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The immunosuppressive tumor microenvironment in some cancer types, such as luminal breast cancer, supports tumor growth and limits therapeutic efficacy. Identifying approaches to induce an immunostimulatory environment could help improve cancer treatment. Here, we demonstrate that inhibition of cancer-intrinsic EZH2 promotes antitumor immunity in estrogen receptor α–positive (ERα+) breast cancer. EZH2 is a component of the polycomb-repressive complex 2 (PRC2) complex, which catalyzes trimethylation of histone H3 at lysine 27 (H3K27me3). A 53-gene PRC2 activity signature was closely associated with the immune responses of ERα+ breast cancer cells. The stimulatory effects of EZH2 inhibition on immune surveillance required specific activation of type I IFN signaling. Integrative analysis of PRC2-repressed genes and genome-wide H3K27me3 landscape revealed that type I IFN ligands are epigenetically silenced by H3K27me3. Notably, the transcription factor STAT2, but not STAT1, mediated the immunostimulatory functions of type I IFN signaling. Following EZH2 inhibition, STAT2 was recruited to the promoters of IFN-stimulated genes even in the absence of the cytokines, suggesting the formation of an autocrine IFN-STAT2 axis. In patients with luminal breast cancer, high levels of EZH2 and low levels of STAT2 were associated with the worst antitumor immune responses. Collectively, this work paves the way for the development of an effective therapeutic strategy that may reverse immunosuppression in cancer.Significance:Inhibition of EZH2 activates a type I IFN-STAT2 signaling axis and provides a therapeutic strategy to stimulate antitumor immunity and therapy responsiveness in immunologically cold luminal breast cancer.

The immunosuppressive tumor microenvironment in some cancer types, such as luminal breast cancer, supports tumor growth and limits therapeutic efficacy. Identifying approaches to induce an immunostimulatory environment could help improve cancer treatment. Here, we demonstrate that inhibition of cancer-intrinsic EZH2 promotes antitumor immunity in estrogen receptor α–positive (ERα+) breast cancer. EZH2 is a component of the polycomb-repressive complex 2 (PRC2) complex, which catalyzes trimethylation of histone H3 at lysine 27 (H3K27me3). A 53-gene PRC2 activity signature was closely associated with the immune responses of ERα+ breast cancer cells. The stimulatory effects of EZH2 inhibition on immune surveillance required specific activation of type I IFN signaling. Integrative analysis of PRC2-repressed genes and genome-wide H3K27me3 landscape revealed that type I IFN ligands are epigenetically silenced by H3K27me3. Notably, the transcription factor STAT2, but not STAT1, mediated the immunostimulatory functions of type I IFN signaling. Following EZH2 inhibition, STAT2 was recruited to the promoters of IFN-stimulated genes even in the absence of the cytokines, suggesting the formation of an autocrine IFN-STAT2 axis. In patients with luminal breast cancer, high levels of EZH2 and low levels of STAT2 were associated with the worst antitumor immune responses. Collectively, this work paves the way for the development of an effective therapeutic strategy that may reverse immunosuppression in cancer. Significance: Inhibition of EZH2 activates a type I IFN-STAT2 signaling axis and provides a therapeutic strategy to stimulate antitumor immunity and therapy responsiveness in immunologically cold luminal breast cancer.

Down-regulation of HMBOX1 via METTL3-catalyzed m6A causes genomic instability driven by telomere dysfunction in cancer., The role of RNA methylation on N6-adenosine (m6A) in cancer has been acknowledged, but the underlying mechanisms remain obscure. Here, we identified homeobox containing 1 (HMBOX1) as an authentic target mRNA of m6A machinery, which is highly methylated in malignant cells compared to the normal counterparts and subject to expedited degradation upon the modification. m6A-mediated down-regulation of HMBOX1 causes telomere dysfunction and inactivation of p53 signaling, which leads to chromosome abnormalities and aggressive phenotypes. CRISPR-based, m6A-editing tools further prove that the methyl groups on HMBOX1 per se contribute to the generation of altered cancer genome. In multiple types of human cancers, expression of the RNA methyltransferase METTL3 is negatively correlated with the telomere length but favorably with fractions of altered cancer genome, whereas HMBOX1 mRNA levels show the opposite patterns. Our work suggests that the cancer-driving genomic alterations may potentially be fixed by rectifying particular epitranscriptomic program.

In motile cells, the activities of the different Rho family GTPases are spatially segregated within the cell, and during cytokinesis there is evidence that this may also be the case. But while Rho’s role as the central organizer for contractile ring assembly is well established, the role of Rac and the branched actin networks it promotes is less well understood. To characterize the contributions of these proteins during cytokinesis, we manipulated Rac and Arp2/3 activity during mitosis and meiosis in sea urchin embryos and sea star oocytes. While neither Rac nor Arp2/3 were essential for early embryonic divisions, loss of either Rac or Arp2/3 activity resulted in polar body defects. Expression of activated Rac resulted in cytokinesis failure as early as the first division, and in oocytes, activated Rac suppressed both the Rho wave that traverses the oocyte prior to polar body extrusion as well as polar body formation itself. However, the inhibitory effect of Rac on cytokinesis, polar body formation and the Rho wave could be suppressed by effector-binding mutations or direct inhibition of Arp2/3. Together, these results suggest that Rac- and Arp2/3 mediated actin networks may directly antagonize Rho signaling, thus providing a potential mechanism to explain why Arp2/3-nucleated branched actin networks must be suppressed at the cell equator for successful cytokinesis.

