Human fat cells possess a plasma membrane-bound H2O2-generating system that is activated by insulin via a mechanism bypassing the receptor kinase.
Insulin caused a transient increase in H2O2 accumulation in human fat cell suspensions that was observed only in the presence of an inhibitor of catalase and heme-containing peroxidases, such as azide, and reached peak levels of 30 microM within 5 min. The cells contained a plasma membrane-bound NADPH oxidase, producing 1 mol H2O2/mol of NADPH oxidation, that was activated on exposure of intact cells to insulin at contrations that are physiologically relevant (0.1-10 nM). The hormone effect was rapid and was due to a selective increase in substrate affinity. The enzyme was magnesium dependent, required a flavine nucleotide for optimal activity, and was most active at pH 5.0-6.5. In contrast to all other hormone- or cytokine-sensitive NADPH oxidases that have been characterized in sufficient detail, the human fat cell oxidase retained its hormone responsiveness after cell disruption, and only Mn2+, but no ATP, was required for a ligand-induced activation in crude plasma membranes. The results demonstrate that insulin utilizes tyrosine kinase-independent pathways for receptor signaling and strongly support the view that H2O2 contributes to the intracellular propagation of the insulin signal.
Krieger-Brauer
H I
HI
Klinisches Institut für Herzinfarktforschung, Medizinischen Universitätsklinik, Heidelberg, Federal Republic of Germany.
Kather
H
H
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000273:Adipose Tissue / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D008345:Manganese / Q000494:pharmacology; D009249:NADP / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011972:Receptor, Insulin; D015398:Signal Transduction; D013535:Suspensions
D007328:Insulin; D013535:Suspensions; D008345:Manganese; D009249:NADP; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin