Polo like kinase 2 (PLK2) promotes microglial activation via regulation of the HSP90a/IKKß pathway [II]
Microglial overactivation is actively involved in the pathogenesis of neurodegenerative diseases. Polo-like kinase 2 (PLK2) is a serine/threonine protein kinase associated with the regulation of synaptic plasticity and centriole duplication. Here, we identified PLK2 as an important early response gene in lipopolysaccharide (LPS)-stimulated microglial cells. Knockdown or inhibition of PLK2 remarkably attenuated LPS-induced expression of pro-inflammatory factors such as IL-1ß, IL-6, COX2, TNF-a,and iNOS in microglial cells via suppressing the IKKß-NF-?B signaling pathway.Notably, overexpression of PLK2 induced expression of pro-inflammatory factors and NF-?B transcriptional activation in the absence of inflammatory stimuli. Mechanistically,co-immunoprecipitation experiments revealed association between PLK2 and IKKß, whereas GST pull-down assay showed no direct interaction between PLK2 and IKKß. Proteomic analysis and in vitro kinase assay identified heat shock protein 90 alpha (HSP90a), a regulator of IKKß activity, as a novel PLK2 substrate. Knockdown or pharmacological inhibition of HSP90a abolished PLK2-mediated activation of NF-?B transcriptional activity and microglial inflammatory activation. Furthermore,phosphoproteomic analysis pinpointed Ser252 and Ser263 on HSP90a as novel phosphorylation targets of PLK2. Subsequent functional studies demonstrated that re-expression of phosphor-dead mutation of these two phosphorylation sites on HSP90a failed to rescue the PLK2-induced activation of the NF-?B signaling. Lastly, conditional knockout of PLK2 in microglial cells dramatically ameliorated neuroinflammation and subsequent dopaminergic neuron loss in an intracranial LPS-induced mouse PD model. The present study revealed, for the first time, that PLK2 promoted microglial activation through the phosphorylation of HSP90a and subsequent activation of the IKKß-NF-?B signaling pathway. Consequently, PLK2 emerges as a potential therapeutic target for the amelioration of neuroinflammation-related diseases. Overall design: To determine the gene expression profile regulated by PLK2, we overexpressed PLK2, PLK2(D223N), or a control vector in HEK293T cells. RNA-Seq was then performed to compare the changes in gene expression following PLK2 overexpression.There were three groups(Vector/PLK2/PLK2D223N), each with three biological replicates.