Rat growth hormone gene expression is correlated with an unmethylated CGCG sequence near the transcription initiation site.

The methylation status of the rat growth hormone (GH) gene was compared in DNA obtained from GH-producing and GH-nonproducing sources by digestion with three methylation-sensitive restriction enzymes. GH gene expression was correlated with an unmethylated ThaI site (CGCG) 144-bp upstream of the GH RNA transcription initiation site. This ThaI site was unmethylated in nine GH-producing subclones of the rat pituitary tissue culture cell line GH3 and in greater than 50% of the DNA isolated from rat anterior pituitary, a gland containing GH-producing somatotroph cells as well as GH-nonproducing cells. In DNA prepared from GH-nonproducing tissues, e.g., rat spleen, kidney, liver, and brain, this ThaI site was entirely methylated. Furthermore, this site was entirely methylated in hybrid cells formed by the fusion of GH3 cells with mouse fibroblasts in which GH production has been extinguished. DNA methylation at 10 other restriction sites located throughout the rat GH gene region failed to correlate with GH expression in GH-producing subclones of GH3 cells as well as in GH-nonproducing GH3 X LB82 hybrid cells. We suggest that the conserved absence of methylation 144 bp 5' of the RNA transcription initiation site of transcribed GH genes identifies a potential GH gene control region.