DIS3: The Enigmatic Gene in Multiple Myeloma.

Recent studies have revealed the genetic aberrations involved in the initiation and progression of various cancers, including multiple myeloma (MM), via next-generation sequencing analysis. Notably, DIS3 mutations have been identified in approximately 10% of patients with MM. Moreover, deletions of the long arm of chromosome 13, that includes DIS3, are present in approximately 40% of patients with MM. Regardless of the high incidence of DIS3 mutations and deletions, their contribution to the pathogenesis of MM has not yet been determined. Herein, we summarize the molecular and physiological functions of DIS3, focusing on hematopoiesis, and discuss the characteristics and potential roles of DIS3 mutations in MM. Recent findings highlight the essential roles of DIS3 in RNA homeostasis and normal hematopoiesis and suggest that the reduced activity of DIS3 may be involved in myelomagenesis by increasing genome instability.

Diverse Functions of KDM5 in Cancer: Transcriptional Repressor or Activator?

Epigenetic modifications are crucial for chromatin remodeling and transcriptional regulation. Post-translational modifications of histones are epigenetic processes that are fine-tuned by writer and eraser enzymes, and the disorganization of these enzymes alters the cellular state, resulting in human diseases. The KDM5 family is an enzymatic family that removes di- and tri-methyl groups (me2 and me3) from lysine 4 of histone H3 (H3K4), and its dysregulation has been implicated in cancer. Although H3K4me3 is an active chromatin marker, KDM5 proteins serve as not only transcriptional repressors but also transcriptional activators in a demethylase-dependent or -independent manner in different contexts. Notably, KDM5 proteins regulate the H3K4 methylation cycle required for active transcription. Here, we review the recent findings regarding the mechanisms of transcriptional regulation mediated by KDM5 in various contexts, with a focus on cancer, and further shed light on the potential of targeting KDM5 for cancer therapy.

Meiotic gatekeeper STRA8 suppresses autophagy by repressing Nr1d1 expression during spermatogenesis in mice.

The transition from mitotic to meiotic cell cycles is essential for haploid gamete formation and fertility. Stimulated by retinoic acid gene 8 (Stra8) is an essential gatekeeper of meiotic initiation in vertebrates; yet, the molecular role of STRA8 remains principally unknown. Here we demonstrate that STRA8 functions as a suppressor of autophagy during spermatogenesis in mice. Stra8-deficient germ cells fail to enter meiosis and present aberrant upregulation of autophagy-lysosome genes, commensurate with autophagy activation. Biochemical assays show that ectopic expression of STRA8 alone is sufficient to inhibit both autophagy induction and maturation. Studies also revealed that, Nr1d1, a nuclear hormone receptor gene, is upregulated in Stra8-deficient testes and that STRA8 binds to the Nr1d1 promoter, indicating that Nr1d1 is a direct target of STRA8 transcriptional repression. In addition, it was found that NR1D1 binds to the promoter of Ulk1, a gene essential for autophagy initiation, and that Nr1d1 is required for the upregulated Ulk1 expression in Stra8-deficient testes. Furthermore, both genetic deletion of Nr1d1 and pharmacologic inhibition of NR1D1 by its synthetic antagonist SR8278 exhibit rescuing effects on the meiotic initiation defects observed in Stra8-deficient male germ cells. Together, the data suggest a novel link between STRA8-mediated autophagy suppression and meiotic initiation.

Genetic studies in mice directly link oocytes produced during adulthood to ovarian function and natural fertility.

