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Matta C, Mobasheri A, Gergely P, Zákány R. Ser/Thr-phosphoprotein phosphatases in chondrogenesis: neglected components of a two-player game. Cell Signal 2014; 26:2175-85. [PMID: 25007994 DOI: 10.1016/j.cellsig.2014.06.013] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 06/27/2014] [Indexed: 12/13/2022]
Abstract
Protein phosphorylation plays a determining role in the regulation of chondrogenesis in vitro. While signalling pathways governed by protein kinases including PKA, PKC, and mitogen-activated protein kinases (MAPK) have been mapped in great details, published data relating to the specific role of phosphoprotein phosphatases (PPs) in differentiating chondroprogenitor cells or in mature chondrocytes is relatively sparse. This review discusses the known functions of Ser/Thr-specific PPs in the molecular signalling pathways of chondrogenesis. PPs are clearly equally important as protein kinases to counterbalance the effect of reversible protein phosphorylation. Of the main Ser/Thr PPs, some of the functions of PP1, PP2A and PP2B have been characterised in the context of chondrogenesis. While PP1 and PP2A appear to negatively regulate chondrogenic differentiation and maintenance of chondrocyte phenotype, calcineurin is an important stimulatory mediator during chondrogenesis but becomes inhibitory in mature chondrocytes. Furthermore, PPs are implicated to be mediators during the pathogenesis of osteoarthritis that makes them potential therapeutic targets to be exploited in the close future. Among the many yet unexplored targets of PPs, modulation of plasma membrane ion channel function and participation in mechanotransduction pathways are emerging novel aspects of signalling during chondrogenesis that should be further elucidated. Besides the regulation of cellular ion homeostasis, other potentially significant novel roles for PPs during the regulation of in vitro chondrogenesis are discussed.
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Affiliation(s)
- Csaba Matta
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Nagyerdei krt. 98, H-4032, Debrecen, Hungary; School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Duke of Kent Building, Guildford, Surrey GU2 7XH, United Kingdom.
| | - Ali Mobasheri
- School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Duke of Kent Building, Guildford, Surrey GU2 7XH, United Kingdom; Arthritis Research UK Centre for Sport, Exercise and Osteoarthritis, Arthritis Research UK Pain Centre, Medical Research Council and Arthritis Research UK Centre for Musculoskeletal Ageing Research, University of Nottingham, Queen's Medical Centre, Nottingham, NG7 2UH, United Kingdom; Center of Excellence in Genomic Medicine Research (CEGMR), King Fahd Medical Research Center (KFMRC), King AbdulAziz University, Jeddah, 21589, Kingdom of Saudi Arabia
| | - Pál Gergely
- Department of Medical Chemistry, Faculty of Medicine, University of Debrecen, Nagyerdei krt. 98, H-4032, Debrecen, Hungary
| | - Róza Zákány
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Nagyerdei krt. 98, H-4032, Debrecen, Hungary
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Matta C, Mobasheri A. Regulation of chondrogenesis by protein kinase C: Emerging new roles in calcium signalling. Cell Signal 2014; 26:979-1000. [PMID: 24440668 DOI: 10.1016/j.cellsig.2014.01.011] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 01/09/2014] [Indexed: 01/14/2023]
Abstract
During chondrogenesis, complex intracellular signalling pathways regulate an intricate series of events including condensation of chondroprogenitor cells and nodule formation followed by chondrogenic differentiation. Reversible phosphorylation of key target proteins is of particular importance during this process. Among protein kinases known to be involved in these pathways, protein kinase C (PKC) subtypes play pivotal roles. However, the precise function of PKC isoenzymes during chondrogenesis and in mature articular chondrocytes is still largely unclear. In this review, we provide a historical overview of how the concept of PKC-mediated chondrogenesis has evolved, starting from the first discoveries of PKC isoform expression and activity. Signalling components upstream and downstream of PKC, leading to the stimulation of chondrogenic differentiation, are also discussed. Although it is evident that we are only at the beginning to understand what roles are assigned to PKC subtypes during chondrogenesis and how they are regulated, there are many yet unexplored aspects in this area. There is evidence that calcium signalling is a central regulator in differentiating chondroprogenitors; still, clear links between intracellular calcium signalling and prototypical calcium-dependent PKC subtypes such as PKCalpha have not been established. Exploiting putative connections and shedding more light on how exactly PKC signalling pathways influence cartilage formation should open new perspectives for a better understanding of healthy as well as pathological differentiation processes of chondrocytes, and may also lead to the development of novel therapeutic approaches.
