Copper homoeostasis in Drosophila melanogaster S2 cells

Copper homoeostasis was investigated in the Drosophila melanogaster S2 cell line to develop an insect model for the study of copper regulation. Real-time PCR studies have demonstrated expression in S2 cells of putative orthologues of human Cu regulatory genes involved in the uptake, transport, sequestration and efflux of Cu. Drosophila orthologues of the mammalian Cu chaperones, ATOX1 (a human orthologue of yeast ATX1), CCS (copper chaperone for superoxide dismutase), COX17 (a human orthologue of yeast COX 17), and SCO1 and SCO2, did not significantly respond transcriptionally to increased Cu levels, whereas MtnA, MtnB and MtnD (Drosophila orthologues of human metallothioneins) were up-regulated by Cu in a time- and dose-dependent manner. To examine the effect on Cu homoeostasis, expression of several key copper homoeostasis genes was suppressed using double-stranded RNA interference. Suppression of the MTF-1 (metal-regulatory transcription factor 1), reduced both basal and Cu-induced gene expressions of MtnA, MtnB and MtnD, significantly reducing the tolerance of these cells to increased Cu. Suppression of either Ctr1A (a Drosophila orthologue of yeast CTR1) or Ctr1B significantly reduced Cu uptake from media, demonstrating that both these proteins function to transport Cu into S2 cells. Significantly, Cu induced Ctr1B gene expression, and this could be prevented by suppressing MTF-1, suggesting that Ctr1B might be involved in Cu detoxification. Suppression of DmATP7, the putative homologue of human Cu transporter genes ATP7A and ATP7B, significantly increased Cu accumulation, demonstrating that DmATP7 is essential for efflux of excess Cu. This work is consistent with previous studies in mammalian cells, validating S2 cells as a model system for studying Cu transport and identifying novel Cu regulatory mechanisms.