Growth hormone-releasing hormone receptor (GHRH-R) mRNA expression in human pituitary adenomas: A study by catalyzed reporter deposition-In situ hybridization (CARD-ISH)

Abstract

Growth hormone-releasing hormone (GHRH) stimulates growth hormone (GH) gene transcription, synthesis, and secretion of growth hormone via growth hormone-releasing hormone receptor (GHRH-R). In a previous study using reverse transcriptase polymerase chain reaction (RT-PCR) and Northern blotting, GHRH-R mRNA was detected in all types of pituitary adenomas. On the other hand, in a recentin situ hybridization (ISH) study of 16 adenomas, including GH (n=8), PRL (n=1), ACTH (n=2), gonadotroph (n=4), and null-cell (n=1) adenomas, GHRH-R mRNA expression was observed only in GH adenomas and one gonadotroph adenoma. Thus, the extent of GHRH-R mRNA in pituitary adenomas is not clear. To clarify these different findings, we investigated the expression of GHRH-R mRNA in various types of human pituitary adenomas, including GH (n=7), PRL (n=4), ACTH (n=3), gonadotroph (n=8), and null-cell adenomas (n=13) using conventional ISH and the CARD-ISH technique, which is more sensitive than previous nonisotopic ISH techniques. By conventional ISH, GHRH-R was found in 71% of GH, 50% of PRL, 67% of ACTH, 12% of gonadotroph, and 8% of null-cell adenomas. By catalyzed reporter deposition-in situ hybridization (CARD-ISH), GHRH-R mRNA was expressed in 100% of GH, 50% of PRL, 67% of ACTH, 62% of gonadotroph, and 70% of null-cell adenomas. Hybridization with the control sense probe was consistently negative. These results show that GHRH-R mRNA is expressed in all types of adenomas with GH adenomas showing the strongest signal for GHRH-R mRNA, suggesting that GHRH-R has a role mainly in the function of GH adenomas, but may also play a role in tumor growth and/or function of other types of adenomas. These experiments also show that CARD-ISH can be used to detect low copy numbers of specific mRNAs because of the increased sensitivity of this technique.