Induction of mRNAs for the growth hormone receptor gene during mouse 3T3-L1 preadipocyte differentiation

Adipose tissue is a growth hormone (GH)-responsive tissue in which GH regulates energy metabolism. GH exerts its effect by interacting with its specific GH receptor (GHR). In rodents, alternative splicing of the nascent transcript from the GHR gene produces two major transcripts: GHR mRNA and GHR binding protein (GHBP) mRNA. These two transcripts share the common extracellular ligand-binding domain, but differ in the C-terminal sequence. Since GHR plays an important role in mediating the actions of GH in adipose metabolism, we initiated these studies to examine GHR gene expression in the course of mouse 3T3-L1 preadipocyte-adipocyte conversion. GHR and GHBP transcripts were detected by RNase protection assay (RPA) using the antisense riboprobes complementary either to the specific sequence of the GHR or to the sequence shared by both GHR and GHBP mRNAs. After stimulation of differentiation, mRNA abundance increased 28-fold and reached a maximal level by day 7 of adipogenesis. The GHR mRNA:GHBP mRNA ratio was 1.1 +/- 0.12 and remained unchanged during differentiation. The decay rate for both mRNAs, estimated by treating the cells with actinomycin D, was approximately 24 hours and showed no significant difference between preadipocytes and adipocytes. Thus, GHR gene expression is dramatically upregulated during preadipocyte-adipocyte differentiations.