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Journal of Lipid Research, Vol. 47, 643-652, March 2006
Copyright © 2006 by American Society for Biochemistry and Molecular Biology

* Mike Rosenbloom Laboratory for Cardiovascular Research, McGill University Health Center, Montreal, Québec, Canada
Centre de Recherche Hôpital Laval, Université Laval, Québec, Québec, Canada
Published, JLR Papers in Press, December 6, 2005.
1 Present address of F. Assadi: University of Teheran, Teheran, Iran.
2 To whom correspondence should be addressed. e-mail: katherine.cianflone{at}crhl.ulaval.ca
Acylation stimulating protein (ASP; C3adesArg) stimulates triglyceride synthesis (TGS) and glucose transport in preadipocytes/adipocytes through C5L2, a G-protein-coupled receptor. Here, ASP signaling is compared with insulin in 3T3-L1 cells. ASP stimulation is not G
s or G
i mediated (pertussis and cholera toxin insensitive), suggesting G
q as a candidate. Phospholipase C (PLC) is required, because the Ca2+ chelator 1,2-bis(o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester and the PLC inhibitor U73122 decreased ASP stimulation of TGS by 93.1% (P < 0.0.001) and 86.1% (P < 0.004), respectively. Wortmannin and LY294002 blocked ASP effect by 69% (P < 0.001) and 116.1% (P < 0.003), respectively, supporting phosphatidylinositol 3-kinase (PI3K) involvement. ASP induced rapid, transient Akt phosphorylation (maximal, 5 min; basal, 45 min), which was blocked by Akt inhibition, resembling treatment by insulin. Downstream of PI3K, mamalian target of rapaycin (mTOR) is required for insulin but not ASP action. By contrast, both ASP and insulin activate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK1/2) pathway, with rapid, pronounced increases in ERK1/2 phosphorylation, effects partially blocked by PD98059 (64.7% and 65.9% inhibition, respectively; P < 0.001). Time-dependent (maximal, 30 min) transient calcium-dependent phospholipase A2 (cPLA2)-Ser505 phosphorylation (by MAPK/ERK1/2) was demonstrated by Western blot analysis. ASP signaling involves sequential activation of PI3K and PLC, with downstream activation of protein kinase C, Akt, MAPK/ERK1/2, and cPLA2, all of which leads to an effective and prolonged stimulation of TGS.
Supplementary key words insulin 3T3-L1 cells triglyceride synthesis phosphatidylinositol 3-kinase phospholipase C
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