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Massey S, Kongchan N, Gao Y, Chaudhury A, Olokpa E, Karch J, Malovannaya A, Cheng C, Zhang X, Neilson JR. PKC-mediated phosphorylation governs the stability and function of CELF1 as a driver of EMT in breast epithelial cells. J Biol Chem 2024:107826. [PMID: 39343007 DOI: 10.1016/j.jbc.2024.107826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 08/08/2024] [Accepted: 08/12/2024] [Indexed: 10/01/2024] Open
Abstract
Epithelial to mesenchymal transition (EMT) is believed to be a principal factor contributing to cancer metastasis. The post-transcriptional and post-translational mechanisms underlying EMT are comparatively underexplored. We previously demonstrated that the CELF1 RNA binding protein is necessary and sufficient to drive the EMT of breast epithelial cells, and that the relative protein expression of CELF1 in this context was dictated at the post-translational level. Here, we elucidate the mechanism of this regulation. Mass spectrometric analysis of CELF1 isolated from mesenchymal MCF-10A cells identified multiple sites of serine and threonine phosphorylation on the protein, correlating with the increased stability of this protein in this cellular state. Analysis of phosphomimetic and serine/threonine-to-alanine phosphomutant variants of CELF1 revealed that these phosphorylation sites indeed dictate CELF1 stability, ubiquitination state, and function in vitro. Via co-immunoprecipitation and in vitro kinase assays, we identified the Protein Kinase C (PKC) alpha and epsilon isozymes as the kinases responsible for CELF1 phosphorylation in a breast cell line. Genetic epistasis experiments confirmed that these PKCs function upstream of CELF1 in this EMT program, and CELF1 phosphorylation impacts tumor metastasis in a xenograft model. This work is the first to formally establish the mechanisms underlying post-translational control of CELF1 expression and function during EMT of breast epithelial cells. Given the broad dysregulation of CELF1 expression in human breast cancer, our results may ultimately provide knowledge that may be leveraged for novel therapeutic interventions in this context.
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Affiliation(s)
- Shebna Massey
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Natee Kongchan
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Yang Gao
- Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX 77030, USA; Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Arindam Chaudhury
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Emuejevoke Olokpa
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jason Karch
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Anna Malovannaya
- Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Chonghui Cheng
- Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Xiang Zhang
- Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA; McNair Medical Institute, Baylor College of Medicine, Houston, TX 77030, USA
| | - Joel R Neilson
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA; Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, Houston, TX 77030, USA.
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Hou L, Wang L, Zhao Z, Xu W, Wang Y, Cui G. Regulation of dendrite growth by Cdc42 effector protein‑4 in hippocampal neurons in vitro. Mol Med Rep 2022; 25:128. [PMID: 35169866 PMCID: PMC8867466 DOI: 10.3892/mmr.2022.12644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 11/01/2021] [Indexed: 11/21/2022] Open
Abstract
Cell division control protein 42 homolog (Cdc42), one of the most characteristic members of the Rho protein family, is required for multiple aspects of dendritic morphogenesis. However, the proteins mediating the regulatory effects of Cdc42 activity on neuronal morphology are largely unknown. Cdc42 effector protein-4 (CEP4) was identified to be a binding partner of Rho GTPase 4 and is ubiquitously expressed in all adult tissues. However, the physiological function of CEP4 in neurons is unknown. In the present study, immunofluorescence and western blot analysis were conducted, revealing that CEP4 is highly expressed in the brain, and that the expression of CEP4 is gradually increased during neurodevelopment. Knockdown of CEP4 with short hairpin RNA suppressed dendrite growth, whereas overexpression of wild-type CEP4 promoted dendrite growth in primary isolated mouse hippocampal neurons. Collectively, these results indicated an important role for CEP4 in dendrite growth in hippocampal neurons.
