MARK1 and Alzheimer disease: Tau phosphorylation at Ser262/356 by PAR-1/MARK preferentially stabilized less phosphorylated forms of microtubule-detached tau in the cytosol, and blocking this stabilization of tau suppressed Aβ42-induced augmentation of tau toxicity and the increase in the levels of tau phosphorylated at the AD-associated residue Thr231.