Rb family proteins enforce the homeostasis of quiescent hematopoietic stem cells by repressing Socs3 expression

The consequences of climate change and male reproductive health: A review of the possible impact and mechanisms

A global decline in male fertility has been reported, and climate change is considered a major cause of this. Climate change refers to long-term shifts in temperatures and weather patterns, and results from greenhouse gas emissions like carbon dioxide and methane that act as a blanket wrapped around the earth, trapping heat and elevating temperatures. Sad to say, the consequences of climatic variation are beyond the dramatic elevated temperature, they include cold stress, increased malnutrition, air pollution, cardiovascular diseases respiratory tract infections, cancer, sexually transmitted infections, mental stress, and heat waves. These negative effects of climate change impair male reproductive function through multiple pathways, like ROS-sensitive signaling, suppression of steroidogenic markers, and direct damage to testicular cells. The present study aimed to describe the impact of the consequences of climate change on male reproductive health with details of the various mechanisms involved. This will provide an in-depth understanding of the pathophysiological and molecular basis of the possible climatic variation-induced decline in male fertility, which will aid in the development of preventive measures to abate the negative effects of climate change on male reproductive function.

BET inhibitors induce NF-κB and E2F downregulation in Hodgkin and Reed-Sternberg cells

The prognosis of patients with relapsed and/or refractory classic Hodgkin lymphoma (cHL) continues to be poor. Therefore, there is a continuing need to develop novel therapies and to rationalize the use of target combinations. In recent years there has been growing interest in epigenetic targets for hematological malignancies under the rationale of the presence of common alterations in epigenetic transcriptional regulation. Since Hodgkin and Reed-Sternberg (HRS) cells have frequent inactivating mutations of the CREBBP and EP300 acetyltransferases, bromodomain and extra-terminal (BET) inhibitors can be a rational therapy for cHL. Here we aimed to confirm the efficacy of BET inhibitors (iBETs) using representative cell models and functional experiments, and to further explore biological mechanisms under iBET treatment using whole-transcriptome analyses. Our results reveal cytostatic rather than cytotoxic activity through the induction of G1/S and G2/M cell-cycle arrest, in addition to variable MYC downregulation. Additionally, massive changes in the transcriptome induced by the treatment include downregulation of relevant pathways in cHL disease: NF-kB and E2F, among others. Our findings support the therapeutic use of iBETs in selected cHL patients and reveal previously unknown biological mechanisms and consequences of pan-BET inhibition.

Regulation of adult stem cell quiescence and its functions in the maintenance of tissue integrity

Adult stem cells are important for mammalian tissues, where they act as a cell reserve that supports normal tissue turnover and can mount a regenerative response following acute injuries. Quiescent stem cells are well established in certain tissues, such as skeletal muscle, brain, and bone marrow. The quiescent state is actively controlled and is essential for long-term maintenance of stem cell pools. In this Review, we discuss the importance of maintaining a functional pool of quiescent adult stem cells, including haematopoietic stem cells, skeletal muscle stem cells, neural stem cells, hair follicle stem cells, and mesenchymal stem cells such as fibro-adipogenic progenitors, to ensure tissue maintenance and repair. We discuss the molecular mechanisms that regulate the entry into, maintenance of, and exit from the quiescent state in mice. Recent studies revealed that quiescent stem cells have a discordance between RNA and protein levels, indicating the importance of post-transcriptional mechanisms, such as alternative polyadenylation, alternative splicing, and translation repression, in the control of stem cell quiescence. Understanding how these mechanisms guide stem cell function during homeostasis and regeneration has important implications for regenerative medicine.

Retinoblastoma Protein Paralogs and Tumor Suppression

The retinoblastoma susceptibility gene (RB1) is the first tumor suppressor gene discovered and a prototype for understanding regulatory networks that function in opposition to oncogenic stimuli. More than 3 decades of research has firmly established a widespread and prominent role for RB1 in human cancer. Yet, this gene encodes but one of three structurally and functionally related proteins that comprise the pocket protein family. A central question in the field is whether the additional genes in this family, RBL1 and RBL2, are important tumor suppressor genes. If so, how does their tumor suppressor activity overlap or differ from RB1. Here we revisit these questions by reviewing relevant data from human cancer genome sequencing studies that have been rapidly accumulating in recent years as well as pertinent functional studies in genetically engineered mice. We conclude that RBL1 and RBL2 do have important tumor suppressor activity in some contexts, but RB1 remains the dominant tumor suppressor in the family. Given their similarities, we speculate on why RB1 tumor suppressor activity is unique.

