ABSTRACT
Deregulation of G1 cyclins has been reported in several human and rodent tumors including colon cancer. To investigate the expression pattern of G1 cyclins in 1,2- dimethyl-hydrazine dihydrochloride (DMH)-induced rat colon carcinogenesis, we studied the expression of cyclin D1 and cyclin E by quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis and immunohistochemistry (IHC). The mRNA level of cyclin D1 was increased 1.2-fold in adenocarcinomas but not significantly in adenomas, when compared with normal rat colonic mucosa (p<0.05). The cyclin E mRNA level was increased 2.7-fold in adenomas and 3.3-fold in adenocarcinomas (p<0.05). The PCNA mRNA level was also increased 1.9-fold in adenomas and 1.8-fold in adenocarcinomas (p<0.05). Immunohistochemical staining revealed exclusive nuclear staining of the neoplastic cells for cyclin D1, cyclin E and PCNA. Cyclin D1 expression was detected in 56.3% of the adenomas and in 61.5% of the adenocarcinomas examined, whereas cyclin E expression was detected in 87.5% of the adenomas and in 92.3% of the adenocarcinomas. Overall, cyclin D1, cyclin E and PCNA expression was significantly increased at both the mRNA and protein levels in normal colonic mucosa, adenomas and adenocarcinomas, but there was no significant difference in the degree of expression of these genes in adenomas and adenocarcinomas. Our results indicate that the overexpression of cyclin D1 and cyclin E may play an important role during the multistage process of rat colon carcinogenesis, at a relatively early stage, and may disturb cell-cycle control in benign adenomas, and thereafter, participate in tumor progression.
Subject(s)
Animals , Male , Rats , 1,2-Dimethylhydrazine/toxicity , Adenocarcinoma/chemically induced , Adenoma/chemically induced , Carcinogens/toxicity , Cell Cycle/drug effects , Colon/metabolism , Colonic Neoplasms/chemically induced , Cyclin D1/biosynthesis , Cyclin E/biosynthesis , Gene Expression Regulation, Neoplastic , Immunohistochemistry , Proliferating Cell Nuclear Antigen/biosynthesis , RNA, Messenger/metabolism , Rats, Sprague-Dawley , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
PURPOSE: p16Ink4A and p15lnk4B, encoded by the genes located on chromosome 9p21, are cyclin-dependent kinase 4 inhibitors and are the upstream regulators of pRB (retinoblastoma protein) function and are involved in the regulation of cell cycle in mammalian cells. It has been demonstrated that p16 and p15 genes are frequently deleted, mutated, and hypermethylated in many malignancies and cancer cell lines. This study was performed to investigate the genetic alteration and immunohistochemical profile of p16 and p15 in gastric carcinomas. MATERIALS AND METHODS: We examined 30 primary gastric cancer samples using PCR- SSCP (Polymerase chain reaction-single strand conformation polymorphism), DNA sequencing, PCR-based hypermethylation assay, and immunohistochemistry. RESULTS: No homozygous deletion was detected in either pl6 or p15 gene, and only one gastric carcinoma sample showed mutation of p16 gene and p15 gene. However, hyper-methylation of 5' CpG islands was observed in 53.6% of exon1 of p16 gene and in 46.4% of exon 1 of pl5 gene. By immunohistochemistry of p16, nuclear under-expression was observed in 58.6%, whereas nuclear over-expression was detected in 31% of formalin-fixed, paraffin-embedded gastric cancer tissues. CONCLUSIONS: Our results suggest that the p16 and p15 tumor suppressor genes may play an important role in gastric carcinogenesis and may be inactivated not by deletions or mutations but mainly by hypermethylation of their 5' CpG islands. There was a good correlation between methylation study and immunohistochemical results in p16 genes.