Inhibition of mitogen-activated protein kinase by a Drosophila dual-specific phosphatase

The Drosophila extracellular signal-regulated kinase (DERK) mitogen-activat ed protein kinase (MAPK) is involved in the regulation of multiple differen tiation and developmental processes. Tight control of MAPK activity is crit ical for normal cell behaviour. We identified a novel Drosophila MAPK phosp hatase (DMKP) cDNA from the expressed-sequence-tag database and characteriz ed it. Analysis of the nucleotide sequence revealed an open reading frame e ncoding the 203-amino acid protein, with a calculated molecular mass of 23 kDa, which has a high amino acid sequence similarity with 'VH1-like' dual-s pecific phosphatases at the broad region near the catalytic sites. The expr ession of DMKP mRNA occurs from the late larval stages to adulthood in Dros ophila development. The recombinant DMKP protein produced in yeast retained its phosphatase activity. When expressed in Schneider cells, DMKP dose-dep endently inhibited DERK and Drosophila c-Jun N-terminal kinase activities w ith high selectivity towards DERK. However, DMKP did not have any affect on Drosophila p38 activity. When DMKP was expressed in yeast, it down-regulat ed the fus1-lacZ trans-reporter gene of the pheromone MAPK pathway without any significant effect on the high-osmolarity-glycerol-response pathway.