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Poster Full Abstracts - Cell Death
Poster board number is above title. The first author is the presenter
215
NMDA receptor and protein tyrosine phosphatase Ptpmeg implicate calcium signaling in the control of developmental cell death in
Drosophila
.
Brandy C. Ree, Yanling Liu, Michael Lehmann. University of Arkansas, Fayetteville, AR.
Excessive activation of the NMDA receptor (NMDAR) is a major cause of excitatory cell death in the nervous system. This type of cell death is triggered
by neurotoxins (e.g. alcohol) or brain injury, and is involved in neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. Surprisingly, we
found that loss of function of the
Drosophila NMDAR1
gene leads to defects in developmentally programmed cell death (PCD). We identified the protein
tyrosine phosphatase Ptpmeg as a potential interaction partner of NMDAR1 in PCD control. Both NMDAR1 and Ptpmeg are required for normal functioning
of the mushroom body, the center for olfactory learning and memory in the
Drosophila
brain. Control of developmental cell death is a novel role for these
two proteins. Our results show that both NMDAR1 and Ptpmeg are required for the accurately timed removal of the larval salivary glands during
metamorphosis. Loss of either
NMDAR1
or
Ptpmeg
leads to salivary gland persistence with an enhanced penetrance of this phenotype in double-knockdown
animals. NMDAR1 is a phospho-tyrosine protein that forms a calcium channel in the cell membrane. Importantly, in
Ptpmeg
mutants we found decreased
levels of cellular Ca++ in the salivary glands. These data support a model in which dephosphorylation of NMDAR1 by the tyrosine phosphatase activity of
Ptpmeg is required for normal Ca++ influx and cell death. Interestingly, whereas levels of active caspase are reduced in
Ptpmeg
mutants, transcriptional
activation of the death genes
hid
and
reaper
does not seem to be affected. This suggests that Ptpmeg and NMDAR1 define a novel calcium-dependent
pathway that controls PCD independent of these death genes or at the level of hid and reaper protein activity. The larval salivary glands of
Drosophila
provide an excellent experimental system to further test this model.
311B
Translational repression by reaper is mediated by targeted degradation of a translation factor.
ROLANDO RIVERA-POMAR
1,2
, CARLOS
BERTONCINI
3
, M. PAULA VAZQUEZ-PIANZOLA
4
, DIEGO VAISMAN
1,5
, PAOLA FERRERO
1,5
. 1) Centro de Bioinvestigaciones,, UNNOBA,
Pergamino, Buenos Aires, Argentina; 2) Centro Regional de Estudios Genómicos, UNLP, Florencio Varela, Buenos Aires, Argentina; 3) University of
Cambridge, Cambridge, UK; 4) University of Bern, Bern, Switzerland; 5) Departamento de Ciencias Básicas y Experimentales, UNNOBA, Pergamino,
Argentina.
Inhibition of protein synthesis is a key process during apoptosis. We have previously demonstrated that the pro-apoptotic genes reaper, hid and grim are
translated in a cap-independent manner and escape cap-dependent translational repression during the early apoptosis phase (Hernandez et al., 2005;
Vazquez-Pianzola et al., 2007). However, all translational mechanisms are shut off in later steps. It has been demonstrated that the ribosome is a primary
target of RPR to repress translation (Colon-Ramos et al., 2006). Here we propose an additional, redundant mechanism for translational repression. We show
that recombinant RPR represses translation in vitro in Drosophila and mammalian cells extracts. By co-purification we have identified RPR-interactig
proteins in the translation extracts. We demonstrate that RPR interacts with the eukaryotic elongation 2 (eEF2) in vitro in both, mammalian and Drosophila
cells. Upon addition of recombinant RPR eEF2 is degraded in translation extracts, thus, translation is impaired. This effect was not observed in other
translation factors. The degradation of eEF2 is temperature-dependent and can be blocked by proteasome inhibitors. We propose a model in which RPR acts
at different levels of the translational machinery for a complete shut off of protein synthesis. This work was supported by ANPCyT and MPG grants to RRP,
and CONICET and UNNOBA grants to PVF.
312C
An epigenetically regulated enhancer region mediates cell competition -induced cell death.
Can Zhang
1
, Sergio Casas Tintó
2
, Michelle Chang
1
, Eduardo
Moreno
3
, Lei Zhou
1
. 1) Dept of Molecular Genetics and Microbiology, Univ of Florida, Gainesville, FL; 2) Cajal Institute, CSIC, Madrid, Spain; 3)
Molecular Oncology Program, CNIO, Madrid, Spain.
Previous work from our lab has identified that an epigenetically regulated, irradiation responsive enhancer region (IRER) is required for radiation-induced
expression of pro-apoptotic genes in early stage embryos. Here we demonstrate that IRER is also required for cell competition-induced cell death. Cell
competition has been implicated in growth control and early steps of tumorigenesis, which occurs between cells with different metabolic properties or
growth rates and results in growth of the stronger population at the expense of the weaker. It has been well documented that expression of the
Drosophila
growth regulator dMyc transforms the cell into supercompetitors and induces apoptosis from neighboring wild-type cells in developing wings. However, the
mechanism controlling the induction of cell death genes in response to cell competition remains largely unknown. In this study, we observed that cell
competition-induced cell death was attenuated in IRER-deficient background. In the absence of IRER, the induction of pro-apoptotic gene
hid
upon cell
competition was significantly blocked. To monitor the epigenetic status of IRER in individual cells, a reporter strain was generated by introducing an
ubiquitin-DsRed transgene into IRER through homologous recombination. Interestingly, we noticed that cells with higher level of DsRed (open IRER) were
preferentially eliminated from wing discs upon dMyc-induced cell competition, indicating that the epigenetic status of IRER determines sensitivity to dMyc
supercompetitor-induced apoptosis. Moreover, IRER-deficient flies displayed an overgrown phenotype from multiple organs such as the wing and the
central nervous system. Our work demonstrated that modulating cellular sensitivity to stress-induced cell death through epigenetic regulation may be an
important mechanism of preventing tumorigenesis and achieving homeostasis.
313A
Identification of CDK7 as a protein required for IAP-antagonist-induced apoptosis.
Jun Morishita Funabiki, Min-Ji Kang, Kevin Fidelin, Hyung Don
Ryoo. Cell Biology, New York Univ Sch Medicine, New York, NY.
It is now established that certain cellular genes help cells die in response to injury and stress. However, the underlying mechanisms that contribute to this
process are not well understood. To investigate how misfolded proteins trigger apoptosis, we developed a system where we overexpress a mutant rhodopsin-
1 protein that fails to fold properly in the developing fly eye. This generates a malformed eye, in part, due to excessive cell death. Through an RNAi screen
for suppressors of this phenotype, we identified CDK7 and MAT1. CDK7, MAT1 and cyclin H are known to form the Cyclin-Dependent kinase (CDK)
Activating Kinase (CAK) complex. CAK phosphorylates other CDKs to be activated during cell cycle progression. It is also involved in general
transcription by the phosphorylating the RNA polymerase II. To independently validate the role of CDK7, we used a hypomorphic allele, that has its own T-
loop phospho-acceptor sites (S164 and T170) mutated to alanines which acts a temperature-sensitive allele. In semi-permissive temperature, we found no
defects in developmental gene expression or cell cycle progression, but the mutant rhodopsin-1 overexpression phenotype was suppressed. Furthermore, it