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The Mitochondrial Biogenesis Regulator PGC‐1alpha is Degraded by the Proteasome and Calpain Pathways in Renal Cells
Author(s) -
Rasbach Kyle A.,
Green Peter T.,
Schnellmann Rick G
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.605.10
Subject(s) - mg132 , calpain , proteasome , mitochondrial biogenesis , coactivator , biology , microbiology and biotechnology , proteasome inhibitor , protein degradation , proteolysis , ubiquitin , cycloheximide , biochemistry , mitochondrion , transcription factor , protein biosynthesis , gene , enzyme
Peroxisome proliferator activator receptor γ coactivator 1α (PGC‐1 α) is a transcriptional coactivator known to mediate mitochondrial biogenesis. While PGC‐1α transcription is regulated by a variety of signaling cascades including, p38 MAPK, CAMK, calcineurin A, and nitric oxide, there has been little investigation into the mechanisms of PGC‐1α degradation. The goal of this study was to determine the mechanisms responsible for PGC‐1α degradation in renal proximal tubular cells (RPTC). Amino acid sequence analysis of the PGC‐1α protein revealed three regions enriched in PEST sequences, predictive of proteolysis by calpains and/or the proteasome. Under basal conditions, treatment with the protein synthesis inhibitor cycloheximide, to block PGC1α synthesis, resulted in the rapid degradation of PGC‐1α with t 1/2 of 38 min. This degradation was blocked by the calpain and proteasome inhibitor, MG‐132 (10 μM) and the specific proteasome inhibitor epoxomicin (10 μM), but not the specific calpain inhibitor calpeptin (100 μM). Similarly, treatment with MG‐132 and epoxomicin promoted the accumulation of both adenoviral expressed and endogenous PGC‐1α. To determine if the Ca 2+ activation of calpains results in cleavage of PGC‐1α, RPTC over‐expressing PGC‐1α were lysed and the addition of Ca 2+ resulted in the degradation of PGC‐1α in 5 min. This degradation was blocked by the calpeptin (100μM) but not epoxomicin (10μM). In summary, this investigation reveals two distinct mechanisms of PGC‐1α regulation; 1) basal turnover of PGC‐1α is controlled by the proteasome degradation pathway and 2) increased Ca 2+ levels result in proteolysis of PGC‐1α through calpain.