Cell-intrinsic Signaling Research Articles

Rapid cell cycling of both circulating and resident memory CD8+ T cells driven by common gamma chain-dependent cytokines

Abstract Diverse populations of resident leukocytes live and self-renew within the tissues of the body, but the mechanisms controlling their proliferation are poorly understood. Among these populations are many memory CD8+ T cells, which are found throughout the body and can locally control reinfection. A poor ability of vaccines to elicit stable and appropriate tissue-resident CD8+ T cell populations has likely contributed to long-standing challenges in vaccinating against several important pathogens. The factors required to support TRM proliferation in homeostasis are not well understood. We propose that proliferating TRMs flexibly use the available members of the common gamma chain-(γC)-dependent cytokine family to persist as bystanders during other immune responses. We have found that many γC-dependent cytokines can mediate cell-intrinsic signaling to drive proliferation of both circulating and resident memory CD8+ T cells of known antigen specificities without cognate antigen. Via transcriptional analysis of resting and in vivo cytokine-stimulated TRMs, we are elucidating downstream signaling and the gene expression signature of cytokine-driven TRM proliferation. We have also found that memory CD8+ T cells proliferate similarly in response to exogenous cytokines or unrelated pathogens, consistent with pathogen-elicited γC-dependent cytokine signals driving memory CD8+ T cell proliferation. These data support the concept that TRMs use γC-dependent cytokines produced during infections to support enhanced proliferation, likely to promote their maintenance. Our findings may lead to novel methods to therapeutically enhance TRM immunity.

Fibroblastic reticular cells sustain innate lymphoid cell niches in the intestinal lamina propria

Abstract Innate lymphoid cells (ILC) in the small intestine govern immune homeostasis and protect the host against gut pathogens. While distinct cell-intrinsic signals have been identified that determine ILC development and differentiation, it has remained unclear which cell population regulates ILC sustenance. Using unbiased transcriptomic analysis of intestinal fibroblasts, we have identified a specialized Ccl19-expressing fibroblastic reticular cell (FRC) population that underpins solitary intestinal lymphoid tissue (SILT) structures including cryptopatches and isolated lymphoid follicles. Conditional ablation of lymphotoxin-β receptor (LTβR) signalling in SILT FRC impeded the maturation of isolated lymphoid follicles and blocked ILC maintenance resulting in the elevated susceptibility to bacterial infection. Moreover, specific Ltbr ablation in FRC during adulthood revealed that sustained LTβR-dependent FRC-ILC interaction is required to maintain SILT structures and ILC populations. Taken together, our study unveils a critical intestinal FRC niche that secures protective gut immunity.

Bladder cancer cell-intrinsic PD-L1 signals promote mTOR and autophagy activation that can be inhibited to improve cytotoxic chemotherapy.

Tumor cell‐intrinsic programmed death‐ligand 1 (PD‐L1) signals mediate immunopathologic effects in breast, colon, and ovarian cancers and in melanomas, but bladder cancer (BC) effects are unreported. We show here that BC cell‐intrinsic PD‐L1 signals in mouse MB49 and human RT4, UM‐UC3, and UM‐UC‐14 BC cells regulate important pathologic pathways and processes, including effects not reported in other cancers. α‐PD‐L1 antibodies reduced BC cell proliferation in vitro, demonstrating direct signaling effects. BC cell‐intrinsic PD‐L1 promoted mammalian target of rapamycin complex 1 (mTORC1) signals in vitro and augmented in vivo immune‐independent cell growth and metastatic cancer spread, similar to effects we reported in melanoma and ovarian cancer. BC cell‐intrinsic PD‐L1 signals also promoted basal and stress‐induced autophagy, whereas these signals inhibited autophagy in melanoma and ovarian cancer cells. BC cell‐intrinsic PD‐L1 also mediated chemotherapy resistance to the commonly used BC chemotherapy agents cis‐platinum and gemcitabine and to the mTORC1 inhibitor, rapamycin. Thus, BC cell‐intrinsic PD‐L1 signals regulate important virulence and treatment resistance pathways that suggest novel, actionable treatment targets meriting additional studies. As a proof‐of‐concept, we showed that the autophagy inhibitor chloroquine improved cis‐platinum treatment efficacy in vivo, with greater efficacy in PD‐L1 null versus PD‐L1‐replete BC.

