Induction of mitogen-activated protein kinase phosphatase 1 by the stress-activated protein kinase signaling pathway but not by extracellular signal-regulated kinase in fibroblasts

The intracellular mechanisms involved in the activation of extracellular signal-regulated kinase (ERK) are relatively well understood. However, the intracellular signaling pathways which regulate the termination of ERK activity remain to be elucidated. Mitogen-activated protein kinase phosphatase 1 (MKP-1) has been shown to dephosphorylate and inactivate ERK in vitro and in vivo. In the present study, we show in NIH3T3 fibroblasts that activation of the stress-activated protein kinase (SAPK) pathway by either specific extracellular stress stimuli or via induction of MEKK, an upstream kinase of SAPK, results in MKP-1 gene expression, In contrast, selective stimulation of the ERK pathway by 12-O-tetradecanoylphorbol-13-acetate or following expression of constitutively active MEK, the upstream dual specificity kinase of ERK did not induce the transcription of MKP-1, Hence, these findings demonstrate the existence of cross-talk between the ERK and SAPK signaling cascades since activation of SAPK induced the expression of MKP-1 that can inactivate ERK, This mechanism may modulate the cellular response to stimuli which employ the SAPK signal transduction pathway.