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 phosphory lation or activation of platelet-derived growth factor receptors in vascula r smooth muscle cells (VSMCs) followed by activation of mitogen-activated p rotein kinases (MAPKs) and AP-1 transcription factors (Hu, Y,, Beck, G,, Wi ck, G., and Xu, Q, (1998) FASEB J. 12, 1135-1142). Herein, we provide evide nce that VSMC responses to mechanical stress also include induction of MAPK phosphatase-1 (MKP-1), which may serve as a negative regulator of MAPK sig naling pathways. When rat VSMCs cultivated on a flexible membrane were subj ected to cyclic strain stress (60 cycles/ min, 5-30% elongation), induction of MKP-1 proteins and mRNA was observed in time- and strength-dependent ma nners. Concomitantly, mechanical forces evoked rapid and transient activati on of all three members of MAPKs, i.e. extracellular signal-regulated kinas es (ERKs), c-Jun NH2-terminal protein kinases (JNKs), or stress-activated p rotein kinases (SAPKs), and p38 MAPKs. Suramin, a growth factor receptor an tagonist, completely abolished ERK activation, significantly blocked MKP-1 expression, but not JNK/SAPKs and p38 MAPK activation, in response to mecha nical stress. Interestingly, VSMC lines stably expressing dominant negative Ras (Ras N17) or Rac (Rac N17) exhibited a marked decrease in MKP-1 expres sion; the inhibition of ERK kinases (MEK1/2) by PD 98059 or of p38 MAPKs by SE 202190 resulted in a down-regulation of MKP-1 induction. Furthermore, o verexpressing MKP-1 in VSMCs led to the dephosphorylation and inactivation of ERKs, JNKs/SAPKs, and p38 MAPKs and inhibition of DNA synthesis. Taken t ogether, our findings demonstrate that mechanical stress induces MKP-1 expr ession regulated by two signal pathways, including growth factor receptor-R as-ERK and Rac-JNK/SAPK or p38 MAPK, and that MKP-1 inhibits VSMC prolifera tion via MAPK inactivation. These results suggest that MKP-1 plays a crucia l role in mechanical stress-stimulated signaling leading to VSMC growth and differentiation.