Premium
The unimportance of being (protein kinase C) epsilon 1
Author(s) -
Walker Lori A.,
Gailly Philippe,
Jensen Peter E.,
Somlyo Avril V.,
Somlyo Andrew P.
Publication year - 1998
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.12.10.813
Subject(s) - myosin light chain kinase , protein kinase c , phosphatase , phosphorylation , myosin , myosin light chain phosphatase , contraction (grammar) , phorbol , autophosphorylation , microbiology and biotechnology , muscle contraction , biology , medicine , chemistry , protein kinase a , biochemistry , endocrinology
The purpose of our study was to determine the mechanism through which phorbol esters and smooth muscle myosin phosphatase inhibitors can induce contraction of smooth muscle in the absence of Ca 17+ . Protein kinase C‐ε (PKC‐ε) was previously implicated in this process based largely on its supposed absence in the ferret portal vein, and a correlation was drawn between the presence of this isoform and the ability of smooth muscle to contract independently of Ca 2+ and phosphorylation of the 20 kDa regulatory light chains of myosin (MLC 20 ). We demonstrate here, with two antibodies, one to the NH 2 terminus and the other to the COOH terminus of PKC‐ε, that ε is present in both ferret portal vein and rabbit portal vein smooth muscle, neither of which exhibits phorbol ester‐induced contraction in the absence of Ca 2+ . However, in the presence of clamped submaximal Ca 2+ , phorbol ester increased MLC 20 phosphorylation from 17.7 ± 1.7% to 46.4 ± 3.6% in ferret portal vein smooth muscle and evoked an increase in force. Prolonged (48 h) incubation of ferret portal vein with phorbol esters completely down‐regulated PKC‐ε, as shown by Western blots, and abolished the phorbol ester‐evoked contraction at submaximal Ca 2+ , but not Ca 2+ ‐independent, contractions induced by the phosphatase inhibitor microcystin. Contractions induced by microcystin in Ca 2+ ‐free solution were associated with increased phosphorylation of myosin light chain kinase (MLCK). Activation of MLCK by autophosphorylation in the absence of Ca 2+ occurs in vitro (1). We conclude that PKC‐ε is neither necessary nor sufficient for Ca 2+ ‐independent regulation of myosin II in smooth muscle, but contractions induced by agents that inhibit smooth muscle myosin phosphatase in the absence of Ca 2+ may be mediated by MLCK autophosphorylated or activated by another Ca 2+ ‐independent kinase.—Walker, L. A., Gailly, P., Jensen, P. E., Somlyo, A. V., Somlyo, A. P., The unimportance of being (protein kinase C) epsilon1. FASEB J . 12, 813–821 (1998)