IL-27 Negatively Regulates Tip-DC Development during Infection.

ABSTRACTTumor necrosis factor (TNF)/inducible nitric oxide synthase (iNOS)-producing dendritic cells (Tip-DCs) have profound impacts on host immune responses during infections. The mechanisms regulating Tip-DC development remain largely unknown. Here, using a mouse model of infection with African trypanosomes, we show that a deficiency in interleukin-27 receptor (IL-27R) signaling results in escalated intrahepatic accumulation of Ly6C-positive (Ly6C+) monocytes and their differentiation into Tip-DCs. Blocking Tip-DC development significantly ameliorates liver injury and increases the survival of infected IL-27R−/− mice. Mechanistically, Ly6C+ monocyte differentiation into pathogenic Tip-DCs in infected IL-27R−/− mice is driven by a CD4+ T cell-interferon gamma (IFN-γ) axis via cell-intrinsic IFN-γ signaling. In parallel, hyperactive IFN-γ signaling induces cell death of Ly6C-negative (Ly6C−) monocytes in a cell-intrinsic manner, which in turn aggravates the development of pathogenic Tip-DCs due to the loss of the negative regulation of Ly6C− monocytes on Ly6C+ monocyte differentiation into Tip-DCs. Thus, IL-27 inhibits the dual-track exacerbation of Tip-DC development induced by a CD4+ T cell–IFN-γ axis. We conclude that IL-27 negatively regulates Tip-DC development by preventing the cell-intrinsic effects of IFN-γ and that the regulation involves CD4+ T cells and Ly6C− monocytes. Targeting IL-27 signaling may manipulate Tip-DC development for therapeutic intervention.

Tumor cell intrinsic RON signaling suppresses innate immune responses in breast cancer through inhibition of IRAK4 signaling.

Increasing evidence suggests that cancer cells require both alterations in intrinsic cellular processes and the tumor microenvironment for tumor establishment, growth, and progression to metastatic disease. Despite this, knowledge of tumor-cell intrinsic molecular mechanisms controlling both tumor cell processes as well as the tumor microenvironment is limited. In this study, we provide evidence demonstrating the novel role of RON signaling in regulating breast cancer initiation, progression, and metastasis through modulation of tumor cell intrinsic processes and the tumor microenvironment. Using clinically relevant models of breast cancer, we show that RON signaling in the mammary epithelial tumor cells promotes tumor cell survival and proliferation as well as an immunopermissive microenvironment associated with decreased M1 macrophage, natural killer (NK) cell, and CD8+ T cell recruitment. Moreover, we demonstrate that RON signaling supports these phenotypes through novel mechanisms involving suppression of IRAK4 signaling and inhibition of type I Interferons. Our studies indicate that activation of RON signaling within breast cancer cells promotes tumor cell intrinsic growth and immune evasion which support breast cancer progression and highlight the role of targeting RON signaling as a potential therapeutic strategy against breast cancer.

Spliceosome-targeted therapies trigger an antiviral immune response in triple-negative breast cancer

Many oncogenic insults deregulate RNA splicing, often leading to hypersensitivity of tumors to spliceosome-targeted therapies (STTs). However, the mechanisms by which STTs selectively kill cancers remain largely unknown. Herein, we discover that mis-spliced RNA itself is a molecular trigger for tumor killing through viral mimicry. In MYC-driven triple-negative breast cancer, STTs cause widespread cytoplasmic accumulation of mis-spliced mRNAs, many of which form double-stranded structures. Double-stranded RNA (dsRNA)-bindingproteins recognize these endogenous dsRNAs, triggering antiviral signaling and extrinsic apoptosis. In immune-competent models of breast cancer, STTs cause tumor cell-intrinsic antiviral signaling, downstream adaptive immune signaling, and tumor cell death. Furthermore, RNA mis-splicing in human breast cancers correlates with innate and adaptive immune signatures, especially in MYC-amplified tumors that are typically immune cold. These findings indicate that dsRNA-sensing pathways respond to global aberrations of RNA splicing in cancer and provoke the hypothesis that STTs may provide unexplored strategies to activate anti-tumor immune pathways.

