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Novel mutant mouse line emphasizes the importance of protein kinase C theta for CD4 + T lymphocyte activation. Cell Commun Signal 2019; 17:56. [PMID: 31138259 PMCID: PMC6537413 DOI: 10.1186/s12964-019-0364-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 05/14/2019] [Indexed: 11/10/2022] Open
Abstract
Background The protein kinase C theta (PKCθ) has an important and non-redundant function downstream of the antigen receptor and co-receptor complex in T lymphocytes. PKCθ is not only essential for activation of NF-κB, AP-1 and NFAT and subsequent interleukin-2 expression, but also critical for positive selection and development of regulatory T lymphocytes in the thymus. Several domains regulate its activity, such as a pseudosubstrate sequence mediating an auto-inhibitory intramolecular interaction, the tandem C1 domains binding diacylglycerol, and phosphorylation at conserved tyrosine, threonine as well as serine residues throughout the whole length of the protein. To address the importance of the variable domain V1 at the very N-terminus, which is encoded by exon 2, a mutated version of PKCθ was analyzed for its ability to stimulate T lymphocyte activation. Methods T cell responses were analyzed with promoter luciferase reporter assays in Jurkat T cells transfected with PKCθ expression constructs. A mouse line expressing mutated instead of wild type PKCθ was analyzed in comparison to PKCθ-deficient and wild type mice for thymic development and T cell subsets by flow cytometry and T cell activation by quantitative RT-PCR, luminex analysis and flow cytometry. Results In cell lines, the exon 2-replacing mutation impaired the transactivation of interleukin-2 expression by constitutively active mutant form of PKCθ. Moreover, analysis of a newly generated exon 2-mutant mouse line (PKCθ-E2mut) revealed that the N-terminal replacement mutation results in an hypomorph mutant of PKCθ combined with reduced PKCθ protein levels in CD4+ T lymphocytes. Thus, PKCθ-dependent functions in T lymphocytes were affected resulting in impaired thymic development of single positive T lymphocytes in vivo. In particular, there was diminished generation of regulatory T lymphocytes. Furthermore, early activation responses such as interleukin-2 expression of CD4+ T lymphocytes were significantly reduced even though cell viability was not affected. Thus, PKCθ-E2mut mice show a phenotype similar to conventional PKCθ-deficient mice. Conclusion Taken together, PKCθ-E2mut mice show a phenotype similar to conventional PKCθ-deficient mice. Both our in vitro T cell culture experiments and ex vivo analyses of a PKCθ-E2-mutant mouse line independently validate the importance of PKCθ downstream of the antigen-receptor complex for activation of CD4+ T lymphocytes. Electronic supplementary material The online version of this article (10.1186/s12964-019-0364-0) contains supplementary material, which is available to authorized users.
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Siegmund K, Thuille N, Posch N, Fresser F, Leitges M, Baier G. Novel mutant mouse line emphasizes the importance of protein kinase C theta for CD4 + T lymphocyte activation. Cell Commun Signal 2019. [PMID: 31138259 PMCID: PMC6537413 DOI: 10.1186/s12964-019-0364-0#] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The protein kinase C theta (PKCθ) has an important and non-redundant function downstream of the antigen receptor and co-receptor complex in T lymphocytes. PKCθ is not only essential for activation of NF-κB, AP-1 and NFAT and subsequent interleukin-2 expression, but also critical for positive selection and development of regulatory T lymphocytes in the thymus. Several domains regulate its activity, such as a pseudosubstrate sequence mediating an auto-inhibitory intramolecular interaction, the tandem C1 domains binding diacylglycerol, and phosphorylation at conserved tyrosine, threonine as well as serine residues throughout the whole length of the protein. To address the importance of the variable domain V1 at the very N-terminus, which is encoded by exon 2, a mutated version of PKCθ was analyzed for its ability to stimulate T lymphocyte activation. METHODS T cell responses were analyzed with promoter luciferase reporter assays in Jurkat T cells transfected with PKCθ expression constructs. A mouse line expressing mutated instead of wild type PKCθ was analyzed in comparison to PKCθ-deficient and wild type mice for thymic development and T cell subsets by flow cytometry and T cell activation by quantitative RT-PCR, luminex analysis and flow cytometry. RESULTS In cell lines, the exon 2-replacing mutation impaired the transactivation of interleukin-2 expression by constitutively active mutant form of PKCθ. Moreover, analysis of a newly generated exon 2-mutant mouse line (PKCθ-E2mut) revealed that the N-terminal replacement mutation results in an hypomorph mutant of PKCθ combined with reduced PKCθ protein levels in CD4+ T lymphocytes. Thus, PKCθ-dependent functions in T lymphocytes were affected resulting in impaired thymic development of single positive T lymphocytes in vivo. In particular, there was diminished generation of regulatory T lymphocytes. Furthermore, early activation responses such as interleukin-2 expression of CD4+ T lymphocytes were significantly reduced even though cell viability was not affected. Thus, PKCθ-E2mut mice show a phenotype similar to conventional PKCθ-deficient mice. CONCLUSION Taken together, PKCθ-E2mut mice show a phenotype similar to conventional PKCθ-deficient mice. Both our in vitro T cell culture experiments and ex vivo analyses of a PKCθ-E2-mutant mouse line independently validate the importance of PKCθ downstream of the antigen-receptor complex for activation of CD4+ T lymphocytes.
