Protein Phosphatase 2A Inhibitors, I1 PP2A and I2 PP2A, Associate with and Modify the Substrate Specificity of Protein Phosphatase 1

• Published in: The Journal of biological chemistry 2000-03, Vol.275 (13), p.9209
• Main Authors: Yoshihisa Katayose, Mei Li, Samer W. K. Al-Murrani, Shirish Shenolikar, Zahi Damuni
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.275.13.9209

Recombinant I 1 PP2A and I 2 PP2A did not affect the activity of the catalytic subunit of protein phosphatase 1 (PP1 C ) with 32 P-labeled myelin basic protein, histone H1, and phosphorylase when assayed in the absence of divalent cations. However, in the presence of Mn 2+ , I 1 PP2A and I 2 PP2A stimulated PP1 C activity by 15–20-fold with myelin basic protein and histone H1 but not phosphorylase. Half-maximal stimulation occurred at 2 and 4 n m I 1 PP2A and I 2 PP2A , respectively. Moreover, I 1 PP2A and I 2 PP2A reduced the Mn 2+ requirement by about 30-fold to 10 μ m . In contrast, PP1 C activity was unaffected by I 1 PP2A and I 2 PP2A in the presence of Co 3+ (0.1 m m ), Mg 2+ (2 m m ), Ca 2+ (0.5 m m ), and Zn 2+ (0.1 m m ). Following gel filtration chromatography on Sephacryl S-200 in the presence of Mn 2+ , PP1 C coeluted with I 1 PP2A and I 2 PP2A in the void volume. However, when I 1 PP2A and I 2 PP2A or Mn 2+ were omitted, PP1 C emerged with a V e / V 0 of ∼1.6. The results demonstrate that I 1 PP2A and I 2 PP2A associate with and modify the substrate specificity of PP1 C in the presence of physiological concentrations of Mn 2+ . A novel role is suggested for I 1 PP2A and I 2 PP2A in the reciprocal regulation of two major mammalian serine/threonine phosphatases, PP1 and PP2A .