Application of a newly-developed cynomolgus macaque BiTE-mediated cytotoxic T-lymphocyte activity assay to various immunomodulatory agents in vitro

The immunotoxic potential of drug candidates is assessed through the examination of results from a variety of in vitro and in vivo immunophenotyping and functional study endpoints in pre-clinical studies. CD8+ cytotoxic T-lymphocyte (CTL) activity impairment by immunosuppressive agents is recognized to be a potentiating factor for decreased antiviral defense and increased cancer risk. A bi-specific T-cell engager (BiTE®)-mediated CTL activity assay that applies to ex vivo experimentation in non-human primates in the context of toxicology studies was successfully developed and applied in cynomolgus monkey regulatory studies. While an ex vivo analysis conducted in the context of repeat-dose toxicology studies focuses on the long-term impact on CTL function, an in vitro assay with the same experimental design captures acute effects in the presence of the test article. Here, the in vitro assay was applied to a list of drugs with known clinical immunomodulatory impact to understand the applicability of the assay. The results showed this assay was sensitive to a wide range of immunosuppressants directly targeting cell-intrinsic signaling pathways in activated CTL. However, agents executing immuno-modulation through inhibiting cytokines/cytokine receptors, co-stimulatory molecules, and cell adhesion and migration pathways did not impair the CTL activity in this short-term in vitro culture. In addition, anti-PD-1/PD-L1 immune checkpoint blockers enhanced the CTL activity. Taken together, the results here demonstrate that in concordance with their mechanism of action, the in vitro BiTE®-mediated CTL assay is applicable and sensitive to immunomodulatory agents acting via a variety of mechanisms.

Abstract PO-076: miR-181a initiates and perpetuates ovarian cancer transformation through inhibition of the tumor suppressors RB1 and stimulator of interferon genes (STING)

Abstract Genomic instability predisposes cells to malignant transformation, however the molecular mechanisms that allow for the propagation of cells with a high-degree of genomic instability remains unclear. Here we report that miR-181a is able to transform fallopian tube secretory epithelial cells (FTSECs, the precursor cell type for the majority of high-grade serous ovarian cancers) through the inhibition of RB1. Increased miR-181a expression simultaneously drives cell protective inhibition of the stimulator-of-interferon-genes (STING) in order to maintain a microenvironment conducive to the propagation of cells with a high-degree of genomic instability. We found that miR-181a inhibition of RB1 leads to profound nuclear defects, genomic instability, and nuclear rupture resulting in a persistence of genomic material in the cytoplasm. Normally, this persistence of genomic material in the cytoplasm induces a cell-intrinsic interferon response through STING to drive cell death. However, miR-181a directly downregulates STING and prevents interferon induction and cell death in the FTSECs. The most common mechanism by which oncogenic miRNAs promote tumorigenesis is through the direct inhibition of tumor suppressor genes. However, our studies highlight a new mechanism of oncomiR transformation through the combination of tumor suppressor gene and intrinsic interferon signaling inhibition that initiates and propagates tumor cell survival. Importantly, we found that miR-181a induction in ovarian patient tumors is tightly associated with decreased IFNγ response and downregulation of lymphocyte infiltration and leukocyte fraction. Our findings are the first to identify a miRNA, miR-181a, that can downregulate STING expression and suppress activation of cell-intrinsic innate immune signaling in precursor cells undergoing oncogenic transformation to create a survival advantage. Our studies support the notion that the induction of STING-mediated signaling in developing cancer cells could lead directly to cancer cell death, and that these effects can be inhibited by miR-181a. Given the recent interest in the development of STING agonists as a strategy to harness the immune system to treat cancer, this study introduces miR-181a as a novel patient selective biomarker as well as potential therapeutic target for HGSOC treatment. Citation Format: Matthew Knarr, Rita Avelar, Sreeja Sekhar, Lily Kwiatkowski, Michele Dziubinski, Jessica McAnulty, Stephanie Skala, Stefanie Avril, Ronny Drapkin, Analisa DiFeo. miR-181a initiates and perpetuates ovarian cancer transformation through inhibition of the tumor suppressors RB1 and stimulator of interferon genes (STING) [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-076.

