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[摘要]：The mitochondrial cAMP-dependent protein kinase (PICA) is activatable in a cAMP-independent fashion. The regulatory (R) subunits of the PKA holoenzyme (R2C2), but not the catalytic (C) subunits, suffer proteolysis upon exposure of bovine heart mitochondria to digitonin, Ca2+, and a myriad of electron transport inhibitors. Selective loss of both the RI- and Rh-type subunits was demonstrated via Western blot analysis, and activation of the C subunit was revealed by phosphorylation of a validated PKA peptide substrate. Selective proteolysis transpires in a calpain-dependent fashion as demonstrated by exposure of the R and C subunits of PKA to calpain and by attenuation of R and C subunit proteolysis in the presence of calpain inhibitor I. By contrast, exposure of mitochondria to cAMP fails to promote R subunit degradation, although it does result in enhanced C subunit catalytic activity. Treatment of mitochondria with electron transport chain inhibitors rotenone, antimycin A, sodium azide, and oligomycin, as well as an uncoupler of oxidative phosphorylation, also elicits enhanced C subunit activity. These results are consistent with the notion that signals, originating from cAMP-independent sources, elicit enhanced mitochondrial PKA activity. |
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