The purpose of this study is to investigate how the activity of the glucocorticoid receptor (GR) is orchestrated to drive the development of enzalutamide resistance in metastatic, castration resistant prostate cancer (mCRPC). Enzalutamide (Enz) is the second-generation antagonist of the androgen receptor, the fuel for the development and progression of prostate cancer. Even though enzalutamide is an effective and well-tolerated treatment in a broad spectrum of patients with castration-resistant prostate cancer, almost all the patients become resistant to the drug eventually. One of the plausible mechanisms to account for the development of enzalutamide resistance is the activation of GR signaling. Upon Enz treatment, GR is upregulated, binds to the cis-regulatory elements of some AR target genes, activates the transcription of these downstream genes and thus circumvents the inhibitory effect of the AR antagonist on prostate cancer cell growth. Unfortunately, it is still unknown how GR-mediated enzalutamide resistance is controlled. Recently, a group of epigenetic regulators, bromodomain (BRD)-containing proteins, have been indicated to promote prostate cancer progression. They function as AR cofactors and dictate the transcriptional activity of the nuclear receptor in response to different ligands. Our prior work found that one of the BRD family members, called ATAD2, plays an essential role in orchestration of GR signaling in the presence of enzalutamide. ATAD2 is significantly elevated upon GR activation and positively regulates GR expression in return. Coimmunoprecipitation demonstrated that ATAD2 binds to GR in enzalutamide-resistant CRPC cells, and it is required for the GR-dependent transcriptional reprogramming in the presence of Enz. Most importantly, we demonstrated that CRPC cells that are Enz-refractory due to the activation of GR signaling become Enz sensitive when ATAD2 is depleted All these findings suggest that ATAD2 acts as a cofactor for GR to induce a gene expression pattern that results in Enz-refractory phenotype in CRPC cells. Our work will not only provide an in-depth insight into the mechanisms underlying enzalutamide resistance, but also lay the foundation for the development of novel therapeutic strategies targeting glucocorticoid receptor (GR) signaling to treat this lethal disease. Citation Format: Richard De La Rosa. The bromodomain-containing protein ATAD2 promotes GR-mediated enzalutamide resistance in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2109.

SUMMARY The function of enhancer RNAs (eRNAs) in transcriptional regulation remains obscure. By analyzing the genome-wide nascent transcript profiles in breast cancer cells, we identify a special group of eRNAs that are essential for estrogen-induced transcriptional repression. Using eRNAs of TM4SF1 and EFEMP1 as the paradigms, we find that these RNA molecules not only stabilize promoter-enhancer interactions but also recruit liganded estrogen receptor α (ERα) to particular enhancer regions, facilitate the formation of a functional transcriptional complex, and cause gene silencing. Interestingly, ERα is shown to directly bind with eRNAs by its DNA-binding domain. These eRNAs help with the formation of a specific ERα-centered transcriptional complex and promote the association of the histone demethylase KDM2A, which dismisses RNA polymerase II from designated enhancers and suppresses the transcription of target genes. Our work demonstrates a complete mechanism underlying the action of eRNAs in modulating and refining the locus-specific transcriptional program., In Brief Yang et al. identified a group of eRNAs that are essential for estrogen-induced transcriptional repression by assisting with the chromatin recruitment of ERα through binding to its DNA-binding domain and facilitating the interaction of ERα with its cofactors, which leads to the dismissal of RNA polymerase II., Graphical Abstract

Although accumulating evidence has demonstrated that individual enhancer RNAs (eRNAs) exert critical biological functions rather than being passive transcriptional byproducts, the mechanisms of action of these non-coding transcripts remain obscure and divergent. By analyzing genome-wide nascent transcript profiling in breast cancer cells, we identified a special group of eRNAs that are functionally important for estrogen-induced transcriptional repression. Using eRNAs of TM4SF1 and EFEMP1 as the paradigms, we found that these RNA molecules not only stabilize promoter-enhancer looping structure, but also recruit liganded estrogen receptor α (ERα) to particular enhancers of target genes, facilitate the hierarchical formation of a functional transcriptional complex, and cause gene downregulation. Interestingly, we found that ERα directly binds to eRNAs via its DNA-binding domain. These eRNAs help with the formation of a specific ERa-centered transcriptional complex and promote the association of the histone demethylase KDM2A, which dismisses RNA polymerase II from designated enhancers and suppresses transcription of target genes. Our work demonstrated a complete mechanism underlying the function of eRNAs, as a distinctive class of cis-acting RNA molecules, in modulating and refining locus-specific transcriptional program.