GSK3B and Alzheimer disease: Moreover, a recent study that screens for the effect of 352 human kinases has shown that glycogen synthase kinase 3β (GSK-3β) and stress-activated protein kinase 4 (SAPK4) were the most active protein kinases phosphorylating tau at AD-specific epitopes that were recognized by phospho-tau specific antibodies including AT8 (pSer202 and pThr205), AT180 (pThr231), AT100 (pThr212 and pSer214), and PHF-1 (pSer396 and pSer404)10,14 (the phospho-residues are numbered according to the longest 2N4R tau isoform).