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Affiliation(s)
- Kerstin Siegmund
- 0000 0000 8853 2677grid.5361.1Department for Pharmacology and Genetics, Medical University Innsbruck, Division of Translational Cell Genetics, Peter Mayr Str. 1a, A-6020 Innsbruck, Austria
| | - Nikolaus Thuille
- 0000 0000 8853 2677grid.5361.1Department for Pharmacology and Genetics, Medical University Innsbruck, Division of Translational Cell Genetics, Peter Mayr Str. 1a, A-6020 Innsbruck, Austria
| | - Nina Posch
- 0000 0000 8853 2677grid.5361.1Department for Pharmacology and Genetics, Medical University Innsbruck, Division of Translational Cell Genetics, Peter Mayr Str. 1a, A-6020 Innsbruck, Austria
| | - Friedrich Fresser
- 0000 0000 8853 2677grid.5361.1Department for Pharmacology and Genetics, Medical University Innsbruck, Division of Translational Cell Genetics, Peter Mayr Str. 1a, A-6020 Innsbruck, Austria
| | | | - Gottfried Baier
- 0000 0000 8853 2677grid.5361.1Department for Pharmacology and Genetics, Medical University Innsbruck, Division of Translational Cell Genetics, Peter Mayr Str. 1a, A-6020 Innsbruck, Austria
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3
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Abstract
Protein kinase C (PKC) isozymes belong to a family of Ser/Thr kinases whose activity is governed by reversible release of an autoinhibitory pseudosubstrate. For conventional and novel isozymes, this is effected by binding the lipid second messenger, diacylglycerol, but for atypical PKC isozymes, this is effected by binding protein scaffolds. PKC shot into the limelight following the discovery in the 1980s that the diacylglycerol-sensitive isozymes are "receptors" for the potent tumor-promoting phorbol esters. This set in place a concept that PKC isozymes are oncoproteins. Yet three decades of cancer clinical trials targeting PKC with inhibitors failed and, in some cases, worsened patient outcome. Emerging evidence from cancer-associated mutations and protein expression levels provide a reason: PKC isozymes generally function as tumor suppressors and their activity should be restored, not inhibited, in cancer therapies. And whereas not enough activity is associated with cancer, variants with enhanced activity are associated with degenerative diseases such as Alzheimer's disease. This review describes the tightly controlled mechanisms that ensure PKC activity is perfectly balanced and what happens when these controls are deregulated. PKC isozymes serve as a paradigm for the wisdom of Confucius: "to go beyond is as wrong as to fall short."
