Browsing by Subject "Mitogen-Activated Protein Kinases"

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    Hyperactive Ras/MAPK signaling is critical for tibial nonunion fracture in neurofibromin-deficient mice
    (Oxford University Press, 2013-12-01) Sharma, Richa; Wu, Xiaohua; Rhodes, Steven D.; Chen, Shi; He, Yongzheng; Yuan, Jin; Li, Jiliang; Yang, Xianlin; Li, Xiaohong; Jiang, Li; Kim, Edward T.; Stevenson, David A.; Viskochil, David; Xu, Mingjiang; Yang, Feng-Chun; Department of Pediatrics, IU School of Medicine
    Neurofibromatosis type 1 (NF1) is a common genetic disorder affecting 1 in 3500 individuals. Patients with NF1 are predisposed to debilitating skeletal manifestations, including osteopenia/osteoporosis and long bone pseudarthrosis (nonunion fracture). Hyperactivation of the Ras/mitogen-activated protein kinase (MAPK) pathway in NF1 is known to underlie aberrant proliferation and differentiation in cell lineages, including osteoclast progenitors and mesenchymal stem cells (MSCs) also known as osteoblast progenitors (pro-OBLs). Our current study demonstrates the hyper Ras/MAPK as a critical pathway underlying the pathogenesis of NF1-associated fracture repair deficits. Nf1-deficient pro-OBLs exhibit Ras/MAPK hyperactivation. Introduction of the NF1 GTPase activating-related domain (NF1 GAP-related domain) in vitro is sufficient to rescue hyper Ras activity and enhance osteoblast (OBL) differentiation in Nf1−/− pro-OBLs and NF1 human (h) MSCs cultured from NF1 patients with skeletal abnormalities, including pseudarthrosis or scoliosis. Pharmacologic inhibition of mitogen-activated protein kinase kinase (MEK) signaling with PD98059 partially rescues aberrant Erk activation while enhancing OBL differentiation and expression of OBL markers, osterix and osteocalcin, in Nf1-deficient murine pro-OBLs. Similarly, MEK inhibition enhances OBL differentiation of hMSCs. In addition, PD98059 rescues aberrant osteoclast maturation in Nf1 haploinsufficient bone marrow mononuclear cells (BMMNCs). Importantly, MEK inhibitor significantly improves fracture healing in an NF1 murine model, Col2.3Cre
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    The roles of stress-activated Sty1 and Gcn2 kinases and proto-oncoprotein homologue Int6/eIF3e in responses to endogenous oxidative stress during histidine starvation
    (Elsevier, 2010-11-26) Nemoto, Naoki; Udagawa, Tsuyoshi; Ohira, Takahiro; Jiang, Li; Hirota, Kouji; Wilkinson, Caroline R. M.; Bähler, Jürg; Jones, Nic; Ohta, Kunihiro; Wek, Ronald C.; Asano, Katsura; Department of Biochemistry & Molecular Biology, IU School of Medicine
    In fission yeast, Sty1 and Gcn2 are important protein kinases regulating gene expression in response to amino acid starvation. The translation factor subunit eIF3e/Int6 promotes the Sty1-dependent response by increasing the abundance of Atf1, a transcription factor targeted by Sty1. While Gcn2 promotes expression of amino acid biosynthesis enzymes, the mechanism and function for Sty1 activation and Int6/eIF3e involvement during this nutrient stress is not understood. Here we show that mutants lacking sty1+ or gcn2+ display reduced viabilities during histidine depletion stress in a manner suppressible by the antioxidant, N-acetyl cysteine, suggesting that these protein kinases function to alleviate endogenous oxidative damage generated during nutrient starvation. Int6/eIF3e also promotes cell viability by a mechanism involving stimulation of the Sty1 response to oxidative damage. In further support of these observations, microarray data suggests that, during histidine starvation, int6Δ increases the duration of Sty1-activated gene expression linked to oxidative stress due to the initial attenuation of Sty1-dependent transcription. Moreover, loss of gcn2 induces the expression of a new set of genes not activated in wild-type cells starved for histidine. These genes encode heatshock proteins, redox enzymes and proteins involved in mitochondrial maintenance, in agreement with the idea that oxidative stress is imposed onto gcn2Δ cells. Furthermore, the early Sty1 activation promotes a rapid Gcn2 activation on histidine starvation. These results suggest that Gcn2, Sty1, and Int6/eIF3e are functionally integrated and cooperate to respond to oxidative stress that is generated during histidine starvation.