Nox4 acts as a switch between differentiation and proliferation in preadipocytes.
OBJECTIVE
Insulin promotes differentiation of preadipocytes into adipocytes. Insulin also stimulates reactive oxygen species (ROS) production, and the NADPH oxidases Nox1 and Nox4 are important sources of ROS. We determined in human and mouse preadipocytes whether Nox proteins contribute to ROS formation and differentiation in response to insulin.


RESULTS
The expression of Nox1 and Nox4 was increased during insulin-induced differentiation, and insulin increased ROS production. SiRNA against Nox4 but not Nox1 inhibited insulin-induced differentiation and ROS production but promoted proliferation. Nox4 overexpression yielded the opposite effect. As observed by siRNA and overexpression, Nox4 controlled the expression of MAP kinase phosphatase-1 (MKP-1), which reduces insulin-induced ERK1/2 activation. Consequently, downregulation of Nox4 promoted ERK1/2 signaling: Proliferation was increased and through phosphorylation of the inhibitory site serine612, ERK1/2 inhibited the activation of the insulin-receptor substrate-1 (IRS-1) and thereby prevented differentiation in response to insulin. Inhibition of ERK1/2 or overexpression of MPK-1 promoted insulin-induced differentiation. Accordingly, insulin-induced proliferation was enhanced by siRNA against MKP-1, whereas inhibition of ERK1/2 or overexpression of MKP-1 attenuated proliferation.


CONCLUSIONS
Nox4 acts as a switch from insulin-induced proliferation to differentiation by controlling MKP-1 expression, which limits ERK1/2 signaling.
Schröder
Katrin
K
Institut für Kardiovaskuläre Physiologie, Goethe-Universität, Theodor-Stern-Kai 7, D-60596 Frankfurt am Main, Germany.
Wandzioch
Katalin
K
Helmcke
Ina
I
Brandes
Ralf P
RP
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000201:enzymology*; D050156:Adipogenesis / Q000187:drug effects; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D000074624:NADPH Oxidase 1; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D009247:NADH, NADPH Oxidoreductases; D000074624:NADPH Oxidase 1; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C402799:NOX1 protein, human; C000614711:NOX1 protein, mouse; C498910:NOX4 protein, human; C422943:Nox4 protein, mouse; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D054638:Dual Specificity Phosphatase 1; C517020:Dusp1 protein, mouse