Structural basis of protein kinase C isoform function - PubMed (original) (raw)

Review

Structural basis of protein kinase C isoform function

Susan F Steinberg. Physiol Rev. 2008 Oct.

Abstract

Protein kinase C (PKC) isoforms comprise a family of lipid-activated enzymes that have been implicated in a wide range of cellular functions. PKCs are modular enzymes comprised of a regulatory domain (that contains the membrane-targeting motifs that respond to lipid cofactors, and in the case of some PKCs calcium) and a relatively conserved catalytic domain that binds ATP and substrates. These enzymes are coexpressed and respond to similar stimulatory agonists in many cell types. However, there is growing evidence that individual PKC isoforms subserve unique (and in some cases opposing) functions in cells, at least in part as a result of isoform-specific subcellular compartmentalization patterns, protein-protein interactions, and posttranslational modifications that influence catalytic function. This review focuses on the structural basis for differences in lipid cofactor responsiveness for individual PKC isoforms, the regulatory phosphorylations that control the normal maturation, activation, signaling function, and downregulation of these enzymes, and the intra-/intermolecular interactions that control PKC isoform activation and subcellular targeting in cells. A detailed understanding of the unique molecular features that underlie isoform-specific posttranslational modification patterns, protein-protein interactions, and subcellular targeting (i.e., that impart functional specificity) should provide the basis for the design of novel PKC isoform-specific activator or inhibitor compounds that can achieve therapeutically useful changes in PKC signaling in cells.

PubMed Disclaimer

Figures

FIG. 1

FIG. 1

Domain structure of protein kinase C (PKC) isoforms. Top: PKCs have a conserved kinase domain (depicted in teal) and more variable regulatory domains. All PKC regulatory domains have a pseudosubstrate motif (shown in green) NH2 terminal to the C1 domain (shown in pink). Tandem C1 domains are the molecular sensors of phorbol 12-myristate 13-acetate (PMA)/diacylglycerol (DAG) in cPKC and nPKC isoforms, whereas the single aPKC C1 domain does not bind DAG/PMA. The C2 domains (in yellow) function as calcium-dependent phospholipid binding modules in cPKCs. nPKC C2 domains do not bind calcium; the PKC_δ_-C2-like domain is a phosphotyrosine interaction module. PKC isoform variable regions are shown in gray. Bottom: ribbon diagrams of PKC C1B domain, C2 domain, and kinase domain structures. Kinase domain phosphorylation sites are discussed in the text. (Figure courtesy of Dr. Alexandra Newton.)

FIG. 2

FIG. 2

Alignment of PKC C1 domains. Numbering is based on PKC_α_. Conserved cysteine and histidine residues are in blue. Other structural determinants of C1 domain function are as indicated on the figure.

FIG. 3

FIG. 3

Alignment of PKC C2 domains.

FIG. 4

FIG. 4

Alignment of the ATP binding site, invariant lysine, and gatekeeper residues in PKC kinase domains. NES sequences NH2 terminal to aPKC ATP binding sites are depicted.

FIG. 5

FIG. 5

Alignment of kinase domain activation loops. A: Mg positioning loop (in green), activation loop phosphorylation site, invariant tyrosines that are phosphorylated in certain PKCs, and the unique structural features of PKC_δ_ that recently have been considered a mechanism to render this isoform catalytically competent without activation loop phosphorylation are depicted. B: sequence alignment for the A-helix in PKC_δ_ and protein kinase A (PKA) (see text). C: activation loop phosphorylation mechanisms and functions.

FIG. 6

FIG. 6

Alignment of kinase domain V5 domain.