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Affiliation(s)
- Alexandra C Newton
- a Department of Pharmacology , University of California at San Diego , La Jolla , CA , USA
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Yuan LL, Zhang M, Yan X, Bian YW, Zhen SM, Yan YM. Dynamic Phosphoproteome Analysis of Seedling Leaves in Brachypodium distachyon L. Reveals Central Phosphorylated Proteins Involved in the Drought Stress Response. Sci Rep 2016; 6:35280. [PMID: 27748408 PMCID: PMC5066223 DOI: 10.1038/srep35280] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 09/16/2016] [Indexed: 01/18/2023] Open
Abstract
Drought stress is a major abiotic stress affecting plant growth and development. In this study, we performed the first dynamic phosphoproteome analysis of Brachypodium distachyon L. seedling leaves under drought stress for different times. A total of 4924 phosphopeptides, contained 6362 phosphosites belonging to 2748 phosphoproteins. Rigorous standards were imposed to screen 484 phosphorylation sites, representing 442 unique phosphoproteins. Comparative analyses revealed significant changes in phosphorylation levels at 0, 6, and 24 h under drought stress. The most phosphorylated proteins and the highest phosphorylation level occurred at 6 h. Venn analysis showed that the up-regulated phosphopeptides at 6 h were almost two-fold those at 24 h. Motif-X analysis identified the six motifs: [sP], [Rxxs], [LxRxxs], [sxD], [sF], and [TP], among which [LxRxxs] was also previously identified in B. distachyon. Results from molecular function and protein-protein interaction analyses suggested that phosphoproteins mainly participate in signal transduction, gene expression, drought response and defense, photosynthesis and energy metabolism, and material transmembrane transport. These phosphoproteins, which showed significant changes in phosphorylation levels, play important roles in signal transduction and material transmembrane transport in response to drought conditions. Our results provide new insights into the molecular mechanism of this plant’s abiotic stress response through phosphorylation modification.
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Affiliation(s)
- Lin-Lin Yuan
- College of Life Science, Capital Normal University, 100048 Beijing, China
| | - Ming Zhang
- College of Life Science, Capital Normal University, 100048 Beijing, China.,College of Life Science, Heze University, 274015 Shandong, China
| | - Xing Yan
- College of Life Science, Capital Normal University, 100048 Beijing, China
| | - Yan-Wei Bian
- College of Life Science, Capital Normal University, 100048 Beijing, China
| | - Shou-Min Zhen
- College of Life Science, Capital Normal University, 100048 Beijing, China
| | - Yue-Ming Yan
- College of Life Science, Capital Normal University, 100048 Beijing, China
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Qiu W, Zhang F, Steinberg SF. The protein kinase D1 COOH terminus: marker or regulator of enzyme activity? Am J Physiol Cell Physiol 2014; 307:C606-10. [PMID: 25080487 DOI: 10.1152/ajpcell.00155.2014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Protein kinase D1 (PKD1) is a Ser/Thr kinase implicated in a wide variety of cellular responses. PKD1 activation is generally attributed to a PKC-dependent pathway that leads to phosphorylation of the activation loop at Ser(744)/Ser(748). This modification increases catalytic activity, including that toward an autophosphorylation site (Ser(916)) in a postsynaptic density-95/disks large/zonula occludens-1 (PDZ)-binding motif at the extreme COOH terminus. However, there is growing evidence that PKD1 activation can also result from a PKC-independent autocatalytic reaction at Ser(744)/Ser(748) and that certain stimuli increase in PKD1 phosphorylation at Ser(744)/S(748) without an increase in autophosphorylation at Ser(916). This study exposes a mechanism that results in a discrepancy between PKD1 COOH-terminal autocatalytic activity and activity toward other substrates. We show that PKD1 constructs harboring COOH-terminal epitope tags display high levels of in vitro activation loop autocatalytic activity and activity toward syntide-2 (a peptide substrate), but no Ser(916) autocatalytic activity. Cell-based studies show that the COOH-terminal tag, adjacent to PKD1's PDZ1-binding motif, does not grossly influence PKD1 partitioning between soluble and particulate fractions in resting cells or PKD1 translocation to the particulate fraction following treatment with PMA. However, a COOH-terminal tag that confers a high level of activation loop autocatalytic activity decreases the PKC requirement for agonist-dependent PKD1 activation in cells. The recognition that COOH-terminal tags alter PKD1's pharmacological profile is important from a technical standpoint. The altered dynamics and activation mechanisms for COOH-terminal-tagged PKD1 enzymes also could model the signaling properties of localized pools of enzyme anchored through the COOH terminus to PDZ domain-containing scaffolding proteins.
