Functional proteomic analysis of a three-tier PKCepsilon-Akt-eNOS signaling module in cardiac protection.

Cardiac protective signaling networks have been shown to involve PKCepsilon. However, the molecular mechanisms by which PKCepsilon interacts with other members of these networks to form task-specific modules remain unknown. Among 93 different PKCepsilon-associated proteins that have been identified, Akt and endothelial nitric oxide (NO) synthase (eNOS) are of importance because of their independent abilities to promote cell survival and prevent cell death. The simultaneous association of PKCepsilon, Akt, and eNOS has not been examined, and, in particular, the formation of a module containing these three proteins and the role of such a module in the regulation of NO production and cardiac protection are unknown. The present study was undertaken to determine whether these molecules form a signaling module and, thereby, play a collective role in cardiac signaling. Using recombinant proteins in vitro and PKCepsilon transgenic mouse hearts, we demonstrate the following: 1) PKCepsilon, Akt, and eNOS interact and form signaling modules in vitro and in the mouse heart. Activation of either PKCepsilon or Akt enhances the formation of PKCepsilon-Akt-eNOS signaling modules. 2) PKCepsilon directly phosphorylates and enhances activation of Akt in vitro, and PKCepsilon activation increases phosphorylation and activation of Akt in PKCepsilon transgenic mouse hearts. 3) PKCepsilon directly phosphorylates eNOS in vitro, and this phosphorylation enhances eNOS activity. Activation of PKCepsilon in vivo increased phosphorylation of eNOS at Ser(1177), indicating eNOS activation. This study characterizes, for the first time, the physical, as well as functional, coupling of PKCepsilon, Akt, and eNOS in the heart and implicates these PKCepsilon-Akt-eNOS signaling modules as critical signaling elements during PKCepsilon-induced cardiac protection.

Cardioprotection involves activation of NF-kappa B via PKC-dependent tyrosine and serine phosphorylation of I kappa B-alpha.

Previous studies indicated that activation of PKC and Src tyrosine kinases by ischemic preconditioning (PC) may participate in the activation of NF-kappa B. However, the molecular mechanisms underlying activation of NF-kappa B during ischemic PC remain unknown. In the hearts of conscious rabbits, it was found that ischemic PC (6 cycles of 4-min coronary occlusion and 4-min reperfusion) significantly induced both tyrosine (+226.9 +/- 42%) and serine (+137.0 +/- 36%) phosphorylation of the NF-kappa B inhibitory protein I kappa B-alpha, concomitant with increased activation of the I kappa B-alpha kinases IKK alpha (+255.0 +/- 46%) and IKK beta (+173.1 +/- 35%). Furthermore, both tyrosine and serine phosphorylation of I kappa B-alpha were blocked by pretreatment with either the nonreceptor tyrosine kinase inhibitor lavendustin-A (LD-A) or the PKC inhibitor chelerythrine (Che) (both given at doses previously shown to block ischemic PC). Interestingly, Che completely abolished PC-induced activation of IKK alpha/beta, whereas LD-A had no effect. In addition, I kappa B-alpha protein level did not change during ischemic PC. Together, these data indicate that ischemic PC-induced activation of NF-kappa B occurs through both tyrosine and serine phosphorylation of I kappa B-alpha and is regulated by nonreceptor tyrosine kinases and PKC.

Protein kinase Cepsilon interacts with and inhibits the permeability transition pore in cardiac mitochondria.

Although functional coupling between protein kinase Cepsilon (PKCepsilon) and mitochondria has been implicated in the genesis of cardioprotection, the signal transduction mechanisms that enable this link and the identities of the mitochondrial proteins modulated by PKCepsilon remain unknown. Based on recent evidence that the mitochondrial permeability transition pore may be involved in ischemia/reperfusion injury, we hypothesized that protein-protein interactions between PKCepsilon and mitochondrial pore components may serve as a signaling mechanism to modulate pore function and thus engender cardioprotection. Coimmunoprecipitation and GST-based affinity pull-down from mouse cardiac mitochondria revealed interaction of PKCepsilon with components of the pore, namely voltage-dependent anion channel (VDAC), adenine nucleotide translocase (ANT), and hexokinase II (HKII). VDAC1, ANT1, and HKII were present in the PKCepsilon complex at approximately 2%, approximately 0.2%, and approximately 1% of their total expression, respectively. Moreover, in vitro studies demonstrated that PKCepsilon can directly bind and phosphorylate VDAC1. Incubation of isolated cardiac mitochondria with recombinant PKCepsilon resulted in a significant inhibition of Ca2+-induced mitochondrial swelling, an index of pore opening. Furthermore, cardiac-specific expression of active PKCepsilon in mice, which is cardioprotective, greatly increased interaction of PKCepsilon with the pore components and inhibited Ca2+-induced pore opening. In contrast, cardiac expression of kinase-inactive PKCepsilon did not affect pore opening. Finally, administration of the pore opener atractyloside significantly attenuated the infarct-sparing effect of PKCepsilon transgenesis. Collectively, these data demonstrate that PKCepsilon forms physical interactions with components of the cardiac mitochondrial pore. This in turn inhibits the pathological function of the pore and contributes to PKCepsilon-induced cardioprotection.

