From ecology to oncology: To understand cancer stem cell dormancy, ask a Brine shrimp (Artemia).

The brine shrimp (Artemia), releases embryos that can remain dormant for up to a decade. Molecular and cellular level controlling factors of dormancy in Artemia are now being recognized or applied as active controllers of dormancy (quiescence) in cancers. Most notably, the epigenetic regulation by SET domain-containing protein 4 (SETD4), is revealed as highly conserved and the primary control factor governing the maintenance of cellular dormancy from Artemia embryonic cells to cancer stem cells (CSCs). Conversely, DEK, has recently emerged as the primary factor in the control of dormancy exit/reactivation, in both cases. The latter has been now successfully applied to the reactivation of quiescent CSCs, negating their resistance to therapy and leading to their subsequent destruction in mouse models of breast cancer, without recurrence or metastasis potential. In this review, we introduce the many mechanisms of dormancy from Artemia ecology that have been translated into cancer biology, and herald Artemia's arrival on the model organism stage. We show how Artemia studies have unlocked the mechanisms of the maintenance and termination of cellular dormancy. We then discuss how the antagonistic balance of SETD4 and DEK fundamentally controls chromatin structure and consequently governs CSCs function, chemo/radiotherapy resistance, and dormancy in cancers. Many key stages from transcription factors to small RNAs, tRNA trafficking, molecular chaperones, ion channels, and links with various pathways and aspects of signaling are also noted, all of which link studies in Artemia to those of cancer on a molecular and/or cellular level. We particularly emphasize that the application of such emerging factors as SETD4 and DEK may open new and clear avenues for the treatment for various human cancers.

Embryogenic stem cell-derived intestinal crypt fission directs de novo crypt genesis.

Intestinal epithelial replenishment is fueled by continuously dividing intestinal stem cells (ISCs) resident at the crypt niche. However, the cell type(s) enabling replenishment upon damage and subsequent loss of whole crypts remain largely unclear. Using Set domain-containing protein 4 (Setd4), we identify a small population with reserve stem cell characteristics in the mouse intestine. Upon irradiation-induced injury, Setd4-expressing (Setd4+) cells survive radiation exposure and then activate to produce Sca-1-expressing cell types to restore the epithelial wall and regenerate crypts de novo via crypt fission. Setd4+ cells are confirmed to originate from the early fetal period, subsequently contributing to the development of embryonic gut and the establishment of postnatal crypts. Setd4+ cells are therefore represented as both originators and key regenerators of the intestine.

SETD4 cells contribute to brain development and maintain adult stem cell reservoir for neurogenesis.

Cellular quiescence facilitates maintenance of neural stem cells (NSCs) and their subsequent regenerative functions in response to brain injury and aging. However, the specification and maintenance of NSCs in quiescence from embryo to adulthood remain largely unclear. Here, using Set domain-containing protein 4 (SETD4), an epigenetic determinant of cellular quiescence, we mark a small but long-lived NSC population in deep quiescence in the subventricular zone of adult murine brain. Genetic lineage tracing shows that SETD4+ cells appear before neuroectoderm formation and contribute to brain development. In the adult, conditional knockout of Setd4 resulted in quiescence exit of NSCs, generating newborn neurons in the olfactory bulb and contributing to damage repair. However, long period deletion of SETD4 lead to exhaustion of NSC reservoir or SETD4 overexpression caused quiescence entry of NSCs, leading to suppressed neurogenesis. This study reveals the existence of long-lived deep quiescent NSCs and their neurogenetic capacities beyond activation.

Exosomal DEK removes chemoradiotherapy resistance by triggering quiescence exit of breast cancer stem cells.

