Rottlerin is a mitochondrial uncoupler that decreases cellular ATP levels and indirectly blocks protein kinase Cδ tyrosine phosphorylation

Protein kinase C delta (PKC delta) is activated by stimuli that increase its tyrosine phosphorylation, including neurotransmitters that initiate fluid secretion in salivary gland (parotid) epithelial cells. Rottlerin, a compound reported to be a PKC delta -selective inhibitor, rapidly increased the rate of oxygen consumption (QO(2)) of parotid acinar cells and PC12 cells. In parotid cells, this was distinct from the effects of the muscarinic receptor ligand carbachol, which promoted a sodium pump-dependent increase in respiration. Rottlerin increased the QO(2) of isolated rat liver mitochondria to a level similar to that produced when oxidative phosphorylation was initiated by ADP or when mitochondria were uncoupled by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). The effects of rottlerin on mitochondrial QO(2) were neither mimicked nor blocked by the PKC inhibitor GF109203X. Rottlerin was not effective in blocking PKC delta activity in vitro. Exposure of freshly isolated parotid acinar cells to rottlerin and FCCP reduced cellular ATP levels and reduced stimuli-dependent increases in tyrosine phosphorylation of PKCS. Neither rottlerin nor FCCP reduced stimuli-dependent PKC delta tyrosine phosphorylation in RPG1 cells (a salivary ductal line) or PC12 cells, consistent with their dependence on glycolysis rather than oxidative phosphorylation for energy-dependent processes. These results demonstrate that rottlerin directly uncouples mitochondrial respiration from oxidative phosphorylation. Previous studies using rottlerin should be evaluated cautiously.