Heterogeneity in Collective Endothelial Cell Behavior is a Driver of Arterio-Venous Remodeling

During vascular development, arteries and veins form in a stepwise process that combines vasculogenesis and sprouting angiogenesis. Despite extensive data on the mechanisms governing blood vessel assembly at the single cell level, little is known about how cell populations migrate in a finely tuned and coordinated manner, and distribute precisely between arteries and veins. Here, we use an endothelial-specific zebrafish reporter, arteriobow, to label small cohorts of arterial cells and trace their progeny from the initial events of vasculogenesis through the process of arterio-venous remodeling. We reveal that the genesis of both arteries and veins relies on the coordination of ten types of collective cell behaviors originating from discrete endothelial cell clusters. Within these behavioral categories, we identify a heterogeneity of collective cell dynamics specific to either arterial or venous remodeling. Using pharmacological blockade, we further show that factors known to control vascular patterning such as cell-intrinsic Notch signaling and cell-extrinsic blood flow, potentially act as regulators by coordinating endothelial cohorts behavior, which in turn instructs the future territory of arterio-venous remodeling.

IL-22 receptor signaling in Paneth cells is critical for their maturation, microbiota colonization, Th17-related immune responses, and anti-Salmonella immunity

Interleukin-22 (IL-22) signaling in the intestines is critical for promoting tissue-protective functions. However, since a diverse array of cell types (absorptive and secretory epithelium as well as stem cells) express IL-22Ra1, a receptor for IL-22, it has been difficult to determine what cell type(s) specifically respond to IL-22 to mediate intestinal mucosal host defense. Here, we report that IL-22 signaling in the small intestine is positively correlated with Paneth cell differentiation programs. Our Il22Ra1fl/fl;Lgr5-EGFP-creERT2-specific knockout mice and, independently, our lineage-tracing findings rule out the involvement of Lgr5+ intestinal stem cell (ISC)-dependent IL-22Ra1 signaling in regulating the lineage commitment of epithelial cells, including Paneth cells. Using novel Paneth cell-specific IL-22Ra1 knockout mice (Il22Ra1fl/fl;Defa6-cre), we show that IL-22 signaling in Paneth cells is required for small intestinal host defense. We show that Paneth cell maturation, antimicrobial effector function, expression of specific WNTs, and organoid morphogenesis are dependent on cell-intrinsic IL-22Ra1 signaling. Furthermore, IL-22 signaling in Paneth cells regulates the intestinal commensal bacteria and microbiota-dependent IL-17A immune responses. Finally, we show ISC and, independently, Paneth cell-specific IL-22Ra1 signaling are critical for providing immunity against Salmonella enterica serovar Typhimurium. Collectively, our findings illustrate a previously unknown role of IL-22 in Paneth cell-mediated small intestinal host defense.

P50 suppresses cytotoxic T lymphocyte effector function to regulate tumor immune escape and response to immunotherapy

BackgroundNF-κB is a key link between inflammation and cancer. Previous studies of NF-κB have largely focused on tumor cells, and the intrinsic function of NF-κB in T cells in tumor...

