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Fibroblast growth factor-2 promotes catabolism via FGFR1-Ras-Raf-MEK1/2-ERK1/2 axis that coordinates with the PKC? pathway in human articular chondrocytes.

ABSTRACT: Fibroblast growth factor 2 (FGF-2) has been found to play an anti-anabolic and/or a catabolic role in adult human articular cartilage via regulation of multiple signaling pathways. Upon FGF-2 stimulation, a molecular crosstalk between the mitogen activated protein kinase (MAPK) and protein kinase C ? (PKC?) pathways are initiated, where PKC? positively regulates downstream MAPK signaling. In this study, we explored the relationship between fibroblast growth factor receptor 1 (FGFR1), Ras, and PKC? in FGF-2 signaling in human articular chondrocytes. Pathway-specific inhibition using both chemical inhibitors and siRNA targeting FGFR1 demonstrated that, upon FGF-2 stimulation, FGFR1 controlled both Ras and PKC? activation, which converged on the Raf-MEK1/2-ERK1/2 axis. No crosstalk was observed between Ras and PKC?. Quantitative PCR analyses revealed that both Ras and PKC? contributed to FGF-2-mediated upregulation of MMP-13, ADAMTS5, and repression of aggrecan gene. Correspondingly, FGF-2-mediated proteoglycan loss was effectively reversed by individual pathway-specific inhibitor of Ras, PKC?, and ERK1/2 in both 3-dimensional alginate bead culture and cartilage organ culture systems. Our findings suggest that FGFR1 interacts with FGF-2 and then activates Ras and PKC?, which concertedly drive MAPK signaling to mediate biological effects of FGF-2. Such an integration of dual inputs constitutes a novel mechanism of FGF-2 signaling cascade in human articular chondrocytes.

SUBMITTER: Yan D

PROVIDER: S-EPMC3684697 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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Fibroblast growth factor-2 promotes catabolism via FGFR1-Ras-Raf-MEK1/2-ERK1/2 axis that coordinates with the PKCδ pathway in human articular chondrocytes.

Yan Dongyao D Chen Di D Im Hee-Jeong HJ

Journal of cellular biochemistry 20120901 9

Fibroblast growth factor 2 (FGF-2) has been found to play an anti-anabolic and/or a catabolic role in adult human articular cartilage via regulation of multiple signaling pathways. Upon FGF-2 stimulation, a molecular crosstalk between the mitogen activated protein kinase (MAPK) and protein kinase C δ (PKCδ) pathways are initiated, where PKCδ positively regulates downstream MAPK signaling. In this study, we explored the relationship between fibroblast growth factor receptor 1 (FGFR1), Ras, and PK ...[more]