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Affiliation(s)
- Weihua Qiu
- Department of Pharmacology, Columbia University, New York, New York
| | - Fan Zhang
- Department of Pharmacology, Columbia University, New York, New York
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Swanson CJ, Ritt M, Wang W, Lang MJ, Narayan A, Tesmer JJ, Westfall M, Sivaramakrishnan S. Conserved modular domains team up to latch-open active protein kinase Cα. J Biol Chem 2014; 289:17812-29. [PMID: 24790081 DOI: 10.1074/jbc.m113.534750] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Signaling proteins comprised of modular domains have evolved along with multicellularity as a method to facilitate increasing intracellular bandwidth. The effects of intramolecular interactions between modular domains within the context of native proteins have been largely unexplored. Here we examine intra- and intermolecular interactions in the multidomain signaling protein, protein kinase Cα (PKCα). We identify three interactions between two activated PKC molecules that synergistically stabilize a nanomolar affinity homodimer. Disruption of the homodimer results in a loss of PKC-mediated ERK1/2 phosphorylation, whereas disruption of the auto-inhibited state promotes the homodimer and prolongs PKC membrane localization. These observations support a novel regulatory mechanism wherein homodimerization dictates the equilibrium between the auto-inhibited and active states of PKC by sequestering auto-inhibitory interactions. Our findings underscore the physiological importance of context-dependent modular domain interactions in cell signaling.
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Affiliation(s)
| | | | - William Wang
- Department of Cell and Developmental Biology, Department of Cardiac Surgery
| | | | - Arvind Narayan
- Department of Biomedical Engineering, Life Sciences Institute, and
| | - John J Tesmer
- From the Biophysics Program, the Departments of Pharmacology and Biological Sciences, University of Michigan, Ann Arbor, Michigan 48109
| | - Margaret Westfall
- Department of Cardiac Surgery, Department of Biomedical Engineering, Life Sciences Institute, and
| | - Sivaraj Sivaramakrishnan
- From the Biophysics Program, Department of Cell and Developmental Biology, Department of Biomedical Engineering, Life Sciences Institute, and
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Shigdar S, Qian C, Lv L, Pu C, Li Y, Li L, Marappan M, Lin J, Wang L, Duan W. The use of sensitive chemical antibodies for diagnosis: detection of low levels of EpCAM in breast cancer. PLoS One 2013; 8:e57613. [PMID: 23460885 PMCID: PMC3584034 DOI: 10.1371/journal.pone.0057613] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Accepted: 01/24/2013] [Indexed: 12/31/2022] Open
Abstract
EpCAM is expressed at low levels in a variety of normal human epithelial tissues, but is overexpressed in 70–90% of carcinomas. From a clinico-pathological point of view, this has both prognostic and therapeutic significance. EpCAM was first suggested as a therapeutic target for the treatment of epithelial cancers in the 1990s. However, following several immunotherapy trials, the results have been mixed. It has been suggested that this is due, at least in part, to an unknown level of EpCAM expression in the tumors being targeted. Thus, selection of patients who would benefit from EpCAM immunotherapy by determining EpCAM status in the tumor biopsies is currently undergoing vigorous evaluation. However, current EpCAM antibodies are not robust enough to be able to detect EpCAM expression in all pathological tissues. Here we report a newly developed EpCAM RNA aptamer, also known as a chemical antibody, which is not only specific but also more sensitive than current antibodies for the detection of EpCAM in formalin-fixed paraffin-embedded primary breast cancers. This new aptamer, together with our previously described aptamer, showed no non-specific staining or cross-reactivity with tissues that do not express EpCAM. They were able to reliably detect target proteins in breast cancer xenograft where an anti-EpCAM antibody (323/A3) showed limited or no reactivity. Our results demonstrated a more robust detection of EpCAM using RNA aptamers over antibodies in clinical samples with chromogenic staining. This shows the potential of aptamers in the future of histopathological diagnosis and as a tool to guide targeted immunotherapy.
