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dictyNews Volume 28 Number 12
dictyNews
Electronic Edition
Volume 28, number 12
May 11, 2007
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
Back issues of dictyNews, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
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Abstracts
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G Protein-Independent Ras/PI3K/F-Actin Circuit Regulates Basic Cell Motility
Atsuo T. Sasaki, Chris Janetopoulos, Susan Lee, Pascale G. Charest, Kosuke Takeda,
Lauren W. Sundheimer, Ruedi Meili, Peter N. Devreotes and Richard A. Firtel
J. Cell Biology
PI3Kgamma and Dictyostelium PI3K are activated via G-protein coupled receptors
through binding to the Gbeta/gamma subunit and Ras. However, the mechanistic
role(s) of Gbeta/gamma and Ras in PI3K activation remain elusive. Furthermore,
the dynamics and function of PI3K activation in the absence of extracellular
stimuli have not been fully investigated. We report that Gbeta null cells
display PI3K and Ras activation, as well as the reciprocal localization of
PI3K and PTEN, which lead to local accumulation of PI(3,4,5)P3. Simultaneous
imaging analysis reveals that, in the absence of extracellular stimuli,
autonomous PI3K and Ras activation occur, concurrently, at the same sites
where F-actin projection emerges. The loss of PI3K binding to Ras-GTP
abolishes this PI3K activation, while prevention of PI3K activity suppresses
autonomous Ras activation, suggesting that PI3K and Ras form a positive-feedback
circuit. This circuit is associated with both random cell migration and
cytokinesis and may have initially evolved to control stochastic changes
in the cytoskeleton.
Submitted by: Rick Firtel [rafirtel@ucsd.edu]
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STATc is a key regulator of the transcriptional response to hyperosmotic shock
Jianbo Na, Budi Tunggal and Ludwig Eichinger
Institute for Biochemistry I, Medical Faculty, University of Cologne,
Joseph-Stelzmann-Strasse 52, 50931 Cologne, Germany
BMC Genomics, in press
Dictyostelium discoideum is frequently subjected to environmental changes
in its natural habitat, the forest soil. In order to survive, the organism
had to develop effective mechanisms to sense and respond to such changes.
When cells are faced with a hypertonic environment a complex response is
triggered. It starts with signal sensing and transduction and leads to
changes in cell shape, the cytoskeleton, transport processes, metabolism
and gene expression. Certain aspects of the Dictyostelium osmotic stress
response have been elucidated, however, no comprehensive picture was
available up to now.
To better understand the D. discoideum response to hyperosmotic conditions,
we performed gene expression profiling using DNA microarrays. The
transcriptional profile of cells treated with 200 mM sorbitol during a
2-hour time course revealed a time-dependent induction or repression of 809
genes, more than 15% of the genes on the array, which peaked 45 to 60
minutes after the hyperosmotic shock. The differentially regulated genes
were applied to cluster analysis and functional annotation using gene
ontology (GO) terms. Two main responses appear to be the down-regulation of
the metabolic machinery and the up-regulation of the stress response
system, including STATc. Further analysis of STATc revealed that it is a
key regulator of the transcriptional response to hyperosmotic shock.
Approximately 20% of the differentially regulated genes were dependent on
the presence of STATc. At least two signalling pathways are activated
in Dictyostelium cellssubjected to hypertonicity. STATc is responsible
for the transcriptional changes of one of them.
Submitted by: Ludwig Eichinger [ludwig.eichinger@uni-koeln.de]
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[End dictyNews, volume 28, number 12]