Dissecting Tumor Growth: The Role of Cancer Stem Cells in Drug Resistance and Recurrence

Simple Summary

Cancer is one of the most debated problems all over the world. Cancer stem cells are considered responsible of tumor initiation, metastasis, drug resistance, and recurrence. This subpopulation of cells has been found into the tumor bulk and showed the capacity to self-renew, differentiate, up to generate a new tumor. In the last decades, several studies have been set on the molecular mechanisms behind their specific characteristics as the Wnt/β-catenin signaling, Notch signaling, Hedgehog signaling, transcription factors, etc. The most powerful part of CSCs is represented by the niches as “promoter” of their self-renewal and “protector” from the common oncological treatment as chemotherapy and radiotherapy. In our review article we highlighted the primary mechanisms involved in CSC tumorigenesis for the setting of further targets to control the metastatic process.

Abstract

Emerging evidence suggests that a small subpopulation of cancer stem cells (CSCs) is responsible for initiation, progression, and metastasis cascade in tumors. CSCs share characteristics with normal stem cells, i.e., self-renewal and differentiation potential, suggesting that they can drive cancer progression. Consequently, targeting CSCs to prevent tumor growth or regrowth might offer a chance to lead the fight against cancer. CSCs create their niche, a specific area within tissue with a unique microenvironment that sustains their vital functions. Interactions between CSCs and their niches play a critical role in regulating CSCs’ self-renewal and tumorigenesis. Differences observed in the frequency of CSCs, due to the phenotypic plasticity of many cancer cells, remain a challenge in cancer therapeutics, since CSCs can modulate their transcriptional activities into a more stem-like state to protect themselves from destruction. This plasticity represents an essential step for future therapeutic approaches. Regarding self-renewal, CSCs are modulated by the same molecular pathways found in normal stem cells, such as Wnt/β-catenin signaling, Notch signaling, and Hedgehog signaling. Another key characteristic of CSCs is their resistance to standard chemotherapy and radiotherapy treatments, due to their capacity to rest in a quiescent state. This review will analyze the primary mechanisms involved in CSC tumorigenesis, with particular attention to the roles of CSCs in tumor progression in benign and malignant diseases; and will examine future perspectives on the identification of new markers to better control tumorigenesis, as well as dissecting the metastasis process.

CITED2 coordinates key hematopoietic regulatory pathways to maintain the HSC pool in both steady-state hematopoiesis and transplantation

Hematopoietic stem cells (HSCs) reside at the apex of the hematopoietic differentiation hierarchy and sustain multilineage hematopoiesis. Here, we show that the transcriptional regulator CITED2 is essential for life-long HSC maintenance. While hematopoietic-specific Cited2 deletion has a minor impact on steady-state hematopoiesis, Cited2-deficient HSCs are severely depleted in young mice and fail to expand upon aging. Moreover, although they home normally to the bone marrow, they fail to reconstitute hematopoiesis upon transplantation. Mechanistically, CITED2 is required for expression of key HSC regulators, including GATA2, MCL-1, and PTEN. Hematopoietic-specific expression of anti-apoptotic MCL-1 partially rescues the Cited2-deficient HSC pool and restores their reconstitution potential. To interrogate the Cited2→Pten pathway in HSCs, we generated Cited2;Pten compound heterozygous mice, which had a decreased number of HSCs that failed to reconstitute the HSC compartment. In addition, CITED2 represses multiple pathways whose elevated activity causes HSC exhaustion. Thus, CITED2 promotes pathways necessary for HSC maintenance and suppresses those detrimental to HSC integrity.

