Knocking down gene expression for growth hormone-releasing hormone inhibits proliferation of human cancer cell lines
Various attempts to detect human pituitary growth hormone-releasing hormone receptor (pGHRH-R) in neoplastic extrapituitary tissues have thus far failed. Recently, four splice variants (SVs) of GHRH-R have been described, of which SV1 has the highest structural homology to pGHRH-R and likely plays a role in tumor growth. The aim of this study was to reinvestigate whether human tumors and normal human extrapituitary tissues express the pGHRH-R and to corroborate our previous findings on its SVs. Thus, we developed a real-time PCR method for the detection of the mRNA for the pGHRH-R, its SVs, and the GHRH peptide. Using real-time PCR, Western blotting, and radioligand-binding assays, we detected the mRNA for pGHRH-R and pGHRH-R protein in various human cancer cell lines grown in nude mice and in surgical specimens of human lung cancers. The expression of mRNA for SVs of pGHRH-R and GHRH was likewise found in xenografts of human non-Hodgkin's lymphomas, pancreatic cancer, glioblastoma, small-cell lung carcinomas, and in human nonmalignant prostate, liver, lung, kidney, and pituitary. Western blots showed that these normal and malignant human tissues contain SV1 protein and immunoreactive GHRH. Our results demonstrate that some normal human tissues and tumors express mRNA and protein for the pGHRH-R and its splice variants. These findings confirm and extend the concept that GHRH and its receptors play an important role in the pathophysiology of human cancers.