Analysis of SMAD4/DPC4 gene alterations in multiploid colorectal carcinomas.
BACKGROUND
Although recent animal studies have shown that SMAD4/DPC4 gene alterations are essential for late-stage intestinal tumorigenesis, the role of SMAD4/DPC4 gene alterations in primary human colorectal carcinomas is not fully understood. Therefore, we attempted to clarify the role of the SMAD4/DPC4 gene during tumor progression of colorectal carcinoma.


METHODS
Differences in allelic imbalance (AI) and mutations of the SMAD4/DPC4 gene between diploid and aneuploid populations were analyzed for 30 sporadic DNA multiploid colorectal carcinomas (used as a tumor progression model and defined as the coexistence of diploid and aneuploid cells within the same tumor). The crypt isolation technique was coupled with DNA cytometric sorting and a polymerase chain reaction assay. In addition, hypermethylation of the promoter region was examined to clarify whether inactivation of gene expression occurred.


RESULTS
Although a SMAD4/DPC4 gene AI was detected in only 5 of 27 informative diploid populations, 25 of 27 aneuploid populations had a SMAD4/DPC4 gene AI. Mutation of the SMAD4/DPC4 gene was detected in only one aneuploid population of multiploid colorectal carcinomas, but not in the corresponding diploid population. In total, 20 available multiploid carcinomas were selected for methylation analysis, and no evidence of hypermethylation of the promoter region was found.


CONCLUSIONS
We suggest that, although mutation of the SMAD4/DPC4 gene and hypermethylation of the promoter region are infrequent events in colorectal tumorigenesis, AI at the SMAD4/DPC4 gene locus may play a key role in the progression of colorectal carcinomas.
Ando
Tatsuya
T
First Department of Internal Medicine, Iwate Medical University, Morioka, Japan.
Sugai
Tamotsu
T
Habano
Wataru
W
Jiao
Yu-Fei
YF
Suzuki
Kazuyuki
K
D000230:Adenocarcinoma / Q000235:genetics* / Q000473:pathology; D000368:Aged; D000369:Aged, 80 and over; D001483:Base Sequence; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000032:analysis; D004268:DNA-Binding Proteins / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D016147:Genes, Tumor Suppressor; D020022:Genetic Predisposition to Disease; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009154:Mutation; D011003:Ploidies; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics*
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; D015534:Trans-Activators