AR-V7 Utilizes a Noncanonical Nuclear Localization Signal to Sustain Androgen-Independent Nuclear Import and Signaling

AR-V7, the most common androgen receptor splice variant present in advanced prostate cancer that is resistant to castration, has long puzzled researchers regarding its unique method of entering the cell nucleus. While full-length AR relies on a microtubule-based, importin-/{beta}- and Ran-dependent process, AR-V7 uses a different nuclear localization signal (NLS) that defies this conventional mechanism.

To uncover the details of this alternative nuclear import pathway, scientists employed systematic truncation and alanine-scanning mutagenesis to pinpoint a non-classical NLS at the junction of AR-V7's DNA-binding domain and a cryptic exon 3. This specific region, containing essential basic residues, not only facilitates AR-V7's nuclear entry but also plays a crucial role in its transcriptional activity.

Intriguingly, mutations that still allow limited nuclear localization were found to be transcriptionally inactive, indicating that the CE3 segment contributes to AR-V7's gene expression through mechanisms distinct from its nuclear transport. Genome-wide transcriptomic analysis of a mutant with severely impaired nuclear import further supported this notion, revealing that the absence of nuclear entry effectively halts the AR-V7 transcriptional program.

To delve deeper into the interaction networks of AR-V7, researchers utilized antibody-guided photocatalytic proximity labeling. This technique showed that functional AR-V7 predominantly interacts with canonical BAF and PBAF SWI/SNF chromatin remodeling complexes, alongside transcriptional coregulators and DNA-repair factors within the nucleus.

Conversely, a cytoplasm-restricted mutant engages different protein networks, focusing on mRNA deadenylation and decay, cytoskeletal regulation, and chaperone systems. These findings collectively highlight the importance of a variant-specific NLS, the separation of AR-V7's nuclear import process from its CE3-dependent transcriptional competence, and the identification of specific cytoplasmic networks that become active when AR-V7's nuclear entry is disrupted.

The study ultimately uncovers two distinct vulnerabilities in AR-V7 signaling: inhibiting nuclear translocation and impeding CE3-dependent transcriptional engagement within the nucleus, offering potential targets for therapeutic intervention.