Identification of Drosophila Gene Products Required for Phagocytosis of Candida albicans

Abstract

Phagocytosis is a highly conserved aspect of innate immunity. We used Drosophila melanogaster S2 cells as a model system to study the phagocytosis of Candida albicans, the major fungal pathogen of humans, by screening an RNAi library representing 7,216 fly genes conserved among metazoans. After rescreening the initial genes identified and eliminating certain classes of housekeeping genes, we identified 184 genes required for efficient phagocytosis of C. albicans. Diverse biological processes are represented, with actin cytoskeleton regulation, vesicle transport, signaling, and transcriptional regulation being prominent. Secondary screens using Escherichia coli and latex beads revealed several genes specific for C. albicans phagocytosis. Characterization of one of those gene products, Macroglobulin complement related (Mcr), shows that it is secreted, that it binds specifically to the surface of C. albicans, and that it promotes its subsequent phagocytosis. Mcr is closely related to the four Drosophila thioester proteins (Teps), and we show that TepII is required for efficient phagocytosis of E. coli (but not C. albicans or Staphylococcus aureus) and that TepIII is required for the efficient phagocytosis of S. aureus (but not C. albicans or E. coli). Thus, this family of fly proteins distinguishes different pathogens for subsequent phagocytosis.

Drosophila Hemopoiesis and Cellular Immunity

“…Recently, the TEP proteins have been linked to phagocytosis in Drosophila (58). Previously, Moita et al (54) showed that three mosquito TEP proteins (TEP1, TEP3, and TEP4) are required for efficient phagocytosis of bacteria.…”

Genomic RNAi screening in Drosophila S2 cells: what have we learned about host–pathogen interactions?

“…Using phagocytic S2 cells infected with GFP-expressing Candida, Stroschein-Stevenson et al screened a library of 7,000 conserved genes for factors required for engulfment [31] (Table 1). They identified 184 genes that were required for efficient uptake.…”

“…In addition to known factors, RNAi screens were the first to identify the coatamer complexes (COPI and COPII) in uptake [26,[31][32][33]35,36]. The COPI and COPII complexes are required for vesicular trafficking between the ER and golgi [37], are found to associate with the phagosome, and are required in S2 cells for the uptake of a wide variety of pathogens, although the mechanism of this requirement has not yet been established.…”

Fruit Flies Like A (Rotten) Banana

“…Tep1 expression was previously shown to be induced by the JAK-STAT pathway in the fat body, while Tep2, 3 and 6 were shown to be important for phagocytosis. 17,18 Bou Aoun found that all five functional TEPs (Tep1, 2, 3, 4 and 6) are expressed by plasmatocytes, and that the expression of TEPs 1, 2, 3 and 4 were induced by bacterial infection. However, constitutive expression of all five TEPs also occurred in a variety of larval and adult tissues.…”