dictyNews
Electronic Edition
Volume 44, number 26
September 21, 2018
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Abstracts
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ATG16 mediates the autophagic degradation of the 19S proteasomal
subunits PSMD1 and PSMD2
Qiuhong Xiong1,2, Sarah Fischer1, Malte Karow1, Rolf Müller1, Susanne
Meßling1 and Ludwig Eichinger1
1Center for Biochemistry, Medical Faculty, University of Cologne,
Joseph-Stelzmann-Str. 52, 50931 Cologne, Germany
2 Institute of Biomedical Sciences, Shanxi University, No. 92 Wucheng
Road, 030006 Taiyuan, Shanxi, China
Eur. J. Cell Biol., in press.
Autophagy and the ubiquitin proteasome system are the two major cellular
processes for protein and organelle recycling and clearance in eukaryotic
cells. Evidence is accumulating that these two pathways are interrelated
through adaptor proteins. Here, we found that PSMD1 and PSMD2, both
components of the 19S regulatory particle of the proteasome, directly
interact with Dictyostelium discoideum autophagy 16 (ATG16), a core
autophagosomal protein. ATG16 is composed of an N-terminal domain,
which is responsible for homo-dimerization and binding to ATG5 and a
C-terminal beta-propeller structure. Deletion analysis of ATG16 showed
that the N-terminal half of ATG16 interacted directly only with PSMD1,
while the C-terminal half interacted with both, PSMD1 and PSMD2. RFP-
tagged PSMD1 as well as PSMD2 were enriched in large puncta,
reminiscent of autophagosomes, in wild-type cells. These puncta were
absent in atg16- and atg9-/16- cells and weaker and less frequent in
atg9- cells, showing that ATG16 was crucial and the autophagic process
important for their formation. Co-expression of ATG16-GFP or
GFP-ATG8a(LC3) with RFP-PSMD1 or RFP-PSMD2, respectively, in
atg16- or wild-type cells revealed many instances of co-localization,
suggesting that RFP-PSMD1 or RFP-PSMD2 positive puncta constitute
autophagosomes. LysoTracker® labeling and a proteolytic cleavage assay
confirmed that PSMD1 and PSMD2 were present in lysosomes in wild-type
cells. In vivo, ATG16 is required for their enrichment in ATG8a positive
puncta, which mature into autolysosomes. We propose that ATG16 links
autophagy and the ubiquitin proteasome system.
submitted by: Ludwig Eichinger [[log in to unmask]]
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Species recognition in social amoebae
Ikumi Shibano Hayakawa 1,2, and Kei Inouye 1
1 Department of Botany, 2 Department of Physics, Graduate School of
Science,Kyoto University, Kyoto 606-8502, Japan
(Email: [log in to unmask])
Journal of Biosciences, accepted
Aggregative multicellularity requires the ability of cells to recognise
conspecifics. Social amoebae are among the best studied of such
organisms, but the mechanism and evolutionary background of
species recognition remained to be investigated. Here we show that
heterologous expression of a single Dictyostelium purpureum gene is
sufficient for D. discoideum cells to efficiently make chimaeric fruiting
bodies with D. purpureum cells. This gene forms a bidirectional pair
with another gene on the D. purpureum genome, and they are both
highly polymorphic among independent wild isolates of the same
mating group that do not form chimaeric fruiting bodies with each other.
These paired genes are both structurally similar to D. discoideum
tgrB1/C1 pair, which is responsible for clonal discrimination within that
species, suggesting that these tgr genes constitute the species
recognition system that has attained a level of precision capable of
discriminating between clones within a species. Analysis of the
available genome sequences of social amoebae revealed that such
gene pairs exist only within the clade composed of species that
produce precursors of sterile stalk cells (prestalk cells), suggesting
concurrent evolution of a precise allorecognition system and a new
”worker” cell-type dedicated to transporting and supporting the
reproductive cells.
submitted by: kumi Shibano Hayakawa [[log in to unmask]]
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