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Dephosphorylation of Microtubule Proteins by Brain Protein Phosphatases 1 and 2A, and Its Effect on Microtubule Assembly
Author(s) -
Yamamoto Hideyuki,
Saitoh Yoshiki,
Fukunaga Kohji,
Nishimura Hiroshi,
Miyamoto Eishichi
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb03051.x
Subject(s) - dephosphorylation , phosphatase , phosphorylation , protein kinase a , calmodulin , tubulin , kinase , biochemistry , protein phosphorylation , biology , microbiology and biotechnology , protein subunit , c raf , cyclin dependent kinase 2 , chemistry , microtubule , enzyme , gene
Protein phosphatase C was purified 140‐fold from bovine brain with 8% yield using histone H1 phosphorylated by the catalytic subunit of cyclic AMP‐dependent protein kinase (cyclic AMP‐kinase). Brain protein phosphatase C was considered to consist of 10 and 90%, respectively, of the catalytic subunits of protein phosphatases 1 and 2A on the basis of the effects of ATP and inhibitor‐2. Protein phosphatase C dephosphorylated microtubule‐associated protein 2 (MAP2), τ factor, and tubulin phosphorylated by a multifunctional Ca 2+ /calmodulin‐dependent protein kinase (calmodulin‐kinase) and the catalytic subunit of cyclic AMP‐kinase. The properties of dephosphorylation of MAP2, τ factor, and tubulin were compared. The K m values were in the ranges of 1.6–2.7 μ M for MAP2 and τ factor. The K m value for tubulin decreased from 25 to 10–12.5 μ M in the presence of 1.0 μ M Mn 2+ . No difference in kinetic properties of dephosphorylation was observed between the substrates phosphorylated by the two kinases. Protein phosphatase C did not dephosphorylate the native tubulin, but universally dephosphorylated tubulin phosphorylated by the two kinases. The holoenzyme of protein phosphatase 2A from porcine brain could also dephosphorylate MAP2, τ factor, and tubulin phosphorylated by the two kinases. The phosphorylation of MAP2 and τ factor by calmodulin‐kinase separately induced the inhibition of microtubule assembly, and the dephosphorylation by protein phosphatase C removed its inhibitory effect. These data suggest that brain protein phosphatases 1 and 2A are involved in the switch‐off mechanism of both Ca 2+ /calmodulin‐dependent and cyclic AMP‐dependent regulation of microtubule formation.