Crittenden PL, Filipov NM. Manganese modulation of MAPK pathways: effects on upstream mitogen activated protein kinase kinases and mitogen activated kinase phosphatase-1 in microglial cells.
J Appl Toxicol 2011;
31:1-10. [PMID:
20589745 DOI:
10.1002/jat.1552]
[Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
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.
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