Smooth muscle myosin phosphatase-associated kinase induces Ca2+ sensitization via myosin phosphatase inhibition.
Smooth muscle calcium sensitization reflects an inhibition of myosin light chain phosphatase (SMPP-1m) activity; however, the underlying mechanisms are not well understood. SMPP-1m activity can be modulated through phosphorylation of the myosin targeting subunit (MYPT1) by the endogenous myosin phosphatase-associated kinase, MYPT1 kinase (MacDonald, J. A., Borman, M. A., Muranyi, A., Somlyo, A. V., Hartshorne, D. J., and Haystead, T. A. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 2419-2424). Recombinant chicken gizzard MYPT1 (M130) was phosphorylated in vitro by a recombinant MYPT1 kinase, and the sites of phosphorylation were identified as Thr(654), Ser(808), and Thr(675). Introduction of recombinant MYPT1 kinase elicited a calcium-independent contraction in beta-escin-permeabilized rabbit ileal smooth muscle. Using an antibody that specifically recognizes MYPT1 phosphorylated at Thr(654) (M130 numbering), we determined that this calcium-independent contraction was correlated with an increase in MYPT1 phosphorylation. These results indicate that SMPP-1m phosphorylation by MYPT1 kinase is a mechanism of smooth muscle calcium sensitization.
Borman
Meredith A
MA
Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, USA.
MacDonald
Justin A
JA
Murányi
Andrea
A
Hartshorne
David J
DJ
Haystead
Timothy A J
TA
D000595:Amino Acid Sequence; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D064550:Death-Associated Protein Kinases; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D021122:Protein Subunits; D011817:Rabbits; D013379:Substrate Specificity
D051017:Apoptosis Regulatory Proteins; D018994:Myosin Light Chains; D021122:Protein Subunits; D064550:Death-Associated Protein Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; D002118:Calcium