Downregulation of AMP-activated protein kinase by Cidea-mediated ubiquitination and degradation in brown adipose tissue

Abstract

We previously showed that Cidea À/À mice are resistant to diet-induced obesity through the upregulation of energy expenditure. The AMP-activated protein kinase (AMPK), consisting of catalytic a subunit and regulatory subunits b and c, has a pivotal function in energy homoeostasis. We show here that AMPK protein levels and enzymatic activity were significantly increased in the brown adipose tissue of Cidea À/À mice. We also found that Cidea is colocalized with AMPK in the endoplasmic reticulum and forms a complex with AMPK in vivo through specific interaction with the b subunit of AMPK, but not with the a or c subunit. When co-expressed with Cidea, the stability of AMPK-b subunit was dramatically reduced due to increased ubiquitinationmediated degradation, which depends on a physical interaction between Cidea and AMPK. Furthermore, AMPK stability and enzymatic activity were increased in Cidea À/À adipocytes differentiated from mouse embryonic fibroblasts or preadipocytes. Our data strongly suggest that AMPK can be regulated by Cidea-mediated ubiquitindependent proteosome degradation, and provide a molecular explanation for the increased energy expenditure and lean phenotype in Cidea-null mice.

Functional analysis of FSP27 protein regions for lipid droplet localization, caspase-dependent apoptosis, and dimerization with CIDEA

“…Studies to date indicate that protein-protein interactions are important to CIDE protein function, and both CIDEA and CIDEB have been studied somewhat in this regard. Homo-and heterodimeric interaction of CIDEA and/or CIDEB (i.e., CIDEA:CIDEA, CIDEB:CIDEB, and CIDEA:CIDEB) has been reported (5,8,11,19,27). CIDEB interacts with viral protein NS2 (8) and apolipoprotein B (42) and CIDEA with AMPK (27); such interactions appear to impact the physiological function of these CIDE partner proteins.…”

“…Ectopic expression of an HA-tagged or eGFP fusion construct containing amino acids 166 -195 of CIDEB was sufficient for lipid droplet targeting in lipid-loaded COS cells and HepG2 hepatocytes, respectively (42). CIDEA and CIDEB are also reportedly localized to the endoplasmic reticulum, an organelle from which biogenesis of intracellular lipid droplets initiates (27,42). Moreover, in addition to being lipid droplet-localized proteins per se, ectopic expression of FSP27 and CIDEA has been demonstrated to promote the formation and/or enlargement of lipid droplets in several nonadipocyte cell types, a phenomenon that is particularly evident with addition of exogenous oleic acid to culture media.…”

“…CIDEA-null mice exhibit elevated lipolysis in BAT and resist diet-induced obesity (44). A recent report demonstrated that one mechanism of CIDEA action is via its interaction with the major metabolic regulator AMP-activated protein kinase (AMPK), which reduces AMPK protein level by enhancing proteosome-mediated AMPK degradation (27). The phenotype of CIDEA-null mice was attributed initially to the ability of CIDEA to regulate thermogenesis via interaction with uncoupling protein-1 (UCP1) to inhibit UCP1 activity (44).…”

“…The phenotype of CIDEA-null mice was attributed initially to the ability of CIDEA to regulate thermogenesis via interaction with uncoupling protein-1 (UCP1) to inhibit UCP1 activity (44). Given that the initial mitochondrial localization reported for CIDEA appears to not be the case (27), CIDEA interaction with UCP1 remains to be fully clarified. CIDEB interacts with apolipoprotein B and promotes the formation of triacylglycerol-enriched VLDL particles (42).…”

Augmenting energy expenditure by mitochondrial uncoupling: a role of AMP-activated protein kinase

“…, independent of AMP (Hardie 2008;McGee and Hargreaves 2010). As described in BAT (Qi et al 2008), AMPK is negatively regulated by cell-deathinducing like effector A (Cidea), inducing ubiquitination of the b subunit of AMPK and degradation of the enzyme. Also protein kinase A-mediated phosphorylation of a1-AMPK subunit at Ser-173 prevents activation of AMPK by LKB1-mediated phosphorylation of the a1-AMPK subunit at Thr-172, as found recently in white adipocytes (Djouder et al 2010).…”