Distribution and characterization of helix-loop-helix enhancer-binding proteins from pancreatic β cells and lymphocytes

Open Access
Publisher Website
Google Scholar
Abstract
Transcription of a number of mammalian genes is controlled in part by closely-related DNA elements sharing a CAxxTG consensus sequence (E boxes). In this report, we survey cell extracts from a variety of mammalian cell lineages for ability to bind to the E box denoted IEB1/×E1, which plays an important role in expression of both insulin and immunoglobulln x genes. Insulin enhancer factor 1 (IEF1), a binding activity previously identified in β cells, was also present in pituitary endocrine cells but absent in 7 other mammalian cell lines tested. A distinct binding activity, lymphold enhancer factor 1 (LEF1), was observed in several lymphold cell lines, but was absent from all non-lymphoid cells tested. IEF1 and LEF1 were distinct according to electrophoretic mobility, and DNA binding specificity. As previously reported, both β cell and lymphoid cell factors are recognized by antibodies to helix-loop-helix (HLH) proteins, Indicating that they may contain functional helix-loop-helix dimerization domains. To directly demonstrate this, we showed that the binding factors are able to interact In vitro with the HLH domain of a characterized HLH protein. These results support the notion that HLH proteins play a key role in cell-specific transcrlptional regulation in cells from endocrine and lymphocyte lineages.