SCF^Cdc4 acts antagonistically to the PGC-1α transcriptional coactivator by targeting it for ubiquitin-mediated proteolysis

Abstract

Peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1alpha (PGC-1alpha) is a highly regulated transcriptional coactivator that coordinates energy metabolism in mammals. Misregulation of PGC-1alpha has been implicated in the pathogenesis of several human diseases, including diabetes, obesity, and neurological disorders. We identified SCF(Cdc4) as an E3 ubiquitin ligase that regulates PGC-1alpha through ubiquitin-mediated proteolysis. PGC-1alpha contains two Cdc4 phosphodegrons that bind Cdc4 when phosphorylated by Glycogen Synthase Kinase 3beta (GSK3beta) and p38 MAPK, leading to SCF(Cdc4)-dependent ubiquitylation and proteasomal degradation of PGC-1alpha. Furthermore, SCF(Cdc4) negatively regulates PGC-1alpha-dependent transcription. We demonstrate that RNAi-mediated reduction of Cdc4 in primary neurons results in an increase of endogenous PGC-1alpha protein, while ectopic expression of Cdc4 leads to a reduction of endogenous PGC-1alpha protein. Finally, under conditions of oxidative stress in neurons, Cdc4 levels are decreased, leading to an increase in PGC-1alpha protein and PGC-1alpha-dependent transcription. These results suggest that attenuation of SCF(Cdc4)-dependent proteasomal degradation of PGC-1alpha has a role in mediating the PGC-1alpha-dependent transcriptional response to oxidative stress.