PMID: 22488450

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Project description:A switch from autophagy to apoptosis is implicated in chondrocytes during the osteoarthritis (OA) progression with currently unknown mechanism(s). In this study we utilized a flow fluid shear stress (FFSS) model in cultured chondrocytes and a unilateral anterior crossbite (UAC) animal model. We found that both FFSS and UAC actively induced endoplasmic reticulum stress (ERS) in the temporomandibular joints (TMJ) chondrocytes, as demonstrated by dramatic increases in expression of HSPA5, p-EIF2AK3, p-ERN1 and ATF6. Interestingly, both FFSS and UAC activated not only pro-death p-EIF2AK3-mediated ERS-apoptosis programs but also pro-survival p-ERN1-mediated autophagic flux in chondrocytes. Data from FFSS demonstrated that MTORC1, a downstream of p-ERN1, suppressed autophagy but promoted p-EIF2AK3 mediated ERS-apoptosis. Data from UAC model demonstrated that at early stage both the p-ERN1 and p-EIF2AK3 were activated and MTORC1 was inhibited in TMJ chondrocytes. At late stage, MTORC1-p-EIF2AK3-mediated ERS apoptosis were predominant, while p-ERN1 and autophagic flux were inhibited. Inhibition of MTORC1 by TMJ local injection of rapamycin in rats or inducible ablation of MTORC1 expression selectively in chondrocytes in mice promoted chondrocyte autophagy and suppressed apoptosis, and reduced TMJ cartilage loss induced by UAC. In contrast, MTORC1 activation by TMJ local administration of MHY1485 or genetic deletion of Tsc1, an upstream MTORC1 suppressor, resulted in opposite effects. Collectively, our results establish that aberrant mechanical loading causes cartilage degeneration by activating, at least in part, the MTORC1 signaling which modulates the autophagy and apoptosis programs in TMJ chondrocytes. Thus, inhibition of MTORC1 provides a novel therapeutic strategy for prevention and treatment of OA.Abbreviations : ACTB: actin beta; ATF6: activating transcription factor 6; BECN1: beclin 1; BFL: bafilomycin A1; CASP12: caspase 12; CASP3: caspase 3; DAPI: 4',6-diamidino-2-phenylindole; DDIT3: DNA-damage inducible transcript 3; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERS: endoplasmic reticulum stress; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; FFSS: flow fluid shear stress; HSPA5/GRP78/BiP: heat shock protein 5; LAMP2: lysosome-associated membrane protein 2; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin complex 1; OA: osteoarthritis; PRKAA1/2/AMPK1/2: protein kinase, AMP-activated, alpha 1/2 catalytic subunit; RPS6: ribosomal protein S6; Rapa: rapamycin; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; TG: thapsigargin; TMJ: temporomandibular joints; TSC1/2: tuberous sclerosis complex 1/2; UAC: unilateral anterior crossbite; UPR: unfolded protein response; XBP1: x-box binding protein 1.

Project description:Aberrant fibroblast growth factor receptor 3 (FGFR3) signaling disrupts chondrocyte proliferation and growth plate size and architecture, leading to various chondrodysplasias or bone overgrowth. These observations suggest that the duration, intensity and cellular context of FGFR signaling during growth plate chondrocyte maturation require tight, regulated control for proper bone elongation. However, the machinery fine-tuning FGFR signaling in chondrocytes is incompletely defined. We report here that neurofibromin, a Ras-GAP encoded by Nf1, has an overlapping expression pattern with FGFR1 and FGFR3 in prehypertrophic chondrocytes, and with FGFR1 in hypertrophic chondrocytes during endochondral ossification. Based on previous evidence that neurofibromin inhibits Ras-ERK signaling in chondrocytes and phenotypic analogies between mice with constitutive FGFR1 activation and Nf1 deficiency in Col2a1-positive chondrocytes, we asked whether neurofibromin is required to control FGFR1-Ras-ERK signaling in maturing chondrocytes in vivo. Genetic Nf1 ablation in Fgfr1-deficient chondrocytes reactivated Ras-ERK1/2 signaling in hypertrophic chondrocytes and reversed the expansion of the hypertrophic zone observed in mice lacking Fgfr1 in Col2a1-positive chondrocytes. Histomorphometric and gene expression analyses suggested that neurofibromin, by inhibiting Rankl expression, attenuates pro-osteoclastogenic FGFR1 signaling in hypertrophic chondrocytes. We also provide evidence suggesting that neurofibromin in prehypertrophic chondrocytes, downstream of FGFRs and via an indirect mechanism, is required for normal extension and organization of proliferative columns. Collectively, this study indicates that FGFR signaling provides an important input into the Ras-Raf-MEK-ERK1/2 signaling axis in chondrocytes, and that this input is differentially regulated during chondrocyte maturation by a complex intracellular machinery, of which neurofibromin is a critical component.

