SUMMARY Small cell lung carcinoma (SCLC) is a high-grade pulmonary neuroendocrine tumor. The transcription factors ASCL1 and NEUROD1 play crucial roles in promoting malignant behavior and survival of human SCLC cell lines. We find ASCL1 and NEUROD1 identify heterogeneity in SCLC, bind distinct genomic loci, and regulate mostly distinct genes. ASCL1 but not NEUROD1 is present in mouse pulmonary neuroendocrine cells and only ASCL1 is required in vivo for tumor formation in mouse models of SCLC. ASCL1 targets oncogenic genes including MYCL1, RET, SOX2, and NFIB, while NEUROD1 targets MYC. ASCL1 and NEUROD1 regulate different genes that commonly contribute to neuronal function. ASCL1 also regulates multiple genes in the NOTCH pathway including DLL3. Together, ASCL1 and NEUROD1 distinguish heterogeneity in SCLC with distinct genomic landscapes and distinct gene expression programs.

The transcription factor E-twenty-six related gene (ERG), which is overexpressed through gene fusion with the androgen-responsive gene transmembrane protease, serine 2 (TMPRSS2) in ∼40% of prostate tumors, is a key driver of prostate carcinogenesis. Ablation of ERG would disrupt a key oncogenic transcriptional circuit and could be a promising therapeutic strategy for prostate cancer treatment. Here, we show that ubiquitin-specific peptidase 9, X-linked (USP9X), a deubiquitinase enzyme, binds ERG in VCaP prostate cancer cells expressing TMPRSS2-ERG and deubiquitinates ERG in vitro. USP9X knockdown resulted in increased levels of ubiquitinated ERG and was coupled with depletion of ERG. Treatment with the USP9X inhibitor WP1130 resulted in ERG degradation both in vivo and in vitro, impaired the expression of genes enriched in ERG and prostate cancer relevant gene signatures in microarray analyses, and inhibited growth of ERG-positive tumors in three mouse xenograft models. Thus, we identified USP9X as a potential therapeutic target in prostate cancer cells and established WP1130 as a lead compound for the development of ERGdepleting drugs. P rostate cancer is the most common malignancy in men and the second or third leading cause of male cancer-related death in most Western countries, including the United States (1). Advanced prostate cancer initially responds to androgen ablation therapy, but hormone-refractory prostate cancer often times recurs, which has limited treatment options. Fusions of E-twentysix (ETS) transcription factor genes with androgen-responsive genes (2), mainly transmembrane protease, serine 2 (TMPRSS2), are present in up to 80% of prostate cancers. Patients with the most common ETS gene fusion TMPRSS2-ETS related gene (TMPRSS2-ERG) have a higher incidence of metastatic disease and cancer-related death compared with fusion-negative patients (3, 4), and in castration-resistant prostate cancer, TMPRSS2-ERG expression is frequently reactivated (5). In support of ERG being a key driver of prostate cancer, depletion of ERG by RNAi decreases proliferation and/or invasiveness in prostate cancer cell lines (2, 6), and ectopic expression of ERG in transgenic mice was shown to promote prostate oncogenesis in cooperation with the loss of tumor suppressors (7-12). TMPRSS2-driven overexpression of ERG controls a transcriptional network related to the development of prostate cancer and its progression to metastatic disease (13,14). This crucial role of ERG and the high incidence of the TMPRSS2-ERG gene fusion in prostate cancer have catapulted this protein into the forefront of new targets for therapeutic intervention (3,8). In the present study, we report the discovery of a deubiquitinase that stabilizes ERG in prostate cancer cells and demonstrate that pharmacological inhibition of this enzyme causes ERG depletion. Results USP9X is an ERG-Binding Protein.Proteins that interact with ERG in prostate cancer cells may modulate its activity, localization, or stability and could be harnessed as therapeutic target...

Tumours frequently activate genes whose expression is otherwise biased to the testis, collectively known as cancer–testis antigens (CTAs). The extent to which CTA expression represents epiphenomena or confers tumorigenic traits is unknown. In this study, to address this, we implemented a multidimensional functional genomics approach that incorporates 7 different phenotypic assays in 11 distinct disease settings. We identify 26 CTAs that are essential for tumor cell viability and/or are pathological drivers of HIF, WNT or TGFβ signalling. In particular, we discover that Foetal and Adult Testis Expressed 1 (FATE1) is a key survival factor in multiple oncogenic backgrounds. FATE1 prevents the accumulation of the stress-sensing BH3-only protein, BCL-2-Interacting Killer (BIK), thereby permitting viability in the presence of toxic stimuli. Furthermore, ZNF165 promotes TGFβ signalling by directly suppressing the expression of negative feedback regulatory pathways. This action is essential for the survival of triple negative breast cancer cells in vitro and in vivo. Thus, CTAs make significant direct contributions to tumour biology.

SUMMARY Efforts to identify and target glioblastoma (GBM) drivers have primarily focused on receptor tyrosine kinases (RTKs). Clinical benefits, however, have been elusive. Here, we identify a SRY-related box 2 (SOX2) transcriptional regulatory network that is independent of upstream RTKs and is capable of driving glioma initiating cells. We identified oligodendrocyte lineage transcription factor 2 (OLIG2) and zinc finger E-box binding homeobox 1 (ZEB1) as potential SOX2 targets, which are frequently co-expressed irrespective of driver mutations. In murine glioma models, we show that different combinations of tumor suppressor and oncogene mutations can activate Sox2, Olig2, and Zeb1 expression. We demonstrate that ectopic co-expression of the three transcription factors can transform tumor suppressor deficient astrocytes into glioma initiating cells in the absence of an upstream RTK oncogene. Finally, we demonstrate that the transcriptional inhibitor mithramycin downregulates SOX2 and its target genes, resulting in markedly reduced proliferation of GBM cells in vivo.