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Affiliation(s)
- Csaba Matta
- Department of Anatomy, Histology and Embryology, Medical and Health Science Centre, University of Debrecen, Nagyerdei krt. 98, H-4032 Debrecen, Hungary.
| | - Ali Mobasheri
- D-BOARD European Consortium for Biomarker Discovery, Arthritis Research UK Centre for Sport, Exercise and Osteoarthritis, Arthritis Research UK Pain Centre, Medical Research Council and Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Medicine, Faculty of Medicine and Health Sciences, The University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, United Kingdom; School of Pharmacy, University of Bradford, Richmond Road, Bradford BD7 1DP, United Kingdom; School of Life Sciences, University of Bradford, Richmond Road, Bradford BD7 1DP, United Kingdom; Center of Excellence in Genomic Medicine Research (CEGMR), King Abdulaziz University, Jeddah 21589, Saudi Arabia
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Kim D, Song J, Kim S, Park HM, Chun CH, Sonn J, Jin EJ. MicroRNA-34a modulates cytoskeletal dynamics through regulating RhoA/Rac1 cross-talk in chondroblasts. J Biol Chem 2012; 287:12501-9. [PMID: 22351754 DOI: 10.1074/jbc.m111.264382] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MicroRNAs (miRNAs) have been implicated in various cellular processes, such as cell fate determination, cell death, and tumorigenesis. In the present study, we investigated the role of miRNA-34a (miR-34a) in the reorganization of the actin cytoskeleton, which is essential for chondrocyte differentiation. miRNA arrays to identify genes that appeared to be up-regulated or down-regulated during chondrogenesis were applied with chondrogenic progenitors treated with JNK inhibitor. PNA-based antisense oligonucleotides and miRNA precursor were used for investigation of the functional roles of miR-34a. We found that, in chick chondroprogenitors treated with JNK inhibitor, which suppresses chondrogenic differentiation, the expression levels of miR-34a and RhoA1 are up-regulated through modulation of Rac1 expression. Blockade of miR-34a via the use of PNA-based antisense oligonucleotides was associated with decreased protein expression of RhoA (a known modulator of stress fiber expression), down-regulation of stress fibers, up-regulation of Rac1, and recovery of protein level of type II collagen. miR-34a regulates RhoA/Rac1 cross-talk and negatively modulates reorganization of the actin cytoskeleton, which is one of the essential processes for establishing chondrocyte-specific morphology.
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Affiliation(s)
- Dongkyun Kim
- Department of Biological Sciences, College of Natural Sciences, Wonkwang University, Iksan, Chunbuk 570-749, Korea
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Lee SJ, Jeon HB, Lee JH, Yoo JS, Chun JS, Yoo YJ. Identification of proteins differentially expressed during chondrogenesis of mesenchymal cells. FEBS Lett 2004; 563:35-40. [PMID: 15063719 DOI: 10.1016/s0014-5793(04)00243-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2004] [Revised: 02/19/2004] [Accepted: 02/25/2004] [Indexed: 10/26/2022]
Abstract
We performed comparative proteome analysis of mesenchymal cells and chondrocytes to identify proteins differentially expressed during chondrogenesis. Nine such proteins were identified. Type II collagen, matrilin-1, carbonic anhydrase-II (CA-II), 3'-phosphoadenosine 5'-phosphosulfate (PAPS) synthetase-2, and aldo-keto reductase were increased during chondrogenesis, whereas cellular retinoic acid binding protein-I (CRABP-I), CRABP-II, cytoplasmic type 5 actin, and fatty acid binding protein were decreased or almost disappeared. Expression of type II collagen, matrilin-1, PAPS synthetase-2, and CA-II was regulated by extracellular signal-regulated protein kinase, protein kinase C, and p38 kinase, signaling molecules known to regulate chondrogenesis.
