The overexpression of the full-length androgen receptor (AR-FL) and/or the constitutively active AR splicing
variants (AR-Vs), such as AR-V7 and ARv567es lacking all or part of the ligand binding domain, contributes to
the development and progression of castration resistant prostate cancers (CRPC). Androgen deprivation therapy
(ADT) is not effective in CRPC overexpressing the AR-Vs and can even induce AR-V overexpression.
Proliferating cell nuclear antigen (PCNA), preferentially overexpressed in all tumor cells, is a non-oncogenic
protein essential for DNA replication and repair as well as cell growth and survival. Native PCNA is a ring-shaped
homotrimer located mainly in the nucleoplasm. To be functional, PCNA must be linearized or monomerized for
relocalization to chromatin, cytoplasm, or cell membrane, and serves as a platform for and executes its function
through interaction with partner proteins containing the PCNA-interacting protein box (PIP-box) and other motifs.
The PI’s group identified a consensus sequence of the PIP-box at the N-terminus of AR. PCNA complexes with
AR-FL and AR-V7, which can be attenuated by a PIP-box-specific inhibitor T2AA. PCNA also binds to ARv567es
and directly to recombinant AR protein. PCNA-I1S, a small molecule PCNA inhibitor developed by PI’s group,
binds at the interface of two monomers, stabilizes trimer structure, and attenuates PCNA association to
chromatin. PCNA-I1S and T2AA inhibit AR transcriptional activity and expression of AR target genes in CRPC
LNCaP-AI and 22Rv1 cells. The knockdown expression of PCNA reduces dihydrotestosterone-stimulated AR
transcriptional activity and abolishes the inhibitory effects of PCNA-I1S on AR activity. More importantly, an AR-
specific PIP-box peptide inhibitor R9-AR-PIP, developed recently in the PI’s lab, binds to PCNA and inhibits AR
transcriptional activity, expression of AR target genes, and growth of AR-positive cells. Based on these
observations, the PI hypothesizes that PCNA interacts with AR-FL and AR-Vs through the AR PIP-box and
enhances AR transcriptional activities and that targeting the PCNA-AR interaction will attenuate AR-FL-
and AR-V-mediated signaling and inhibit growth of CRPC overexpressing AR-FL and/or AR-Vs. Two
specific aims are proposed. Studies in aim 1 will further elucidate the role of the AR PIP-box in the interaction of
AR-FL and AR-Vs with PCNA by protein mutagenesis and investigate the inhibitory effects of PCNA-I1S, T2AA,
and R9-AR-PIP on the colocalization and chromatin association of PCNA with AR-FL and AR-Vs, the role of
PCNA-AR interaction in recruitment of AR-FL and AR-Vs to chromatin, and the selective inhibitory effects of R-
9-AR-PIP on AR-PCNA interaction. Studies in aim 2 will determine the inhibitory effects of PCNA-I1S, T2AA,
and R9-AR-PIP on the occupancy of the androgen response elements by AR-FL and AR-Vs, the transcriptional
activity of AR-FL and AR-V7, and expression of AR-V-specific genes. Moreover, the cytotoxic effects of R9-AR-
PIP on CRPC cells in culture, the therapeutic effects of R9-AR-PIP against CRPC xenograft tumors in mice, and
the selective inhibitory effects of R9-AR-PIP on AR signaling in the CRPC tumors will be investigated.