Cell-intrinsic Fgf signaling contributes to primordial germ cell homing in zebrafish

Primordial germ cells (PGCs) are specified before gastrulation and migrate toward the developing gonads. Previous in vitro studies have demonstrated a cell-intrinsic requirement of fibroblast growth factors (FGFs) by PGCs; however, no evidence suggests FGFs signal directly to PGCs in vivo. Here, using zebrafish as the animal model, we identified the mRNA expressions of Fgf receptors (Fgfrs) and determined the roles of Fgf signaling in migrating PGCs. To clarify the functions of Fgf signaling, we manipulated Fgf signaling specifically in PGCs using dominant-negative (dn) and constitutively-active (ca) Fgfrs and revealed a requirement of a basal Fgf signaling level for the robust arrival of PGCs. Repression of Fgf signaling in PGCs swayed the marginal positioning of PGCs as early as 6 h post-fertilization (6 hpf) and disrupted their arrival at the gonadal ridge at 24 hpf. On the other hand, the ectopic PGC phenotypes caused by the dn-Fgfrs could be alleviated by constitutive activation of Fgf signaling. In addition, we carefully ruled out the somatic effects in mosaic embryos by injecting RNA materials into one blastomere of the four- or eight-cell stage embryos. Injection of dn-Fgfrs into one of eight blastomeres hampered the arrival of only the treated PGCs, while the other PGCs remained unaffected. Furthermore, mosaic treatment of ca-Fgfrs rescued the ectopic rates of dn-Fgfr treated PGCs, while the other PGCs remained more ectopic within the same embryos. Interestingly, PGC-specific repression of Fgf signaling did not compromise the PGC number. To our knowledge, this is the first in vivo evidence to show that Fgf signaling plays a cell-intrinsic role in the migration of vertebrate PGCs.

Chronic Stress Physically Spares But Functionally Impairs Innate-Like Invariant T Cells

Long-term stress disrupts the neuroimmune interface, often resulting in immunosuppression. The deleterious effects of stress on mainstream T cells are well-documented. However, innate-like invariant T cells have been overlooked. Chief among these are invariant natural killer T (iNKT) and mucosa-associated invariant T (MAIT) cells, which fulfill important functions in anticancer and antimicrobial immunity. We found stress to surprisingly abrogate both TH1- and TH2-type responses mediated by iNKT cells. This was not due to cell death since iNKT cells were unusually refractory to stress-inflicted apoptosis. Activated iNKT cells in stressed mice triggered an abnormal response characterized by a ‘split’ inflammatory signature along with a sudden and robust induction of IL-10, IL-23 and IL-27. Pharmacological inhibitors, conditional knockout systems and gene expression analyses revealed that dysregulated iNKT cell responses were driven by iNKT cell-intrinsic glucocorticoid receptor signaling. Accordingly, the inhibitory effects of chronic stress on iNKT cell functions were lost upon habituation to predictable stressors. Importantly, iNKT cells in stressed mice failed to potentiate cytotoxicity against lymphoma targets or promote immune surveillance against metastatic melanoma. Using a congenic mouse model in which MAIT cells are abundant, these cells remained resistant to stress-induced death but demonstrated hindered TH1- and TH2-type cytokine responses, reminiscent of their iNKT cell counterparts. This was corroborated in culture systems in which we interrogated human peripheral blood and hepatic iNKT and MAIT cells. Our findings uncover a previously unappreciated mechanism of stress-induced immunosuppression and implicate the stress response as a potential barrier to iNKT cell- and MAIT cell-based immunotherapies.

Contribution of DOCK11 to the Expansion of Antigen-Specific Populations among Germinal Center B Cells.

Germinal centers (GCs) are a structure in which B cell populations are clonally expanded, depending on their affinities to Ag. Although we previously isolated a characteristic protein called dedicator of cytokinesis 11 (DOCK11) from GC B cells, limited information is available on the roles of DOCK11 in GC B cells. In this study, we demonstrate that DOCK11 may contribute to the expansion of Ag-specific populations among GC B cells upon immunization of mice. The lack of DOCK11 in B cells resulted in the lower frequency of Ag-specific GC B cells along with enhanced apoptosis upon immunization. Under competitive conditions, DOCK11-deficient B cells were dramatically prevented from participating in GCs, in contrast to DOCK11-sufficient B cells. However, minor impacts of the DOCK11 deficiency were identified on somatic hypermutations. Mechanistically, the DOCK11 deficiency resulted in the suppression of B cell-intrinsic signaling in vitro and in vivo. Although DOCK11 expression by B cells was required for the induction of T follicular helper cells at the early stages of immune responses, minor impacts were identified on the expansion of Ag-specific populations among GC B cells. Thus, DOCK11 appears to contribute to the expansion of Ag-specific populations among GC B cells through the stimulation of B cell-intrinsic signaling.

