Absence of mutations in the growth hormone (GH)-releasing hormone receptorgene in GH-secreting pituitary adenomas

OBJECTIVE GH-releasing hormone (GHRH) is a potent stimulator of somatotroph cell proliferation and on secretion. GHRH acts via binding to a G-protein coupled receptor (GPCR) (GHRH-R), that activates adenylyl cyclase (AC) and increases growth and function of somatotroph cells. Indeed, a subset (30-40 %) of somatotrophic adenomas contain somatic mutations of the GNAS1 gene th at encodes the alpha subunit of the G-protein (G(s)alpha) that stimulates A C. As activating mutations of other GPCRs cause development of endocrine tu mours, we hypothesized that somatic activating mutations of the GHRH-R migh t provide the molecular basis for somatotroph cell proliferation in a subse t of human GH-secreting pituitary adenomas. DESIGN We analysed genomic DNA isolated from 26 somatotrophinomas, 17 of wh ich lacked activating mutations in the GNAS1 gene. We individually amplifie d via polymerase chain reaction all 13 coding exons and the exon-intron bou ndaries of the GHRH-R gene. We used denaturing gradient gel electrophoresis to search for abnormalities in exons 1 through 11. Abnormally migrating ba nds were subjected to direct sequencing. Exons 12 and 13, encoding for the intracellular C-terminal domain, were subjected to direct sequencing. RESULTS Mutations were not detected in any of the tumours, but a rare polym orphism in codon 225 corresponding to the third transmembrane domain (V225I ) was discovered. CONCLUSIONS GHRH-R mutations are absent or rare in somatotrophinomas, and o ther mechanisms must explain the somatotroph cell proliferation in the aden omas that lack activating mutations in GNAS1 gene.