Protein Kinase Cζ Attenuates Hypoxia-induced Proliferation of Fibroblasts by Regulating MAP Kinase Phosphatase-1 Expression

Developmental Lung Biology Research Laboratory, Department of Pediatrics, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 05/2006; 17(4):1995-2008. DOI: 10.1091/mbc.E05-09-0869
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We have previously found that hypoxia stimulates proliferation of vascular fibroblasts through Galphai-mediated activation of ERK1/2. Here, we demonstrate that hypoxia also activates the atypical protein kinase Czeta (PKCzeta) isozyme and stimulates the expression of ERK1/2-specific phosphatase, MAP kinase phosphatase-1 (MKP-1), which attenuates ERK1/2-mediated proliferative signals. Replication repressor activity is unique to PKCzeta because the blockade of classical and novel PKC isozymes does not affect fibroblast proliferation. PKCzeta is phosphorylated upon prolonged (24 h) exposure to hypoxia, whereas ERK1/2, the downstream kinases, are maximally activated in fibroblasts exposed to acute (10 min) hypoxia. However, PKCzeta blockade results in persistent ERK1/2 phosphorylation and marked increase in hypoxia-induced replication. Similarly prolonged ERK1/2 phosphorylation and increase in hypoxia-stimulated proliferation are also observed upon blockade of MKP-1 activation. Because of the parallel suppressive actions of PKCzeta and MKP-1 on ERK1/2 phosphorylation and proliferation, the role of PKCzeta in the regulation of MKP-1 expression was evaluated. PKCzeta attenuation reduces MKP-1 expression, whereas PKCzeta overexpression increases MKP-1 levels. In conclusion, our results indicate for the first time that hypoxia activates PKCzeta, which acts as a terminator of ERK1/2 activation through the regulation of downstream target, MKP-1 expression and thus serves to limit hypoxia-induced proliferation of fibroblasts.

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Available from: Kurt Stenmark, Mar 10, 2014
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    • "Das et al. found that bovine pulmonary artery adventitial fibroblasts expressed cPKCα, βI and βII, nPKCδ and ɛ, and aPKCζ, but only cPKCβI and aPKCζ activations were associated with the exaggerated growth responses of pulmonary artery adventitial fibroblasts under chronic hypoxia condition [16,22]. However, Short et al. found that aPKCζ attenuates hypoxia-induced proliferation of fibroblasts by regulating MAP kinase phosphatase-1 (MKP-1) expression [23]. "
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    • "After 1 h, cell fractions were analyzed by western analyses. PKCz has been implicated in ERK1/2 activation and was therefore selected as the focused isotype (Short et al. 2006). The results shown in Fig. 3B indicate activated PKCz in membrane fractions (PKCz (M), row 1) whereas the inactivated forms are detected in the cytosolic fraction (PKCz (C), row 2). "
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    • "TGF-β signaling and retinoid acid signaling upregulate MKP-1 expression [53] [54]. Moreover, while PKCζ induces MKP-1 expression in response to hypoxia [55], PKCδ triggers MKP-1 degradation in glutamate-induced cell death [56]. In addition, MKP-1 is induced by several hormones, such as glucocorticoids , endocannabinoid and parathyroid [57] [58] [59]. "
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