Extinction of E-cadherin expression in breast cancer via a dominant repression pathway acting on proximal promoter elements

Inactivation of the E-cadherin cell adhesion molecule is believed critical in the development and behavior of many epithelial cancers, though mutation s in the E-cadherin gene account for inactivation in only a fraction of cas es, In many breast cancer lines, E-cadherin transcription is extinguished, but the role and significance of alterations in trans-acting transcription factors, promoter hypermethylation, and chromatin changes remain unresolved , To gain further insights into mechanisms underlying E-cadherin in inactiv ation in breast cancer, we analysed somatic cell hybrids resulting from pai rwise fusions between breast cancer lines with intact E-cadherin transcript ion (E-cad+) and lines lacking E-cadherin transcription (E-cad-), All hybri d lines failed to express E-cadherin transcripts and protein, despite the f act that E-cadherin alleles from E-cad+ lines were present in the hybrids, Elements in the proximal 108 bp of the E-cadherin promoter, when present in reporter gene constructs, mere sufficient to direct strong transcription i n E-cad+ breast lines, but displayed weak activity in E-cad- parental lines and hybrids, E-cadherin expression could not be restored in E-cad- lines o r hybrids by treatment with a DNA demethylating agent and/or a histone deac etylase inhibitor, Our findings suggest loss of E-cadherin expression in so me breast cancers may be due to dominant repression of the trans-acting pat hways that regulate E-cadherin transcription.