Transportation Course of Macromolecules to the Nucleus from the Extracellular Environment: Steroid Hormones’ Cellular Entry Mode Revisited

Polyomavirus virions such as simian virus 40 (SV40), antinuclear antibodies such as immunoglobulin G (IgG) and steroid hormones all enter the nucleus from the extracellular environment. Testosterone-bovine serum albumin conjugate labeled with 2 nm colloidal gold (testosterone-BSA-gold) is taken up by endocytosis into target cells, and enter the nucleus through a similar route as SV40 nuclear migration. Upon injection into the vascular system of rats, IgG coupled with hydrocortisone also enters the hormone-target cell nuclei with intact antigenicity. These results suggest that steroid hormones could act as transporters to deliver exogenous macromolecules, e.g. drugs, into their target cell nuclei in vivo, although further studies are required on whether steroid hormones coupled with proteins exert genomic actions in the nucleus, etc. Finally, testosterone-BSA-gold seems to be isolated from the cytosol in the processes of nuclear entry. Together, these findings challenge the popular belief that steroid hormones mostly enter the cell in unbound form via uncontrolled passive diffusion