The NBL1 tumor suppressor gene is downregulated in colon cancer by promoter methylation

Abstract Introduction: We have recently identified the novel finding that TSG is a tumor suppressor gene that is down-regulated in v-Srctransformed rat fibroblasts through the mechanism of promoter hypermethylation and gene silencing. We hypothesized that the human homologue of TSG, NBL1 (Neuroblastoma, suppression of tumorigenicity 1), might be affected through a similar mechanism in human cancer. Thus, NBL1 may represent a new candidate tumor suppressor gene regulated by promoter hypermethylation through DNA methyltransferases. Methods: We evaluated colon cancers (n = 10) of similar stage and grade and their matched normal tissues for NBL1 expression by real-time RT-PCR and western blots. In addition, we assessed the promoter region of NBL1 for presence of CpG islands and for hypermethylation of these regions though bisulfite sequencing and methylation specific PCR. Results: The mRNA levels and protein of the expressed NBL1 gene were significantly reduced in 70% tumors with respect to their normal matched controls. Evaluation identified NBL1 promoter site to be CpG island rich. Methylation analysis of human colon cancer specimens confirmed hypermethlation of NBL1 promoter site. Conclusions: NBL1 is a transcription factor that plays a role in the negative regulation of the cell cycle. Our data suggest, for the first time, that the down regulation of NBL1 in human colon cancer through promoter hypermethylation may play an important role in colon cancer development and/or progression.