Nuclear Localization of Bovine Immunoglobulin G (bIgG) in the Liver of Rats Injected with Hydrocortisone-bIgG Conjugate Intravenously

Abstract

Summary: Bovine serum albumin conjugated with steroid hormone injected intravenously into rats can enter the hormone-target cell nuclei with its antigenicity kept intact (Nishimura and Nakano, 2000). Antinuclear antibodies (ANA) such as immunoglobulin G (IgG) are found in some autoimmune diseases. To confirm immunocytochemically whether immunoglobulin G (IgG) conjugated with steroid hormone enters in the hormone-target cell nuclei, bovine IgG (bIgG) was conjugated with hydrocortisone 21-hemisuccinate. The hydrocortisone-bIgG conjugate was injected into the vascular system of adrenalectomized rats. Then the rats were killed 2 or 3 h after injection to detect bovine IgG in the hormone-target cell nuclei of the liver by fluorescein-isothiocyanate labeled-anti bovine IgG antibody under confocal laser scanning microscopy. In the liver of both rats injected with hydrocortisone-bIgG, the fluorescence was observed in not only the cytoplasm but also the nuclei of liver cells. In control rat injected with bIgG, few nuclei showed fluorescence. These results demonstrate that bovine IgG conjugated with steroid hormone can enter the hormonetarget cell nuclei of rat with its antigenicity kept intact, and suggest that antinuclear antibody in some autoimmune diseases may be transported from blood plasma into the nucleus.Antinuclear antibodies (ANA) such as immunoglobulin G (IgG) are found in some autoimmune diseases such as autoimmune hepatitis (Alvarez et al., 1999;Nishioka and Morshed, 1999). IgG injected into the cytoplasm does not enter the nucleus (Lanford et al., 1986). Modified IgG combined with a short amino acid sequence (nuclear localization signal) can enter the nucleus from cytoplasm through the nuclear pore complex (NPC) (Lanford et al. , 1986;Nigg, 1997). However, the macromolecules, e.g., IgG, are not likely to pass freely through the cell membrane by passive transport. Accordingly, it is unclear how ANA enter the nucleus.Glucocorticoid receptor is detected in the nuclei of isolated hepatocytes, hepatic stellate cells and Kupffer cells of rat (Raddatz et aL, 1996). In neutrophil, the immunostaining of the glucocorticoid receptor is also visible in the cytoplasm, not in the segmented nucleus (Miller et al., 1998), as antineutrophil cytoplasmic antibodies (ANCA) in autoimmune liver diseases (Niles, 1996;Roozendaal et al., 2000). Thus, the distribution of antibodies in autoimmune liver diseases seems to correlate with that of glucocorticoid receptors.Radiolabeled steroid hormones like [3H]-hydrocortisone, may enter the target cell nuclei in vivo (Beato et al., 1969; Riistow et al., 1975). In the classic, or genomic model of steroid hormones, free lipophilic nonproteinbound hormones cross the cell membrane under passive transport to bind to the receptor in the cytoplasm, and the hormonereceptor complex is translocated into the target cell nucleus to exert genomic effects (Bamberger et al., 1996;Guiochon-Mantel et aL, 1996;Htun et al., 1996;Jensen and DeSombre, 1972;Madan and DeFranco, 1993;Mangelsdorf et al., 1995;Men...

Steroid Hormones as Transporters to Carry Exogenous Macromolecules into the Target Cell Nuclei in Vivo

“…When an antibody is introduced in the cytoplasm, the antibody reacts to its antigen [32]. Bovine IgG coupled with hydrocortisone injected into rat vascular system enters the hormone-target cell nuclei in the liver, maintaining the antigenicity [33]. This last finding also confirms that steroid hormones act as carriers to convey exogenous proteins into the target cell nuclei.…”

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

“…Steroid-BSA binds to nuclear receptors [24,25]. Bovine IgG coupled with hydrocortisone injected into adrenalectomized rat vascular system enters the hormone-target cell nuclei in the liver, maintaining the antigenicity [26]. Together, these findings support the idea that steroid hormones could be useful as target cell-specific carriers to deliver exogenous macromolecules into cell nuclei.…”