Expression of Growth Hormone Receptor Isoform Exon-3-Excluding and Exon-3-Retaining Messenger RNAs in Peripheral Lymphocytes from Normal and Acromegalic Subjects

Abstract

Aim: To determine the expression of two isoforms of the growth hormone (GH) receptor (GHR), which differ by the presence (GHR3+) or absence (GHR3–) of exon 3, and their correlation with circulating GH and insulin-like growth factor I (IGF-I) in normal subjects and in acromegalic patients. Methods: The expression of GHR isoforms was determined by reverse-transcriptase polymerase chain reaction in lymphocytes from 12 normal subjects and from 11 patients with acromegaly. The levels of GHR mRNA were normalized to those of β-actin, and ratios were calculated to assess the relative levels of expression. Results: All samples showed expression of both GHR isoforms, but the expression of GHR3+ and GHR3– was similar in acromegalic patients (6.0 ± 1.7 vs. 8.3 ± 2.0%, mean ± SE). In contrast, in healthy subjects, GHR3– was the predominant isoform (11.8 ± 3.0 vs. 5.1 ± 0.68%; p < 0.05), and the levels of expression of GHR3– correlated significantly with IGF-I. Conclusions: These data demonstrate coexpression of both GHR isoforms under normal and pathological conditions; however, GHR3– is the predominant form in normal subjects and shows a negative correlation with IGF-I levels.