Related Experiment Video
Updated: Aug 9, 2026

Recombinant α- β- and γ-Synucleins Stimulate Protein Phosphatase 2A Catalytic Subunit Activity in Cell Free Assays
Published on: August 13, 2017
Protein phosphatase-1 alpha, gamma 1, and delta: changes in phosphorylation and activity in mitotic HeLa cells and in
1Department of Biomedicine, University of Pisa, Italy.
Abstract:
Protein phosphatase-1 is phosphorylated "in vitro" by cdc2-cyclin B (E. Villa-Moruzzi, FEBS Lett. 304, 211-215, 1992). In the present study the phosphatase-1 isoforms alpha, gamma 1, and delta were analyzed in mitotic (nocodazole-blocked) HeLa cells. Phosphorylation on threonine increased in gamma 1 and delta at mitosis. alpha was phosphorylated only in mitotic cells and mainly on serine. Exposure of permeabilized mitotic cells to a peptide that inhibits cdc2 decreased the phosphorylation of the isoforms. Cell fractionation indicated that phosphatase-1 was over 90% inactivated and phosphorylated in the soluble, but not in the chromosomal fraction of mitotic cells. Immunoprecipitation from the mitotic soluble fraction indicated that only gamma 1 and delta, but not alpha, were inactivated. Altogether the data pointed to a correlation between phosphatase-1 inactivation and phosphorylation in mitotic cells. cdc2-cyclin B might be the kinase (or one of the kinases) that phosphorylates phosphatase-1. In cells released from the mitotic block, the phosphatase-1 activity in the soluble, but not in the nuclear fraction, increased progressively, reaching control values by 16 h. Immunoprecipitation indicated that the increase in activity was due to alpha and delta only. On the other hand, the activity of gamma 1 remained low, and this was also the only isoform that remained phosphorylated, though less than in mitotic cells. Also in the case of the cells released from mitosis, a correlation may exist between phosphorylation and inactivation of phosphatase-1. However, the regulation of phosphatase-1 is complex and may involve also regulatory subunits that are still unknown. Altogether, the results indicated the differential regulation of the phosphatase-1 isoforms both at mitosis and in G1 cells.
Related Concept Videos
Phosphorylation
During phosphorylation, protein kinases transfer the terminal phosphate group of ATP to specific amino acid side chains of substrate proteins. Serine, threonine, and tyrosine are the most commonly...
Protein Kinases and Phosphatases
Protein kinases
Many proteins in the cell are regulated by phosphorylation, the addition of a phosphate group. A family of enzymes called kinases...
Positive Regulator Molecules
Inhibition of Cdk Activity
Amplifying Signals via Enzymatic Cascade
Calmodulin-dependent Signaling
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...

