Page 124 - 53rd Annual Drosophila Research Conference

Full Abstracts – IMMUNITY AND PATHOGENESIS
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Ras-oncogenic Drosophila hindgut cells use an “inflammatory-like cell program” to migrate to distant sites. Yiorgos Apidianakis1,2, Erdem Bangi3 ,
Laurence Rahme1 , Ross Cagan3. 1) Department of Surgery, MGH, Harvard University, Boston, MA; 2) Department of Biological Sciences, University of
Cyprus, Nicosia, Cyprus; 3) Department of Developmental and Regenerative Biology, Mt Sinai School of Medicine, New York, NY.
Cell migration is the property of eukaryotic cells during tumor cell metastasis or inflammatory cell response to injury and infection. Here we find that adult
Ras-oncogenic Drosophila hindgut cells migrate to distant sites when challenged by intestinal bacteria. While RasV12 ongogene suffices to induce
migration, intestinal infection with the human pathogen Pseudomonas aeruginosa potentiates and induces an earlier onset of migration in adult flies. This
cooperative migration progresses over time, is reversible upon bacterial clearance and can be inhibited by genetic and pharmacological means. We
demonstrate that the Imd pathway converges with Ras signaling to induce JNK and Metalloproteinase 1 (MMP1), which in turn digests extra-cellular matrix
(EMC) to promote hindgut cell migration. This property of genetically predisposed epithelial cells to produce MMP1, degrade EMC and migrate upon innate
immunity stimulation resembles infiltrating macrophage activities , thus depicting innate immune response as a common trigger of inflammatory and
metastatic tumor cell functions. Our previous work on the Drosophila midgut shows that virulent bacteria induce enterocyte compensatory proliferation that
can be diverted in the presence of a tumorigenic genetic background to induce intestinal tumors. This mechanism is drastically different from the one we
now propose for tumor cell migration in the fly hindgut. During tumor formation pathogenic bacteria use their virulence factors to cause cytotoxicity and
enterocyte apoptosis, which in turn drives stem cell proliferation to promote tumor formation in genetically predisposed Drosophila midguts. While during
tumor cell migration bacterial infection induces oncogenic cells to migrate via an innate immune response; independently of bacterial virulence factors that
mediate damage to host cells.
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Mediating a balance between tolerance and resistance. Moria C. Chambers, Karla L. Lightfield, David S. Schneider. MicroBiol & Immunology, Stanford
Univ, Stanford, CA.
Immunity is a combination of both microbe clearance (resistance) and the host’s ability to withstand the damage induced during infection (tolerance).
Ets21c, a putative transcription factor, belongs to a newly characterized class of Drosophila mutants defective in tolerance to Listeria monocytogenes. Ets21c
mutants don’t affect all infections in this way, for example, we find that Et21c mutants more resistance to Streptococcus pneumoniae, as shown by increased
survival and decreased bacterial loads. Microarray analysis of the Ets21c mutants after infection suggests that their phenotypes may be due to a combination
of effects. Ets21c mutants show mis-regulation of melanization, metabolism and WntD, a negative regulator of the NFkB pathway. Melanization has been
previously shown to impact both resistance and tolerance, and we can now show that that genetic modulation of metabolism and WntD independently affect
both tolerance and resistance. These findings support a complex relationship between tolerance and resistance during infection and stress the importance of
examining multiple infections when classifying genes as part of resistance or tolerance.
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Virus recognition by Toll-7 activates antiviral autophagy in Drosophila. Ryan H. Moy, Margaret Nakamoto, Jie Xu, Shelly Bambina, Ari Yasunaga,
Spencer S. Shelly, Beth Gold, Sara Cherry. Department of Microbiology, Penn Genome Frontiers Institute, Perelman School of Medicine at the University
of Pennsylvania, Philadelphia, PA 19104.
The innate immune system relies on germline-encoded pattern recognition receptors (PRRs) for the detection and clearance of invading pathogens. The
canonical PRRs are the mammalian Toll-like receptors (TLRs), which were originally identified through their homology to Drosophila Toll. Flies encode
nine Toll receptors; however, whereas the immune functions for Toll are well-characterized, roles for the eight remaining Toll receptors have remained
elusive. By using RNA interference screening techniques, we have identified a role for an additional Toll receptor, Toll-7, in conferring antiviral immunity
to the negative-sense RNA virus Vesicular Stomatitis virus (VSV). Toll-7 knockdown in cells leads to increased VSV infection. Similarly, flies depleted of
Toll-7 by RNAi or mutant for Toll-7 exhibit increased viral RNA replication and mortality upon VSV challenge. Like many mammalian antiviral PRRs,
Toll-7 is transcriptionally induced by viral infection along with several other Toll receptors. Moreover, Toll-7 is present at the plasma membrane and binds
VSV by co-immunoprecipitation, which is fundamentally distinct from the mode of recognition for Toll and more similar to that of mammalian TLRs. This
interaction is required in both cells and flies to activate autophagy, an ancient pathway involved in the degradation of cytoplasmic components including
pathogens. Taken together, these data unveil an evolutionarily conserved role for a second Drosophila Toll receptor that links virus recognition to autophagy
and defense, suggesting that the mammalian TLRs and Drosophila Tolls are in fact more alike than previously appreciated.
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Study of Pallbearer, an E3-ubiquitin ligase that regulates phagocytosis of apoptotic cells in Drosophila. Hui Xiao, Nathalie Franc. The Department of
Genetics, The Scripps Research Institute, La Jolla, CA.
The swift removal of apoptotic cells by phagocytes is a critical event during development of all multi-cellular organisms. Yet, little is known about the
molecular mechanisms regulating phagocytosis of apoptotic cells. In a quest to genetically dissect the molecular mechanisms of apoptotic cell clearance in
Drosophila, we previously identified pallbearer (pall), a gene encoding a novel F-Box protein. F-box proteins form multi-molecular Skp/Cullin/F-Box
(SCF) complexes, which act as E3 ligases that target modified proteins to degradation via the ubiquitin-proteasome pathway. In these complexes, the F-Box
protein provides the substrate-binding function and specificity. Identifying the PALL substrate(s) is important to further our understanding of the molecular
mechanisms of phagocytosis. We have identified the ribosomal protein RpS6 as a putative substrate for PALL by co-immunoprecipitation and mass
spectrometry. RpS6 plays a role in immune cells, as RpS6 mutants have melanotic tumors, the sign of an aberrant immune response, as well as enlarged
macrophages, the opposite phenotype of pall mutants. We have also found that RpS6 RNAi enhances apoptotic cell clearance in a genome-wide RNAi
screen in S2 cells, and validated this finding using new RpS6 specific siRNAs. Furthermore, we have found that overexpression of RpS6 in macrophages
results in decreased phagocytosis in vivo . We are now testing whether RpS6 and pall genetically interact in vivo. We propose that RpS6 is a substrate of
PALL that negative regulates phagocytosis of apoptotic cells.