Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent phosphoregulation of mitochondrial complex I is inhibited by nucleoside reverse transcriptase inhibitors.
Nucleoside analog reverse transcriptase inhibitors (NRTIs) are known to directly inhibit mitochondrial complex I activity as well as various mitochondrial kinases. Recent observations that complex I activity and superoxide production are modulated through cAMP-dependent phosphorylation suggests a mechanism through which NRTIs may affect mitochondrial respiration via kinase-dependent protein phosphorylation. In the current study, we examine the potential for NRTIs to inhibit the cAMP-dependent phosphorylation of complex I and the associated NADH:CoQ oxidoreductase activities and rates of superoxide production using HepG2 cells. Phosphoprotein staining of immunocaptured complex I revealed that 3'-azido-3'-deoxythymidine (AZT; 10 and 50 microM), AZT monophosphate (150 microM), and 2',3'-dideoxycytidine (ddC; 1 microM) prevented the phosphorylation of the NDUFB11 subunit of complex I. This was associated with a decrease in complex I activity with AZT and AZT monophosphate only. In the presence of succinate, superoxide production was increased with 2',3'-dideoxyinosine (ddI; 10 microM) and ddC (1 microM). In the presence of succinate+cAMP, AZT showed an inverse dose-dependent effect on superoxide production. None of the NRTIs examined inhibit PKA activity suggesting that the observed effects are due to a direct interaction with complex I. These data demonstrate a direct effect of NRTIs on cAMP-dependent regulation of mitochondrial bioenergetics independent of DNA polymerase-gamma activity; in the case of AZT, these observations may provide a mechanism for the observed long-term toxicity with this drug.
Lund
Kaleb C
KC
Department of Biochemistry & Molecular Biology, Toxicology Graduate Program, University of Minnesota Medical School Duluth, 1035 University Drive, Duluth, MN 55812, USA. klund2@d.umn.edu
Wallace
Kendall B
KB
D000255:Adenosine Triphosphate / Q000494:pharmacology; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D042967:Electron Transport Complex I / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D018894:Reverse Transcriptase Inhibitors / Q000633:toxicity*; D013481:Superoxides / Q000378:metabolism; D016047:Zalcitabine / Q000633:toxicity; D015215:Zidovudine / Q000633:toxicity
D018894:Reverse Transcriptase Inhibitors; D013481:Superoxides; D015215:Zidovudine; D016047:Zalcitabine; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D042967:Electron Transport Complex I