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A more recent version of this article appeared on March 1, 2007 Originally published as MBC in Press, 10.1091/mbc.E06-05-0402 on January 17, 2007
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Submitted on May 8, 2006
Revised on November 9, 2006
Accepted on December 21, 2006
*Department of Medical Sciences, University of Piemonte Orientale "Amedeo Avogadro," 28100 Novara, Italy; Divisions of
Anatomy and
Pharmacology, Department of Anatomy, Pharmacology, and Forensic Medicine, University of Turin, 10125 Turin, Italy;
Department of Traumatology, Orthopaedics, and Occupational Medicine, University of Torino, 10126 Torino, Italy
Monitoring Editor: Carl-Henrik Heldin
Ghrelin is an acylated peptidyl gastric hormone acting on the pituitary and hypothalamus to stimulate appetite, adiposity and GH release, through activation of GHSR-1a receptor. Moreover, ghrelin features several activities such as inhibition of apoptosis, regulation of differentiation, and stimulation or inhibition of proliferation of several cell types. Ghrelin acylation is absolutely required for both GHSR-1a binding and its central endocrine activities. However, the unacylated ghrelin form, des-acyl ghrelin, which does not bind GHSR-1a and is devoid of any endocrine activity, is far more abundant than ghrelin in plasma, and shares with ghrelin some of its cellular activities. Inhere we show that both ghrelin and des-acyl ghrelin stimulate proliferating C2C12 skeletal myoblasts to differentiate and to fuse into multinucleated myotubes in vitro through activation of p38. Consistently, both ghrelin and des-acyl ghrelin inhibit C2C12 proliferation in growth medium. Moreover, the ectopic expression of ghrelin in C2C12 enhances differentiation and fusion of these myoblasts in differentiation medium. Finally, we show that C2C12 cells do not express GHSR-1a, but contain a common high-affinity binding site recognized by both acylated and des-acylated ghrelin, suggesting that the described activities on C2C12 are likely mediated by this novel yet unidentified receptor for both ghrelin forms.
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