Multiple labs have reported that mammalian ovaries contain oogonial stem cells (OSCs), which can differentiate into oocytes that fertilize to produce offspring. However, the physiological relevance of these observations to adult ovarian function is unknown. Here we performed targeted and reversible ablation of premeiotic germ cells undergoing differentiation into oocytes in transgenic mice expressing the suicide gene, herpes simplex virus thymidine kinase (HSVtk), driven by the promoter of stimulated by retinoic acid gene 8 (Stra8), a germ cell-specific gene activated during meiotic commitment. Over a 21-day ablation phase induced by the HSVtk pro-drug, ganciclovir (GCV), oocyte numbers declined due to a disruption of new oocyte input. However, germ cell differentiation resumed after ceasing the ablation protocol, enabling complete regeneration of the oocyte pool. We next employed inducible lineage tracing to fate map, through Cre recombinase-mediated fluorescent reporter gene activation only in Stra8-expressing cells, newly-formed oocytes. Induction of the system during adulthood yielded a mosaic pool of unmarked (pre-existing) and marked (newly-formed) oocytes. Marked oocytes matured and fertilized to produce offspring, which grew normally to adulthood and transmitted the reporter to second-generation offspring. These findings establish that oocytes generated during adulthood contribute directly to ovarian function and natural fertility in mammals.

Quantitative analysis of male germline stem cell differentiation reveals a role for the p53-mTORC1 pathway in spermatogonial maintenance.

p53 protects cells from DNA damage by inducing cell-cycle arrest upon encountering genomic stress. Among other pathways, p53 elicits such an effect by inhibiting mammalian target of rapamycin complex 1 (mTORC1), the master regulator of cell proliferation and growth. Although recent studies have indicated roles for both p53 and mTORC1 in stem cell maintenance, it remains unclear whether the p53-mTORC1 pathway is conserved to mediate this process under normal physiological conditions. Spermatogenesis is a classic stem cell-dependent process in which undifferentiated spermatogonia undergo self-renewal and differentiation to maintain the lifelong production of spermatozoa. To better understand this process, we have developed a novel flow cytometry (FACS)-based approach that isolates spermatogonia at consecutive differentiation stages. By using this as a tool, we show that genetic loss of p53 augments mTORC1 activity during early spermatogonial differentiation. Functionally, loss of p53 drives spermatogonia out of the undifferentiated state and causes a consistent expansion of early differentiating spermatogonia until the stage of preleptotene (premeiotic) spermatocyte. The frequency of early meiotic spermatocytes is, however, dramatically decreased. Thus, these data suggest that p53-mTORC1 pathway plays a critical role in maintaining the homeostasis of early spermatogonial differentiation. Moreover, our FACS approach could be a valuable tool in understanding spermatogonial differentiation.

Loss of LKB1 and PTEN tumor suppressor genes in the ovarian surface epithelium induces papillary serous ovarian cancer.

Epithelial ovarian cancer presents mostly with serous, endometrioid or mucinous histology but is treated as a single disease. The development of histotype-specific therapy has been challenging because of the relative lack of studies attributing disrupted pathways to a distinct histotype differentiation. mTOR activation is frequently associated with poor prognosis in serous ovarian cancer, which is the most common and most deadly histotype. However, the mechanisms dysregulating mTOR in the pathogenesis of ovarian cancer are unknown. We detected copy number loss and correlated lower expression levels of LKB1, TSC1, TSC2 and PTEN tumor suppressor genes for upstream regulators of mTOR activity in up to 80% in primary ovarian serous tumor databases, with LKB1 allelic loss-predominant. Reduced LKB1 protein was usually associated with increased mTOR activity in both serous ovarian cancer cell lines and primary tumors. Conditional deletion of Lkb1 in murine ovarian surface epithelial (OSE) cells caused papillary hyperplasia and shedding but not tumors. Simultaneous deletion of Lkb1 and Pten, however, led to development of high-grade ovarian serous histotype tumors with 100% penetrance that expressed WT1, ERα, PAX8, TP53 and cytokeratin 8, typical markers used in the differential diagnosis of serous ovarian cancer. Neither hysterectomy nor salpingectomy interfered with progression of ovarian tumorigenesis, suggesting that neither uterine nor Fallopian tube epithelial cells were contributing to tumorigenesis. These results implicate LKB1 loss in the OSE in the pathogenesis of serous ovarian cancer and provide a compelling rationale for investigating the therapeutic potential of targeting LKB1 signaling in patients with this deadly disease.