dictyNews
Electronic Edition
Volume 36, number 5
Feb 11, 2011

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Abstracts
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The dual-specificity protein phosphatase MkpB, homologous to mammalian 
MKP phosphatases, is required for D. discoideum postaggregative development 
and cisplatin response

Verónica Moncho-Amor, María Galardi-Castilla, Rosario Perona and Leandro Sastre


Differentiation, in press

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 
amoeba 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 amoeba at growth but it is greatly 
induced at 12 hours of multi-cellular 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. 


Submitted by Leandro Sastre [[log in to unmask]]
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Legionella pneumophila infection is enhanced in a RacH-null mutant of 
Dictyostelium

Alessandra Balest, Barbara Peracino and Salvatore Bozzaro


Communicative and integrative Biology, in press

Recently we reported that Dictyostelium cells ingest Legionella pneumophila 
by macropinocytosis, whereas other bacteria, such as Escherichia coli, 
Mycobacterium avium, Neisseria meningitidis or Salmonella typhimurium, are 
taken up by phagocytosis.1 In contrast to phagocytosis, macropinocytosis is 
partially inhibited by PI3K or PTEN inactivation, whereas both processes are 
sensitive to PLC inhibition. Independently from reduced uptake, L. pneumophila 
proliferates more efficiently in PI3K-null than in wild type cells. PI3K inactivation 
also overcomes the resistance to infection conferred by constitutively expressing 
the endo-lysosomal iron transporter Nramp1. We have shown this to be due to
altered recruitment of the V-H+ ATPase, but not Nramp1, in the Legionella-
containing vacuole (LCV) early during infection.1 As further evidence for 
impaired LCV acidification we examine here the effects of disrupting the 
small G protein RacH on Legionella infection.


Submitted by: salvatore bozzaro [[log in to unmask]]
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[End dictyNews, volume 36, number 5]