Abstract 840: Pathway enrichment analysis of gene expression data from formalin-fixed paraffin embedded (FFPE) samples using the GeoMx™ DSP Platform

Abstract The GeoMx Digital Spatial Profiling (DSP) Platform enables robust detection of high-plex protein and RNA expression from user-defined sections within FFPE samples. As the number of targets detected within such tissues increases, it becomes important to apply systems biology strategies in order to better interpret the complex biology of the tumor microenvironment. In this study, we investigated the expression profiles of more than 1600 genes by utilizing more than 10,000 DSP-specific in situ hybridized (ISH) probes on FFPE samples. The bioinformatics tools we have development are enabling us to move beyond single-gene profiling to a better understanding of pathway-based expression. Our study includes colorectal cancer patient samples from which we have matching bulk RNA sequencing and NanoString analysis to compare. The panel of genes profiled have a strong focus around capturing biological signaling along canonical signaling pathways and cell-intrinsic signaling from immune cells and other cell types. We demonstrate the ability to leverage foundational pathway interrogation tools, including Reactome, with the data to capture spatially-resolved pathway interactions and signaling within FFPE tissues. As we look towards the future of the GeoMx platform and high-plex RNA profiling of tissue samples, these experiments highlight not only the need but the capacity for this platform to derive deep understanding of the biology within and across a single slide of tissue. These experiments are being used to drive development of the software features within the GeoMx ecosystem, which will provide further support for pathway-level exploration of expression when working with highly multiplexed reagents in future platform offerings. GeoMx™ DSP technology is for Research Use Only and not for use in diagnostic procedures. Citation Format: Tressa R. Hood, Jason Reeves, Zach Norgaard, Margaret Hoang, Sarah Warren, Erin Piazza, Rich Boykin, Joseph Beechem. Pathway enrichment analysis of gene expression data from formalin-fixed paraffin embedded (FFPE) samples using the GeoMx™ DSP Platform [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 840.

Glucagonotropic and Glucagonostatic Effects of KATP Channel Closure and Potassium Depolarization.

The role of depolarization in the inverse glucose-dependence of glucagon secretion was investigated by comparing the effects of KATP channel block and of high potassium. The secretion of glucagon and insulin by perifused mouse islets was simultaneously measured. Lowering glucose raised glucagon secretion before it decreased insulin secretion, suggesting an alpha cell-intrinsic signal recognition. Raising glucose affected glucagon and insulin secretion at the same time. However, depolarization by tolbutamide, gliclazide, or 15 mM KCl increased insulin secretion before the glucagon secretion receded. In contrast to the robust depolarizing effect of arginine and KCl (15 and 40 mM) on single alpha cells, tolbutamide was of variable efficacy. Only when applied before other depolarizing agents had tolbutamide a consistent depolarizing effect and regularly increased the cytosolic Ca2+ concentration. When tested on inside-out patches tolbutamide was as effective on alpha cells as on beta cells. In the presence of 1 µM clonidine, to separate insulinotropic from glucagonotropic effects, both 500 µM tolbutamide and 30 µM gliclazide increased glucagon secretion significantly, but transiently. The additional presence of 15 or 40 mM KCl in contrast led to a marked and lasting increase of the glucagon secretion. The glucagon secretion by SUR1 knockout islets was not increased by tolbutamide, whereas 40 mM KCl was of unchanged efficiency. In conclusion a strong and sustained depolarization is compatible with a marked and lasting glucagon secretion. KATP channel closure in alpha cells is less readily achieved than in beta cells, which may explain the moderate and transient glucagonotropic effect.

The activation trajectory of plasmacytoid dendritic cells in vivo during a viral infection.

