Cyclic strain stress-induced mitogen-activated protein kinase (MAPK) phosphatase 1 expression in vascular smooth muscle cells is regulated by Ras/Rac-MAPK pathways.
Recently, we demonstrated that mechanical stress results in rapid phosphorylation or activation of platelet-derived growth factor receptors in vascular smooth muscle cells (VSMCs) followed by activation of mitogen-activated protein kinases (MAPKs) and AP-1 transcription factors (Hu, Y., Bock, G., Wick, G., and Xu, Q. (1998) FASEB J. 12, 1135-1142). Herein, we provide evidence that VSMC responses to mechanical stress also include induction of MAPK phosphatase-1 (MKP-1), which may serve as a negative regulator of MAPK signaling pathways. When rat VSMCs cultivated on a flexible membrane were subjected to cyclic strain stress (60 cycles/min, 5-30% elongation), induction of MKP-1 proteins and mRNA was observed in time- and strength-dependent manners. Concomitantly, mechanical forces evoked rapid and transient activation of all three members of MAPKs, i.e. extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal protein kinases (JNKs), or stress-activated protein kinases (SAPKs), and p38 MAPKs. Suramin, a growth factor receptor antagonist, completely abolished ERK activation, significantly blocked MKP-1 expression, but not JNK/SAPK and p38 MAPK activation, in response to mechanical stress. Interestingly, VSMC lines stably expressing dominant negative Ras (Ras N17) or Rac (Rac N17) exhibited a marked decrease in MKP-1 expression; the inhibition of ERK kinases (MEK1/2) by PD 98059 or of p38 MAPKs by SB 202190 resulted in a down-regulation of MKP-1 induction. Furthermore, overexpressing MKP-1 in VSMCs led to the dephosphorylation and inactivation of ERKs, JNKs/SAPKs, and p38 MAPKs and inhibition of DNA synthesis. Taken together, our findings demonstrate that mechanical stress induces MKP-1 expression regulated by two signal pathways, including growth factor receptor-Ras-ERK and Rac-JNK/SAPK or p38 MAPK, and that MKP-1 inhibits VSMC proliferation via MAPK inactivation. These results suggest that MKP-1 plays a crucial role in mechanical stress-stimulated signaling leading to VSMC growth and differentiation.
Li
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Institute for Biomedical Aging Research, Austrian Academy of Sciences, A-6020 Innsbruck, Austria.
Hu
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Y
Mayr
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Xu
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D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D054638:Dual Specificity Phosphatase 1; D019204:GTP-Binding Proteins / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000096:biosynthesis*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000473:pathology; D010749:Phosphoprotein Phosphatases; D010766:Phosphorylation; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis*; D051381:Rats; D015398:Signal Transduction; D013314:Stress, Mechanical; D020744:rac GTP-Binding Proteins; D018631:ras Proteins / Q000378:metabolism*
D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D018631:ras Proteins