Valanne, S., Myllymäki, H., Kallio, J., Schmid, M.R., Kleino, A., Murumägi, A., Airaksinen, L., Kotipelto, T., Kaustio, M., Ulvila, J., Esfahani, S.S., Engström, Y., Silvennoinen, O., Hultmark, D., Parikka, M., Rämet, M. (2010). Genome-wide RNA interference in Drosophila cells identifies G protein-coupled receptor kinase 2 as a conserved regulator of NF-kappaB signaling.  J. Immunol. 184(11): 6188--6198.

FBrf0210846

Research paper

Because NF-kappaB signaling pathways are highly conserved in evolution, the fruit fly Drosophila melanogaster provides a good model to study these cascades. We carried out an RNA interference (RNAi)-based genome-wide in vitro reporter assay screen in Drosophila for components of NF-kappaB pathways. We analyzed 16,025 dsRNA-treatments and identified 10 novel NF-kappaB regulators. Of these, nine dsRNA-treatments affect primarily the Toll pathway. G protein-coupled receptor kinase (Gprk)2, CG15737/Toll pathway activation mediating protein, and u-shaped were required for normal Drosomycin response in vivo. Interaction studies revealed that Gprk2 interacts with the Drosophila IkappaB homolog Cactus, but is not required in Cactus degradation, indicating a novel mechanism for NF-kappaB regulation. Morpholino silencing of the zebrafish ortholog of Gprk2 in fish embryos caused impaired cytokine expression after Escherichia coli infection, indicating a conserved role in NF-kappaB signaling. Moreover, small interfering RNA silencing of the human ortholog GRK5 in HeLa cells impaired NF-kappaB reporter activity. Gprk2 RNAi flies are susceptible to infection with Enterococcus faecalis and Gprk2 RNAi rescues Toll(10b)-induced blood cell activation in Drosophila larvae in vivo. We conclude that Gprk2/GRK5 has an evolutionarily conserved role in regulating NF-kappaB signaling.