Detailed analysis of hypersensitive site III of the human growth hormone locus control region

The LCR of the human growth hormone genes is denned by five DNase I hypersentive sites (HS) located upstreajn of the multigene cluster. HS I and II are restricted to the pituitary chromatin, HS IV is specific to the placenta and HS III and V are common to both tissues. When contained on a cosmid, these sites direct high level, tissue-specific and copy number dependent expression of the hGH-N in transgenic mice (1). Transient transfection and a stable transfection neoT colony formation assays showed that the 3.1 kb fragment encompassing the HS III site has both LCR and enhancer activities in GHFT 1 (presomatotrope) and GH3 (mammosomatotrope) cells but shows no effects in JEG3 (choriocarcinoma) and NIH3T3 (fibroblasts) cells. This fragment increases colony number by 10 fold in neoT assays and by 4 fold the CAT activity. Deletional analysis showed that a 500 bp fragment is sufficient to direct a high level of expression comparable to the activity mediated by the 3,1 kb fragment in transient transfection assays. Furthermore we show that the HS III site 0) can reform in chromosomal DNA isolated from stable transformants carry.ng the 3.1 kb fragment and (ii) is located within the same 500 bp fragment which contain the functional activity. Taken together, these results suggest that the sequences within HS III may function as positive regulatory elements probably by mediating a chromatin opening of the cluster leading to hGH gene expression. (1) B. K. Jones et al., 1995. Mol. Cell Biol. 15: 7010-7021.