Targeting chemoresistance in Xp11.2 translocation renal cell carcinoma using a novel polyamide-chlorambucil conjugate

Renal cell carcinoma with Xp11.2 translocation involving the TFE3 gene (TFE3‐RCC) is a recently identified subset of RCC with unique morphology and clinical presentation. The chimeric PRCC‐TFE3 protein produced by Xp11.2 translocation has been shown to transcriptionally activate its downstream target genes that play important roles in carcinogenesis and tumor development of TFE3‐RCC. However, the underlying molecular mechanisms remain poorly understood. Here we show that in TFE3‐RCC cells, PRCC‐TFE3 controls heme oxygenase 1 (HMOX1) expression to confer chemoresistance. Inhibition of HMOX1 sensitized the PRCC‐TFE3 expressing cells to genotoxic reagents. We screened for a novel chlorambucil–polyamide conjugate (Chb) to target PRCC‐TFE3‐dependent transcription, and identified Chb16 as a PRCC‐TFE3‐dependent transcriptional inhibitor of HMOX1 expression. Treatment of the patient‐derived cancer cells with Chb16 exhibited senescence and growth arrest, and increased sensitivity of the TFE3‐RCC cells to the genotoxic reagent etoposide. Thus, our data showed that the TFE3‐RCC cells acquired chemoresistance through HMOX1 expression and that inhibition of HMOX1 by Chb16 may be an effective therapeutic strategy for TFE3‐RCC.

Depth-targeted intracortical microstroke by two-photon photothrombosis in rodent brain

Significance: Photothrombosis is a widely used model of ischemic stroke in rodent experiments. In the photothrombosis model, the photosensitizer rose bengal (RB) is systemically introduced into the blood stream and activated by green light to induce aggregation of platelets that eventually cause vessel occlusion. Since the activation of RB is a one-photon phenomenon and the molecules in the illuminated area (light path) are subject to excitation, targeting of thrombosis is unspecific, especially in the depth dimension. We developed a photothrombosis protocol that can target a single vessel in the cortical parenchyma by two-photon excitation. Aim: We aim to induce a thrombotic stroke in the cortical parenchyma by two-photon activation of RB to confine photothrombosis within a vessel of a target depth. Approach: FITC-dextran is injected into the blood stream to visualize the cerebral blood flow in anesthetized adult mice with a cranial window. After a target vessel is chosen by two-photon imaging (950 nm), RB is injected into the blood stream. The scanning wavelength is changed to 720 nm, and photothrombosis is induced by scanning the target vessel. Results: Two-photon depth-targeted single-vessel photothrombosis was achieved with a success rate of 84.9 % ± 1.7 % and an irradiation duration of < 80    s . Attempts without RB (i.e., only with FITC) did not result in photothrombosis at the excitation wavelength of 720 nm. Conclusions: We described a protocol that achieves depth-targeted single-vessel photothrombosis by two-photon excitation. Simultaneous imaging of blood flow in the targeted vessel using FITC dextran enabled the confirmation of vessel occlusion and prevention of excess irradiation that possibly induces unintended photodamage.

ATP citrate lyase controls hematopoietic stem cell fate and supports bone marrow regeneration

In order to support bone marrow regeneration after myeloablation, hematopoietic stem cells (HSCs) actively divide to provide both stem and progenitor cells. However, the mechanisms regulating HSC function and cell fate choice during hematopoietic recovery remain unclear. We herein provide novel insights into HSC regulation during regeneration by focusing on mitochondrial metabolism and ATP citrate lyase (ACLY). After 5-fluorouracil-induced myeloablation, HSCs highly expressing endothelial protein C receptor (EPCR^high ) were enriched within the stem cell fraction at the expense of more proliferative EPCR^Low HSCs. These EPCR^High HSCs were initially more primitive than EPCR^Low HSCs and enabled stem cell expansion by enhancing histone acetylation, due to increased activity of ACLY in the early phase of hematopoietic regeneration. In the late phase of recovery, HSCs enhanced differentiation potential by increasing the accessibility of cis-regulatory elements in progenitor cell-related genes, such as CD48. In conditions of reduced mitochondrial metabolism and ACLY activity, these HSCs maintained stem cell phenotypes, while ACLY-dependent histone acetylation promoted differentiation into CD48⁺ progenitor cells. Collectively, these results indicate that the dynamic control of ACLY-dependent metabolism and epigenetic alterations is essential for HSC regulation during hematopoietic regeneration.

