TY - JOUR
T1 - gCap39 is phosphorylated
T2 - Stimulation by okadaic acid and preferential association with nuclei
AU - Onoda, Koji
AU - Yin, Helen L.
N1 - Copyright:
Copyright 2004 Elsevier B.V., All rights reserved.
PY - 1993/2/25
Y1 - 1993/2/25
N2 - gCap39 is an actin filament end-capping protein which is a member of the gelsolin family. Unlike gelsolin, gCap39 does not sever actin filaments and is a cytoplasmic as well as nuclear protein. We report here that gCap39 is phosphorylated, while gelsolin is not. gCap39 is phosphorylated on serines and threonines at multiple sites, and phospho-gCap39 is resolved by isofocusing into multiple isoforms which are more acidic than unphosphorylated gCap39. In vitro dephosphorylation eliminates the acidic isoforms. Okadaic acid, a protein phosphatase inhibitor, stimulates gCap39 phosphorylation in vivo. It preferentially increases labeling of several peptides and enhances labeling of phosphothreonines relative to phosphoserines. The phosphorylation state of gCap39 in cells is therefore regulated by a balance between kinases and okadaic acid-sensitive phosphatases, and phosphorylation sites containing threonines appear to be particularly sensitive to the phosphatases. Subcellular fractionation shows that the nuclear fraction contains 17 ± 5% (n = 3) of total gCap39. Compared with the soluble cytoplasm, nuclear gCap39 has a 1.7 ± 0.2 (n = 3) fold increase in the amount of 32P label incorporation and a higher ratio of acidic/basic gCap39. We conclude that phospho-gCap39 is preferentially associated with nuclei and suggest that phosphorylation of gCap39 is functionally significant.
AB - gCap39 is an actin filament end-capping protein which is a member of the gelsolin family. Unlike gelsolin, gCap39 does not sever actin filaments and is a cytoplasmic as well as nuclear protein. We report here that gCap39 is phosphorylated, while gelsolin is not. gCap39 is phosphorylated on serines and threonines at multiple sites, and phospho-gCap39 is resolved by isofocusing into multiple isoforms which are more acidic than unphosphorylated gCap39. In vitro dephosphorylation eliminates the acidic isoforms. Okadaic acid, a protein phosphatase inhibitor, stimulates gCap39 phosphorylation in vivo. It preferentially increases labeling of several peptides and enhances labeling of phosphothreonines relative to phosphoserines. The phosphorylation state of gCap39 in cells is therefore regulated by a balance between kinases and okadaic acid-sensitive phosphatases, and phosphorylation sites containing threonines appear to be particularly sensitive to the phosphatases. Subcellular fractionation shows that the nuclear fraction contains 17 ± 5% (n = 3) of total gCap39. Compared with the soluble cytoplasm, nuclear gCap39 has a 1.7 ± 0.2 (n = 3) fold increase in the amount of 32P label incorporation and a higher ratio of acidic/basic gCap39. We conclude that phospho-gCap39 is preferentially associated with nuclei and suggest that phosphorylation of gCap39 is functionally significant.
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M3 - Article
C2 - 8382692
AN - SCOPUS:0027480928
SN - 0021-9258
VL - 268
SP - 4106
EP - 4112
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 6
ER -