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Affiliation(s)
- Lei Hou
- Department of Neurosurgery, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China
| | - Lufeng Wang
- Department of Neurology, Shanghai East Hospital, Tongji University School of Medicine, Shanghai 200120, P.R. China
| | - Zhijie Zhao
- Department of Neurosurgery, Tongren Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200336, P.R. China
| | - Wei Xu
- Department of Neurosurgery, Huashan Hospital, Fudan University, Shanghai 200040, P.R. China
| | - Yang Wang
- Department of Emergency, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Yangpu, Shanghai 200092, P.R. China
| | - Gang Cui
- Department of Neurosurgery, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China
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Wakeham CM, Wilmarth PA, Cunliffe JM, Klimek JE, Ren G, David LL, Morgans CW. Identification of PKCα-dependent phosphoproteins in mouse retina. J Proteomics 2019; 206:103423. [PMID: 31255707 DOI: 10.1016/j.jprot.2019.103423] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 06/11/2019] [Accepted: 06/19/2019] [Indexed: 12/11/2022]
Abstract
Adjusting to a wide range of light intensities is an essential feature of retinal rod bipolar cell (RBC) function. While persuasive evidence suggests this modulation involves phosphorylation by protein kinase C-alpha (PKCα), the targets of PKCα phosphorylation in the retina have not been identified. PKCα activity and phosphorylation in RBCs was examined by immunofluorescence confocal microscopy using a conformation-specific PKCα antibody and antibodies to phosphorylated PKC motifs. PKCα activity was dependent on light and expression of TRPM1, and RBC dendrites were the primary sites of light-dependent phosphorylation. PKCα-dependent retinal phosphoproteins were identified using a phosphoproteomics approach to compare total protein and phosphopeptide abundance between phorbol ester-treated wild type and PKCα knockout (PKCα-KO) mouse retinas. Phosphopeptide mass spectrometry identified over 1100 phosphopeptides in mouse retina, with 12 displaying significantly greater phosphorylation in WT compared to PKCα-KO samples. The differentially phosphorylated proteins fall into the following functional groups: cytoskeleton/trafficking (4 proteins), ECM/adhesion (2 proteins), signaling (2 proteins), transcriptional regulation (3 proteins), and homeostasis/metabolism (1 protein). Two strongly differentially expressed phosphoproteins, BORG4 and TPBG, were localized to the synaptic layers of the retina, and may play a role in PKCα-dependent modulation of RBC physiology. Data are available via ProteomeXchange with identifier PXD012906. SIGNIFICANCE: Retinal rod bipolar cells (RBCs), the second-order neurons of the mammalian rod visual pathway, are able to modulate their sensitivity to remain functional across a wide range of light intensities, from starlight to daylight. Evidence suggests that this modulation requires the serine/threonine kinase, PKCα, though the specific mechanism by which PKCα modulates RBC physiology is unknown. This study examined PKCα phosophorylation patterns in mouse rod bipolar cells and then used a phosphoproteomics approach to identify PKCα-dependent phosphoproteins in the mouse retina. A small number of retinal proteins showed significant PKCα-dependent phosphorylation, including BORG4 and TPBG, suggesting a potential contribution to PKCα-dependent modulation of RBC physiology.
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Affiliation(s)
- Colin M Wakeham
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Phillip A Wilmarth
- Proteomics Shared Resource, Oregon Health and Science University, Portland, OR 97239, USA
| | - Jennifer M Cunliffe
- Proteomics Shared Resource, Oregon Health and Science University, Portland, OR 97239, USA
| | - John E Klimek
- Proteomics Shared Resource, Oregon Health and Science University, Portland, OR 97239, USA
| | - Gaoying Ren
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Larry L David
- Proteomics Shared Resource, Oregon Health and Science University, Portland, OR 97239, USA; Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, OR 97239, USA
| | - Catherine W Morgans
- Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA.
