The transcription factor Zic4 acts as a transdifferentiation switch

The molecular mechanisms that maintain cell identities and prevent transdifferentiation remain mysterious. Interestingly, both dedifferentiation and transdifferentiation are transiently reshuffled during regeneration. Therefore, organisms that regenerate readily offer a fruitful paradigm to investigate the regulation of cell fate stability. Here, we used Hydra as a model system and show that Zic4 silencing is sufficient to induce transdifferentiation of tentacle into foot cells. We identified a Wnt-controlled Gene Regulatory Network that controls a transcriptional switch of cell identity. Furthermore, we show that this switch also controls the re-entry into the cell cycle. Our data indicate that maintenance of cell fate by a Wnt-controlled GRN is a key mechanism during both homeostasis and regeneration.

Interchromosomal interaction of homologous Stat92E alleles regulates transcriptional switch during stem-cell differentiation

The strength of pairing of homologous chromosomes differs in a locus-specific manner and is correlated to gene expression states. However, the functional impact of homolog pairing on local transcriptional activity is still unclear. Drosophila male germline stem cells (GSCs) constantly divide asymmetrically to produce one GSC and one differentiating gonialblast (GB). The GB then enters the differentiation program in which stem cell specific genes are quickly downregulated. Here we demonstrate that a change in local pairing state of Stat92E locus is required for the downregulation of the Stat92E gene during differentiation. Using OligoPaint fluorescent in situ hybridization (FISH), we show that the interaction between homologous loci of Stat92E is always tight in GSCs and immediately loosened in GBs. When one of the Stat92E locus was absent or relocated to another chromosome, Stat92E did not pair and failed to downregulate, suggesting that the pairing is required for switching of transcriptional activity. The defect in downregulation of Stat92E was also observed upon knockdown of global pairing or anti-pairing factors. Moreover, the Stat92E enhancer element, but not cis-transcription, is required for the change in pairing state, indicating that it is not a consequence of transcriptional changes. GSCs are known to inherit pre-existing histones H3 and H4, while newly synthesized histones are distributed in GBs. When this histone inheritance was compromised, the change in Stat92E pairing did not occur, suggesting that it is an intrinsically programmed process during asymmetric stem cell division. We propose that the change of local pairing state may be a common process to reprogram gene activity during cell-differentiation.

CBIO-10. TARGETING HISTONE H4 Lys 20 MONOMETHYLATION IN THE TREATMENT OF GLIOBLASTOMA

BACKGROUND Glioblastoma (GBM) is the most malignant primary tumor of the central nervous system, while the pathogenesis remains unclear. Protein lysine methyltransferase SETD8, which is responsible for the modification of histone H4K20me1, has been shown to play an important role in cellular transcriptional regulation and the development of a variety of tumors, yet its role in the malignant progression of GBM has not been elucidated. MATERIAL AND METHODS In the present study, we used primary GBM cell lines, intracranial xenograft model, transcriptome sequencing together with ChIP-sequencing, aiming to elucidate the molecular mechanism of SETD8-mediated H4K20me1 transcriptional regulation in promoting GBM progression. Furthermore, we evaluated the potential therapeutic significance in GBM using SETD8 small molecule inhibitor, UNC0379. RESULTS We found that SETD8 is aberrantly expressed in GBM tissues, accompanied by the dysregulation of H4K20me1 modification, which is associated with tumor pathology and prognosis. Using SETD8 inhibitor UNC0379 or knockdown of SETD8 significantly inhibited GBM cell proliferation in vitro and in vivo, and downregulated H4K20me1 modification level as well as transcriptome expression. CONCLUSION In summary, our work provide a novel insight into the role of SETD8/H4K20me1 axis. SETD8 overexpression mediated aberrant H4K20me1 modification act as a novel "transcriptional switch" in the malignant progression of glioma.

Integrative genomics uncover mechanisms of renal medullary carcinoma transformation, microenvironment landscape and therapeutic vulnerabilities.

Renal medullary carcinoma (RMC) is an aggressive desmoplastic tumour driven by bi-allelic loss of SMARCB1, however the cell-of-origin, the oncogenic mechanism and the features of its microenvironment remain poorly understood. Using single-cell and multi-region sequencing of human RMC, we defined transformation of thick ascending limb (TAL) cells into at least three RMC cell states along an epithelial-mesenchymal gradient through a transcriptional switch involving loss of renal transcription factor TFCP2L1 and gain of a NFE2L2-associated ferroptosis resistance program. SMARCB1 re-expression in cultured RMC cells reactivates TFCP2L1 that relocates SWI/SNF from the promoters of the MYC-driven oncogenic program to the enhancers of TAL identity genes followed by ferroptotic cell death. We further show that RMC is associated with abundant M2-type macrophages and cancer-associated fibroblasts (CAFs) and we identify key regulatory cross-talks that shape this immunosuppressive microenvironment. Together our data describe the molecular events of RMC transformation and identify novel therapeutically targetable vulnerabilities.

