cancer and since gastric and colon tumors share some common genetic lesions, it is relevant to investigate the role of APC tumor suppressor gene in gastric cancer.MethodsWe investigated for somatic mutations in the Exons 14 and 15 of APC gene from 40 diffuse type gastric cancersamples. Rabbit polyclonal anti-APC antibody was used, which detects the wild-type APC protein and was recommended for detection of the respective protein in human tissues. Cell cycle analysis was done from tumor and adjacent normal tissue.ResultsAPC immunoreactivity showed positive expression of the protein in stages I, II, III and negative expression in Stages III and IV. Two novel deleterious variations (g.127576C > A, g.127583C > T) in exon 14 sequence were found to generate stop codon (Y622* and Q625*)in the tumor samples. Due to the generation of stop codon, the APC protein might be truncated and all the regulatory features could be lost which has led to the down-regulation of protein expression. Our results indicate that aneuploidy might occurdue to the codon 622 and 625 APC-driven gastric tumorigenesis, in agreement with our cell cycle analysis. The APC gene function in mitosis and chromosomal stability might be lost and G1 might be arrested with high quantity of DNA in the S phase. Six missense somatic mutations in tumor samples were detected in exon 15 A-B, twoof which showed pathological and disease causing effects based on SIFT, Polyphen2 and SNPs & GO score and were not previously reported in the literature or the public mutation databases.ConclusionThe two novel pathological somatic mutations (g.127576C > A, g.127583C > T) in exon 14 might be altering the protein expression leading to development of gastric cancer in the study population. Our study showed that mutations in the APC gene alter the protein expression and cell cycle regulation in diffuse type gastric adenocarcinoma.

Highlights

The role of adenomatous polyposis coli (APC) gene in mitosis might be critical for regulation of genomic stability and chromosome segregation
To clarify the role of APC gene mutations in the development of diffuse type gastric adenocarcinoma, we have investigated the mutations in the exons 14 and 15 of APC gene in a North East Indian population
The tumor samples used in the present study were diffuse type gastric adenocarcinoma as confirmed after H&E staining

Summary

Introduction

The role of adenomatous polyposis coli (APC) gene in mitosis might be critical for regulation of genomic stability and chromosome segregation. The human APC (adenomatous polyposis coli) gene is a tumor suppressor gene located on the long (q) arm of chromosome 5 and it encodes a protein of 312 kDa with 2843 amino acids. Germline mutations of the APC gene are responsible for familial adenomatous polyposis (FAP) [4, 5]. Role of APC in mitosis is critical for regulation of genomic stability and chromosome segregation [13]. Somatic mutations in the APC gene have been described in several tumour types such as pancreatic cancer [14], oral squamous-cell carcinoma [15] and oesophageal cancer [16]. Frequent loss of heterozygosity on chromosome 5q has been detected in gastric carcinomas, in well-differentiated type [20].some differentiated types of gastric carcinoma are thought to originate from the intestinal metaplastic regions in gastric mucosa [21]

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