Oxidants and Ca+2 induce PGC-1α degradation through calpain

Peroxisome proliferator activator receptor gamma coactivator 1 alpha (PGC-1 alpha) is a transcriptional coactivator known to mediate mitochondrial biogenesis. Whereas PGC-1 alpha transcription is regulated by a variety of signaling cascades, the mechanisms of PGC-1 alpha degradation have received less investigation. Thus, we investigated the mechanisms responsible for PGC-1 alpha degradation in renal proximal tubular cells (RPTC). Amino acid sequence analysis of the PGC-1 alpha protein revealed three PEST sequence-rich regions, predictive of proteolysis by calpains and/or the proteasome. Under basal conditions, treatment with the protein synthesis inhibitor cycloheximide resulted in rapid degradation of PGC-1 alpha (t(1/2) = 38 min), which was blocked by the proteasome inhibitor epoxomicin, but not the calpain inhibitor calpeptin. Oxidant exposure resulted in the degradation of both endogenous and adenovirally over-expressed PGC-1 alpha, which was inhibited by calpeptin but not epoxomicin. Thapsigargin-induced release of ER Ca2+ also stimulated calpain-dependent, epoxomicin-independent degradation of PGC-1 alpha. Finally, Ca2+ addition to lysates of RPTC over-expressing PGC-1 alpha resulted in calpeptin-sensitive, epoxomicin-insensitive degradation of PGC-1 alpha. In summary, we suggest two distinct mechanisms regulate PGC-1 alpha basal PGC-1 alpha turnover by proteasome degradation and oxidant- and Ca2+-mediated PGC-1 alpha degradation through calpain. (c) 2008 Published by Elsevier Inc.