Roles of Histone Deacetylases in Acute Myeloid Leukemia With Fusion Proteins

Accurate orchestration of gene expression is critical for the process of normal hematopoiesis, and dysregulation is closely associated with leukemogenesis. Epigenetic aberration is one of the major causes contributing to acute myeloid leukemia (AML), where chromosomal rearrangements are frequently found. Increasing evidences have shown the pivotal roles of histone deacetylases (HDACs) in chromatin remodeling, which are involved in stemness maintenance, cell fate determination, proliferation and differentiation, via mastering the transcriptional switch of key genes. In abnormal, these functions can be bloomed to elicit carcinogenesis. Presently, HDAC family members are appealing targets for drug exploration, many of which have been deployed to the AML treatment. As the majority of AML events are associated with chromosomal translocation resulting in oncogenic fusion proteins, it is valuable to comprehensively understand the mutual interactions between HDACs and oncogenic proteins. Therefore, we reviewed the process of leukemogenesis and roles of HDAC members acting in this progress, providing an insight for the target anchoring, investigation of hyperacetylated-agents, and how the current knowledge could be applied in AML treatment.

EGR4-dependent decrease of UTF1 is associated with failure to reserve spermatogonial stem cells in infertile men

Despite the high incidence of male infertility, about 70% of infertile men do not receive a causative diagnosis. To gain insights into the regulatory mechanisms governing human germ cell function in normal and impaired spermatogenesis (cryptozoospermic patients, crypto), we combined single cell RNA sequencing (>30.000 cells), proteome, and histomorphometric analyses of testicular tissues. We found major alterations in the crypto spermatogonial compartment with increased numbers of the most undifferentiated spermatogonia (PIWIL4+ State 0 cells). We also observed a transcriptional switch within the spermatogonial compartment driven by the increased and prolonged expression of the transcription factor EGR4. Intriguingly, EGR4-regulated genes included the chromatin-associated transcriptional repressor UTF1, which was downregulated. Histomorphometrical analyses showed that these transcriptional changes were mirrored at the protein level and accompanied by a change in the chromatin structure of spermatogonia. This resulted in a reduction of Adark spermatogonia - characterized by tightly compacted chromatin and serving as reserve stem cells. These findings suggest that crypto patients are at a disadvantage especially in cases of gonadotoxic damage as they have less cells safeguarding the genetic integrity of the germline. We hypothesize that the more relaxed chromatin status of spermatogonia is dependent on decreased UTF1 expression caused by EGR4 activation. These identified regulators of the spermatogonial compartment will be highly interesting targets to uncover genetic causes of male infertility.One Sentence SummaryReserve spermatogonial stem cell depletion in infertile men is regulated by an EGR4-dependent UTF1 decrease, which changes chromatin morphology.

CTIM-27. PHASE I/II STUDY OF CONTROLLED IL-12 AS IMMUNOTHERAPY FOR DIFFUSE INTRINSIC PONTINE GLIOMA (DIPG)

DIPG, which is the leading cause of pediatric brain cancer death with no effective treatment, has neither a highly immunosuppressive nor inflammatory tumor microenvironment (TME). Therefore, eliciting a pro-inflammatory TME may provide therapeutic benefit. We previously demonstrated in adults with recurrent glioblastoma that loco-regional delivery of interleukin 12 administered under the control of the proprietary transcriptional switch RheoSwitch Therapeutic Systemâ (RTSâ) delivered via a replication-incompetent adenovirus (“Controlled IL-12”) turned “cold” tumors “hot” for up to 5.8 months (Sci Transl Med. 2019;11(505)) and seemed to improve median overall survival as compared with historical controls (SNO 2020). A multicenter, phase I/II, open-label study (NCT03330197) is determining the safety and tolerability of Ad (2 x 1011 viral particles) administered by stereotactic intratumoral injection (Day 0) and 14 daily (Days 1 to 14) V doses (10 or 20 mg, body surface area adjusted). The first DIPG subject enrolled was in April 2020 with completion of the first cohort (arm 1, n=3) enrollment anticipated by September 2020. The first subject has tolerated treatment well with no SAEs during the evaluation period. Endogenous serum cytokines increased (including IFN-g 11.4 pg/mL, Day 3), consistent with V crossing the blood-brain barrier and activating the RTSâ switch to conditionally produce recombinant IL-12. Other biomarkers include plasma PK and circulating DNA. Follow-up is ongoing and enrollment is proceeding. Since development of effective immunotherapy for DIPG likely depends on eliciting a tumor-specific effector immune response, Controlled IL-12 is a promising immunotherapy candidate. The first DIPG subject shows encouraging data on safety, tolerability, serum cytokines and early signs consistent with a clinical response. After completion of dose-escalation, the study may be expanded up to 30 patients, which will be considered the phase II component of the study.