Intracellular signaling by the insulin receptor kinase

Albert Einstein College Of Medicine, Inc, Bronx NY

Investigators

Linked publications & trials

Abstract

? DESCRIPTION (provided by applicant): The regulation of the NF-?B inflammatory signaling pathways has primarily focused on immune cell systems that underlie the production of pro-inflammatory cytokines mediating infection as well as sterile immune responses. Recent studies have also clearly established an important role of adipose tissue inflammation and activation of pro-inflammatory cytokines mediating diet induced insulin resistance. However, the transduction pathways and regulatory control of NF-?B signaling within non-immune cells and in particular adipocytes has not been examined and is essential for not only our basic understanding of adipocyte biology but also in the mediation of insulin resistance and diabetes. In this regard, our preliminary data has demonstrated a novel and completely unexpected role for the TIGAR protein as a major regulator of NF-?B signaling adipocytes, insulin sensitivity and adipose tissue inflammation in vivo. Specifically, our preliminary data has demonstrated that TIGAR is highly expressed in adipocytes and is markedly down regulated in ob/ob and db/db mice and following high fat diet (HFD) induced obesity. Moreover, knockdown of TIGAR in 3T3L1 adipocytes resulted in marked inhibition of insulin signaling with increased basal and TNF? stimulated NF-?B signaling. In contrast, over expression of TIGAR enhanced insulin signaling and inhibited basal and TNF?- stimulated NF-?B signaling. Detailed analyses demonstrated that TIGAR suppressed NF-?B signaling upstream of IKK? and surprisingly independent of the TIGAR phosphatase enzymatic activity. Based upon these data and recent preliminary data, we hypothesize that TIGAR suppresses NF-?B signaling through inhibition of the upstream IKK?/IKK? /NEMO ternary complex by directly binding to the HOIL/HOIP- 1L/Sharpin complex responsible for NEMO and RIP1 linear ubiquitination. We further predict the preventing/reversing diet induced obesity down regulation of adipocyte TIGAR protein will protect adipocytes/adipose tissue from metabolic dysfunction. The innovations of this proposal are based upon the identification of a novel regulatory mechanism for a new critical control element in NF-?B signaling and its role in the pathophysiologic dysfunction of diet induced insulin resistance. Thus, three central questions of this proposal are 1) what is the molecular basis for TIGAR inhibition of NF-?B signaling, 2) does TIGAR deficiency cause, contribute to or is a consequence of impaired insulin signaling through promotion of inflammatory signaling; and 3) can physiologic re-expression of TIGAR suppress adipocyte dysfunction in diet-induced obesity and insulin resistance.