TRANSCRIPTIONAL ACTIVATION AND TRANSIENT EXPRESSION OF THE HUMAN ANDROGEN RECEPTOR

A series of cDNAs containing deletions within the open-reading frame o f the human androgen receptor (AR) were constructed and transiently ex pressed in CV1 cells to investigate the effects of these alterations o n the level of expression of the protein and on its capacity to activa te a model reporter gene (MMTV-luciferase). The levels of AR expressio n were assayed using immunoblots made using an antibody directed at an epitope (amino acids 1-21) preserved in all of the deletions. Treatme nt of the transfected cells with androgen increased the level of norma l or mutant AR approximately five-fold in all constructs in which the hormone-binding domain was intact. This finding indicates that an inta ct hormone-binding domain is necessary and sufficient for the androgen -dependent increase in AR levels. Contraction of expansion or the glut amine repeat or deletion of the glycine repeat in the amino terminus d iminished the capacity of the mutant ARs to activate the MMTV lucifera se gene. The presence of a large-scale deletion within the amino termi nus (amino acid residues 96-483), abolished receptor function, and two smaller deletions (bounded by residues 80-93 and 245-485) within the amino terminus substantially impaired receptor function. As previously described, deletion of the hormone-binding domain (amino acids 708-91 7) resulted in a constitutively active receptor. Unexpectedly, the lar ge-scale deletion within the amino terminus (amino acids 96-483), in c ombination with deletion of the carboxy terminus also produced a const itutively active receptor that was almost as active as ligand-activate d normal AR. None of the alterations in AR function could be explained by changes in the level of AR expression and the function of some mut ant receptors was even more defective when the relative levels of muta nt ARs expressed was considered. These findings imply that interaction of the sequences within the amino- and carboxyterminal portions of th e AR, or proteins that interact with these segments, is critical for r egulation of transcription by the AR. Copyright (C) 1996 Elsevier Scie nce Ltd.