Dual-specificity protein phosphatases participate in signal transduction 
pathways inactivating mitogen-activated protein kinases (MAP kinases). These 
signaling pathways are of critical importance in the regulation of numerous 
biological processes, including cell proliferation, differentiation and 
development. The social ameba Dictyostelium discoideum harbors 14 genes coding 
for proteins containing regions very similar to the dual-specificity protein 
phosphatase domain. One of these genes, mkpB, additionally codes for a region 
similar to the Rhodanase domain, characteristic of animal MAP 
kinase-phosphatases, in its N-terminal region. Cells that over-express this gene 
show increased protein phosphatase activity. mkpB is expressed in D. discoideum 
ameba at growth but it is greatly induced at 12h of multicellular development. 
Although it is expressed in all the cells of developmental structures, mkpB mRNA 
is enriched in cells with a distribution typical of anterior-like cells. Cells 
that express a catalytically inactive mutant of MkpB grow and aggregate like 
wild-type cells but show a greatly impaired post-aggregative development. In 
addition, the expression of cell-type specific genes is very delayed, indicating 
that this protein plays an important role in cell differentiation and 
development. Cells expressing the MkpB catalytically inactive mutant show 
increased sensitivity to cisplatin, while cells over-expressing wild type MkpB, 
or MkpA, proteins or mutated in the MAP kinase erkB gene are more resistant to 
this chemotherapeutic drug, as also shown in human tumor cells.