The cytokine interleukin-5 (IL-5) effects cotransport of its receptor subunits to the nucleus in vitro

Interleukin (IL)-5 is central in regulating eosinophilia in allergic disease and parasitic infections, We have recently shown that human (h) IL-5 both possesses a functional nuclear localization signal capable of targeting a heterologous protein to the nucleus and localises to the nucleus of intact receptor-expressing cells, In this study, the extracellular domains of the hIL-5 alpha- and beta-receptor subunits were expressed in baculovirus, fluorescently labelled and assayed for nuclear targeting in vitro in the absence and presence of IL-5, The beta-subunit, which lacks IL-5 binding activity, only accumulated in the nucleus in the presence of both the hIL-5 binding alpha-subunit and hIL-5, The IL-5-binding alpha-subunit showed similar results, IL-5 thus effected nuclear transport of its alpha- and beta-receptor subunits apparently through a 'piggy back' mechanism, raising the possibility that IL-5's nuclear signalling role may be to cotarget its receptor subunits to the nucleus, This is the first demonstration of nuclear protein piggy back transport in vitro. (C) 1997 Federation of European Biochemical Societies.