zo-2 gene alternative promoters in normal and neoplastic human pancreatic duct cells

We have observed that 2 forms of zonula occludens 2 (ZO-2) protein, ZO-2A a nd ZO-2C, are expressed in normal human pancreatic duct cells, but only ZO- 2C in pancreatic duct adenocarcinoma. We report here partial organization o f the zo-2 gene. Transcription of 2 forms of ZO-2 mRNA is driven by alterna tive promoters P-A and P-C. Lack of expression of ZO-2A in neoplastic cells is caused by inactivation of the downstream promoter P-A. Analysis of the promoter P-A sequence and function in normal and neoplastic cells demonstra ted that neither structural changes (mutations) nor a change in the pool of transcription factors is responsible for its inactivation. Although hyperm ethylation was found in a large number of cancer clones, treatment with 5-a za-2'-deoxycytidine did not fully cause the promoter function to recover. W e conclude that the initial down-regulation of zo-2 promoter P-A activity i n pancreatic duct carcinomas is due to the structural or functional alterat ion(s) in the regulatory elements, localized outside the analyzed promoter region. Methylation of P-A is responsible for the inactivation of the suppr essed promoter at the late stages of tumor development. (C) 1999 Wiley-Liss , Inc.