The Raf-MEK-ERK cascade represents a common pathway for alteration of intracellular calcium by Ras and protein kinase C in cardiac myocytes.
Ras and protein kinase C (PKC), which regulate the Raf-MEK-ERK cascade, may participate in the development of cardiac hypertrophy, a condition characterized by diminished and prolonged contractile calcium transients. To directly examine the influence of this pathway on intracellular calcium ([Ca2+]i), cardiac myocytes were cotransfected with effectors of this pathway and with green fluorescent protein, which allowed the living transfected myocytes to be identified and examined for [Ca2+]i via indo-1. Transfection with constitutively active Ras (Ha-RasV12) increased cell size, decreased expression of the myofibrils and the calcium-regulatory enzyme SERCA2, and reduced the magnitude and prolonged the decay phase of the contractile [Ca2+]i transients. Similar effects on [Ca2+]i were obtained with Ha-RasV12S35, a Ras mutant that selectively couples to Raf, and with constitutively active Raf. In contrast, Ha-RasV12C40, a Ras mutant that activates the phosphatidylinositol 3-kinase pathway, had a lesser effect. The PKC-activating phorbol ester, phorbol 12-myristate 13-acetate, also prolonged the contractile [Ca2+]i transients. Cotransfection with dnMEK inhibited the effects of Ha-RasV12, Raf, and phorbol 12-myristate 13-acetate on [Ca2+]i. The effects of Ha-RasV12 and Raf on [Ca2+]i were also counteracted by SERCA2 overexpression. Both Ras and PKC may thus regulate cardiac [Ca2+]i via the Raf-MEK-ERK cascade, and this pathway may represent a critical determinant of cardiac physiological function.
Ho
P D
PD
Department of Biology and the Molecular Biology Institute, San Diego State University, San Diego, California 92182, USA.
Zechner
D K
DK
He
H
H
Dillmann
W H
WH
Glembotski
C C
CC
McDonough
P M
PM
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002478:Cells, Cultured; D048669:MAP Kinase Kinase 6; D009206:Myocardium / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D018631:ras Proteins / Q000378:metabolism*
D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048669:MAP Kinase Kinase 6; D018631:ras Proteins; D000252:Calcium-Transporting ATPases; D002118:Calcium