Chronic infection drives Dnmt3a-loss-of-function clonal hematopoiesis via IFNγ signaling

Age-related clonal hematopoiesis (CH) is a risk factor for malignancy, cardiovascular disease, and all-cause mortality. Somatic mutations in DNMT3A are drivers of CH, but decades may elapse between the acquisition of a mutation and CH, suggesting that environmental factors contribute to clonal expansion. We tested whether infection provides selective pressure favoring the expansion of Dnmt3a mutant hematopoietic stem cells (HSCs) in mouse chimeras. We created Dnmt3a-mosaic mice by transplanting Dnmt3a-/- and WT HSCs into WT mice and observed the substantial expansion of Dnmt3a-/- HSCs during chronic mycobacterial infection. Injection of recombinant IFNγ alone was sufficient to phenocopy CH by Dnmt3a-/- HSCs upon infection. Transcriptional and epigenetic profiling and functional studies indicate reduced differentiation associated with widespread methylation alterations, and reduced secondary stress-induced apoptosis accounts for Dnmt3a-/- clonal expansion during infection. DNMT3A mutant human HSCs similarly exhibit defective IFNγ-induced differentiation. We thus demonstrate that IFNγ signaling induced during chronic infection can drive DNMT3A-loss-of-function CH.

JMJD6 promotes self-renewal and regenerative capacity of hematopoietic stem cells

Lifelong multilineage hematopoiesis critically depends on rare hematopoietic stem cells (HSCs) that reside in the hypoxic bone marrow microenvironment. Although the role of the canonical oxygen sensor hypoxia-inducible factor prolyl hydroxylase has been investigated extensively in hematopoiesis, the functional significance of other members of the 2-oxoglutarate (2-OG)-dependent protein hydroxylase family of enzymes remains poorly defined in HSC biology and multilineage hematopoiesis. Here, by using hematopoietic-specific conditional gene deletion, we reveal that the 2-OG-dependent protein hydroxylase JMJD6 is essential for short- and long-term maintenance of the HSC pool and multilineage hematopoiesis. Additionally, upon hematopoietic injury, Jmjd6-deficient HSCs display a striking failure to expand and regenerate the hematopoietic system. Moreover, HSCs lacking Jmjd6 lose multilineage reconstitution potential and self-renewal capacity upon serial transplantation. At the molecular level, we found that JMJD6 functions to repress multiple processes whose downregulation is essential for HSC integrity, including mitochondrial oxidative phosphorylation (OXPHOS), protein synthesis, p53 stabilization, cell cycle checkpoint progression, and mTORC1 signaling. Indeed, Jmjd6-deficient primitive hematopoietic cells display elevated basal and maximal mitochondrial respiration rates and increased reactive oxygen species (ROS), prerequisites for HSC failure. Notably, an antioxidant, N-acetyl-l-cysteine, rescued HSC and lymphoid progenitor cell depletion, indicating a causal impact of OXPHOS-mediated ROS generation upon Jmjd6 deletion. Thus, JMJD6 promotes HSC maintenance and multilineage differentiation potential by suppressing fundamental pathways whose activation is detrimental for HSC function.

Stem cell quiescence and its clinical relevance

Quiescent state has been observed in stem cells (SCs), including in adult SCs and in cancer SCs (CSCs). Quiescent status of SCs contributes to SC self-renewal and conduces to averting SC death from harsh external stimuli. In this review, we provide an overview of intrinsic mechanisms and extrinsic factors that regulate adult SC quiescence. The intrinsic mechanisms discussed here include the cell cycle, mitogenic signaling, Notch signaling, epigenetic modification, and metabolism and transcriptional regulation, while the extrinsic factors summarized here include microenvironment cells, extracellular factors, and immune response and inflammation in microenvironment. Quiescent state of CSCs has been known to contribute immensely to therapeutic resistance in multiple cancers. The characteristics and the regulation mechanisms of quiescent CSCs are discussed in detail. Importantly, we also outline the recent advances and controversies in therapeutic strategies targeting CSC quiescence.

