Phorbol ester and dioctanoylglycerol stimulate membrane association of protein kinase C and have a negative inotropic effect mediated by changes in cytosolic Ca2+ in adult rat cardiac myocytes.

We hypothesized that thromboxane A2 (TxA2) receptor stimulation directly induces apoptosis in adult cardiac myocytes. To investigate this, we exposed cultured adult rat ventricular myocytes (ARVM) to a TxA2 mimetic [1S-[1α,2α(Z),3β(1E,3S*),4α]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) for 24 h. Stimulation with I-BOP induced apoptosis in a dose-dependent manner and was completely prevented by a TxA2 receptor antagonist, SQ-29548. We further investigated the role of protein kinase C (PKC) in this process. TxA2 stimulation resulted in membrane translocation of PKC-ζ but not PKC-α, -βII, -δ, and -ε at 3 min and 1 h. The activation of PKC-ζ by I-BOP was confirmed using an immune complex kinase assay. Treatment of ARVM with a cell-permeable PKC-ζ pseudosubstrate peptide (ζ-PS) significantly attenuated apoptosis by I-BOP. In addition, I-BOP treatment decreased baseline Akt activity and its decrease was reversed by treatment with ζ-PS. The inhibition of phosphatidylinositol 3-kinase upstream of Akt by wortmannin or LY-294002 abolished the antiapoptotic effect of ζ-PS. Therefore, our results suggest that the activation of PKC-ζ modulates TxA2 receptor-mediated apoptosis at least, in part, through Akt activity in adult cardiac myocytes.

Download Full-text

Protein kinase C translocation and PKC-dependent protein phosphorylation during myocardial ischemia

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.2.h642 ◽

1999 ◽

Vol 276 (2) ◽

pp. H642-H650 ◽

Cited By ~ 23

Author(s):

Carolyn J. Albert ◽

David A. Ford

Keyword(s):

Protein Kinase C ◽

Protein Kinase ◽

Myocardial Ischemia ◽

Protein Phosphorylation ◽

Phorbol Ester ◽

Adult Rat ◽

Kinase C ◽

Associated Proteins ◽

Dependent Protein ◽

Pkc Isozymes

The present study demonstrates that the α, ε, and ι isozymes of protein kinase C (PKC) are translocated to particulate fractions from the cytosol during brief intervals of global ischemia as well as reperfusion of ischemic rat myocardium. In contrast, phorbol ester treatment of perfused hearts resulted in the translocation of the α, δ, and ε isozymes of PKC to particulate fractions. Additionally, the α, δ, and ε isozymes of PKC are translocated to particulate fractions in phorbol ester-stimulated, isolated adult rat cardiac myocytes. Concomitant with the translocation of PKC isozymes to particulate fractions during myocardial ischemia, increased protein phosphorylation was observed, which was blocked by pretreatment of hearts with the selective PKC inhibitor bisindolylmaleimide I (50 nM). In particular, ischemia resulted in the phosphorylation of 26-, 20-, and 17-kDa particulate-associated proteins. Taken together, the present findings are the first to demonstrate that specific PKC isozymes are translocated to particulate fractions in the ischemic and the reperfused ischemic rat heart, resulting in the phosphorylation of specific particulate-associated proteins.

Download Full-text