MONKEY GROWTH-HORMONE (GH) RECEPTOR GENE-EXPRESSION - EVIDENCE FOR 2 MECHANISMS FOR THE GENERATION OF THE GH BINDING-PROTEIN

The growth hormone receptor (GHR) cDNA was cloned from the liver of Rh esus macaque using polymerase chain reaction. As deduced from the nucl eotide sequence, the mature GHR is a protein of 620 amino acids which presents 94.1% identity with the human receptor. The monkey GHR (mkGHR ) expressed in 293 cells presented the expected specificity for a prim ate GHR and was able to transduce a transcriptional effect of GH. Huma n GH was able to activate tyrosine phosphorylation of both the tyrosin e kinase JAK2 and the receptor in 293 cells co-transfected with mkGHR and JAK2 cDNAs. The GH binding protein (GHBP), the soluble short form of the GHR, was also present in monkey serum. Expression of the GHR cD NA in eucaryotic cells indicated that the GHBP can be produced by prot eolytic cleavage of the membrane receptor. Northern blot analysis of G HR gene expression in different tissues allowed us to identify three d ifferent transcripts of 5.0 and 2.8 kilobase pairs and a smaller one o f 1.7 kilobase pairs which could encode a GHBP. Rapid amplification of cDNA extremities (3'-RACE-polymerase chain reaction) was used to iden tify a cDNA encoding a protein in which the transmembrane and cytoplas mic domains of the receptor are substituted by a short sequence of 9 a mino acids. This transcript was present in various tissues and could e ncode a GHBP as well, suggesting for the first time that two different mechanisms can coexist for the generation of the GHBP: proteolytic cl eavage of the membrane receptor and a specific mRNA produced by altern ative splicing.