Positive regulation of ERK activation and MKP-1 expression by peroxovanadium complex bpV (phen).

Lower micromolar concentrations of peroxovanadium compound potassium bisperoxo(1,10-phenanthroline)oxovanadate (V) [bpV (phen)] stimulate RINm5F cell metabolic activity. 1 and 3 micromol/L bpV (phen) induces strong and sustained activation of extracellular signal-regulated kinase (ERK). However, it seems that bpV (phen) does not effect c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) phosphorylation. In addition, bpV (phen) induces mitogen-activated protein kinase phosphatase-1 (MKP-1) expression. We found that ERK activation could be completely abolished if RINm5F cells were incubated with both bpV (phen) and PD 98059, a specific inhibitor of upstream ERK kinase MEK1. On the other hand, this combined treatment up-regulated activation of stress kinases, JNK and p38 MAPK, significantly suppressed MKP-1 expression and induced cell death. Thus, our results suggest that the mechanism underlying bpV (phen) survival-enhancing effect could be associated with induced ERK activation and MKP-1 expression.

MKP-1 as a target for pharmacological manipulations in PC12 cell survival.

Dual specificity mitogen activated protein kinase phosphatase-1 (MKP-1) inactivates extracellular signal-regulated kinase (ERK), p38 and/or c-jun N-terminal protein kinase (JNK) by dephosphorylation via a negative feed-back loop. The aim of the present study was to assess the role of expression of MKP-1 and phosphorylation status of mitogen-activated protein kinases (MAPKs) in promoting cell survival in PC12 cells. We used FK506 and three different monoperoxovanadium complexes (mpVs) as pharmacological tools for manipulation of MKP-1 expression. Peroxovanadium compounds, known to be insulinomimetic agents and protein tyrosine phosphatase inhibitors, are cytotoxic to the cells, they activate JNK and down-regulate MPK-1. On the other hand, FK 506 has transient effect on ERK activation. However, when the agents are used in combination, ERK phosphorylation is prolonged and intensified, MKP-1 expression is increased, and cell survival is enhanced. The concomitant alterations observed in intensities and duration of phospho-ERKs and phospho-JNKs signals suggest that monoperoxovanadium complexes in combination with FK 506 enhance survival of PC12 cells by an induction of MKP-1 expression.

Differential regulation of JNK activation and MKP-1 expression by peroxovanadium complexes.

Bisperoxovanadium complexes have been identified as insulinomimetic agents and protein tyrosine phosphatase inhibitors. The aim of the present study was to examine the effects of the most potent bisperoxovanadium complex, potassium bisperoxo (1,10-phenanthroline) oxovanadate (V) [bpV(phen)], on expression and activation of c-jun N-terminal protein kinases (JNK) and on expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) in different cell lines. We compared the effects of bpV(phen) with the effects of tumor necrosis factor-alpha (TNF-alpha), a known regulator of JNK phosphorylation and inducer of MKP-1. Treatment with bpV(phen) causes significant and sustained down-regulation of MKP-1 expression both in PC12 and HeLa cells. In contrast, TNF-alpha induces MKP-1 expression in PC12 cells and does not alter MKP-1 expression in HeLa cells. Both bpV(phen) and TNF-alpha induce MKP-1 expression in OVCAR-3 cell line but with different dynamics: TNF-alpha causes transient and bpV(phen) sustained induction of MKP-1 expression. Temporal pattern of level of MKP-1 expression correlates with the regulation of JNK phosphorylation by bpV(phen) and TNF-alpha in PC12 cells. However, no detectable phospho-JNK signal is observed in either OVCAR-3 or HeLa cells treated with bpV(phen). In contrast, TNF-alpha causes strong and sustained JNK phosphorylation in OVCAR-3 cell line, and strong but transient JNK activation in HeLa cells. BpV(phen) and TNF-alpha does not alter JNK expression in any of the cell lines studied. We demonstrate that the effect of two stressors, bpV(phen) and TNF-alpha, on MKP-1 expression and JNK phosphorylation are strikingly different, depending on the cell type. These results suggest the possible role of MKP-1 in regulation of JNK phosphorylation in both PC12 and OVCAR-3 cell lines treated with bpV(phen).