mthl1, a potential Drosophila homologue of mammalian adhesion GPCRs, is involved in antitumor reactions to injected oncogenic cells in flies

Injection of OCs into adult male flies induces a strong transcriptomic response in the host flies featuring in particular genes encoding bona fide G coupled proteins, among which the gene for methuselah like 1 is prominent. The injection is followed after a 3-d lag period, by the proliferation of the oncogenic cells. We hypothesized that through the product of mthl1 the host might control, at least in part, this proliferation as a defense reaction. Through a combination of genetic manipulations of the mthl1 gene (loss of function and overexpression of mthl1), we document that indeed this gene has an antiproliferative effect. Parallel injections of primary embryonic Drosophila cells or of various microbes do not exhibit this effect. We further show that mthl1 controls the expression of a large number of genes coding for chemoreceptors and genes implicated in regulation of development. Of great potential interest is our observation that the expression of the mouse gene coding for the adhesion G-protein-coupled receptor E1 (Adgre1, also known as F4/80), a potential mammalian homologue of mthl1, is significantly induced by B16-F10 melanoma cell inoculation 3 d postinjection in both the bone marrow and spleen (nests of immature and mature myeloid-derived immune cells), respectively. This observation is compatible with a role of this GPCR in the early response to injected tumor cells in mice.