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dictyNews Volume 38 Number 20
dictyNews
Electronic Edition
Volume 38, number 20
August 10, 2012
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
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Abstracts
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Arachidonic Acid Enhances Caffeine-Induced Cell Death via
Caspase-Independent Cell Death
Hidekazu Kuwayama
Scientific Reports, in press
Caffeine is a globally consumed psychostimulant but can be fatal to cells
at overdose exposures. Although caspase-dependent apoptosis plays a role
in caffeine-induced cell death, the responsible intracellular signalling
cascade remains incompletely understood. The cellular slime mould,
Dictyostelium discoideum, does not possess caspase-dependent apoptotic
machinery. Here, we observed that ablation of D. discoideum plaA, which
encodes a phospholipase A2 (PLA2) homolog, leads to a decreased rate of
cell death under high caffeine concentrations and to enhanced cell death
with the addition of arachidonic acid. Moreover, the inhibition of PLA2
activity lead to a recovery of the survival rate in caspase-inhibited Hela
cervical carcinoma cells under high caffeine concentrations, indicating
that caffeine-induced cell death is enhanced via PLA2-dependent signalling.
Our results indicate that arachidonic acid may be a general second messenger
that negatively regulates caffeine tolerance via a caspase-independent cell
death cascade, which leads to multiple effects in eukaryotic cells.
Submitted by Hidekazu Kuwayama [hidekuwayama@biol.tsukuba.ac.jp]
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Extracellular Calmodulin regulates growth and cAMP-mediated chemotaxis in
Dictyostelium discoideum
Danton H. O’Day1,2, Robert J. Huber1 and Andres Suarez2
1Department of Cell and Systems Biology, University of Toronto, 25 Harbord
St., Toronto, Ontario, Canada, M5S 3G5.
2Department of Biology, University of Toronto Mississauga, 3359 Mississauga
Rd. N., Mississauga, Ontario, Canada, L5L 1C6.
Biochemical Biophysical Research Communications (in press)
The existence of extracellular calmodulin (CaM) has had a long and
controversial history. CaM is a ubiquitous calcium-binding protein that
has been found in every eukaryotic cell system. Calcium-free apo-CaM and
Ca2+/CaM exert their effects by binding to and regulating the activity of
CaM-binding proteins (CaMBPs). Most of the research done to date on CaM and
its CaMBPs has focused on their intracellular functions. The presence of
extracellular CaM is well established in a number of plants where it
functions in proliferation, cell wall regeneration, gene regulation and
germination. While CaM has been detected extracellularly in several animal
species, including frog, rat, rabbit and human, its extracellular
localization and functions are less well established. In contrast the study
of extracellular CaM in eukaryotic microbes remains to be done. Here we show
that CaM is constitutively expressed and secreted throughout asexual
development in Dictyostelium where the presence of extracellular CaM
dose-dependently inhibits cell proliferation but increases cAMP mediated
chemotaxis. During development, extracellular CaM localizes within the slime
sheath where it coexists with at least one CaMBP, the matricellular
CaM-binding protein CyrA. Coupled with previous research, this work provides
direct evidence for the existence of extracellular CaM in the Dictyostelium
and provides insight into its functions in this model amoebozoan.
Submitted by Dan O’Day [danton.oday@utoronto.ca]
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MicroRNAs in Amoebozoa: Deep sequencing of the small RNA population in the social
amoeba Dictyostelium discoideum reveals developmentally regulated microRNAs.
Lotta Avesson, Johan Reimegård, E. Gerhart H. Wagner and Fredrik Söderbom
RNA, in press
The RNA interference machinery has served as a guardian of eukaryotic genomes
since the divergence from prokaryotes. Although the basic components have a
shared origin, silencing pathways directed by small RNAs have evolved in diverse
directions in different eukaryotic lineages. Micro (mi)RNAs regulate
protein-coding genes and play vital roles in plants and animals but less is known
about their functions in other organisms. Here we report, for the first time,
deep sequencing of small RNAs from the social amoeba Dictyostelium discoideum.
RNA from growing single cell amoeba as well as from two multicellular
developmental stages was sequenced. Computational analyses combined with
experimental data reveal the expression of miRNAs, several of them exhibiting
distinct expression patterns during development. To our knowledge, this is the
first report of miRNAs in the Amoebozoa supergroup. We also show that
overexpressed miRNA precursors generate miRNAs and, in most cases, miRNA*
sequences whose biogenesis are dependent of the Dicer-like protein DrnB, further
supporting the presence of miRNAs in D. discoideum. In addition, we find miRNAs
processed from hairpin structures originating from an intron as well as from a
class of repetitive elements. We believe that these repetitive elements are
sources for newly evolved miRNAs.
Submitted by Lotta Avesson [l.avesson@garvan.org.au]
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[End dictyNews, volume 38, number 20]
