Citations

AbstractDNA‐binding proteins, including transcription factors (TFs), play essential roles in various cellular processes and pathogenesis of diseases, deeming to be potential therapeutic targets. However, these proteins are generally considered undruggable as they lack an enzymatic catalytic site or a ligand‐binding pocket. Proteolysis‐targeting chimera (PROTAC) technology has been developed by engineering a bifunctional molecule chimera to bring a protein of interest (POI) to the proximity of an E3 ubiquitin ligase, thus inducing the ubiquitination of POI and further degradation through the proteasome pathway. Here, the development of oligonucleotide‐based PROTAC (O'PROTACs), a class of noncanonical PROTACs in which a TF‐recognizing double‐stranded oligonucleotide is incorporated as a binding moiety of POI is reported. It is demonstrated that O'PROTACs of lymphoid enhancer‐binding factor 1 (LEF1) and ETS‐related gene (ERG), two highly cancer‐related transcription factors, successfully promote degradation of these proteins, impede their transcriptional activity, and inhibit cancer cell growth in vitro and in vivo. The programmable nature of O'PROTACs indicates that this approach is also applicable to destruct other TFs. O'PROTACs not only can serve as a research tool but also can be harnessed as a therapeutic arsenal to target DNA binding proteins for effective treatment of diseases such as cancer.

Abstract Molecular mechanisms underlying intratumoral androgenesis and aberrant androgen receptor (AR) activation in prostate cancer remain poorly understood. Here we demonstrate that ectopic expression of the E3 ubiquitin ligase adaptor speckle-type poxvirus and zinc finger domain protein (SPOP) stabilizes 17βHSD4. SPOP bound a functional substrate-binding consensus (SBC) motif 315RATST319 in 17βHSD4 and promoted nondegradable K27- and K29-linked polyubiquitination of 17βHSD4. The effect of SPOP was antagonized by serum- and glucocorticoid kinase-3 (SGK3)-mediated phosphorylation of serine 318 (S318) in the SBC and S318 phosphorylation-dependent binding of SKP2 E3 ligase and subsequent K48-linked polyubiquitination and proteasomal degradation of 17βHSD4. Prostate cancer–associated SPOP mutations impaired the SPOP-17βHSD4 interaction, caused 17βHSD4 protein destruction in prostate cancer cells in culture and patient specimens, and increased testosterone production and prostate cancer cell growth in vitro and in mouse models. Thus, we have identified SPOP and SKP2 as two essential E3 ubiquitin ligases that exert opposite effects on 17βHSD4 protein degradation and intratumoral androgenesis in prostate cancer cells. We further demonstrate that SPOP mutations or SKP2 overexpression contribute to prostate cancer progression by decreasing 17βHSD4 expression and increasing intratumoral androgen synthesis. Significance: This study reveals a novel mechanism of aberrant AR activation in SPOP-mutated prostate cancer and uncovers putative biomarkers for effective treatment by AR-targeted therapies.

Abstract Purpose: Deletions or mutations in PTEN and TP53 tumor suppressor genes have been linked to lineage plasticity in therapy-resistant prostate cancer. Fusion-driven overexpression of the oncogenic transcription factor ERG is observed in approximately 50% of all prostate cancers, many of which also harbor PTEN and TP53 alterations. However, the role of ERG in lineage plasticity of PTEN/TP53–altered tumors is unclear. Understanding the collective effect of multiple mutations within one tumor is essential to combat plasticity-driven therapy resistance. Experimental Design: We generated a Pten-negative/Trp53-mutated/ERG-overexpressing mouse model of prostate cancer and integrated RNA-sequencing with ERG chromatin immunoprecipitation-sequencing (ChIP-seq) to identify pathways regulated by ERG in the context of Pten/Trp53 alteration. We investigated ERG-dependent sensitivity to the antiandrogen enzalutamide and cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor palbociclib in human prostate cancer cell lines, xenografts, and allografted mouse tumors. Trends were evaluated in TCGA, SU2C, and Beltran 2016 published patient cohorts and a human tissue microarray. Results: Transgenic ERG expression in mice blocked Pten/Trp53 alteration–induced decrease of AR expression and downstream luminal epithelial genes. ERG directly suppressed expression of cell cycle–related genes, which induced RB hypophosphorylation and repressed E2F1-mediated expression of mesenchymal lineage regulators, thereby restricting adenocarcinoma plasticity and maintaining antiandrogen sensitivity. In ERG-negative tumors, CDK4/6 inhibition delayed tumor growth. Conclusions: Our studies identify a previously undefined function of ERG to restrict lineage plasticity and maintain antiandrogen sensitivity in PTEN/TP53–altered prostate cancer. Our findings suggest ERG fusion as a biomarker to guide treatment of PTEN/TP53-altered, RB1-intact prostate cancer. Clin Cancer Res; 24(18); 4551–65. ©2018 AACR.

