Protein kinase A phosphorylates titin's cardiac-specific N2B domain and reduces passive tension in rat cardiac myocytes.
beta-Adrenergic stimulation of cardiac muscle activates protein kinase A (PKA), which is known to phosphorylate proteins on the thin and thick filaments of the sarcomere. Cardiac muscle sarcomeres contain a third filament system composed of titin, and here we demonstrate that titin is also phosphorylated by the beta-adrenergic pathway. Titin phosphorylation was observed after beta-receptor stimulation of intact cardiac myocytes and incubation of skinned cardiac myocytes with PKA. Mechanical experiments with isolated myocytes revealed that PKA significantly reduces passive tension. In vitro phosphorylation of recombinant titin fragments and immunoelectron microscopy suggest that PKA targets a subdomain of the elastic segment of titin, referred to as the N2B spring element. The N2B spring element is expressed only in cardiac titins, in which it plays an important role in determining the level of passive tension. Because titin-based passive tension is a determinant of diastolic function, these results suggest that titin phosphorylation may modulate cardiac function in vivo.
Yamasaki
R
R
Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, USA.
Wu
Y
Y
McNabb
M
M
Greaser
M
M
Labeit
S
S
Granzier
H
H
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001696:Biomechanical Phenomena; D064211:Connectin; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D016253:Microscopy, Immunoelectron; D009124:Muscle Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011433:Propranolol / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012518:Sarcomeres / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D064211:Connectin; D009124:Muscle Proteins; D011433:Propranolol; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D007545:Isoproterenol