👤 Caroline E Nunes-Xavier

MAPK (MAP kinase) phosphatase 3 (DUSP6/MKP3) is a cytosolic MKP (MAPK phosphatase) that regulates negatively ERK1/2 downstream to growth factor or apoptotic signaling. Transcription of DUSP6 gene is activated through the ERK1/2 pathway, which constitutes a feedback regulatory loop of ERK1/2 activation. However, the regulation of the function of the DUSP6/MKP3 protein is poorly known. MKP3 possesses a linker region between its N-terminal MAPK-binding domain and its C-terminal catalytic domain, which is conserved in the related MKPs DUSP7/MKPX and DUSP9/MKP4. In MKP3, the interdomain linker region contains a secondary ERK1/2 binding motif and an active nuclear export sequence. Here, we report that MKP3 protein levels are decreased in cells upon apoptotic stimulation in a caspase-dependent manner, and we identify a novel MKP3 regulatory mechanism mediated by the pro-apoptotic protease caspase-3, which involves the MKP3 interdomain linker region. Active caspase-3 targeted the linker region of MKP3 at several residues, rendering N-terminal and C-terminal MKP3 fragments that contain specific arrangements of nuclear export sequence and ERK1/2 interaction motifs. MKP3 caspase-3-generated fragments displayed differential properties to regulate ERK1/2 nuclear/cytosolic localization and activity. Our results indicate that caspase-3 cleavage of MKP3 down-regulates MKP3 full length and renders active MKP3 fragments, which may participate in novel regulatory pathways controlling the subcellular localization and activation of ERK1/2 during apoptosis. Show less

Different levels of regulation account for the inactivation of MAP kinases by MAPK phosphatases (MKPs), in a cell type- and stimuli-dependent manner. MCF-7 human breast carcinoma cells treated with the phorbol 12-myristate 13-acetate (PMA) suffer growth arrest and show morphological alterations, which depend on the activation of the ERK1/2 MAP kinases. MKP3/DUSP6 and DUSP5 MAP kinase phosphatases, two negative regulators of ERK1/2, were specifically up-regulated in MCF-7 and SKBR3 cells in response to PMA. MKP3 and DUSP5 up-regulation required the prolonged activation of the ERK1/2 pathway, and correlated with the shutdown of this route. MKP3 induction relied on the activation of the Ets2 transcription factor, whereas DUSP5 induction depended on the activation of c-Jun. Diminishing the expression of MKP3 and DUSP5 raised the activation of ERK1/2, and accelerated growth arrest of PMA-treated MCF-7 cells. Conversely, MCF-7 cell lines expressing high levels of MKP3 or DUSP5 did not undergo PMA-triggered growth arrest, displayed a migratory phenotype, and formed colonies in soft agar. We propose that the differential up-regulation of MKP3 by Ets2 and of DUSP5 by c-Jun may converge in similar functional roles for these MAP kinase phosphatases in the growth arrest versus proliferation decisions of breast cancer cells. Show less