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Affiliation(s)
- Sarah Shigdar
- School of Medicine, Deakin University, Waurn Ponds, Victoria, Australia
| | - Christine Qian
- School of Medicine, Deakin University, Waurn Ponds, Victoria, Australia
- Department of Histopathology, St John of God Pathology, Geelong, Victoria, Australia
| | - Li Lv
- Second Affiliated Hospital of Dalian Medical University, Dalian, China
| | - Chunwen Pu
- Dalian Sixth People’s Hospital, Dalian, China
| | - Yong Li
- Cancer Care Centre, St. George Hospital, and St George Clinical School, Faculty of Medicine, University of New South Wales, Kensington, Australia
| | - Lianhong Li
- Department of Pathology and Forensic Science, Dalian Medical University, Dalian, China
| | - Manju Marappan
- School of Medicine, Deakin University, Waurn Ponds, Victoria, Australia
| | - Jia Lin
- School of Medicine, Deakin University, Waurn Ponds, Victoria, Australia
| | - Lifen Wang
- Second Affiliated Hospital of Dalian Medical University, Dalian, China
- * E-mail: (WD); (LW)
| | - Wei Duan
- School of Medicine, Deakin University, Waurn Ponds, Victoria, Australia
- * E-mail: (WD); (LW)
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8
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Oruganty K, Kannan N. Design principles underpinning the regulatory diversity of protein kinases. Philos Trans R Soc Lond B Biol Sci 2012; 367:2529-39. [PMID: 22889905 PMCID: PMC3415841 DOI: 10.1098/rstb.2012.0015] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Protein phosphorylation in eukaryotes is carried out by a large and diverse family of protein kinases, which display remarkable diversity and complexity in their modes of regulation. The complex modes of regulation have evolved as a consequence of natural selection operating on protein kinase sequences for billions of years. Here we describe how quantitative comparisons of protein kinase sequences from diverse organisms, in particular prokaryotes, have contributed to our understanding of the structural organization and evolution of allosteric regulation in the protein kinase domain. An emerging view from these studies is that regulatory diversity and complexity in the protein kinase domain evolved in a ‘modular’ fashion through elaboration of an ancient core component, which existed before the emergence of eukaryotes. The core component provided the conformational flexibility required for ATP binding and phosphoryl transfer in prokaryotic kinases, but evolved into a highly regulatable domain in eukaryotes through the addition of exaggerated structural features that facilitated tight allosteric control. Family and group-specific features are built upon the core component in eukaryotes to provide additional layers of control. We propose that ‘modularity’ and ‘conformational flexibility’ are key evolvable traits of the protein kinase domain that contributed to its extensive regulatory diversity and complexity.
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Affiliation(s)
- Krishnadev Oruganty
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, USA
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9
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Abstract
The monoclonal antibody against the AC133 epitope of CD133 has been widely used as a cell surface marker of cancer stem cells in several different cancer types. Here, we describe the isolation and characterisation of two RNA aptamers, including the smallest described 15 nucleotide RNA aptamer, which specifically recognise the AC133 epitope and the CD133 protein with high sensitivity. As well, both these aptamers show superior tumour penetration and retention when compared to the AC133 antibody in a 3-D tumour sphere model. These novel CD133 aptamers will aid future development of cancer stem cell targeted therapeutics and molecular imaging.
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10
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Gould CM, Kannan N, Taylor SS, Newton AC. The chaperones Hsp90 and Cdc37 mediate the maturation and stabilization of protein kinase C through a conserved PXXP motif in the C-terminal tail. J Biol Chem 2009; 284:4921-35. [PMID: 19091746 PMCID: PMC2643500 DOI: 10.1074/jbc.m808436200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 12/16/2008] [Indexed: 12/29/2022] Open
Abstract
The life cycle of protein kinase C (PKC) is tightly controlled by mechanisms that mature the enzyme, sustain the activation-competent enzyme, and degrade the enzyme. Here we show that a conserved PXXP motif (Kannan, N., Haste, N., Taylor, S. S., and Neuwald, A. F. (2007) Proc. Natl. Acad. Sci. U. S. A. 104, 1272-1277), in the C-terminal tail of AGC (c-AMP-dependent protein kinase/protein kinase G/protein kinase C) kinases, controls the processing phosphorylation of conventional and novel PKC isozymes, a required step in the maturation of the enzyme into a signaling-competent species. Mutation of both Pro-616 and Pro-619 to Ala in the conventional PKC betaII abolishes the phosphorylation and activity of the kinase. Co-immunoprecipitation studies reveal that conventional and novel, but not atypical, PKC isozymes bind the chaperones Hsp90 and Cdc37 through a PXXP-dependent mechanism. Inhibitors of Hsp90 and Cdc37 significantly reduce the rate of processing phosphorylation of PKC. Of the two C-terminal sites processed by phosphorylation, the hydrophobic motif, but not the turn motif, is regulated by Hsp90. Overlay of purified Hsp90 onto a peptide array containing peptides covering the catalytic domain of PKC betaII identified regions surrounding the PXXP segment, but not the PXXP motif itself, as major binding determinants for Hsp90. These Hsp90-binding regions, however, are tethered to the C-terminal tail via a "molecular clamp" formed between the PXXP motif and a conserved Tyr (Tyr-446) in the alphaE-helix. Disruption of the clamp by mutation of the Tyr to Ala recapitulates the phosphorylation defect of mutating the PXXP motif. These data are consistent with a model in which a molecular clamp created by the PXXP motif in the C-terminal tail and determinants in the alphaE-helix of the catalytic domain allows the chaperones Hsp90 and Cdc37 to bind newly synthesized PKC, a required event in the processing of PKC by phosphorylation.