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Cooke M, Magimaidas A, Casado-Medrano V, Kazanietz MG. Protein kinase C in cancer: The top five unanswered questions. Mol Carcinog 2017; 56:1531-1542. [PMID: 28112438 DOI: 10.1002/mc.22617] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 01/04/2017] [Accepted: 01/20/2017] [Indexed: 12/29/2022]
Abstract
Few kinases have been studied as extensively as protein kinase C (PKC), particularly in the context of cancer. As major cellular targets for the phorbol ester tumor promoters and diacylglycerol (DAG), a second messenger generated by stimulation of membrane receptors, PKC isozymes play major roles in the control of signaling pathways associated with proliferation, migration, invasion, tumorigenesis, and metastasis. However, despite decades of research, fundamental questions remain to be answered or are the subject of intense controversy. Primary among these unresolved issues are the role of PKC isozymes as either tumor promoter or tumor suppressor kinases and the incomplete understanding on isozyme-specific substrates and effectors. The involvement of PKC isozymes in cancer progression needs to be reassessed in the context of specific oncogenic and tumor suppressing alterations. In addition, there are still major hurdles in addressing isozyme-specific function due to the limited specificity of most pharmacological PKC modulators and the lack of validated predictive biomarkers for response, which impacts the translation of these agents to the clinic. In this review we focus on key controversial issues and upcoming challenges, with the expectation that understanding the intricacies of PKC function will help fulfill the yet unsuccessful promise of targeting PKCs for cancer therapeutics.
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Affiliation(s)
- Mariana Cooke
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Andrew Magimaidas
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Victoria Casado-Medrano
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Marcelo G Kazanietz
- Department of Systems Pharmacology and Translational Therapeutics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
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Zhao X, Rotenberg SA. Phosphorylation of Cdc42 effector protein-4 (CEP4) by protein kinase C promotes motility of human breast cells. J Biol Chem 2014; 289:25844-54. [PMID: 25086031 DOI: 10.1074/jbc.m114.577783] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Cdc42 effector protein-4 (CEP4) was recently identified by our laboratory to be a substrate of multiple PKC isoforms in non-transformed MCF-10A human breast cells. The significance of phosphorylated CEP4 to PKC-stimulated motility of MCF-10A cells was evaluated. Single site mutants at Ser residues embedded in potential PKC consensus sites (Ser(18), Ser(77), Ser(80), and Ser(86)) were individually replaced with Asp residues to simulate phosphorylation. Following expression in weakly motile MCF-10A cells, the S18D and S80D mutants each promoted increased motility, and the double mutant (S18D/S80D) produced a stronger effect. MS/MS analysis verified that Ser(18) and Ser(80) were directly phosphorylated by PKCα in vitro. Phosphorylation of CEP4 severely diminished its affinity for Cdc42 while promoting Rac activation and formation of filopodia (microspikes). In contrast, the phosphorylation-resistant double mutant S18A/S80A-CEP4 blocked CEP4 phosphorylation and inhibited motility of MCF-10A cells that had been stimulated with PKC activator diacylglycerol lactone. In view of the dissociation of phospho-CEP4 from Cdc42, intracellular binding partners were explored by expressing each CEP4 double mutant from a tandem affinity purification vector followed by affinity chromatography, SDS-PAGE, and identification of protein bands evident only with S18D/S80D-CEP4. One binding partner was identified as tumor endothelial marker-4 (TEM4; ARHGEF17), a guanine nucleotide exchange factor that is involved in migration. In motile cells expressing S18D/S80D-CEP4, knockdown of TEM4 inhibited both Rac activation and motility. These findings support a model in which PKC-mediated phosphorylation of CEP4 at Ser(18) and Ser(80) causes its dissociation from Cdc42, thereby increasing its affinity for TEM4 and producing Rac activation, filopodium formation, and cell motility.
