An Overview of GHSR
Growth hormone secretagogue receptor (GHSR) is the corresponding receptor for the growth hormone secretagogue. Like growth hormone releasing hormone (GHRH) and somatostatin (SRIF), GHSR plays a role in regulating the secretion of growth hormone. GHSR isolated from human, pig and rat was analyzed and found to have the characteristics of a typical G protein. GHSR is abundantly distributed in the anterior pituitary and central nervous system. GHSR is also widely distributed in tissues including heart, adipose tissue, gonads, tumors, and immune systems that are not directly related to GH secretion regulation. This suggests that in addition to promoting the secretion of GH, there may be other autocrine, paracrine and endocrine functions. The most important biological role of GHSR is shown by its binding to its ligand, ghrelin.
Major type of GHSR
In 1996, Howard et al. successfully isolated two different GHSRs from human and pig pituitary cDNA libraries, named GHSR Ia and GHSR Ib. The human and pig GHSR Ia subtype encodes 366 amino acid residues with a similarity of 98%. However, the GHSR Ib subtype isolated from human and pig pituitary encodes only 289 amino acids.
GHSR and diseases
GHSR has an effect on tumorigenesis. It was reported that only the GHSR Ia subtype were found in the normal prostate cDNA library. However, both GHSR Ia and Ib subtypes and GHSR Ia ligand ghrelin were simultaneously found in tumor cells of the prostate, and thus GHSR Ib also played a role in the occurrence and growth of the tumor. In addition, the distribution of GHSR was also found in liver tumor cells and some neuroendocrine tumor cells. Therefore, ghrelin plays a role in tumorigenesis and growth through autocrine and paracrine. Studies have found that GHSR and ghrelin are not only distributed in B cells of the immune system, but also in T cells and neutrophils that do not express large amounts of growth hormone. Therefore, GHSR will promote the secretion of growth hormone in the immune system. It can be seen that GHSR will be a useful target for disease diagnosis.
Howard, A. D., Feighner, S. D., Cully, D. F., et al. (1996) A receptor in pituitary and hypothalamus that functions in growth hormone release. Science, 273: 974-977.