Mitogen-activated protein kinase phosphatase-2 (MKP-2) is a type 1 nuclear dual specific phosphatase (DUSP) implicated in a number of cancers. We examined the role of MKP-2 in the regulation of MAP kinase phosphorylation, cell proliferation, and survival responses in mouse embryonic fibroblasts (MEFs) derived from a novel MKP-2 (DUSP-4) deletion mouse. We show that serum and PDGF induced ERK-dependent MKP-2 expression in wild type METs but not in MKP-2(-/-) MEFs. PDGF stimulation of sustained ERK phosphorylation was enhanced in MKP-2(-/-) MEFs, whereas anisomycin-induced JNK was only marginally increased. However, marked effects upon cell growth parameters were observed. Cellular proliferation rates were significantly reduced in MKP-2(-/-) MEFs and associated with a significant increase in cell doubling time. Infection with adenoviral MKP-2 reversed the decrease in proliferation. Cell cycle analysis revealed a block in G(2)/M phase transition associated with cyclin B accumulation and enhanced cdc2 phosphorylation. MEFs from MKP-2(-/-) mice also showed enhanced apoptosis when stimulated with anisomycin correlated with increased caspase-3 cleavage and gamma H2AX phosphorylation. Increased apoptosis was reversed by adenoviral MKP-2 infection and correlated with selective inhibition of JNK signaling. Collectively, these data demonstrate for the first time a critical non-redundant role fir MKP-2 in regulating cell cycle progression and apoptosis.

Background and purpose: Sphingosine‐1‐phosphate and its receptors may be involved in vascular smooth muscle cell (VSMC) proliferation following vascular injury. Here, we evaluate the effect of d ‐ erythro ‐ N , N ‐dimethylsphingosine (DMS), a sphingosine kinase (SK) inhibitor, on VSMC proliferation, apoptosis and neointimal formation. Experimental approach: Growth responses in vitro to fetal calf serum (FCS) were measured by [ 3 H]‐thymidine incorporation and extracellular signal‐regulated kinase‐1/2 (ERK‐1/2) activation in quiescent primary cultures of porcine VSMC in the presence and absence of various concentrations of the SK inhibitor DMS. In vivo treatment with DMS was delivered with a local endoluminal catheter, following balloon injury of coronary arteries. The artery intimal formation was investigated by angiography, myography and histomorphometry. Key results: In vitro experiments indicated that DMS induced a dose‐dependent reduction in [ 3 H]‐thymidine incorporation and ERK‐1/2 activation via a protein kinase C (PKC) independent mechanism with an IC 50 value of 12 ± 6 and 15 ± 10 µM respectively. DMS also reduced Akt signalling. Four weeks following in vivo delivery of DMS, complete functional endothelial regeneration was observed in all treatment groups, with significant reduction of intimal formation (vehicle 23.7 ± 4.6% vs. DMS infusion 8.92 ± 2.9%, P < 0.05). Conclusions and implications: Taken together, these results demonstrate that local administration of the SK inhibitor, DMS, reduced neointimal formation, and this effect could involve inhibition of ERK‐1/2 and Akt signalling, and modulation of smooth muscle growth.