DNASE I-HYPERSENSITIVE SITES IN THE CHROMATIN OF RAT GROWTH-HORMONE GENE LOCUS AND ENHANCER ACTIVITY OF REGIONS WITH THESE SITES

In this study, a determination was made of the chromatin structure of the rat growth hormone (GH) gene locus by DNase I sensitivity analysis using GC [GH(+), prolactin (PRL)(-)], 235 (GH(-), PRL(+)), GH3 (GH(+), PRL(+)) and liver (GH(-), PRL(-)) cells. From 7 kb upstream from the transcription start site to 19 kb downstream from the polyadenylation site, two major DNase I-hypersensitive sites (M-DHS; UIA, UIIA) and three M-DHS (DIA, DII, DIII) were found within 2 kb upstream and 7 kb downstream regions, respectively. Two minor DHS (m-DHS; UIB, UIIB) in the upstream region and one m-DHS (DIB) downstream were shown to be associated with M-DHS. Thus, a total of five M-DHS and three m-DHS were mapped on the rat GH gene locus. Among these, five (UIIB, UIA, UIB, DIB, DIA) including two (UIA, DIA) M-DHS were specific for GH-producing cells. UIIA and Dill were M-DHS only in PRL-producing 235 cells while the major hypersensitivity of DH was detected in GH-producing cells and liver cells. Assessment of the enhancing activity of the DHS regions indicated navel enhancers in one upstream and two downstream regions that function well with the GH promoter in GC cells. These enhancers, each appearing different, coincided with m-DHS but not M-DHS in GC cells, and were not activated by Pit-1. Based on these observations, the following functions of five M-DHS and three m-DHS regions were defined: enhancer; locus control region (LCR); switch region serving for conversion from GH/PRL-producing cells to PRL-producing cells; and a region having a structural function in chromatin.