DISTRIBUTION OF GROWTH-HORMONE RECEPTOR MESSENGER-RIBONUCLEIC-ACID CONTAINING AND LACKING EXON-3 IN HUMAN TISSUES

The extent of expression of the GH receptor (GHR) in human tissues is largely unknown. In some cell lines and placenta, the GHR gene generates two different mRNAs by alternative splicing of exon 3, one coding for a full-length receptor (GHR+3) and the other for a receptor isoform that lacks exon 3 (GHR-3), with deletion of amino acid residues 7-28. To determine the distribution of the GHR and the relative abundance of its two isoforms in man, we studied a variety of tissues obtained at autopsy by reverse transcription and polymerase chain reaction (PCR) amplification, using isoform-specific primers. The nature of the PCR products was verified by restriction analysis and DNA sequencing. The relative proportions of the two GHR isoforms were determined by competitive PCR using a P-32-labeled antisense primer and a mixture of both isoform-specific sense primers in equimolar amounts. Electrophoretic bands corresponding to the amplification products were excised and counted, or quantitated by laser densitometry. Restriction analysis and sequencing of the amplified products were consistent with their predicted sequence. Both GHR transcripts were found in all 19 tissues tested, but their relative proportions varied depending on the tissue and, to a lesser extent, between subjects. They ranged from a preponderance of GHR-3 (kidney, bladder, adrenal, and brain stem) to a predominance of GHR+3 (skeletal muscle and liver). We conclude that the GHR gene is widely expressed in human tissues. Both GHR+3 and GHR-3 transcripts are present, but their relative proportions depend on the tissue and, possibly, the metabolic status. The physiological significance of the existence of two human GHR forms remains to be elucidated.