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Affiliation(s)
- Xin Zhao
- From the Department of Chemistry and Biochemistry, Queens College, Flushing, New York 11367 and The Graduate Center, The City University of New York, New York, New York 10016
| | - Susan A Rotenberg
- From the Department of Chemistry and Biochemistry, Queens College, Flushing, New York 11367 and
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De S, Tsimounis A, Chen X, Rotenberg SA. Phosphorylation of α-tubulin by protein kinase C stimulates microtubule dynamics in human breast cells. Cytoskeleton (Hoboken) 2014; 71:257-72. [PMID: 24574051 PMCID: PMC4113324 DOI: 10.1002/cm.21167] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 11/18/2013] [Accepted: 02/03/2014] [Indexed: 01/27/2023]
Abstract
Protein kinase C (PKC) engenders motility through phosphorylation of α-tubulin at Ser-165 in nontransformed MCF-10A cells. Live cell imaging explored the impact of PKC-mediated phosphorylation on microtubule (MT) dynamics. MTs fluorescently labeled with GFP-α-tubulin were treated with diacylglycerol (DAG)-lactone (a membrane-permeable PKC activator), or cotransfected with a pseudophosphorylated S165D-α6-tubulin mutant. Each condition increased the dynamicity of MTs by stimulating the rate and duration of the growth phase and decreasing the frequency of catastrophe. In MDA-MB-231 metastatic breast cells where the intrinsic PKC activity is high, these MT growth parameters were also high but could be suppressed by expression of phosphorylation-resistant S165N-α6-tubulin or by treatment with a pan-PKC inhibitor (bis-indoleylmaleimide). Subcellular fractionation and immunofluorescence of MCF-10A cells showed that phosphorylation (via DAG-lactone) or pseudophosphorylation of α6-tubulin increased its partitioning into MTs as compared to controls, and produced longer, more stable MTs. Following expression of the plus-end binding protein GFP-EB1, DAG-lactone accelerated the formation and increased the number of nascent MTs. Expression of S165D-α6-tubulin promoted Rac1 activation and Rac1-dependent cell motility. These findings call attention to PKC-mediated phosphorylation of α-tubulin as a novel mechanism for controlling the dynamics of MTs that result in cell movement.
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Affiliation(s)
- Shatarupa De
- Department of Chemistry & Biochemistry, The City University of New York
- The Graduate Center, The City University of New York
| | - Areti Tsimounis
- Department of Biology of Queens College, The City University of New York
| | - Xiangyu Chen
- Department of Chemistry & Biochemistry, The City University of New York
- The Graduate Center, The City University of New York
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Dana D, Davalos AR, De S, Rathod P, Gamage RK, Huestis J, Afzal N, Zavlanov Y, Paroly SS, Rotenberg SA, Subramaniam G, Mark KJ, Chang EJ, Kumar S. Development of cell-active non-peptidyl inhibitors of cysteine cathepsins. Bioorg Med Chem 2013; 21:2975-87. [PMID: 23623677 DOI: 10.1016/j.bmc.2013.03.062] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Revised: 03/15/2013] [Accepted: 03/23/2013] [Indexed: 11/26/2022]
Abstract
Cysteine cathepsins are an important class of enzymes that coordinate a variety of important cellular processes, and are implicated in various types of human diseases. However, small molecule inhibitors that are cell-permeable and non-peptidyl in nature are scarcely available. Herein the synthesis and development of sulfonyloxiranes as covalent inhibitors of cysteine cathepsins are reported. From a library of compounds, compound 5 is identified as a selective inhibitor of cysteine cathepsins. Live cell imaging and immunocytochemistry of metastatic human breast carcinoma MDA-MB-231 cells document the efficacy of compound 5 in inhibiting cysteine cathepsin activity in living cells. A cell-motility assay demonstrates that compound 5 is effective in mitigating the cell-migratory potential of highly metastatic breast carcinoma MDA-MB-231 cells.
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Affiliation(s)
- Dibyendu Dana
- Department of Chemistry and Biochemistry, Queens College and the Graduate Center of The City University of New York, Queens, NY 11367-1597, USA
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