Protein kinase C epsilon signaling complexes include metabolism- and transcription/translation-related proteins: complimentary separation techniques with LC/MS/MS.

The serine/threonine kinase protein kinase C epsilon (PKC epsilon) has been shown to be a critical component in the heart's resistance to cell death following ischemic insult. Recent studies have indicated that PKC epsilon forms multi-protein signaling complexes to accomplish signal transduction in cardiac protection. Using two-dimensional electrophoresis (2DE), combined with matrix-assisted laser desorption ionization mass spectrometry (MS), the initial analysis of these complexes identified signaling molecules, structural proteins, and stress-activated proteins. The initial analysis, although fruitful, was limited by the number of proteins revealed on the 2D gels. It was also apparent that many known cardiac protective functions of PKC epsilon could not be fully accounted for by the proteins identified in the initial analysis. Here we reported the identification of an additional 57 proteins in PKC epsilon complexes using complimentary separation techniques, combined with high sensitivity MS. These techniques include 2DE or large format 1D SDS-PAGE followed by LC/MS/MS and solution trypsin digestion followed by LC/MS/MS, all of which yielded novel data regarding PKC epsilon protein complexes. Nanoscale LC/MS/MS for the analysis of gel-isolated proteins was performed with sub-femtomole sensitivity. In contrast to 2DE analyses, the identification of proteins from 1D gels was independent of their visualization via staining and allowed for the identification of proteins with high isoelectric points. We found that PKC epsilon complexes contain numerous structural and signaling molecules that had escaped detection by our previous analyses. Most importantly, we identified two new groups of proteins that were previously unrecognized as components of the PKC epsilon complex: metabolism-related proteins and transcription/translation-related proteins.

Mitochondrial PKCepsilon and MAPK form signaling modules in the murine heart: enhanced mitochondrial PKCepsilon-MAPK interactions and differential MAPK activation in PKCepsilon-induced cardioprotection.

Although activation of protein kinase C (PKC) epsilon and mitogen-activated protein kinases (MAPKs) are known to play crucial roles in the manifestation of cardioprotection, the spatial organization of PKCepsilon signaling modules in naïve and protected myocardium remains unknown. Based on evidence that mitochondria are key mediators of the cardioprotective signal, we hypothesized that PKCepsilon and MAPKs interact, and that they form functional signaling modules in mitochondria during cardioprotection. Both immunoblotting and immunofluorescent staining demonstrated that PKCepsilon, ERKs, JNKs, and p38 MAPK co-localized with cardiac mitochondria. Moreover, transgenic activation of PKCepsilon greatly increased mitochondrial PKCepsilon expression and activity, which was concomitant with increased mitochondrial interaction of PKCepsilon with ERKs, JNKs, and p38 as determined by co-immunoprecipitation. These complex formations appeared to be independent of PKCepsilon activity, as the interactions were also observed in mice expressing inactive PKCepsilon. However, although both active and inactive PKCepsilon bound to all three MAPKs, increased phosphorylation of mitochondrial ERKs was only observed in mice expressing active PKCepsilon but not in mice expressing inactive PKCepsilon. Examination of potential downstream targets of mitochondrial PKCepsilon-ERK signaling modules revealed that phosphorylation of the pro-apoptotic protein Bad was elevated in mitochondria. Together, these data show that PKCepsilon forms subcellular-targeted signaling modules with ERKs, leading to the activation of mitochondrial ERKs. Furthermore, formation of mitochondrial PKCepsilon-ERK modules appears to play a role in PKCepsilon-mediated cardioprotection, in part by the phosphorylation and inactivation of Bad.