Tumor therapeutics often target the primary tumor bulk but fail to eradicate therapy-resistant cancer stem cells (CSCs) in quiescent state. These can then become activated to initiate recurrence and/or metastasis beyond therapy. Here, we identified and isolated chemoradiotherapy-resistant CSCs in quiescent state with high capacity of tumor-initiation and tumorsphere formation from three types of breast tumors in mice. Experiments of knockdown and rescue revealed DEK, a nuclear protein, as essential for CSC activation. Exogenous DEK was then used to trigger quiescence exit of CSCs. ChIP-seq and ATAC-seq showed that DEK directly binds to chromatin, facilitating its genome-wide accessibility. The resulting epigenetic events upregulate the expression of cellular activation-related genes including MYC targets, whereas cellular quiescence-related genes including the p53 signaling pathway are silenced. However, twinned with DEK-induced activation, formerly resistant CSCs were then destroyed by chemotherapy in vitro. In mice, traditional chemoradiotherapy concurrent with the injection of DEK-containing exosomes resulted in eradication of primary tumors together with formerly resistant CSCs without recurrence or metastasis. Our findings advance knowledge of the mechanism of quiescent CSC activation and may provide novel clinical opportunities for removal of quiescence-linked therapy resistance.

SET Domain-Containing Protein 4 Epigenetically Controls Breast Cancer Stem Cell Quiescence.

Quiescent cancer stem cells (CSC) play important roles in tumorigenesis, relapse, and resistance to chemoradiotherapy. However, the determinants of CSC quiescence and how they sustain themselves to generate tumors and relapse beyond resistance to chemoradiotherapy remains unclear. Here, we found that SET domain-containing protein 4 (SETD4) epigenetically controls breast CSC (BCSC) quiescence by facilitating heterochromatin formation via H4K20me3 catalysis. H4K20me3 localized to the promoter regions and regulated the expression of a set of genes in quiescent BCSCs (qBCSC). SETD4-defined qBCSCs were resistant to chemoradiotherapy and promoted tumor relapse in a mouse model. Upon activation, a SETD4-defined qBCSC sustained itself in a quiescent state by asymmetric division and concurrently produced an active daughter cell that proliferated to produce a cancer cell population. Single-cell sequence analysis indicated that SETD4+ qBCSCs clustered together as a distinct cell type within the heterogeneous BCSC population. SETD4-defined quiescent CSCs were present in multiple cancer types including gastric, cervical, ovarian, liver, and lung cancers and were resistant to chemotherapy. SETD4-defined qBCSCs had a high tumorigenesis potential and correlated with malignancy and chemotherapy resistance in clinical breast cancer patients. Taken together, the results from our previous study and current study on six cancer types reveal an evolutionarily conserved mechanism of cellular quiescence epigenetically controlled by SETD4. Our findings provide insights into the mechanism of tumorigenesis and relapse promoted by SETD4-defined quiescent CSCs and have broad implications for clinical therapies. SIGNIFICANCE: These findings advance our knowledge on the epigenetic determinants of quiescence in cancer stem cell populations and pave the way for future pharmacologic developments aimed at targeting drug-resistant quiescent stem cells.

Intrapleural streptokinase for the treatment of childhood empyema.

BACKGROUND: Pleuritis with empyema is a serious complication of bacterial pneumonia, which often causes substantial morbidity and mortality among pediatric patients. Currently percutaneous catheter drainage is the mainstay therapy for loculated empyema. Intrapleural instillation of streptokinase, urokinase, and recombinant tissue plasminogen activator has been reported to facilitate the drainage of viscous fluid and fibrinous debris or multiple loculations from the pleural space of such patients. METHODS: In this study, we compared with the treatments of pleural empyema by instillation of streptokinase through the chest tube and using the conventional chest tube drainage alone. RESULTS: We collected 21 cases from 1999 through 2005. The results of the study showed that streptokinase (SK) group patients revealed a larger volume of drainage in the beginning days of the instillation and required fewer days of drainage than tube drainage (T) group patients [8 (4.5 - 10) days vs. 16 (5.8 - 20.3) days, p = 0.02]; that the SK group patients required average 2.6 instillations. The SK patients had a shorter febrile course than the T group [12.5 (9.5 - 15.5) days vs. 16 (9.5 - 22.5) days, p = 0.14]. None of the SK patients needed additional video-assisted thoracoscopic surgery (VATS) whereas 5 patients in the T group did. The length of hospitalization in the SK group was 21.5 days and the T group patients was 24 days. CONCLUSIONS: Intrapleural instillation of streptokinase seldom caused clinical adverse effect and appears to be a safe adjunctive therapy to facilitate the drainage of empyema in pediatric patients. Further studies with better research design to compare the fibrinolytic agent instillation and the VATS as the first step treatment of childhood empyema are needed.