dictyNews
Electronic Edition
Volume 35, number 4
July 23, 2010
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Abstracts
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Expression of Actin Tyr53Ala in Dictyostelium Disrupts the Cytoskeleton
and Inhibits Intracellular and Intercellular Chemotactic-Signaling
Shi Shu,* Xiong Liu,* Paul W. Kriebel,† Myoung-Soon Hong,*,
Mathew P. Daniels,‡ Carole A. Parent,† and Edward D. Korn*
From the *Laboratory of Cell Biology, National Heart, Lung, and Blood
Institute,
†Laboratory of Cellular and Molecular Biology, Center for Cancer
Research,
National Cancer Institute,
‡Electron Microscopy Core Facility, National Heart, Lung and Blood
Institute,
NIH, Bethesda, MD 20892
Running Head: Inhibition of cAMP signaling by actin Tyr53Ala mutant
Address correspondence to: Edward D. Korn, Ph.D., Laboratory of Cell
Biology,
NHLBI, NIH, Building 50, Room 2517, 9000 Rockville Pike, Bethesda, MD
20892.
Fax: 301-402-1519; [log in to unmask]
J. Biol. Chem., in press
We showed previously that phosphorylation of Tyr-53, or its mutation
to Ala,
inhibits actin polymerization in vitro with formation of aggregates of
short
filaments, and that expression of Y53A-actin in Dictyostelium blocks
differentiation and development at the mound stage (Liu et al. (2006)
Proc. Natl. Acad. Sci. U.S.A. 103, 13694-13699; Liu et al. (2010) J.
Biol.
Chem. 285, 9729-9739). We now show that expression of Y53A-actin, which
does not affect cell growth, phagocytosis or pinocytosis, inhibits the
formation
of head-to-tail cell streams during cAMP-induced aggregation, although
individual
amoebae chemotax normally. We show that expression of Y53A-actin
causes a
50% reduction of cell-surface cAMP-receptors, and inhibits cAMP-induced
increases in adenylyl cyclase A activity, phosphorylation of ERK2 and
actin
polymerization. Trafficking of vesicles containing adenylyl cyclase A
to the rear
of the cell and secretion of the ACA-vesicles are also inhibited. The
actin
cytoskeleton of cells expressing Y53A-actin is characterized by
numerous short
filaments, and bundled and aggregated filaments similar to the
structures formed
by copolymerization of purified Y53A-actin and wild-type actin in
vitro. This
disorganized actin cytoskeleton may be responsible for the inhibition of
intracellular and intercellular cAMP signaling in cells expressing F-Y/
A-actin.
Submitted by Edward Korn [[log in to unmask]]
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Ca++ Chemotaxis in Dictyostelium discoideum
Amanda Scherer, Spencer Kuhl, Deborah Wessels, Daniel F. Lusche,
Brent Raisley and David R. Soll
Journal of Cell Science, in press
Using a newly developed microfluidic chamber, it is demonstrated in
vitro
that Ca++ functions as a chemoattractant of aggregation-competent
D. discoideum amoebae, that parallel spatial gradients of cAMP and
Ca++ are more effective than either alone and that cAMP functions as
a stronger chemoattractant than Ca++ . Effective Ca++ gradients are
extremely steep compared to effective cAMP gradients. This presents
a paradox, since there is no indication to date that steep Ca++
gradients
are generated in aggregation territories. However, given that
Ca++ chemotaxis is co-acquired with cAMP chemotaxis during development,
we speculate on the role Ca++ chemotaxis might play and the possibility
that steep, transient Ca++ gradients may be generated during natural
aggregation in the interstitial regions between cells.
Submitted by Deborah Wessels [[log in to unmask]]
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[End dictyNews, volume 35, number 4]
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