A systems-level interrogation identifies regulators of Drosophila blood cell number and survival.
In multicellular organisms, cell number is typically determined by a balance of intracellular signals that positively and negatively regulate cell survival and proliferation. Dissecting these signaling networks facilitates the understanding of normal development and tumorigenesis. Here, we study signaling by the Drosophila PDGF/VEGF Receptor (Pvr) in embryonic blood cells (hemocytes) and in the related cell line Kc as a model for the requirement of PDGF/VEGF receptors in vertebrate cell survival and proliferation. The system allows the investigation of downstream and parallel signaling networks, based on the ability of Pvr to activate Ras/Erk, Akt/TOR, and yet-uncharacterized signaling pathway/s, which redundantly mediate cell survival and contribute to proliferation. Using Kc cells, we performed a genome wide RNAi screen for regulators of cell number in a sensitized, Pvr deficient background. We identified the receptor tyrosine kinase (RTK) Insulin-like receptor (InR) as a major Pvr Enhancer, and the nuclear hormone receptors Ecdysone receptor (EcR) and ultraspiracle (usp), corresponding to mammalian Retinoid X Receptor (RXR), as Pvr Suppressors. In vivo analysis in the Drosophila embryo revealed a previously unrecognized role for EcR to promote apoptotic death of embryonic blood cells, which is balanced with pro-survival signaling by Pvr and InR. Phosphoproteomic analysis demonstrates distinct modes of cell number regulation by EcR and RTK signaling. We define common phosphorylation targets of Pvr and InR that include regulators of cell survival, and unique targets responsible for specialized receptor functions. Interestingly, our analysis reveals that the selection of phosphorylation targets by signaling receptors shows qualitative changes depending on the signaling status of the cell, which may have wide-reaching implications for other cell regulatory systems.
Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America.
Richelle
R
Sopko
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, California, United States of America.
You Bin
YB
Lin
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, California, United States of America.
Kalpana
K
Makhijani
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, California, United States of America.
Brandy
B
Alexander
Department of Genetics, Harvard Medical School, Boston, Massachusetts, United States of America; Howard Hughes Medical Institute, Boston, Massachusetts, United States of America.
Norbert
N
Perrimon
Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, California, United States of America; Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California, San Francisco, San Francisco, California, United States of America; Cardiovascular Research Institute, University of California, San Francisco, San Francisco, California, United States of America.
Katja
K
Brückner
D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D002470:Cell Survival; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology* / Q000378:metabolism; D055106:Genome-Wide Association Study; D006434:Hemocytes / Q000166:cytology* / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D034622:RNA Interference; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D011987:Receptors, Steroid / Q000378:metabolism; D015398:Signal Transduction
D029721:Drosophila Proteins; D007328:Insulin; D011987:Receptors, Steroid; C055469:ecdysone receptor; C094982:InR protein, Drosophila; C438368:Pvr protein, Drosophila; D020794:Receptor Protein-Tyrosine Kinases