PRMT5 Inhibition Modulates E2F1 Methylation and Gene-Regulatory Networks Leading to Therapeutic Efficacy in JAK2V617F-Mutant MPN

We investigated the role of PRMT5 in myeloproliferative neoplasm (MPN) pathogenesis and aimed to elucidate key PRMT5 targets contributing to MPN maintenance. PRMT5 is overexpressed in primary MPN cells, and PRMT5 inhibition potently reduced MPN cell proliferation ex vivo. PRMT5 inhibition was efficacious at reversing elevated hematocrit, leukocytosis, and splenomegaly in a model of JAK2V617F+ polycythemia vera and leukocyte and platelet counts, hepatosplenomegaly, and fibrosis in the MPLW515L model of myelofibrosis. Dual targeting of JAK and PRMT5 was superior to JAK or PRMT5 inhibitor monotherapy, further decreasing elevated counts and extramedullary hematopoiesis in vivo. PRMT5 inhibition reduced expression of E2F targets and altered the methylation status of E2F1 leading to attenuated DNA damage repair, cell-cycle arrest, and increased apoptosis. Our data link PRMT5 to E2F1 regulatory function and MPN cell survival and provide a strong mechanistic rationale for clinical trials of PRMT5 inhibitors in MPN. SIGNIFICANCE: Expression of PRMT5 and E2F targets is increased in JAK2V617F+ MPN. Pharmacologic inhibition of PRMT5 alters the methylation status of E2F1 and shows efficacy in JAK2V617F/MPLW515L MPN models and primary samples. PRMT5 represents a potential novel therapeutic target for MPN, which is now being clinically evaluated.This article is highlighted in the In This Issue feature, p. 1611.

HSP90 and Co-chaperones: Impact on Tumor Progression and Prospects for Molecular-Targeted Cancer Therapy

Heat shock protein 90 (HSP90), a highly and unique chaperone, presents as a double-edged sword. It plays an essential role in many physiological and pathological processes, including tumor development. The current review highlights a recent understanding of the roles of HSP90 in molecular mechanisms underlying cancer survival and progression. HSP90 and its client proteins through the regulation of oncoproteins including signaling proteins, receptors, and transcriptional factors involved in tumorigenesis. It also has potential clinical application as diagnostic and prognostic biomarkers for assessing cancer progression. In this way, using HSP90 to develop new anticancer therapeutic agents including HSP90 inhibitors, anti-HSP90 antibody, and HSP90-based vaccines has been promising.

Quiescence: Good and Bad of Stem Cell Aging

Stem cells are required for lifelong homeostasis and regeneration of tissues and organs in mammals, but the function of stem cells declines during aging. To preserve stem cells during life, they are kept in a quiescent state with low metabolic and low proliferative activity. However, activation of quiescent stem cells - an essential process for organ homeostasis/regeneration - requires concerted and faithful regulation of multiple molecular circuits controlling biosynthetic processes, repair mechanisms, and metabolic activity. Thus, while protecting stem cell maintenance, quiescence comes at the cost of vulnerability during the process of stem cell activation. Here we discuss molecular and biochemical processes regulating stem cells' maintenance in and exit from quiescence and how age-related failures of these circuits can contribute to organism aging.

Defective germline reprogramming rewires the spermatogonial transcriptome

Defective germline reprogramming in Miwi2- and Dnmt3l-deficient mice results in the failure to reestablish transposon silencing, meiotic arrest and progressive loss of spermatogonia. Here we sought to understand the molecular basis for this spermatogonial dysfunction. Through a combination of imaging, conditional genetics and transcriptome analysis, we demonstrate that germ cell elimination in the respective mutants arises due to defective de novo genome methylation during reprogramming rather than a function for the respective factors within spermatogonia. In both Miwi2^-/- and Dnmt3l^-/- spermatogonia the intracisternal-A particle (IAP) family of endogenous retroviruses is de-repressed, but in contrast to meiotic cells DNA damage is not observed. Instead we find that unmethylated IAP promoters rewire the spermatogonial transcriptome by driving expression of neighboring genes. Finally, spermatogonial numbers, proliferation and differentiation are altered in Miwi2^-/- and Dnmt3l^-/- mice. In summary, defective reprogramming deregulates the spermatogonial transcriptome and may underlie spermatogonial dysfunction.