Growth hormone (GH) receptor and GH-binding protein messenger ribonucleic acids with alternative 5'-untranslated regions are differentially expressed in mouse liver and placenta.

Two 5'-untranslated regions (5'UTRs) with distinctly different sequences, designated 5'UTR L1 and 5'UTR L2, were obtained by amplification of complementary DNA from mouse liver and placenta with primers complementary to sequences from the hormone-binding domain common to GH receptor (GHR) and GH-binding protein (GHBP) messenger RNAs (mRNAs). The presence of an open reading frame in the 5'UTR L2 and the high GC content of this sequence suggest that mRNAs containing this 5'UTR may be translated with a lower efficiency than those containing 5'UTR L1. Expression studies showed that 5'UTR L1 and 5'UTR L2 are present in GHR and GHBP mRNAs in both tissues. However, the relative expression of the two 5'UTRs differs between liver and placenta and in liver from different physiological states. The different expression patterns of the L1 and L2 5'UTRs predict that the corresponding 5'-noncoding exons of the GHR/GHBP gene are associated with different regulatory elements. The expression patterns of the 5'UTRs also indicate that there is a linkage between the 5'UTR present in GHR/GHBP gene transcripts and the alternative splicing of these transcripts to yield either GHR or GHBP mRNAs. The 5'-noncoding exon used for transcription of the GHR/GHBP gene, therefore, may be involved in regulating both the ratio of GHR to GHBP transcripts and the efficiency of translation of these transcripts. Transcription from the different 5'-noncoding exons of the GHR/GHBP gene thus may be a critical element in the regulation of the expression of GHR and GHBP and thereby in the control of the responses of different tissues to GH.