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Affiliation(s)
- Sun Joo Lee
- Department of Life Science, Kwangju Institute of Science and Technology, 1 Oryong-dong, Buk-gu, Gwangju 500-712, South Korea
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Oh CD, Kim SJ, Ju JW, Song WK, Kim JH, Yoo YJ, Chun JS. Immunosuppressant rapamycin inhibits protein kinase C alpha and p38 mitogen-activated protein kinase leading to the inhibition of chondrogenesis. Eur J Pharmacol 2001; 427:175-85. [PMID: 11567647 DOI: 10.1016/s0014-2999(01)01241-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Immunosuppressants are now known to modulate bone metabolism, including bone formation and resorption. Because cartilage, formed by differentiated chondrocytes, serves as a template for endochondral bone formation, we examined the effects of the immunosuppressant rapamycin on the chondrogenesis of mesenchymal cells and on the cell signaling that is required for chondrogenesis, such as protein kinase C, extracellular signal-regulated kinase-1 (ERK-1), and p38 mitogen-activated protein (MAP) kinase pathways. Rapamycin inhibited the expression of type II collagen and the accumulation of sulfate glycosaminoglycan, indicating inhibition of the chondrogenesis of mesenchymal cells. Rapamycin treatment did not affect precartilage condensation, but it prevented cartilage nodule formation. Exposure of chondrifying mesenchymal cells to rapamycin blocked activation of the protein kinase C alpha and p38 MAP kinase, but had no discernible effect on ERK-1 signaling. Selective inhibition of PKCalpha or p38 MAP kinase activity, which is dramatically increased during chondrogenesis, with specific inhibitors in the absence of rapamycin blocked the chondrogenic differentiation of mesenchymal cells. Taken together, our data indicate that the immunosuppressant rapamycin inhibits the chondrogenesis of mesenchymal cells at the post-precartilage condensation stage by modulating signaling pathways including those of PKCalpha and p38 MAP kinase.
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Affiliation(s)
- C D Oh
- National Research Laboratory, Department of Life Science, Kwangju Institute of Science and Technology, Buk-Gu, Kwangju 500-712, South Korea
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Yoon YM, Oh CD, Kang SS, Chun JS. Protein kinase A regulates chondrogenesis of mesenchymal cells at the post-precartilage condensation stage via protein kinase C-alpha signaling. J Bone Miner Res 2000; 15:2197-205. [PMID: 11092400 DOI: 10.1359/jbmr.2000.15.11.2197] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Chondrogenesis of mesenchymal cells during in vitro micromass culture requires the generation of cyclic adenosine monophosphate (cAMP) and subsequent activation of cAMP-dependent protein kinase A (PKA). In this study, we investigated the regulatory activity of PKA during chondrogenesis of chick limb bud mesenchymal cells. PKA activity was high in 1-day and 2-day cultures, which was followed by a slight decrease in 4-day and 5-day old cultures. Inhibition of PKA blocked chondrogenesis. It did not affect precartilage condensation, but it blocked the progression from the precartilage condensation stage to cartilage nodule formation. The PKA inhibition-induced blockage of chondrogenesis was accompanied by an altered expression of N-cadherin. Although expression of N-cadherin was detected during the early period of chondrogenesis, it became reduced as chondrogenesis proceeded. Still, inhibition of PKA maintained expression of N-cadherin throughout the micromass culture period. The inhibition of PKA did not affect expression of protein kinase C-alpha (PKCalpha), PKCepsilon, PKCdelta, and PKClambda/iota, which are the isoforms expressed in differentiating mesenchymal cells. However, PKA inhibition completely blocked activation of PKCalpha. Because PKC activity regulates N-cadherin expression and chondrogenesis, the PKA-mediated regulation of PKCalpha appears to be responsible for the PKA regulation of N-cadherin expression and chondrogenesis. Taken together, our results suggest that PKA regulates chondrogenesis by activating PKCalpha at the stage of post-precartilage condensation.
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Affiliation(s)
- Y M Yoon
- Department of Life Science, Kwangju Institute of Science and Technology, Korea
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Abstract
The long bones of the developing skeleton, such as those of the limb, arise from the process of endochondral ossification, where cartilage serves as the initial anlage element and is later replaced by bone. One of the earliest events of embryonic limb development is cellular condensation, whereby pre-cartilage mesenchymal cells aggregate as a result of specific cell-cell interactions, a requisite step in the chondrogenic pathway. In this review an extensive examination of historical and recent literature pertaining to limb development and mesenchymal condensation has been undertaken. Topics reviewed include limb initiation and axial induction, mesenchymal condensation and its regulation by various adhesion molecules, and regulation of chondrocyte differentiation and limb patterning. The complexity of limb development is exemplified by the involvement of multiple growth factors and morphogens such as Wnts, transforming growth factor-beta and fibroblast growth factors, as well as condensation events mediated by both cell-cell (neural cadherin and neural cell adhesion molecule) and cell-matrix adhesion (fibronectin, proteoglycans and collagens), as well as numerous intracellular signaling pathways transduced by integrins, mitogen activated protein kinases, protein kinase C, lipid metabolites and cyclic adenosine monophosphate. Furthermore, information pertaining to limb patterning and the functional importance of Hox genes and various other signaling molecules such as radical fringe, engrailed, Sox-9, and the Hedgehog family is reviewed. The exquisite three-dimensional structure of the vertebrate limb represents the culmination of these highly orchestrated and strictly regulated events. Understanding the development of cartilage should provide insights into mechanisms underlying the biology of both normal and pathologic (e.g. osteoarthritis) adult cartilage.