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Affiliation(s)
- Christine M Gould
- Pharmacology Department, University of California, San Diego, La Jolla, California 92039-0721, USA
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11
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Zhang W, Smith A, Liu JP, Cheung NS, Zhou S, Liu K, Li QT, Duan W. GSK3β modulates PACAP-induced neuritogenesis in PC12 cells by acting downstream of Rap1 in a caveolae-dependent manner. Cell Signal 2009; 21:237-45. [DOI: 10.1016/j.cellsig.2008.10.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2008] [Revised: 10/15/2008] [Accepted: 10/15/2008] [Indexed: 10/21/2022]
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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.
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Affiliation(s)
- Susan F Steinberg
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
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13
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Lim WG, Chen X, Liu JP, Tan BJ, Zhou S, Smith A, Lees N, Hou L, Gu F, Yu XY, Du Y, Smith D, Verma C, Liu K, Duan W. The C-terminus of PRK2/PKNgamma is required for optimal activation by RhoA in a GTP-dependent manner. Arch Biochem Biophys 2008; 479:170-8. [PMID: 18835241 DOI: 10.1016/j.abb.2008.09.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2008] [Revised: 09/15/2008] [Accepted: 09/15/2008] [Indexed: 01/07/2023]
Abstract
PRK2/PKNgamma is a Rho effector and a member of the protein kinase C superfamily of serine/threonine kinases. Here, we explore the structure-function relationship between various motifs in the C-terminal half of PRK2 and its kinase activity and regulation. We report that two threonine residues at conserved phosphoacceptor position in the activation loop and the turn motif are essential for the catalytic activity of PRK2, but the phosphomimetic Asp-978 at hydrophobic motif is dispensable for kinase catalytic competence. Moreover, the PRK2-Delta958 mutant with the turn motif truncated still interacts with 3-phosphoinositide-dependent kinase-1 (PDK-1). Thus, both the intact hydrophobic motif and the turn motif in PRK2 are dispensable for the binding of PDK-1. We also found that while the last seven amino acid residues at the C-terminus of PRK2 are not required for the activation of the kinase by RhoA in vitro, however, the extreme C-terminal segment is critical for the full activation of PRK2 by RhoA in cells in a GTP-dependent manner. Our data suggest that the extreme C-terminus of PRK2 may represent a potential drug target for effector-specific pharmacological intervention of Rho-medicated biological processes.
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Affiliation(s)
- Wee Guan Lim
- Department of Biochemistry, Yong Loo Lin of Medicine, The National University of Singapore, 8 Medical Drive, Singapore 117597, Singapore
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Lee MR, Duan W, Tan SL. Protein kinase C isozymes as potential therapeutic targets in immune disorders. Expert Opin Ther Targets 2008; 12:535-52. [PMID: 18410238 DOI: 10.1517/14728222.12.5.535] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Members of the protein kinase C (PKC) family are key signalling mediators in immune responses, and pharmacological inhibition of PKCs may be useful for treating immune-mediated diseases. OBJECTIVE To review and discuss the insights gained so far into various PKC isozymes and the therapeutic potential and challenges of developing PKC inhibitors for immune disorder therapy. METHODS A literature review of the role of PKCs in immune cell signalling and recent studies describing immune functions associated with PKC isozyme deficiency in relevant mouse disease models, followed by specific case studies of current and potential therapeutic strategies targeting PKCs. RESULTS/CONCLUSION There is vast amount of data supporting PKC isozymes as attractive drug targets for certain immune disorders. Although the development of specific PKC isozyme inhibitors has been challenging, some progress has been made. It remains to be seen if broad-scale or isozyme-selective inhibition of PKC will have clinical efficacy.
