NF-κB2/p52:c-Myc:hnRNPA1 Pathway Regulates Expression of Androgen Receptor Splice Variants and Enzalutamide Sensitivity in Prostate Cancer

Abstract

Castration resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signaling. Alternative splicing of the AR to generate constitutively active, ligand-independent variants is one of the principal mechanisms that promote the development of resistance to next-generation anti-androgens such as enzalutamide. Here, we demonstrate that the splicing factor heterogeneous nuclear RNA-binding protein A1 (hnRNPA1) plays a pivotal role in the generation of AR splice variants such as AR-V7. HnRNPA1 is overexpressed in prostate tumors compared to benign prostates and its expression is regulated by NF-kappaB2/p52 and c-Myc. CRPC cells resistant to enzalutamide exhibit higher levels of NF-kappaB2/p52, c-Myc, hnRNPA1, and AR-V7. Levels of hnRNPA1 and of AR-V7 are positively correlated with each other in PCa. The regulatory circuit involving NF-kappaB2/p52, c-Myc and hnRNPA1 plays a central role in the generation of AR splice variants. Downregulation of hnRNPA1 and consequently of AR-V7 resensitizes enzalutamide-resistant cells to enzalutamide, indicating that enhanced expression of hnRNPA1 may confer resistance to AR-targeted therapies by promoting the generation of splice variants. These findings may provide a rationale for co-targeting these pathways to achieve better efficacy through AR blockade.

Quercetin Targets hnRNPA1 to Overcome Enzalutamide Resistance in Prostate Cancer Cells

“…Our previous studies showed that the splicing factor, hnRNPA1, plays a critical role in the alternative splicing of the AR to generate splice variants such as AR-V7 (11). We also demonstrated that the suppression of hnRNPA1 expression using siRNA reduces the levels of AR-V7, thereby resensitizing enzalutamide-resistant cells to treatment with enzalutamide.…”

“…The variants confer resistance to not only AR targeted therapies such as enzalutamide and abiraterone (5, 6), but also to conventional chemotherapeutics such as taxanes used as first line therapies against CRPC (7, 8). The mechanisms mediating increased expression of aberrant AR splice variants in PCa are being actively investigated, the possible causes being either genomic rearrangement and/or intragenic deletions of the AR locus (9) or aberrant expression/recruitment of specific splicing factors (10, 11). …”

“…We reported previously that the splicing factor hnRNPA1 plays a major role in the alternative splicing of the AR to generate AR-V7 (11). Based on the hypothesis that the generation of AR-V7 is one of the principal mechanisms of resistance to enzalutamide and targeting alternative splicing would be beneficial in reducing the levels of AR-V7 and overcoming therapy resistance, we set out to identify compounds that target the expression of the splicing factor hnRNPA1.…”

MYCN controls an alternative RNA splicing program in high-risk metastatic neuroblastoma

“…Mutations in HNRNPA1 cause multisystem proteinopathy and ALS [25], and the function of this gene is linked to muscle differentiation and cell survival [22, 62]. Similar to PTBP1, HNRNPA1 is up-regulated in hepatocellular carcinoma and prostate cancer, which result in aberrant splicing in tumors [5, 30]. …”

Androgen receptor splice variant 7 (AR-V7) and drug efficacy in castration-resistant prostate cancer: Biomarker for treatment selection exclusion or inclusion?

“…15 Downregulation of heterogeneous nuclear RNA-binding protein A1 (hnRNPA1) resensitizes enzalutamide-resistant cells to enzalutamide, indicating that this may inhibit the generation of AR splice variants. 16 Stockley et. al.…”