The role of Id-1 in immortalization of esophageal epithelial cells

Abstract

The potential to achieve limitless proliferation is one of the major hallmarks of cancer. Identifying the molecular basis responsible for regulating the replicative potential has important implications for carcinogenesis. It is well documented that the introduction of hTERT, the catalytic subunit of telomerase helps to overcome replicative senescence and acquire immortality. Recently, it has been reported that ectopic expression of Id-1 (Inhibitor of Differentiation), a helix-loop-helix protein which serves as a negative regulator in the regulation of transcription and differentiation, also leads to delayed senescence and even immortalization of human keratinocytes through activation of telomerase. On the other hand, human embryonic fibroblasts transfected with hTERT exhibit increased Id-1 expression. In this study, the role of Id-1 and its relationship with hTERT in immortalization of human esophageal epithelial cells was investigated by overexpressing Id-1 or hTERT, or both Id-1 and hTERT, in esophageal epithelial primary cell lines. Our results showed that in an hTERT-immortalized esophageal cell line, NE083, the expression of Id-1 increased with increasing passages. Knockdown of endogenous Id-1 at late passage (P35) by transfection with antisense Id-1 led to suppressed cell growth, down-regulation of Mdm2 and increased sensitivity to TGF-β-induced differentiation and growth arrest. In another hTERT-transfected primary esophageal cell line, NE2, cells transfected with Id-1 showed elevated growth rate, up-regulation of pMdm2 and down-regulation of p21, compared with cells without Id-1 transfected. These findings suggested that Id-1 may induce proliferation of esophageal epithelial cells and help hTERT promoting immortalization of esophageal epithelial cells, possibly through regulating the p21Waf/Cip/Mdm2 pathway.