Yin-yang 1 and glucocorticoid receptor participate in the Stat5-mediated growth hormone response of the serine protease inhibitor 2.1 gene

A growth hormone-inducible nuclear factor complex (GHINF), affinity-purifie d using the growth hormone response element (GHRE) from the promoter of rat serine protease inhibitor 2.1, was found to contain Stat5a and -5b, as wel l as additional components. The ubiquitous transcription factor yin-yang 1 (YY1) is present in GHINF.An antibody to YY1 inhibited the formation of the GHINF GHRE complex in an electrophoretic mobility shift assay. Furthermore , Stat5 was co-immunoprecipitated from rat hepatic nuclear extracts with an tibodies to YY1. An examination of the GHRE shows that, in addition to two gamma-activated sites, it contains a putative YY1 binding site between the two gamma-activated sites, overlapping them both. Mutation of this putative YY1 site results in a decrease of GHINF GHRE complex formation in an elect rophoretic mobility shift assay and a corresponding decrease in growth horm one (GH) response in functional assays. The glucocorticoid receptor was als o present in GHINF, and StatB co-immunoprecipitates with glucocorticoid rec eptor in hepatic nuclear extracts from rats treated with GH, GH activation of serine protease inhibitor 2.1 requires the unique sequence of the GHRE e ncompassing the recognition sites of several transcription factors, and the interaction of these factors enhances the assembly of the transcription co mplex.