Hypermethylation Of P16,p15 Gene And Transcriptional Repression In Multiple Myeloma

Cyclins, cyclin-dependent kinases (CDKs) and their inhibitors play a major role in cell cycle regulation. p15 and p16 genes, both mapped to the 9p21 region , have emerged as candidate tumor suppressor genes in human neoplasm. They have been identified as inhibitors of the cyclin D-CDK4/6 complexes. These two CDK inhibitors have a high degree of structural and functional homology and thus belong to the same family. Inactivation of the p15 and p16 genes by homozygous deletion, point mutation or by hypermethylation of the CpG sites at the promoter region has been observed in different neoplasias. Whereas point mutations are very rare in hematopoietic malignancies, disruption of the two genes by homozygous deletion, or silencing by promoter hypermethylation, are common in lymphoid malignancies. In recent investigation, no homozygous deletions nor mutations of the p16 and p15 genes were detected in MM patients analysed. Instead, hypermethylation of the p16 and p15 genes was observed at high frequencies. Multiple myeloma (MM) is characterized by neoplastic proliferation of monoclonal plasma cells. These neoplastic plasma cells are believed to arise from a post-germinal center B cell, which migrates to the bone marrow, adheres to the marrow stroma, and triggers subsequent bone resorption and a paracrine cytokine loop. At present, MM is still a uniformly fatal malignancy, even after chemotherapy. The purpose of the present study was to examine the methylation frequency and transcriptional repression of the p16 and p15 gene promoters in 16 patients with multiple myeloma and to related the results to clinical characteristics. In present study, the methylation of the 5' region and the transcriptional repression of the p16 and p15 genes in 16 MM patients was detected by restriction enzymeralated polymeras chain reaction (REP) and RT-PCR. Ten normal controls were obtained from peripheral blood sample of the healthy individuals. Methylation was found in56.25% (9/16) for p16,62.50% (10/16) for p15 and 50.00% (8/16) for both genes in MM. The mRNA expressions of the p16 and p15 genes in MM showed 77.77%(7/9) and 70%(7/10). The results suggested hypermethylation of p16 and p15 genes is a frequent event in multiple myeloma. There is a strong correlation between methylation and transcriptional repression of the p16 and p15 genes. Furthermore, hypermethylation of p16 gene was detected in patients at stage I, untreated patients as well as patients with low percentage of plasma cell. It suggested hypermethylation of p16 and p15 genes is an early event in multiple myeloma. There are some implications for MM from our findings. Our evidence in patients support that hypermethylation of p16 and p15 genes plays an important role in MM tumourigenesis. There is a strong correlation between methylation and transcriptional silencing of the p16 and p15 genes. Because hypermethylation of the p16 and p15 gene is a common event in MM, most patients can benefit from this investigation. With PCR technique, the methylation status can serve as a tumor marker for the detection of minimal residual disease. It can be used to check for tumor contaminations in autologous BMs or peripheral stem cell harvests in autologous BM transplantation. The transcriptional status detected by RT-PCR also could help to identify the stage of pathogenesis. And it throw light on therapeutic innovations of MM treatment. Use of demethylating agents either in vitro as a pretreatment of the autologous graft before transplantation or in vitro as a therapeutic agent incorporated into drug developments or via gene therapy by targeted delivery may be speculative at this stage but speculative at this stage but effective in future. In summary, frequent hypermethylation of the p16 and p15 genes is a early and frequent event in MM. There is a strong correlation between methylation and transcriptional repression of the p16 and p15 genes. Our...