DISTRIBUTION AND CHARACTERIZATION OF HELIX-LOOP-HELIX ENHANCER-BINDING PROTEINS FROM PANCREATIC BETA-CELLS AND LYMPHOCYTES

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/chi E1, which plays an important role in expression of both insulin and immunoglobulin chi genes. Insulin enhancer factor 1 (IEF1), a binding activity previously identified in beta cells, was also present in pituitary endocrine cells but absent in 7 other mammalian cell lines tested. A distinct binding activity, lymphoid enhancer factor 1 (LEF1), was observed in several lymphoid 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 beta cells 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 transcriptional regulation in cells from endocrine and lymphocyte lineages.