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(Circulation Research. 2004;94:135.)
© 2004 American Heart Association, Inc.

Editorials

Lessons From Old and New Kinases

J.E. Van Eyk

From the Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Md.

Correspondence to Jennifer Van Eyk, Johns Hopkins University, Bayview Proteomics Center, Departments of Medicine (Cardiology), Biological Chemistry and Biomedical Engineering, 602 Mason F. Lord Building, Center Tower, Bayview Campus, Johns Hopkins University, Baltimore, MD 21224. E-mail jvaneyk1@jhmi.edu

Key Words: protein phosphorylation • protein kinase A • myocytes

An extract of the first 250 words of the full text is provided, because this article has no abstract.

Elucidating the central role of protein phosphorylation in the regulation of muscle contraction on both beat-to-beat and long-term bases began with a series of classical studies starting in the mid-1970s.^1,2 Despite years of extensive studies, two articles in this issue of Circulation Research^3,4 demonstrate that there is still a great deal to be learned about the complexity of the myocyte and its regulation by kinases.

Protein kinase A (PKA) has been studied using purified proteins, isolated subproteomes, isolated myocytes, intact heart preparations, and in vivo animal studies, and yet we still do not have the whole picture. The work presented by Chu et al³ provides a tantalizing glimpse into widespread protein changes occurring in isolated myocytes with isoproterenol treatment. Although phosphorylation of the regulatory proteins phospholamban and cardiac troponin I (cTnI) under ß-adrenergic stimulation has been well-characterized, it is apparent that many more proteins are phosphorylated. How could we have missed these other proteins in previous work?

In contrast, Ke et al⁴ focus on the role of p21-activated kinase (PAK), a Ser/Thr kinase that is a relative newcomer to muscle research, and demonstrate that overexpression of the active form of PAK1 in isolated myocytes alters cardiac contractility through phosphorylation of the phosphatase, PP2A. Previous work using a variety of PAK isoforms has illustrated the ability of this kinase family to alter smooth^5–8 and cardiac muscle contraction,^9,10 but an incomplete molecular picture has been provided. Why were some protein alterations missed in previous work, and how can the results be melded . . . [Full Text of this Article]

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