Project description:IntroductionThe importance of mechanical signals in normal and inflamed cartilage is well established. Chondrocytes respond to changes in the levels of proinflammatory cytokines and mechanical signals during inflammation. Cytokines like interleukin (IL)-1beta suppress homeostatic mechanisms and inhibit cartilage repair and cell proliferation. However, matrix synthesis and chondrocyte (AC) proliferation are upregulated by the physiological levels of mechanical forces. In this study, we investigated intracellular mechanisms underlying reparative actions of mechanical signals during inflammation.MethodsACs isolated from articular cartilage were exposed to low/physiologic levels of dynamic strain in the presence of IL-1beta. The cell extracts were probed for differential activation/inhibition of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascade. The regulation of gene transcription was examined by real-time polymerase chain reaction.ResultsMechanoactivation, but not IL-1beta treatment, of ACs initiated integrin-linked kinase activation. Mechanical signals induced activation and subsequent C-Raf-mediated activation of MAP kinases (MEK1/2). However, IL-1beta activated B-Raf kinase activity. Dynamic strain did not induce B-Raf activation but instead inhibited IL-1beta-induced B-Raf activation. Both mechanical signals and IL-1beta induced ERK1/2 phosphorylation but discrete gene expression. ERK1/2 activation by mechanical forces induced SRY-related protein-9 (SOX-9), vascular endothelial cell growth factor (VEGF), and c-Myc mRNA expression and AC proliferation. However, IL-1beta did not induce SOX-9, VEGF, and c-Myc gene expression and inhibited AC cell proliferation. More importantly, SOX-9, VEGF, and Myc gene transcription and AC proliferation induced by mechanical signals were sustained in the presence of IL-1beta.ConclusionsThe findings suggest that mechanical signals may sustain their effects in proinflammatory environments by regulating key molecules in the MAP kinase signaling cascade. Furthermore, the findings point to the potential of mechanosignaling in cartilage repair during inflammation.

Project description:Angiogenesis contributes fundamentally to embryonic development, tissue homeostasis, and wound healing. Basic fibroblast growth factor (FGF2) is recognized as the first proangiogenic molecule discovered, and it facilitates angiogenesis by activating FGF receptor 1 (FGFR1) signaling in endothelial cells. However, the precise roles of FGFR and the FGF/FGFR signaling axis in angiogenesis remain unclear, especially because of the contradictory phenotypes of in vivo FGF and FGFR gene deficiency models. Our previous study results suggested a potential role of posttranslational small ubiquitin-like modifier modification (SUMOylation), with highly dynamic regulatory features, in vascular development and disorder. Here, we identified SENP1-regulated endothelial FGFR1 SUMOylation at conserved lysines responding to proangiogenic stimuli, while SENP1 functioned as the deSUMOylase. Hypoxia-enhanced FGFR1 SUMOylation restricted the tyrosine kinase activation of FGFR1 by modulating the dimerization of FGFR1 and FGFR1 binding with its phosphatase PTPRG. Consequently, it facilitated the recruitment of FRS2α to VEGFR2 but limited additional recruitment of FRS2α to FGFR1, supporting the activation of VEGFA/VEGFR2 signaling in endothelial cells. Furthermore, SUMOylation-defective mutation of FGFR1 resulted in exaggerated FGF2/FGFR1 signaling but suppressed VEGFA/VEGFR2 signaling and the angiogenic capabilities of endothelial cells, which were rescued by FRS2α overexpression. Reduced angiogenesis and endothelial sprouting in mice bearing an endothelial-specific, FGFR1 SUMOylation-defective mutant confirmed the functional significance of endothelial FGFR1 SUMOylation in vivo. Our findings identify the reversible SUMOylation of FGFR1 as an intrinsic fine-tuned mechanism in coordinating endothelial angiogenic signaling during neovascularization; SENP1-regulated FGFR1 SUMOylation and deSUMOylation controls the competitive recruitment of FRS2α by FGFR1 and VEGFR2 to switch receptor-complex formation responding to hypoxia and normoxia angiogenic environments.

Dataset Information

Fibroblast growth factor-2 promotes catabolism via FGFR1-Ras-Raf-MEK1/2-ERK1/2 axis that coordinates with the PKC? pathway in human articular chondrocytes.

Publications

Fibroblast growth factor-2 promotes catabolism via FGFR1-Ras-Raf-MEK1/2-ERK1/2 axis that coordinates with the PKCδ pathway in human articular chondrocytes.

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