Melanocortin 5 receptor activates ERK1/2 through a PI3K-regulated signaling mechanism

Abstract

receptor activates ERK1/2 through a PI3K-regulated signaling mechanism. Molecular and Cellular Endocrinology, Elsevier, 2009, 303 (1-2) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A c c e p t e d M a n u s c r i p t SummaryMelanocortin 5 receptor (MC5R) is a G-protein coupled receptor (GPCR) with high affinity for α-MSH. To unravel some of the downstream cell-signaling pathways activated by this receptor, HEK293 cells were transiently and stably transfected with a vector encoding green fluorescent protein (GFP)-tagged MC5R. In these cells the receptor was correctly addressed to the cell surface and was functional, as shown by the MC5R-induced formation of intracellular cAMP. In fact, the MC5R agonist α-MSH induced a 10 or 16 fold increase (transient or stable cells, respectively) above the cAMP levels found in unstimulated cells. Moreover, in cells stably expressing MC5R-GFP, α-MSH promoted ERK1/2 phosphorylation in a dose-dependent manner (EC50=7.3nM) with the maximal effect occurring after 5min of agonist incubation. The signaling pathway conveyed through ERK1/2 is not linked to cAMP, since the phosphorylation of these kinases is unchanged by the inhibition of adenylyl cyclase. Also, ERK1/2 activation is not significantly affected by PKA, PKC and Akt/PKB specific inhibitors. However, α-MSH-induced ERK1/2 activation is abolished by the PI3K inhibitors wortmannin and LY294002. Altogether, these findings demonstrate that MC5R signals through a PI3K-regulated Akt-independent pathway leading to downstream activation of ERK1/2. The involvement of these MAPK suggests that MC5R could be implicated in cellular proliferation or differentiation mechanisms.

Characterization of murine melanocortin receptors mediating adipocyte lipolysis and examination of signalling pathways involved

“…The G s transduction pathway is established to be a validated path of signalling for all MCRs (Barrett et al 1994;Mountjoy et al 1992) all though other signalling pathways have been suggested (Buch et al 2009;Konda et al 1994;Daniels et al 2003;Rodrigues et al 2009). The natural occurring melanocortin peptide family consists of -, -and -melanocyte stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH).…”

“…When a MCR is stimulated, it couples to G s , which activates intracellular adenylyl cyclase and increases cAMP production. -MSH stimulated phosphorylation of extracellular signal-regulated kinase (ERK) has previously been linked to lipolysis in 3T3-L1 cells and MC5R has been established to activate phosphatidylinositol 3-kinase dependent ERK after stimulation by -MSH (Rodrigues et al 2009). In addition, cAMP dependent AMPK has been linked to MC5R mediated fatty acid oxidation stimulated by -MSH in skeletal muscle .…”

Melanocortins: Anti-Inflammatory and Neuroprotective Peptides

“…MC3R has been shown to induce inositol phosphate signaling (Konda et al, 1994) and MC5R was reported to activate the Janus kinase/signal transducer and activator of transcription (Jak/STAT) pathway in B cells (Buggy, 1998). Stimulation of all MCRs leads to activation of mitogen-activated protein kinases (MAPK) ERK-1/2 Chai et al, 2007;Herraiz et al, 2011;Patten et al, 2007, Rodrigues et al, 2009Roy et al, 2011). Depending on the cell type this effect may involve phosphoinositol 3 kinase activation (Rodrigues et al, 2009;Vongs et al, 2004).…”

“…Stimulation of all MCRs leads to activation of mitogen-activated protein kinases (MAPK) ERK-1/2 Chai et al, 2007;Herraiz et al, 2011;Patten et al, 2007, Rodrigues et al, 2009Roy et al, 2011). Depending on the cell type this effect may involve phosphoinositol 3 kinase activation (Rodrigues et al, 2009;Vongs et al, 2004). Some reports also show that ERK activation may be PKAindependent in MCR transfected cell lines Vongs et al, 2004).…”

Melanocortin receptors and their accessory proteins

“…It has emerged that many of the MCRs bind to endogenous peptides beyond the melanocortin peptides, which can act as agonists, antagonists, partial agonists, and even inverse agonists at these receptors (Cone, 2006). Furthermore, although the cAMP pathway continues to serve as the predominant readout of MCR function in many studies, numerous other intracellular signaling cascades for example the mitogen-activated protein kinase pathway have also been implicated in melanocortin signaling (Vongs et al, 2004;Sutton et al, 2005;Patten et al, 2007;Rodrigues et al, 2009). An additional feature of MCR signaling which has come to light over recent years is the presence of accessory proteins which regulate receptor function.…”