Copy Link
Add to Bookmark
Report
dictyNews Volume 21 Number 05
Dicty News
Electronic Edition
Volume 21, number 5
August 22, 2003
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu.
Back issues of Dicty-News, the Dicty Reference database and other
useful information is available at dictyBase - http://dictybase.org.
=============
Abstracts
=============
A PTEN-related 5' phosphatidylinositol phosphatase localized in the Golgi
Sylvain Merlot, Ruedi Meili, David J. Pagliarini, Tomohiko Maehama,
Jack E. Dixon, and Richard A. Firtel
J. Biol. Chem., in press
SUMMARY
Phosphoinositides play important roles as signaling molecules in different
cellular compartments by regulating the localization and activity of
proteins through their interaction with specific domains. The activity of
these lipids depends on which sites on the inositol ring are phosphorylated.
Signaling pathways dependent on phosphoinositides phosphorylated on the D3
position of this ring (3'-phosphoinositides) are negatively regulated by
3'-phosphoinositide-specific phosphatases that include PTEN and myotubularin.
Using the conserved PTEN catalytic core motif, we have identified a new
protein in the Dictyostelium genome called PLIP that defines a new subfamily
family of phosphoinositide phosphatases, clearly distinct from PTEN or other
closely related proteins. We show that PLIP is able to dephosphorylate a
broad spectrum of phosphoinositides, including 3'-phosphoinositides. In
contrast to previously characterized phosphoinositide phosphatases, PLIP has
a strong preference for phosphatidylinositol-5-phosphate , a newly discovered
phosphoinositide. We found that PLIP is localized in the Golgi with its
phosphatase domain facing the cytoplasmic compartment. PLIP null cells
created via homologous recombination are unable to effectively aggregate to
form multicellular organisms at low cell densities. PLIP's presence in the
Golgi suggests that it may be involved in membrane trafficking.
Submitted by: Rick Firtel [rafirtel@ucsd.edu]
-------------------------------------------------------------------------------
The novel ankyrin-repeat containing kinase ARCK-1 acts as a suppressor of the
Spalten signaling pathway during Dictyostelium development
Laurence Aubry, Susan Lee, Kissia Ravanel, and Richard A. Firtel
Devel. Biol., in press
ABSTRACT
Spalten (Spn), a member of the PP2C family of Ser/Thr protein phosphatases, is
required for Dictyostelium cell-type differentiation and morphogenesis. We
have identified a new protein kinase, ARCK-1, through a second site suppressor
screen for mutants that allow spn null cells to proceed further through
development. ARCK-1 has a C-terminal kinase domain most closely related to
Ser/Thr protein kinases and an N-terminal putative regulatory domain with
ankyrin repeats, a 14-3-3 binding domain, and a C1 domain, which is required
for binding to RasBGTP in a two-hybrid assay. Disruption of the gene encoding
ARCK-1 results in weak, late developmental defects. However, overexpression of
ARCK-1 phenocopies the spn null phenotype, consistent with Spn and ARCK-1 being
on the same developmental pathway. Our previous analyses of Spn and the present
analysis of ARCK-1 suggest a model in which Spn and ARCK-1 differentially control
the phosphorylation state of a protein that regulates cell-type differentiation.
Dephosphorylation of the substrate by Spn is required for cell-type
differentiation. Control of ARCK-1 and Spn activities by upstream signals is
proposed to be part of the developmental regulatory program mediating cell-fate
decisions in Dictyostelium.
Submitted by: Rick Firtel [rafirtel@ucsd.edu]
===============================================================================
[End Dicty News, volume 21, number 5]
