Photoinduced inactivation of protein kinase C by dequalinium identifies the RACK-1-binding domain as a recognition site.
1,1'-Decamethylenebis-4-aminoquinaldinium diiodide (DECA; dequalinium) is an anti-tumor agent and protein kinase C (PKC) inhibitor whose mechanism of action with PKC is unknown. This study reports that with human PKC alpha, DECA exhibited competitive inhibition (Ki = 11.5 +/- 5 microM) with respect to RACK-1 (receptor for activated C kinase-1), an adaptor protein that has been proposed to bind activated PKC following translocation (Ron, D., Luo, J., and Mochly-Rosen, D. (1995) J. Biol. Chem. 270, 24180-24187). When exposed to UV light, DECA covalently modified and irreversibly inhibited PKC (alpha or beta), with IC50 = 7-18 microM. UV/DECA treatment of synthetic peptides modeled after the RACK-1-binding site in the C2 region of PKC beta induced modification of Ser218-Leu-Asn-Pro-Glu-Trp-Asn-Glu-Thr226, but not of a control peptide. This modification occurred at a tryptophan residue (Trp223) that is conserved in all conventional PKC isoforms. In overlay assays with native RACK-1 that had been immobilized on nitrocellulose, UV-treated control PKC alpha bound well to RACK-1, whereas UV/DECA-inactivated PKC alpha had reduced binding activity. The significance of these findings is shown with adenocarcinoma cells, which, when pretreated with 10 microM DECA and UV light, exhibited diminished 12-O-tetradecanoylphorbol-13-acetate-induced PKC alpha translocation. Overall, this work identifies DECA as a tool that prevents PKC translocation by inhibiting formation of the PKC.RACK-1 complex.
Rotenberg
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Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing 11367, USA. rotenber@qcvaxa.acc.qc.edu
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D000595:Amino Acid Sequence; D000891:Anti-Infective Agents, Local / Q000378:metabolism / Q000494:pharmacology*; D001665:Binding Sites; D003868:Dequalinium / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008969:Molecular Sequence Data; D010777:Photochemistry; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051571:Protein Kinase C-alpha; D006180:Proton-Translocating ATPases / Q000378:metabolism; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays
D000891:Anti-Infective Agents, Local; D007527:Isoenzymes; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D003868:Dequalinium; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D006180:Proton-Translocating ATPases; D013755:Tetradecanoylphorbol Acetate