Plasmacytoid dendritic cells (pDCs) are a major source of type I interferon (IFN-I). What other functions pDCs exert in vivo during viral infections is controversial and more studies are needed to understand their orchestration. Here, we characterize in-depth and link pDC activation states in animals infected by mouse cytomegalovirus, by combining Ifnb1 reporter mice with flow cytometry, single-cell RNA sequencing, confocal microscopy and a cognate CD4 T cell activation assay. We show that IFN-I production and T cell activation were performed by the same pDC, but sequentially in time and in different micro-anatomical locations. In addition, we show that pDC commitment to IFN-I production was marked early on by their downregulation of LIFR and promoted by cell-intrinsic TNF signaling. We propose a novel model of how individual pDCs are endowed to exert different functions in vivo during a viral infection in a manner tightly orchestrated in time and space.

90 YEARS OF PROGESTERONE: Progesterone receptor signaling in the normal breast and its implications for cancer.

Progesterone is considered as the pregnancy hormone and acts on many different target tissues. Progesterone receptor (PR) signaling is important for normal development and the physiologic function of the breast and impinges on breast carcinogenesis. Both systemically and locally, in the breast epithelium, there are multiple layers of complexity to progesterone action, many of which have been revealed through experiments in mice. The hormone acts via its receptor expressed in a subset of cells, the sensor cells, in the breast epithelium with different signaling outcomes in individual cells eliciting distinct cell-intrinsic and paracrine signaling involving different mediators for different intercellular interactions. PR expression itself is developmentally regulated and the biological outcome of PR signaling depends on the developmental stage of the mammary gland and the endocrine context. During both puberty and adulthood PR activates stem and progenitor cells through Wnt4-driven activation of the myoepithelium with downstream Adamts18-induced changes in extracellualr matrix (ECM) / basal membrane (BM). During estrous cycling and pregnancy, the hormone drives a major cell expansion through Rankl. At all stages, PR signaling is closely tied to estrogen receptor α (ER) signaling. As the PR itself is a target gene of ER, the complex interactions are experimentally difficult to dissect and still poorly understood. Ex vivo models of the human breast and studies on biopsy samples show that major signaling axes are conserved across species. New intraductal xenograft models hold promise to provide a better understanding of PR signaling in the normal breast epithelium and in breast cancer development in the near future.

RNA modifications in the regulation of hematopoiesis and leukemogenesis

<p indent=0mm>Embryonic and adult hematopoiesis is an intricate and highly conserved process, which is regulated by cell-intrinsic transcription factors, signal pathways and epigenetic modifications, and cell-extrinsic factors in hematopoietic microenvironment. RNA modification has been identified as a new layer of epigenetics via post-transcriptional regulation and is required for pivotal biological functions. Recently, growing number of studies have demonstrated that RNA modification acts as a key regulator in hematopoietic processes. In this review, we summarize the functions and underlying mechanisms of RNA modifications in the regulation of embryonic hematopoiesis, homeostatic maintenance and leukemogenesis at the epi-transcriptome level, which will not only shed new light on our understanding of developmental hematopoiesis and the relationship between normal and malignant hematopoiesis, but also provide potential therapeutic targets for leukemia treatment.

Fatty acid β-oxidation is required for the differentiation of larval hematopoietic progenitors in Drosophila.

Cell-intrinsic and extrinsic signals regulate the state and fate of stem and progenitor cells. Recent advances in metabolomics illustrate that various metabolic pathways are also important in regulating stem cell fate. However, our understanding of the metabolic control of the state and fate of progenitor cells is in its infancy. Using Drosophila hematopoietic organ: lymph gland, we demonstrate that Fatty Acid Oxidation (FAO) is essential for the differentiation of blood cell progenitors. In the absence of FAO, the progenitors are unable to differentiate and exhibit altered histone acetylation. Interestingly, acetate supplementation rescues both histone acetylation and the differentiation defects. We further show that the CPT1/whd (withered), the rate-limiting enzyme of FAO, is transcriptionally regulated by Jun-Kinase (JNK), which has been previously implicated in progenitor differentiation. Our study thus reveals how the cellular signaling machinery integrates with the metabolic cue to facilitate the differentiation program.