NUCLEAR IMPORT OF THE HUMAN ANDROGEN RECEPTOR

Nuclear import of the human androgen receptor was investigated by immu nocytochemical analysis of androgen receptor deletion and substitution mutants, which were transiently expressed in COS-1 cells. The signal responsible for nuclear import is encoded by amino-acid residues 608-6 25 and is functionally similar to the bipartite nucleoplasmin nuclear- localization signal. Although the subcellular distribution of androgen receptors mutated in the DNA-binding domain was unchanged compared wi th the wild-type androgen receptor, in the presence of ligand these mu tations resulted in part of the receptor population forming clusters. Depending on the presence or absence of the bipartite nuclear localiza tion signal, clusters were formed in the nucleus or in the cytoplasm, respectively. Expression of the wild-type androgen receptor in differe nt cell lines revealed a cell-line-specific subcellular distribution o f the unliganded receptor. The androgen receptor was predominantly nuc lear when expressed in HeLa cells, whereas mainly cytoplasmic staining was observed when it was expressed in COS-1 cells. In the presence of hormone, the androgen receptor was located in the nucleus. independen t of the cell line that was expressing the receptor. Anti-androgens an d various steroid hormones induced the nuclear localization of the wil d-type androgen receptor in a dose-dependent way, without activating t ranscription of an androgen-regulated reporter gene. This indicates th at the inability of the tested compounds to activate transcription is not due to inhibited nuclear import.