Dual-specificity phosphatases regulate mitogen-activated protein kinase signaling in adipocytes in response to inflammatory stress.

Obesity is a strong predictor of heart disease, insulin resistance, and type II diabetes. Chronic, low-grade inflammation links obesity and insulin resistance through mitogen-activated protein kinase (MAPK) signaling pathways. Upstream kinases activate MAPK signaling, while MAPK-specific dual-specificity phosphatases (DUSPs) act as key modulators and controllers of MAPK deactivation (i.e. dephosphorylation). Using tumor necrosis factor α (TNFα) in 3 T3-L1 adipocytes as a model of inflammation, we report that TNFα-mediated induction of Dusp1, Dusp8 and Dusp16 modulated the transient regulation of MAPK (i.e., ERK, JNK, and p38) phosphorylation and subsequent inflammatory gene expression. All three MAPKs examined were phosphorylated in preadipocytes and adipocytes in response to TNFα, where signaling magnitude and duration were phenotype-specific. Moreover, TNFα increased mRNA abundance of DUSPs in preadipocytes and adipocytes in a phenotype-specific manner, concomitant with dephosphorylation of MAPKs. RNA interference (RNAi)-mediated knockdown of Dusp1, Dusp8 and Dusp16 increased signaling magnitude and duration of ERK, JNK, and p38 that subsequently resulted in significant increases in MAPK-dependent inflammatory gene expression of MCP-1, IL-6, and Cox-2 in response to TNFα. This study highlights important roles for DUSPs as integral components of MAPK signaling and adipocyte inflammatory gene expression.