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Affiliation(s)
- A M DeLise
- Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Lim YB, Kang SS, Park TK, Lee YS, Chun JS, Sonn JK. Disruption of actin cytoskeleton induces chondrogenesis of mesenchymal cells by activating protein kinase C-alpha signaling. Biochem Biophys Res Commun 2000; 273:609-13. [PMID: 10873653 DOI: 10.1006/bbrc.2000.2987] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Disruption of actin cytoskeleton with cytochalasin D has been known to induce chondrogenic differentiation of chick embryo limb bud mesenchymal cells. However, the mechanism(s) for the induction of chondrogenesis by cytochalasin D is not yet clearly known. In the present study, we examined possible involvement of protein kinase C (PKC) and extracellular signal-regulated protein kinase (Erk-1) in chondrogenesis of mesenchymal cells induced by disruption of actin cytoskeleton. Disruption of actin cytoskeleton with cytochalasin D or latrunculin B induced chondrogenesis of mesenchymal cells cultured at subconfluent cell density, as determined by type II collagen expression. Among the expressed PKC isoforms, cytochalasin D dramatically increased expression and activation of PKCalpha in a dose-dependent manner, and inhibition or downregulation of PKCalpha blocked cytochalasin D-induced chondrogenesis. Cytochalasin D also downregulated Erk-1 phosphorylation that is associated with chondrogenesis. Our results, therefore, suggest that disruption of actin cytoskeleton induces chondrogenesis of mesenchymal cells by activating PKCalpha and by inhibiting Erk-1 signaling.
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Affiliation(s)
- Y B Lim
- Department of Biology, Teacher's College, Taegu, 702-701, Korea
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Kulyk WM, Franklin JL, Hoffman LM. Sox9 expression during chondrogenesis in micromass cultures of embryonic limb mesenchyme. Exp Cell Res 2000; 255:327-32. [PMID: 10694448 DOI: 10.1006/excr.1999.4784] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sox9 plays a crucial role in chondrogenesis. It encodes an HMG-domain transcription factor that activates an enhancer in the gene for type II collagen (Col2a1), a principal cartilage matrix protein. We have characterized the temporal pattern of Sox9 RNA expression in micromass culture, a widely used in vitro model for the analysis of embryonic cartilage differentiation. Cultures were prepared from distal subridge mesenchyme of the stage 24/25 chick embryo wing bud, which undergoes uniform chondrogenic differentiation in vitro. The early "prechondrogenic" phase of culture was characterized by the activation of Sox9 RNA expression, which preceded detectable upregulation of Col2a1 transcription. Sox9 RNA levels peaked between 20 and 65 h of culture, a phase of progressive Col2a1 transcript accumulation, then declined in the mature cartilage of 120-h cultures. Staurosporine treatment enhanced chondrogenesis in micromass culture by inducing a rapid quantitative increase in Sox9 transcript levels. However, PMA, a phorbol ester that inhibits Col2a1 expression and chondrocyte differentiation, had an unexpectedly modest effect on Sox9 RNA accumulation.
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Affiliation(s)
- W M Kulyk
- Department of Anatomy, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E5, Canada.
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Ward KW, Rogers EH, Hunter ES. Dysmorphogenic effects of a specific protein kinase C inhibitor during neurulation. Reprod Toxicol 1998; 12:525-34. [PMID: 9763244 DOI: 10.1016/s0890-6238(98)00032-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Protein kinase C (PKC) plays a key role in signal transduction and is an important mediator of events throughout development. However, no information exists regarding the effect of a specific PKC inhibitor on mammalian embryogenesis during neurulation. This investigation was undertaken to examine the effects of a specific inhibitor of PKC, as well as inhibitors of other important kinases, on cultured mouse embryos. CD-1 mouse embryos (3 to 6 somite stage) were exposed to bisindolylmaleimide I (a specific PKC inhibitor) as well as specific inhibitors of PKA, PKG, and MAP kinase kinase for 24 h. The PKC inhibitor was a potent embryotoxicant and elicited malformations at concentrations as low as 0.01 microM. Inhibitors of other kinases also produced malformations but at much higher concentrations than those required to produce similar defects with the PKC inhibitor. These data suggest that PKC plays an important role in mammalian neurulation. Further research is required to clarify the mechanism by which PKC inhibition at this developmental stage produces malformations and the potential effects of environmental toxicants with PKC inhibitory properties on this signal transduction pathway.
