Ghrelin gene-related peptides: multifunctional endocrine / autocrine modulators in health and disease

1. Ghrelin is a multifunctional peptide hormone that affects various processes, including growth hormone and insulin release, appetite regulation, gut motility, metabolism and cancer cell proliferation. Ghrelin is produced in the stomach and in other normal and pathological cell types. It may act as an endocrine or autocrine/paracrine factor. 2. The present article reviews recent findings in the study of ghrelin and its receptor that suggest that the ghrelin gene locus may give rise to a number of functional molecules (peptides and RNA transcripts) in addition to ghrelin. 3. The ghrelin gene encodes a precursor protein, preproghrelin, from which ghrelin and other potentially active peptides are derived by alternative mRNA splicing and/or proteolytic processing. The metabolic role of the peptide obestatin, derived from the preproghrelin C-terminal region, is contentious. However, obestatin has direct effects on cell proliferation. 4. The regulation of ghrelin expression and the mechanisms through which the peptide products arise are unclear. We have recently re-examined the organization of the ghrelin gene and identified several novel exons and transcripts. One transcript, which lacks the ghrelin-coding region of preproghrelin, contains the coding sequence of obestatin. 5. Furthermore, we have identified an overlapping gene on the antisense strand of ghrelin, namely GHRLOS, which generates transcripts that may function as non-coding regulatory RNAs or code for novel, short bioactive peptides. 6. The identification of these novel ghrelin-gene related transcripts and peptides raises critical questions regarding their physiological function and their potential role in obesity, diabetes and cancer.