Manganese modulation of MAPK pathways: effects on upstream mitogen activated protein kinase kinases and mitogen activated kinase phosphatase-1 in microglial cells.
Multiple studies demonstrate that manganese (Mn) exposure potentiates inflammatory mediator output from activated glia; this increased output is associated with enhanced mitogen activated protein kinase (MAPK: p38, ERK and JNK) activity. We hypothesized that Mn activates MAPK by activating the kinases upstream of MAPK, i.e. MKK-3/6, MKK-1/2 and MKK-4 (responsible for activation of p38, ERK, and JNK, respectively), and/or by inhibiting a major phosphatase responsible for MAPK inactivation, MKP-1. Exposure of N9 microglia to Mn (250 µm), LPS (100 ng ml⁻¹) or Mn + LPS increased MKK-3/6 and MKK-4 activity at 1 h; the effect of Mn + LPS on MKK-4 activation was greater than the rest. At 4 h, Mn, LPS, and Mn + LPS increased MKK-3/6 and MKK-1/2 phosphorylation, whereas MKK-4 was activated only by Mn and Mn + LPS. Besides activating MKK-4 via Ser257/Thr261 phosphorylation, Mn (4 h) prevented MKK-4's phosphorylation on Ser80, which negatively regulates MKK-4 activity. Exposure to Mn or Mn + LPS (1 h) decreased both mRNA and protein expression of MKP-1, the negative MAPK regulator. In addition, we observed that at 4 h, but not at 1 h, a time point coinciding with increased MAPK activity, Mn + LPS markedly increased TNF-α, IL-6 and Cox-2 mRNA, suggesting a delayed effect. The fact that all three major groups of MKKs, MKK-1/2, MKK-3/6 and MKK-4, are activated by Mn suggests that Mn-induced activation of MAPK occurs via traditional mechanisms, which perhaps involve the MAPKs furthest upstream, MKKKs (MAP3Ks). In addition, for all MKKs, Mn-induced activation was persistent at least for 4 h, indicating a long-term effect.
Crittenden
Patrick L
PL
Center for Environmental Health Sciences, Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, MS 39762, USA.
Filipov
Nikolay M
NM
D000818:Animals; D002460:Cell Line; D051546:Cyclooxygenase 2 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism; D008345:Manganese / Q000633:toxicity*; D051379:Mice; D017628:Microglia / Q000166:cytology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D015850:Interleukin-6; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D008345:Manganese; C077623:Ptgs2 protein, mouse; D051546:Cyclooxygenase 2; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases