Citations

In this study, we discovered 3-aminophthalic acid as a new ligand of cereblon (CRBN) E3 ubiquitin ligase and developed a phthalic acid-based O’PROTAC for ERG destruction, expanding the pool of ligands for development of PROTACs, especially O’PROTACs.

Abstract Although the Sonic hedgehog (SHH) signaling pathway has been implicated in promoting malignant phenotypes of prostate cancer, details on how it is activated and exerts its oncogenic role during prostate cancer development and progression is less clear. Here, we show that GLI3, a key SHH pathway effector, is transcriptionally upregulated during androgen deprivation and posttranslationally stabilized in prostate cancer cells by mutation of speckle-type POZ protein (SPOP). GLI3 is a substrate of SPOP-mediated proteasomal degradation in prostate cancer cells and prostate cancer driver mutations in SPOP abrogate GLI3 degradation. Functionally, GLI3 is necessary and sufficient for the growth and migration of androgen receptor (AR)–positive prostate cancer cells, particularly under androgen-depleted conditions. Importantly, we demonstrate that GLI3 physically interacts and functionally cooperates with AR to enrich an AR-dependent gene expression program leading to castration-resistant growth of xenografted prostate tumors. Finally, we identify an AR/GLI3 coregulated gene signature that is highly correlated with castration-resistant metastatic prostate cancer and predictive of disease recurrence. Together, these findings reveal that hyperactivated GLI3 promotes castration-resistant growth of prostate cancer and provide a rationale for therapeutic targeting of GLI3 in patients with castration-resistant prostate cancer (CRPC). Implications: We describe two clinically relevant mechanisms leading to hyperactivated GLI3 signaling and enhanced AR/GLI3 cross-talk, suggesting that GLI3-specific inhibitors might prove effective to block prostate cancer development or delay CRPC.

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.

Objectives To investigate the genetic alterations of patients with prostate cancer (PCa) with and without intraductal carcinoma of the prostate (IDC‐P). Patients and Methods We performed targeted sequencing of plasma cell‐free DNA on 161 patients with prostate adenocarcinoma (PAC) with IDC‐P and 84 without IDC‐P. Genomic alterations were compared between these two groups. The association between genetic alterations and patients’ survival outcomes was also explored. Results We identified that 29.8% (48/161) and 21.4% (18/84) of patients with and without IDC‐P harboured genomic alterations in DNA repair pathways, respectively ( P = 0.210). Pathogenic germline DNA repair alterations were frequently detected in IDC‐P carriers compared to IDC‐P non‐carriers (11.8% [19/161] vs 2.4% [two of 84], P = 0.024). Germline BReast CAncer type 2 susceptibility protein ( BRCA2 ) and somatic cyclin‐dependent kinase 12 ( CDK12 ) defects were specifically identified in IDC‐P carriers relative to PAC ( BRCA2 : 8.7% [14/161] vs 0% and CDK12 : 6.8% [11/161] vs 1.2% [one of 84]). Patients with IDC‐P had a distinct androgen receptor (AR) pathway alteration, characterised by an enrichment of nuclear receptor corepressor 2 ( NCOR2 ) mutations compared with patients with pure PAC (21.1% [34/161] vs 6.0% [five of 84], P = 0.004). Increased AR alterations were detected in patients harbouring tumours with an IDC‐P proportion of ≥10% vs those with an IDC‐P proportion of <10% (6.4% [five of 78] vs 18.1% [15/83], P = 0.045). For IDC‐P carriers, tumour protein p53 ( TP53 ) mutation was associated with shorter castration‐resistant‐free survival (median 10.9 vs 28.9 months, P = 0.026), and BRCA2 alteration was related to rapid prostate‐specific antigen progression for those receiving abiraterone treatment (median 9.1 vs 11.9 months, P = 0.036). Conclusion Our findings provide genomic evidence explaining the aggressive phenotype of tumours with IDC‐P, highlighting the potential therapeutic strategies for this patient population.

Abstract Androgen receptor (AR) is a major survival factor for prostate cancer. Inflammation is implicated in many cancer types, including prostate cancer. Activation of MAP3K7 (also termed TAK1) and downstream IκB kinase β (IKKβ) by proinflammatory cytokines such as TNFα stimulates NF-κB survival pathways. Paradoxically, MAP3K7 is often deleted in human prostate cancer. Here, we demonstrate that AR protein expression is lower in inflammatory tumor areas compared with non-inflammatory tissues in patients with prostate cancer. Map3k7 knockout increased AR protein levels and activity in the mouse prostate, and MAP3K7 and AR protein levels were inversely correlated in prostate cancer patient specimens. TNFα treatment increased AR protein ubiquitination and proteasomal degradation. Mechanistically, activation of IKKβ by TNFα induced phosphorylation and TRCP1/2 E3 ligase–mediated polyubiquitination and degradation of AR protein. TNFα suppressed prostate cancer proliferation, which could be rescued by blockade of AR degradation. These findings reveal a previously unrecognized tumor suppressive function of the inflammation-activated MAP3K7–IKKβ axis in degrading AR protein. Moreover, they suggest that aberrant elevation of AR protein could be a prognostic biomarker and therapeutic target for MAP3K7-deficient prostate cancer. Significance: This study identifies that MAP3K7–IKKβ signaling plays a tumor-suppressive role in prostate cancer by degrading AR, revealing potential prognostic and therapeutic strategies for MAP3K7-deficient tumors.

Background: Thousands of gene fusions have been reported in prostate cancer, but their authenticity, incidence, and tumor specificity have not been thoroughly evaluated, nor have their genomic characteristics been carefully explored. Methods: We developed FusionVet to dedicatedly validate known fusion genes using RNA-seq alignments. Using FusionVet, we re-assessed 2727 gene fusions reported from 36 studies using the RNA-seq data generated by The Cancer Genome Atlas (TCGA). We also explored their genomic characteristics and interrogated the transcriptomic and DNA methylomic consequences of the E26 transformation-specific (ETS) fusions. Results: We found that nearly two-thirds of reported fusions are intra-chromosomal, and 80% of them were formed between 2 protein-coding genes. Although most (76%) genes were fused to only 1 partner, we observed many fusion hub genes that have multiple fusion partners, including ETS family genes, androgen receptor signaling pathway genes, tumor suppressor genes, and proto-oncogenes. More than 90% of the reported fusions cannot be validated by TCGA RNA-seq data. For those fusions that can be validated, 5% were detected from tumor and normal samples with similar frequencies, and only 4% (120 fusions) were tumor-specific. The occurrences of ERG, ETV1, and ETV4 fusions were mutually exclusive, and their fusion statuses were tightly associated with overexpressions. Besides, we found ERG fusions were significantly co-occurred with PTEN deletion but mutually exclusive with common genomic alterations such as SPOP mutation and FOXA1 mutation. Conclusions: Most of the reported fusion genes cannot be validated by TCGA samples. The ETS family and androgen response genes were significantly enriched in prostate cancer–specific fusion genes. Transcription activity was significantly repressed, and the DNA methylation was significantly increased in samples carrying ERG fusion.

SPOP mutation disables 53BP1 ubiquitination and exclusion from DNA double-strand break sites and causes genome instability.

The CREB-binding protein (CBP) and p300 are two paralogous lysine acetyltransferases (KATs) that were discovered in the 1980s–1990s. Since their discovery, CBP/p300 have emerged as important regulatory proteins due to their ability to acetylate histone and non-histone proteins to modulate transcription. Work in the last 20 years has firmly established CBP/p300 as critical regulators for nuclear hormone signaling pathways, which drive tumor growth in several cancer types. Indeed, CBP/p300 are critical co-activators for the androgen receptor (AR) and estrogen receptor (ER) signaling in prostate and breast cancer, respectively. The AR and ER are stimulated by sex hormones and function as transcription factors to regulate genes involved in cell cycle progression, metabolism, and other cellular functions that contribute to oncogenesis. Recent structural studies of the AR/p300 and ER/p300 complexes have provided critical insights into the mechanism by which p300 interacts with and activates AR- and ER-mediated transcription. Breast and prostate cancer rank the first and forth respectively in cancer diagnoses worldwide and effective treatments are urgently needed. Recent efforts have identified specific and potent CBP/p300 inhibitors that target the acetyltransferase activity and the acetytllysine-binding bromodomain (BD) of CBP/p300. These compounds inhibit AR signaling and tumor growth in prostate cancer. CBP/p300 inhibitors may also be applicable for treating breast and other hormone-dependent cancers. Here we provide an in-depth account of the critical roles of CBP/p300 in regulating the AR and ER signaling pathways and discuss the potential of CBP/p300 inhibitors for treating prostate and breast 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 TFE3-translocation renal cell carcinoma (TFE3-tRCC) is a rare and heterogeneous subtype of kidney cancer that has no standard treatment for advanced disease. We described comprehensive molecular characteristics of 63 untreated primary TFE3-tRCCs based on whole-exome and RNA sequencing. TFE3-tRCC is highly heterogeneous, both clinicopathologically and genotypically. ASPSCR1-TFE3 fusion, certain fusion isoforms and high somatic copy number alteration burdens were associated with aggressive features and poor outcomes. Apart from tumors with MED15-TFE3 fusion, most TFE3-tRCCs exhibited low PD-L1 expression and low T-cell infiltration. Unsupervised transcriptomic analysis revealed five molecular clusters with distinct angiogenesis, stroma, proliferation and KRAS down signatures, which showed association with fusion patterns and prognosis. Specifically, the high angiogenesis/stroma/proliferation cluster exclusively consisted of tumors with ASPSCR1-TFE3 fusion, which was likely to benefit from combination of immune checkpoint and anti-angiogenesis inhibitors. Our findings reveal the genomic and transcriptomic features of TFE3-tRCC and provide insights into precision medicine for this disease.