Activated Protein Kinase C Isoforms Target to Cardiomyocyte Caveolae

Abstract

Abstract-Protein kinase C (PKC) isoforms constitute an important component of the signal transduction pathway used by cardiomyocytes to respond to a variety of extracellular stimuli. Translocation to distinct intracellular sites represents an essential step in the activation of PKC isoforms, presumably as a prerequisite for stable access to substrate. Caveolae are specialized subdomains of the plasma membrane that are reported to concentrate key signaling proteins and may represent a locus for PKC action, given that PKC activators have been reported to dramatically alter caveolae morphology. Accordingly, this study examines whether PKC isoforms initiate signaling in cardiomyocyte caveolae. Phorbol ester-sensitive PKC isoforms were detected at very low levels in caveolae fractions prepared from unstimulated cardiomyocytes; phorbol 12-myristate 13-acetate (PMA) (but not 4␣-PMA, which does not activate PKC) recruited calcium-sensitive PKC␣ and novel PKC␦ and PKC⑀ to this compartment. The subcellular localization of the phorbol ester-insensitive PKC isoform was not influenced by PMA. Endothelin also induced the selective translocation of PKC␣ and PKC⑀ (but not PKC␦ or PKC) to caveolae. Multiple components of the extracellular signal-regulated protein kinase (ERK) cascade, including A-Raf, c-Raf-1, mitogen-activated protein kinase kinase, and ERK, were detected in caveolae under resting conditions. Although levels of these proteins were not altered by PMA, translocation of phorbol ester-sensitive PKC isoforms to caveolae was associated with the activation of a local ERK cascade as well as the phosphorylation of a Ϸ36-kDa substrate protein in this fraction. Finally, a minor fraction of a protein that has been designated as a receptor for activated protein kinase C resides in caveolae and (along with caveolin-3) could represent a mechanism to target PKC isoforms to cardiomyocyte caveolae. These studies identify cardiomyocyte caveolae as a meeting place for activated PKC isoforms and their downstream target substrates. (Circ Res. 1999;84:980-988.)

Receptor Number and Caveolar Co-localization Determine Receptor Coupling Efficiency to Adenylyl Cyclase

“…Images are representative of at least three experiments. from previous work by our laboratory and others suggest that such caveolin-rich domains represent morphologic caveolae (13,27). Thus spatial, as well as temporal, regulation of signaling can be a critical determinant for individualizing cellular response to extracellular hormones and neurotransmitters (18).…”

“…AC5 and AC6 are similar in their regulation by Ca 2ϩ and PKA, but AC5 is stimulated while AC6 is inhibited by PKC. This difference in regulation may be quite relevant given that PKC translocates to caveolae upon activation (27). However, most previous work has not involved assessment of co-localization of AC and receptors that regulate its activity.…”

Kv1.5 Association Modifies Kv1.3 Traffic and Membrane Localization

“…In addition, kinases are tightly modulated by distinct raft compositions (43,44). PKA and PKC colocalize with caveolin-1 and cholesterol depletion regulates PKA and Kv1.3 (17,44,45). Interestingly, tyrosine phosphorylation of Kv1.3 suppresses currents and targeting of the channel to ceramide enriched platforms (5,18).…”

Connexin 43 Hemichannels and Pharmacotherapy of Myocardial Ischemia Injury

“…Remarkable progress has been made in understanding how extracellular stimuli act as upstream triggers to induce activation of particular PKC isoforms in cardiomyocytes (endothelin, phenylephrine, etc.) (Clerk et al, 1994;Clerk & Sugden, 2001;Rybin et al, 1999). Moreover, there is much evidence supporting the concept that PKC functions in an isoform-dependent manner and that specific cardiac manifestations depend on the activation of individual isoforms, not the activity of the entire PKC family (Chen et al, 2001a;Clerk & Sugden, 2001;Hahn et al, 2002;Mochly-Rosen & Gordon, 1998).…”