Dephosphorylation of r Factor by Protein Phosphatase 2A in Synaptosomal Cytosol Fractions, and Inhibition by Aluminum

Abstract

When the synaptosomal cytosol fraction from rat brain was chromatographed on a DEAE-cellulose column and assayed for protein phosphatases for tau factor and histone H1, two peaks of activities, termed peak 1 (major) and peak 2 (minor), were separated. Each peak was in a single form 2 (minor), were separated. Each peak was in a single form on Sephacryl S-300 column chromatography. Both peaks 1 and 2 dephosphorylated tau factor phosphorylated by Ca2+/calmodulin-dependent protein kinase II and the catalytic subunit of cyclic AMP-dependent protein kinase. The Km values were in the range of 0.42-0.84 microM for tau factor. There were no differences in kinetic properties of dephosphorylation between the substrates phosphorylated by the two kinases. The phosphatase activities did not depend on Ca2+, Mn2+ and Mg2+. Immunoprecipitation and immunoblotting analysis using polyclonal antibodies to the catalytic subunit of brain protein phosphatase 2A revealed that both protein phosphatases are the holoenzymic forms of protein phosphatase 2A. Aluminum chloride inhibited the activities of both peaks 1 and 2 with IC50 values of 40-60 microM. These results suggest that dephosphorylation of tau factor in presynaptic nerve terminals is controlled mainly by protein phosphatase 2A and that the neurotoxic effect of aluminum seems to be related mostly to inhibition of dephosphorylation of tau factor.

Dephosphorylation of tau protein and Alzheimer paired helical filaments by calcmeurin and phosphatase‐2A

“…Other authors had studied more generally the dephosphorylation of MAPS such as MAP2 or tau which share a similar protein character and microtubule binding region [28]. For example, Goto et al [14] reported on the MAP-phosphatase activity of calcineurin, and Yamamoto et al [39] described similar results for PP-2A. Since the protein sequences and phosphorylation sites were not known at the time the data could not be interpreted in detail.…”

“…Several protein kinases were able to phosphorylate tau, and in studying the reverse process it was reported that calcineurin and PP-2A were particularly active in dephosphorylating MAPS such as MAP2 and tau ( [14,31,39]; for review, see [23]). A question not resolved by these earlier studies was the nature of the phosphorylation sites, and which sites were targeted by particular kinases and phosphatases.…”

“…We have now studied the effects of these phosphatases in more detail and conclude that calcineurin and PP-2A are both capable of removing both types of pathological phosphates from tau. These results will be compared with other studies on the dephosphorylation of MAPS in vitro [13,14,31,39] and in situ [19].…”

In situ dephosphorylation of tau by protein phosphatase 2A and 2B in fetal rat primary cultured neurons

“…There are several reports on protein phosphatases that dephosphorylate tau in vitro [13 19]. Although there are some contradictions, protein phosphatase 2A (PP2A) and 2B (PP2B) have been shown to dephosphorylate Alzheimer tau or tau phosphorylated by Ca2+-calmodulin kinase II, cAMP-dependent protein kinase, MAP kinase and cdc2 kinase in vitro [13][14][15][16][17][18][19]. *Corresponding author.…”

Alzheimer's Disease with Markedly Elevated Arsenic and Other Metals Masquerading as Organic Brain Syndrome and Affective Disorder

“…However, limited correlation was also found by others [12]. Mechanistically, Al may facilitate Tau aggregation [20] and appears to be associated with phospho-Tau in Al-induced tangles [21] and inhibit protein phosphatase 2, which dephosphorylates phospho -Tau [22].…”