Abstract Purpose: Intratumoral androgen synthesis (IAS) is a key mechanism promoting androgen receptor (AR) reactivation and antiandrogen resistance in castration-resistant prostate cancer (CRPC). However, signaling pathways driving aberrant IAS remain poorly understood. Experimental Design: The effect of components of the AKT-RUNX2-osteocalcin (OCN)–GPRC6A–CREB signaling axis on expression of steroidogenesis genes CYP11A1 and CYP17A1 and testosterone level were examined in PTEN-null human prostate cancer cell lines. Pten knockout mice were used to examine the effect of Runx2 heterozygous deletion or abiraterone acetate (ABA), a prodrug of the CYP17A1 inhibitor abiraterone on Cyp11a1 and Cyp17a1 expression, testosterone level and tumor microenvironment (TME) remodeling in vivo. Results: We uncovered that activation of the AKT–RUNX2–OCN–GPRC6A–CREB signaling axis induced expression of CYP11A1 and CYP17A1 and testosterone production in PTEN-null prostate cancer cell lines in culture. Deletion of Runx2 in Pten homozygous knockout prostate tumors decreased Cyp11a1 and Cyp17a1 expression, testosterone level, and tumor growth in castrated mice. ABA treatment also inhibited testosterone synthesis and alleviated Pten loss-induced tumorigenesis in vivo. Pten deletion induced TME remodeling, but Runx2 heterozygous deletion or ABA treatment reversed the effect of Pten loss by decreasing expression of the collagenase Mmp9. Conclusions: Abnormal RUNX2 activation plays a pivotal role in PTEN loss-induced IAS and TME remodeling, suggesting that the identified signaling cascade represents a viable target for effective treatment of PTEN-null prostate cancer, including CRPC. Clin Cancer Res; 24(4); 834–46. ©2017 AACR.

Abstract E26 transformation-specific transcription factor ERG is aberrantly overexpressed in approximately 50% of all human prostate cancer due to TMPRSS2-ERG gene rearrangements. However, mice with prostate-specific transgenic expression of prostate cancer–associated ERG alone fail to develop prostate cancer, highlighting that ERG requires other lesions to drive prostate tumorigenesis. Forkhead box (FOXO) transcription factor FOXO1 is a tumor suppressor that is frequently inactivated in human prostate cancer. Here, we demonstrate that FOXO1, but not other FOXO proteins (FOXO3 and FOXO4), binds and inhibits the transcriptional activity of prostate cancer–associated ERG independently of FOXO1 transcriptional activity. Knockdown of endogenous FOXO1 increased invasion of TMPRSS2–ERG fusion–positive VCaP cells, an effect completely abolished by ERG knockdown. Patient specimen analysis demonstrated that FOXO1 and ERG protein expression inversely correlated in a subset of human prostate cancer. Although human ERG transgene expression or homozygous deletion of Foxo1 alone in the mouse prostate failed to promote tumorigenesis, concomitant ERG transgene expression and Foxo1 deletion resulted in upregulation of ERG target genes, increased cell proliferation, and formation of high-grade prostatic intraepithelial neoplasia. Overall, we provide biochemical and genetic evidence that aberrantly activated ERG cooperates with FOXO1 deficiency to promote prostate tumorigenesis and cell invasion. Our findings enhance understanding of prostate cancer etiology and suggest that the FOXO1–ERG signaling axis can be a potential target for treatment of prostate cancer. Cancer Res; 77(23); 6524–37. ©2017 AACR.