This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Langouche, L. Articles by Denef, C. Search for Related Content PubMed PubMed Citation Articles by Langouche, L. Articles by Denef, C.

Stimulation of Intracellular Free Calcium in GH3 Cells by 3-Melanocyte-Stimulating Hormone. Involvement of a Novel Melanocortin Receptor?

Laboratory of Cell Pharmacology, University of Leuven, Medical School, Campus Gasthuisberg, B-3000 Leuven, Belgium

Address all correspondence and requests for reprints to: Prof. Carl Denef, Laboratory of Cell Pharmacology, University of Leuven, Medical School, Campus Gasthuisberg (O&N), B-3000 Leuven, Belgium. E-mail: carl.denef{at}med.kuleuven.ac.be

The melanocortin (MC) 3MSH is a peptide that can be generated from the N-terminal domain of POMC and is believed to signal through the MC3 receptor. We recently showed that it induces a sustained rise in intracellular free calcium levels ([Ca²⁺]_i) in a subpopulation of pituitary cells, particularly in the lactosomatotroph lineage. In the present study we report that 3MSH and some analogs increase [Ca²⁺]_i in the GH- and PRL-secreting GH3 cell line and evaluate on the basis of pharmacological experiments and gene expression studies which MC receptor may be involved.

A dose as low as 1 pM 3MSH induced an oscillating [Ca²⁺]_i increase in a significant percentage of GH3 cells. Increasing the dose recruited an increasing number of responding cells; a maximum was reached at 0.1 nM. 2MSH, MSH, and NDP-MSH displayed a similar effect. SHU9119, an MC3 and MC4 receptor antagonist, and an MC5 receptor agonist, did not affect the number of cells showing a [Ca²⁺]_i rise in response to 3MSH. SHU9119 had also no effect when added alone. MTII, a potent synthetic agonist of the MC3, MC4, and MC5 receptor as well as an N-terminally extended recombinant analog of 3MSH showed low potency in increasing [Ca²⁺]_i in GH3 cells, but high potency in stimulating cAMP accumulation in HEK 293 cells stably transfected with the MC3 receptor. In contrast, a peptide corresponding to the 2MSH sequence of POMC-A of Acipenser transmontanus increased [Ca²⁺]_i in GH3 cells, but was about 50 times less potent than 2- or 3MSH in stimulating cAMP accumulation in the MC3 receptor expressing HEK 293 cells. By means of RT-PCR performed on a RNA extract from GH3 cells, the messenger RNA of the MC2, MC3, and MC4 receptor was undetectable, but messenger RNA of the MC5 receptor was clearly present.

These data suggest that the GH3 cell line does not mediate the effect of 3MSH through the MC3 receptor. The involvement of the MC5 receptor is unlikely, but cannot definitely be excluded. The findings animate the hypothesis that there exists a second, hitherto unidentified, MC receptor that displays high affinity for 3MSH.

This article has been cited by other articles:

				S. C Harmer, D. J Pepper, K. Cooke, H. P J Bennett, and A. B Bicknell Evidence of a possible role for Lys-{gamma}3-MSH in the regulation of adipocyte function J. Endocrinol., January 1, 2008; 196(1): 149 - 158. [Abstract] [Full Text] [PDF]

				J. K Yeh, J. F Evans, Q.-T. Niu, and J. F Aloia A possible role for melanocortin peptides in longitudinal growth J. Endocrinol., December 1, 2006; 191(3): 677 - 686. [Abstract] [Full Text] [PDF]