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dictyNews Volume 35 Number 04
dictyNews
Electronic Edition
Volume 35, number 4
July 23, 2010
Please submit abstracts of your papers as soon as they have been
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or by using the form at
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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; edk@nih.gov
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 [edk@nih.gov]
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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 [deborah-wessels@uiowa.edu]
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[End dictyNews, volume 35, number 4]
