[Alterations of DPC4/SMAD4/MADH4 gene detected in paraffin-embedded tissues of human pancreatic carcinomas].

OBJECTIVE

To demonstrate the alterations of DPC4/SMAD4/MADH4 gene in paraffin-embedded tissues of pancreatic carcinomas.

METHODS

Forty-six cases of resected specimens containing carcinomatous tissue and normal pancreatic tissue were analysed for possible DPC4 gene mutations by polymerase chain reaction (PCR)and single-strand conformation polymorphism (SSCP). The DNA sequencing technique was applied to determine the patterns of gene mutation in the PCR-SSCP positive cases. Fifty-six cases of pancreatic carcinoma along with the specimens corresponding normal pancreatic tissues were studied by in situ hybridization (ISH) and immunohistochemistry (IHC) techniques for gene expression in mRNA and protein level.

RESULTS

The homozygous deletion rate of exon 1, 2, 3, 4, 8, 11 of DPC4 gene in pancreatic carcinoma was 28.26%, while the mutation rate of DPC4 gene was 21.74%. In these tumors, there were 3 cases of nonsense mutation, 5 cases of missense mutation, 1 case of deletion and missense mutation, 1 case of insertion mutation. Positive rates of SMAD4 in carcinomatous tissues detected by the ISH and IHC were 53.57% and 58.93% respectively, whereas they were 91.07% and 89.29% in the matched normal tissue respectively. There were significant difference between cancer and normal tissue (P < 0.05). Thrity-two cases were positive of DPC4/SMAD4 with all methods mentioned above, the coincident rate was 87.50% (28/32). The coincidence between gene detection and ISH of SMAD4 was 87.50%, and it was 96.88% between gene detection and IHC of SMAD4. Of all 56 cases, the coincidence of the positive rates of SMAD4 detected by ISH and IHC was 91.07%. No significant difference among the positive rates of DPC4/SMAD4 as detected by the three different techniques (P > 0.05).

CONCLUSIONS

The main mechanisms of inactivation of DPC4 gene in pancreatic carcinoma are homozygous deletion and mutation. The product of DPC4 expression is significantly decreased in cancer group compared with the normal tissues. As a tumor suppressor gene, DPC4 alteration is an important molecular event in pancreatic carcinoma, and probably plays a crucial role in cancer development and progression.