Integrin αPS3/βν-mediated Phagocytosis of Apoptotic Cells and Bacteria in Drosophila

Integrins exert a variety of cellular functions as heterodimers of two transmembrane subunits named alpha and beta. Integrin beta nu, a beta-subunit of Drosophila integrin, is involved in the phagocytosis of apoptotic cells and bacteria. Here, we searched for an alpha-subunit that forms a complex and cooperates with beta nu. Examinations of RNAi-treated animals suggested that alpha PS3, but not any of four other alpha-subunits, is required for the effective phagocytosis of apoptotic cells in Drosophila embryos. The mutation of alpha PS3-encoding scb, deficiency, insertion of P-element, or alteration of nucleotide sequences, brought about a reduction in the level of phagocytosis. The defect in phagocytosis by deficiency was reverted by the forced expression of scb. Furthermore, flies in which the expression of both alpha PS3 and beta nu was inhibited by RNAi showed a level of phagocytosis almost equal to that observed in flies with RNAi for either subunit alone. A loss of alpha PS3 also decreased the activity of larval hemocytes in the phagocytosis of Staphylococcus aureus. Finally, a co-immunoprecipitation analysis using a Drosophila cell line treated with a chemical cross-linker suggested a physical association between alpha PS3 and beta nu. These results collectively indicated that integrin alpha PS3/beta nu serves as a receptor in the phagocytosis of apoptotic cells and bacteria by Drosophila phagocytes.