FIG. 7

FIG. 7

PKC_ε_ overexpression leads to PKC_δ_-Tyr311/Tyr332 phosphorylation and increased PKC_δ_-Thr505 autophosphorylation; the mechanisms that control activation loop phosphorylation on native PKC_δ_ do not influence the heterologously overexpressed enzyme. A: schematic of PKC_ε_-PKC_δ_ cross-talk in cells (see text). B: green fluorescent protein (GFP)-tagged PKC_δ_ was heterologously overexpressed in COS7 cells (lanes 2–4). PKC_δ_ overexpression was without (lane 2) or with PKC_ε_ overexpression for 24 h (lane 3) or 48 h (lane 4). Samples were subjected to SDS-PAGE and immunblotting for PKC_δ_ protein and PKC_δ_-Thr505 phosphorylation. The heterologously overexpressed protein (labeled in blue) is constitutively Thr505-phosphorylated; GFP-PKC_δ_-Thr505 phosphorylation is not increased by PKC_ε_ overexpression. Note, while this experiment shows a minor decrease in PKC_δ_ protein and Thr505 phosphorylation in the context of PKC_ε_ overexpression for 24 h, this was not a consistent finding in replicates of this experiment. In contrast, native PKC_δ_ (labeled in red, which migrates more rapidly than the GFP-tagged PKC_δ_ transgene) is not phosphorylated at Thr505 in resting cultures that do not overexpress PKC_ε_; PKC_ε_ overexpression induces Thr505 (and Tyr311) phosphorylation on native PKC_δ_.

FIG. 8

FIG. 8

Src-dependent PKC_δ_ tyrosine phosphorylation leads to changes in PKC_δ_ phosphorylation of cardiac troponin I; PKC_δ_-Tyr311 and Thr505 critically regulate PKC_δ_ substrate specificity.

FIG. 9

FIG. 9

Evolving concepts of signaling pathway activation. A: the original concepts of linear signal transduction pathways held that stimuli evoke responses via the actions of transducers (such as G proteins or PKC isoforms). B: models of signal transduction were first revised to allow for the presence of multiple stimuli that can converge on a single signaling pathway and alter the amplitude of a signaling response. This could reflect the activation of different pools of a single enzyme. Alternatively, amplitude control might be due to the differential stimulatory properties of full or partial agonists. C: more current models of signaling transduction allow for a high level of signal integration by proteins (such as PKC_δ_) that are regulated through conformational changes, translocation events, and various posttranslational modifications (phosphorylation, oxidation, tyrosine nitration, etc.) that can underlie stimulus-specific signaling responses.

Similar articles

Cited by

References

    1. Aces P, Beheshti M, Szallasi Z, Li L, Yuspa SH, Blumberg PM. Effect of a tyrosine 155 to phenylalanine mutation of protein kinase C-δ on the proliferative and tumorigenic properties of NIH 3T3 fibroblasts. Carcinogenesis. 2000;21:887–891. - PubMed
    1. Alessi DR. The protein kinase C inhibitors Ro 318220 and GF 109203X are equally potent inhibitors of MAPKAP kinase-1β (Rsk-2) and p70 S6 kinase. FEBS Lett. 1997;402:121–123. - PubMed
    1. Ananthanarayanan B, Stahelin RV, Digman MA, Cho W. Activation mechanisms of conventional protein kinase C isoforms are determined by the ligand affinity and conformational flexibility of their C1 domains. J Biol Chem. 2003;278:46886–46894. - PubMed
    1. Anilkumar N, Parsons M, Monk R, Ng T, Adams JC. Interaction of fascin and protein kinase Cα: a novel intersection in cell adhesion and motility. EMBO J. 2003;22:5390–5402. - PMC - PubMed
    1. Arimoto T, Takeishi Y, Takahashi H, Shishido T, Niizeki T, Koyama Y, Shiga R, Nozaki N, Nakajima O, Nishimaru K, Abe J, Endoh M, Walsh RA, Goto K, Kubota I. Cardiac-specific overexpression of diacylglycerol kinase-ζ prevents Gq protein-coupled receptor agonist-induced cardiac hypertrophy in transgenic mice. Circulation. 2006;113:60–66. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources