A CONSENSUS INSULIN-RESPONSE ELEMENT IS ACTIVATED BY AN ETS-RELATED TRANSCRIPTION FACTOR

Insulin increases expression of somatostatin-chloramphenicol acetyltransferase (CAT) constructs 10-fold and thymidine kinase-CAT constructs 5-fold in GH4 cells. These responses are similar to our previously reported data on insulin-increased prolactin-CAT expression, They are also observed in HeLa cells and are thus not cell type specific, The evidence suggests that the insulin responsiveness of these genes is mediated by an Ets-related transcription factor, First, linker-scanning mutations and/or deletions of the prolactin, somatostatin, and thymidine kinase promoters suggest that their insulin responsiveness is mediated by the sequence CGGA, This sequence is identical with the response element of the Ets-related transcription factors, Second, CGGA-containing sequences placed at -88 in the Delta MTV-CAT reporter plasmid conferred insulin responsiveness to the mammary tumor virus promoter, Third, expression of the DNA-binding domain of c-Ets-a, which acts by blocking effects mediated by Ets-related transcription factors, inhibits the response of these promoters to insulin, Finally, the Ets-related proteins Sap and Elk-l bind to the prolactin, somatostatin, and thymidine kinase insulin response elements, An Ets-like element was found in all insulin-sensitive promoters examined and may serve a similar function in those promoters.