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Affiliation(s)
- K W Ward
- Curriculum in Toxicology, University of North Carolina at Chapel Hill, USA
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Chang SH, Oh CD, Yang MS, Kang SS, Lee YS, Sonn JK, Chun JS. Protein kinase C regulates chondrogenesis of mesenchymes via mitogen-activated protein kinase signaling. J Biol Chem 1998; 273:19213-9. [PMID: 9668109 DOI: 10.1074/jbc.273.30.19213] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A possible regulatory mechanism of protein kinase C (PKC) in the chondrogenesis of chick limb bud mesenchymes has been investigated. Inhibition or down-regulation of PKC resulted in the activation of a mitogen-activated protein kinase subtype Erk-1 and the inhibition of chondrogenesis. On the other hand, inhibition of Erk-1 with PD98059 enhanced chondrogenesis and relieved PKC-induced blockage of chondrogenesis. Erk-1 inhibition, however, did not affect expression and subcellular distribution of PKC isoforms expressed in mesenchymes nor cell proliferation. The results suggest that PKC regulates chondrogenesis by modulating Erk-1 activity. Inhibition or depletion of PKC inhibited proliferation of chondrogenic competent cells, and Erk-1 inhibition did not affect PKC modulation of cell proliferation. However, PKC-induced modulation of expression of cell adhesion molecules involved in precartilage condensation was reversed by the inhibition of Erk-1. Expression of N-cadherin was detected at the early period of chondrogenesis. Inhibition or depletion of PKC induced sustained expression of N-cadherin, and Erk-1 inhibition blocked the effects of PKC modulation. The expression of integrin alpha5 beta1 and fibronectin was found to be increased transiently during chondrogenesis. Depletion or inhibition of PKC caused a continuous increase of the expression of these molecules throughout the culture period, and Erk-1 inhibition abolished the modulating effects of PKC. Because reduction of the examined cell adhesion molecule expression is a prerequisite for the progression of chondrogenesis after cell condensation, our results indicate that PKC regulates chondrogenesis by modulating expression of these molecules via Erk-1 signaling.
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Affiliation(s)
- S H Chang
- Department, Kyungpook National University, Taegu 702-701, Korea
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Lee YS, Chuong CM. Activation of protein kinase A is a pivotal step involved in both BMP-2- and cyclic AMP-induced chondrogenesis. J Cell Physiol 1997; 170:153-65. [PMID: 9009144 DOI: 10.1002/(sici)1097-4652(199702)170:2<153::aid-jcp7>3.0.co;2-n] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We studied the roles of protein kinase A (PKA) activation and cyclic AMP response element binding protein (CREB) phosphorylation in chondrogenesis using serum-free chicken limb bud micromass cultures as a model system. We showed the following points: 1) in micromass cultures, activation of PKA enhances chondrogenesis and increases the phosphorylation of CREB; 2) BMP-2, a chondrogenic stimulator, increases PKA activity and the level of phosphorylated CREB (P-CREB); 3) H8, a PKA inhibitor, inhibits chondrogenesis; 4) the chondrogenic activities of BMP-2 and cAMP are suppressed by H8; and 5) long-term TPA treatment (a protein kinase C (PKC) modulator) inhibits chondrogenesis and decreases the levels of CREB and P-CREB. These results suggest that activation of PKA is a physiological event during chondrogenesis that is involved in the chondrogenic effects of both BMP-2 and cyclic AMP (cAMP)-dependent pathways.
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Affiliation(s)
- Y S Lee
- Department of Pathology, University of Southern California, Los Angeles 90033, USA
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Nerve dependent sulphated glycosaminoglycan synthesis in limb regeneration of the newt Pleurodeles waltl. ACTA ACUST UNITED AC 1995; 204:509-512. [DOI: 10.1007/bf00360859] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/1995] [Accepted: 02/17/1995] [Indexed: 10/26/2022]
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