Tumor Necrosis Factor Receptor-1 Can Function through a Gα_q/11-β-Arrestin-1 Signaling Complex^*

Abstract

Tumor necrosis factor-α (TNFα) is a proinflammatory cytokine secreted from macrophages and adipocytes. It is well known that chronic TNFα exposure can lead to insulin resistance both in vitro and in vivo and that elevated blood levels of TNFα are observed in obese and/or diabetic individuals. TNFα has many acute biologic effects, mediated by a complex intracellular signaling pathway. In these studies we have identified new G-protein signaling components to this pathway in 3T3-L1 adipocytes. We found that β-arrestin-1 is associated with TRAF2 (TNF receptor-associated factor 2), an adaptor protein of TNF receptors, and that TNFα acutely stimulates tyrosine phosphorylation of Gα_q/11 with an increase in Gα_q/11 activity. Small interfering RNA-mediated knockdown of β-arrestin-1 inhibits TNFα-induced tyrosine phosphorylation of Gα_q/11 by interruption of Src kinase activation. TNFα stimulates lipolysis in 3T3-L1 adipocytes, and β-arrestin-1 knockdown blocks the effects of TNFα to stimulate ERK activation and glycerol release. TNFα also led to activation of JNK with increased expression of the proinflammatory gene, monocyte chemoattractant protein-1 and matrix metalloproteinase 3, and β-arrestin-1 knockdown inhibited both of these effects. Taken together these results reveal novel elements of TNFα action; 1) the trimeric G-protein component Gα_q/11 and the adapter protein β-arrestin-1 can function as signaling molecules in the TNFα action cascade; 2) β-arrestin-1 can couple TNFα stimulation to ERK activation and lipolysis; 3) β-arrestin-1 and Gα_q/11 can mediate TNFα-induced phosphatidylinositol 3-kinase activation and inflammatory gene expression.