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Affiliation(s)
- Matthew R Lee
- Amgen, Inc., Molecular Structure, 1 Amgen Center Drive, Thousand Oaks, CA 91320, USA
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15
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Solodukhin AS, Kretsinger RH, Sando JJ. Initial three-dimensional reconstructions of protein kinase C δ from two-dimensional crystals on lipid monolayers. Cell Signal 2007; 19:2035-45. [PMID: 17604605 DOI: 10.1016/j.cellsig.2007.05.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Revised: 05/22/2007] [Accepted: 05/25/2007] [Indexed: 01/06/2023]
Abstract
Two-dimensional crystals of protein kinase C delta (PKCdelta) and of its regulatory domain (RDdelta) were grown on lipid monolayers and analyzed by electron microscopy at tilt angles varying from -50 degrees to +55 degrees. Although the crystals exhibit pseudo-3-fold symmetry, analysis of difference phase residuals indicates that there is only one way to align the crystals for merging so the data were processed in plane group P1. Three-dimensional reconstructions generated for several two-dimensional crystals each of PKCdelta and RDdelta show good agreement and are consistent with membrane attachment via a single C1 subdomain, a small surface contact by one or two loops from the C2 domain, and, in intact PKCdelta, a small appendage from the catalytic domain, probably V5. Two-dimensional crystallography with three-dimensional reconstruction should be suitable for examination of additional PKC isozymes and for analysis of the enzymes bound to substrates and other proteins.
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16
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Stensman H, Larsson C. Identification of acidic amino acid residues in the protein kinase C alpha V5 domain that contribute to its insensitivity to diacylglycerol. J Biol Chem 2007; 282:28627-28638. [PMID: 17673466 DOI: 10.1074/jbc.m702248200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The protein kinase C (PKC) isoforms are maintained in an inactive and closed conformation by intramolecular interactions. Upon activation these are disrupted by activators, binding proteins and cellular membrane. We have seen that autophosphorylation of two sites in the C-terminal V5 domain is crucial to keep PKC alpha insensitive to the activator diacylglycerol, which presumably is caused by a masking of the diacylglycerol-binding C1a domain. Here we demonstrate that the diacylglycerol sensitivity of the PKC beta isoforms also is suppressed by autophosphorylation of the V5 sites. To analyze conformational differences, a fusion protein ECFP-PKC alpha-EYFP was expressed in cells and the FRET signal was analyzed. The analogous mutant with autophosphorylation sites exchanged for alanine gave rise to a substantially lower FRET signal than wild-type PKC alpha indicating a conformational difference elicited by the mutations. Expression of the isolated PKC alpha V5 domain led to increased diacylglycerol sensitivity of PKC alpha. We identified acidic residues in the V5 domain that, when mutated to alanines or lysines, rendered PKC alpha sensitive to diacylglycerol. Furthermore, mutation to glutamate of four lysines in a lysine-rich cluster in the C2 domain gave a similar effect. Simultaneous reversal of the charges of the acidic residues in the V5 and the lysines in the C2 domain gave rise to a PKC alpha that was insensitive to diacylglycerol. We propose that these structures participate in an intramolecular interaction that maintains PKC alpha in a closed conformation. The disruption of this interaction leads to an unmasking of the C1a domain and thereby increased diacylglycerol sensitivity of PKC alpha.
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Affiliation(s)
- Helena Stensman
- Department of Laboratory Medicine, Center for Molecular Pathology, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden
| | - Christer Larsson
- Department of Laboratory Medicine, Center for Molecular Pathology, Malmö University Hospital, Lund University, SE-205 02 Malmö, Sweden.
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