title: Cadmium activates the mitogen-activated protein kinase (MAPK) pathway via induction of reactive oxygen species and inhibition of protein phosphatases 2A and 5.
abstract: Cadmium (Cd), a highly toxic environmental pollutant, induces neurodegenerative diseases. Recently we have demonstrated that Cd may induce neuronal apoptosis in part through activation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase 1/2 (Erk1/2) pathways. However, the underlying mechanism remains enigmatic. Here we show that Cd induced generation of reactive oxygen species (ROS), leading to apoptosis of PC12 and SH-SY5Y cells. Pretreatment with N-acetyl-L-cysteine (NAC) scavenged Cd-induced ROS, and prevented cell death, suggesting that Cd-induced apoptosis is attributed to its induction of ROS. Furthermore, we found that Cd-induced ROS inhibited serine/threonine protein phosphatases 2A (PP2A) and 5 (PP5), leading to activation of Erk1/2 and JNK, which was abrogated by NAC. Overexpression of PP2A or PP5 partially prevented Cd-induced activation of Erk1/2 and JNK, as well as cell death. Cd-induced ROS was also linked to the activation of caspase-3. Pretreatment with inhibitors of JNK (SP600125) and Erk1/2 (U0126) partially blocked Cd-induced cleavage of caspase-3 and prevented cell death. However, zVAD-fmk, a pan caspase inhibitor, only partially prevented Cd-induced apoptosis. The results indicate that Cd induction of ROS inhibits PP2A and PP5, leading to activation of JNK and Erk1/2 pathways, and consequently resulting in caspase-dependent and -independent apoptosis of neuronal cells. The findings strongly suggest that the inhibitors of JNK, Erk1/2, or antioxidants may be exploited for prevention of Cd-induced neurodegenerative diseases.
authors.affiliation: Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130-3932, USA.
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.forename: Lei
authors.initials: L
authors.lastname: Liu
authors.forename: Shile
authors.initials: S
authors.lastname: Huang
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002104:Cadmium / Q000633:toxicity*; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects*; D009687:Nuclear Proteins / Q000187:drug effects*; D010749:Phosphoprotein Phosphatases / Q000187:drug effects*; D054648:Protein Phosphatase 2 / Q000187:drug effects*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D009687:Nuclear Proteins; D017382:Reactive Oxygen Species; D002104:Cadmium; D020928:Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C089641:protein phosphatase 5; D000111:Acetylcysteine