Expression Of Functional Growth Hormone Secretagogue Receptors In Human Pituitary Adenomas: Polymerase Chain Reaction, Triple In‐situ Hybridization And Cell Culture Studies¹

Abstract

We examined the expression of functional growth hormone secretagogue receptors (GHS-R) in a series of 30 human pituitary adenomas-six secreting GH, three GH-PRL, six prolactin (PRL), five adrenocorticotrophic hormone (ACTH), one thyroid stimulating hormone (TSH), four gonadotroph and five non-secreting adenomas. By reverse transcriptase polymerase chain reaction (RT-PCR), the coexpression of the two GHS-R isoforms (Ia and Ib) was found in all the GH-, GH-PRL- and PRL-secreting adenomas, and only in two out of three corticotroph, two out of four gonadotroph and one out of five non-secreting tumours. They were absent in the TSH-secreting adenoma. The PCR products of GHS-R Ia and Ib were identical in size to those from two normal pituitaries. PCR cloning and sequencing of isoforms performed in two somatotroph adenomas revealed only two single, silent base mutations. Triple in-situ hybridization showed colocalization of GHS-R mRNA with messengers of GH and PRL, conjointly or separately, in individual cells of somatotroph, mammosomatotroph, and lactotroph adenomas. The presence of GHS-R mRNA in cells expressing PRL mRNA is emphasized. In cultured cells from six somatotroph and two mammosomatotroph adenomas, the powerful GHS MK-0677 stimulated GH release in a dose-dependent manner, with maximal effect at 6 h. Contrarily, when GHRH was applied, only three somatotrophs and two mamosomatotrophs were stimulated. In the two mammosomatotrophs, the PRL response to MK-0677 and to GHRH was similar to the GH response. An homologous desensitization of the GHS-R and the GHRH receptor was observed 24 h after a first stimulation by a single dose of the corresponding agonist. Heterologous desensitization was not observed. Interestingly, MK-0677 also stimulated, in a dose-dependent way, the hormone release of cells from all tested lactotroph and corticotroph adenomas. The existence of a functional expression of GHS-R in somatotroph, mammosomatotroph, lactotroph and corticotroph adenomas rises the question of the role played by GHS-R in pituitary adenomas, particularly those not engaged in GH secretion.

Ghrelin gene products, receptors, and GOAT enzyme: biological and pathophysiological insight

“…Surprisingly, a previous study showed that ghrelin mRNA levels in somatotropinomas were negatively correlated with tumor size and, indeed, high-grade tumors had lower levels of ghrelin mRNA than low-grade adenomas (Kim et al 2001). On the other hand, both GHSR1a and GHSR1b have been found to be highly expressed in somatotropinomas compared with NPs (Barlier et al 1999, Korbonits et al 2001, Rubinfeld et al 2004, which together with the previous data mentioned in this section, might suggest the existence of an autocrine/paracrine role of the ghrelin system in GHproducing adenomas. Moreover, studies in a rat pituitary somatotrope cell line indicate that both AG and UAG can stimulate cell proliferation (Nanzer et al 2004).…”

Imprinting of the Gsα gene GNAS1 in the pathogenesis of acromegaly

“…They were classified using clinical and biochemical findings and immunocytochemical and morphological data, including absence of contamination with normal pituitary (31). Normal human pituitary autopsy specimens were used as controls.…”

“…Total RNA was isolated using the SV kit (Promega Corp., Madison, Wisconsin, USA) or Tri-Reagent (Sigma Chemical Co., St. Louis, Missouri, USA); cDNA was made from 2 µg of total RNA using random-primed reverse transcription as described previously (31,33).…”

Differential expression of genes related to drug responsiveness between sparsely and densely granulated somatotroph adenomas

“…Several studies have shown a positive correlation between GH suppression by octreotide and SSTR2 and/or SSTR5 expression in GH-secreting adenomas [15][16][17][18][19], however to date no studies on differences of SSTR2 and SSTR5 expression between DG-and SG-type adenomas by using quantitative real-time RT-PCR has been reported. The present study revealed for the first time a significant greater SSTR2, but not SSTR5 expression in DG-type adenomas than SG-type adenomas.…”