High-affinity peripheral benzodiazepine receptor ligand, PK11195, regulates protein phosphorylation in rat brain mitochondria under control of Ca(2+).
The effects of PK11195, a high-affinity peripheral benzodiazepine receptor (PBR) ligand, on protein phosphorylation in isolated purified rat brain mitochondria were investigated. The isoquinoline carboxamide ligand of PBR, PK11195, but not the benzodiazepine ligand Ro5-4864, in the nanomolar concentration range strongly increased the phosphorylation of 3.5 and 17 kDa polypeptides. The effect of PK11195 was seen in the presence of elevated Ca(2+) levels (3 x 10(-7) to 10(-6) m), but not at very low Ca(2+) levels (10(-8) to 3 x 10(-8) m). This indicates that PBR involves Ca(2+) as a second messenger in the regulation of protein phosphorylation. Staurosporine, an inhibitor of protein kinase activity was able to suppress the PK11195-promoted protein phosphorylation. When the permeability transition pore (PTP) was opened by threshold Ca(2+) load, phosphorylation of the 3.5-kDa polypeptide was diminished, but strong phosphorylation of the 43-kDa protein was revealed. The 43-kDa protein appears to be a PTP-specific phosphoprotein. If PTP was opened, PK11195 did not increase the phosphorylation of the 3.5 and 17-kDa proteins but suppressed the phosphorylation of the PTP-specific 43-kDa phosphoprotein. The ability of PK11195 to increase the protein phosphorylation, which was lost under Ca(2+)-induced PTP opening, was restored again in the presence of calmidazolium, an antagonist of calmodulin and inhibitor of protein phosphatase PP2B. These results show a tight interaction of PBR with the PTP complex in rat brain mitochondria. In conclusion, a novel function of PBR in brain mitochondria has been revealed, and the PBR-mediated protein phosphorylation has to be considered an important element of the PBR-associated signal transducing cascades in mitochondria and cells.
Azarashvili
T
T
Institut für Neurobiochemie, Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät, Magdeburg, Germany.
Krestinina
O
O
Yurkov
I
I
Evtodienko
Y
Y
Reiser
G
G
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology; D007546:Isoquinolines / Q000378:metabolism / Q000494:pharmacology*; D008024:Ligands; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007093:Imidazoles; D007473:Ion Channels; D007546:Isoquinolines; D008024:Ligands; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009419:Nerve Tissue Proteins; D011963:Receptors, GABA-A; C031938:calmidazolium; D000255:Adenosine Triphosphate; D019311:Staurosporine; D002118:Calcium; C037850:PK 11195