Neurofibrillary tangles, one of the hallmarks of
Alzheimer disease (AD), are composed of paired helical filaments of abnormally hyperphosphorylated tau. The accumulation of these proteinaceous aggregates in AD correlates with synaptic loss and severity of
dementia. Identifying the
kinases involved in the pathological phosphorylation of tau may identify novel targets for AD. We used an unbiased approach to study the effect of 352 human
kinases on their ability to phosphorylate tau at
epitopes associated with AD. The
kinases were overexpressed together with the longest form of human tau in human
neuroblastoma cells. Levels of total and phosphorylated tau (
epitopes Ser(P)-202, Thr(P)-231, Ser(P)-235, and Ser(P)-396/404) were measured in cell lysates using AlphaScreen assays. GSK3α, GSK3β, and MAPK13 were found to be the most active tau
kinases, phosphorylating tau at all four
epitopes. We further dissected the effects of GSK3α and GSK3β using pharmacological and genetic tools in hTau primary cortical neurons. Pathway analysis of the
kinases identified in the screen suggested mechanisms for regulation of total tau levels and tau phosphorylation; for example,
kinases that affect total tau levels do so by inhibition or activation of translation. A network fishing approach with the
kinase hits identified other key molecules putatively involved in tau phosphorylation pathways, including the
G-protein signaling through the Ras family of
GTPases (MAPK family) pathway. The findings identify novel tau
kinases and novel pathways that may be relevant for AD and other
tauopathies.