Environmental toxicants inhibit neuronal Jak tyrosine kinase by mitochondrial disruption.
Cadmium, mercury and rotenone are environmental pollutants whose neurotoxic mechanisms are not fully understood. We have shown previously that exposure of nerve cells to these agents produces oxidative stress which reversibly blocks growth factor and cytokine-mediated Janus kinase (Jak)/signal transducer and activator of transcription (STAT) signaling. Here we determined a critical role for mitochondrial dysfunction in inhibiting Jak/STAT activity in human BE(2)-C neuroblastoma cells. Exposure of BE(2)-C cells to the heavy metals CdCl(2) and HgCl(2) and to the mitochondrial complex I inhibitor rotenone inhibited interleukin-6, interferon-gamma and ciliary neurotrophic factor-mediated Jak/STAT signaling, reduced Jak1 and Jak2 auto-phosphorylation and induced Jak tyrosine nitration. However, identical exposure of HepG2 hepatoma cells produced no inhibition of these cytokine responses. In contrast, mitochondria in both BE(2)-C and HepG2 cells showed reduced mitochondrial membrane potential and increased superoxide production after exposure to CdCl(2), HgCl(2) and rotenone. Further, in an in vitro Jak auto-phosphorylation assay Jak2 isolated from either BE(2)-C or HepG2 cells was equally inhibited by mitochondria made dysfunctional by treatment with CdCl(2), HgCl(2) and rotenone. Each of these pro-oxidant effects was reversed by the mitochondrial antioxidant alpha-lipoic acid. The actions of cadmium were also blocked by the mitochondrial complex III bypass agent, 2,6-dichloroindophenol. Therefore, in BE(2)-C cells CdCl(2), HgCl(2) and rotenone disrupt mitochondria to increase intracellular ROS, which directly inhibits neuronal Jak tyrosine kinase activity. Non-neuronal cells such as HepG2 cells that are resistant to oxidative stress-mediated inhibition of cytokine signaling possess some as yet unknown mechanism that protects Jak kinases from oxidative insults. Pro-oxidant-induced mitochondrial dysfunction resulting in selective neuronal Jak inhibition provides a potential mechanism for environmental agents to promote neurodegeneration.
Monroe
Richard K
RK
Program in Neuroscience, School of Medicine and Biomedical Sciences, University at Buffalo, SUNY, Buffalo, NY 14214-3000, USA.
Halvorsen
Stanley W
SW
D015086:2,6-Dichloroindophenol / Q000633:toxicity; D000975:Antioxidants / Q000633:toxicity; D019256:Cadmium Chloride / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D045744:Cell Line, Tumor; D020934:Ciliary Neurotrophic Factor / Q000378:metabolism; D004347:Drug Interactions; D004785:Environmental Pollutants / Q000633:toxicity*; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D053612:Janus Kinases / Q000378:metabolism*; D008113:Liver Neoplasms / Q000473:pathology; D017669:Mercury Compounds / Q000633:toxicity*; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology; D009447:Neuroblastoma / Q000473:pathology / Q000648:ultrastructure; D050791:STAT Transcription Factors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013054:Spectrophotometry, Atomic / Q000379:methods; D013481:Superoxides / Q000378:metabolism; D008063:Thioctic Acid / Q000633:toxicity; D014162:Transfection / Q000379:methods
D000975:Antioxidants; D020934:Ciliary Neurotrophic Factor; D004785:Environmental Pollutants; D017669:Mercury Compounds; D050791:STAT Transcription Factors; D013481:Superoxides; D008063:Thioctic Acid; D015086:2,6-Dichloroindophenol; D053612:Janus Kinases; C015728:calomel; D019256:Cadmium Chloride