A Novel Function of Sphingolipid Signaling via S1PR3 in Hematopoietic and Leukemic Stem Cells

In this issue of Blood Cancer Discovery, Xie and colleagues describe a novel function of sphingosine-1-phosphate receptor 3 (S1PR3) to regulate myeloid differentiation and activate inflammatory programs in both human hematopoietic stem cells and leukemic stem cells. They propose S1PR3 as a major downstream signaling pathway of a TNFα-NF-κB axis in this study and unlock potential therapeutic opportunities to improve outcomes of patients with acute myeloid leukemia by modulating sphingolipid signaling via S1PR3. See related article by Xie et al., p. 32.

Thrombopoietin maintains cell numbers of hematopoietic stem and progenitor cells with megakaryopoietic potential

Thrombopoietin has long been known to influence megakaryopoiesis and hematopoietic stem and progenitor cells, although the exact mechanisms through which it acts are unknown. Here we show that MPL expression correlates with megakaryopoietic potential of hematopoietic stem and progenitor cells and identify a population of quiescent hematopoietic stem and progenitor cells that show limited dependence on thrombopoietin signaling. We show that thrombopoietin is primarily responsible for maintenance of hematopoietic cells with megakaryocytic differentiation potential and their subsequent megakaryocyte differentiation and maturation. The loss of megakaryocytes in thrombopoietin knockout mouse models results in a reduction of megakaryocyte-derived chemokine platelet factor 4 (CXCL4/PF4) in the bone marrow and administration of recombinant CXCL4/PF4 rescues the loss of quiescence observed in these mice. CXCL4/PF4 treatment does not rescue reduced hematopoietic stem and progenitor cell numbers, suggesting that thrombopoietin maintains hematopoietic stem and progenitor cell numbers directly.

Mitochondria transfer from early stages of erythroblasts to their macrophage niche via tunnelling nanotubes

Adult erythropoiesis entails a series of well-coordinated events that produce mature red blood cells. One of such events is the mitochondria clearance that occurs cell-autonomously via autophagy-dependent mechanisms. Interestingly, recent studies have shown mitochondria transfer activities between various cell types. In the context of erythropoiesis, macrophages are known to interact closely with the early stages of erythroblasts to provide a specialized niche, termed erythroblastic islands (EBI). However, whether mitochondria transfer can occur in the EBI niche has not been explored. Here, we report that mitochondria transfer in the EBI niche occurs in vivo. We observed mitochondria transfer activities from the early stages of erythroblasts to macrophages in the reconstituted in vitro murine EBI via different modes, including tunnelling nanotubes (TNT). Moreover, we demonstrated that Wiskott-Aldrich syndrome protein (WASp) in macrophages mediates TNT formation and mitochondria transfer via the modulation of F-actin filamentation, thus promoting mitochondria clearance from erythroid cells, to potentially enhance their differentiation. Taken together, our findings provide novel insight into the mitochondria clearance machineries that mediate erythroid maturation.

Mitochondria Turnover and Lysosomal Function in Hematopoietic Stem Cell Metabolism

Hematopoietic stem cells (HSCs) reside in a hypoxic microenvironment that enables glycolysis-fueled metabolism and reduces oxidative stress. Nonetheless, metabolic regulation in organelles such as the mitochondria and lysosomes as well as autophagic processes have been implicated as essential for the determination of HSC cell fate. This review encompasses the current understanding of anaerobic metabolism in HSCs as well as the emerging roles of mitochondrial metabolism and lysosomal regulation for hematopoietic homeostasis.

A FLCN-TFE3 Feedback Loop Prevents Excessive Glycogenesis and Phagocyte Activation by Regulating Lysosome Activity

The tumor suppressor folliculin (FLCN) suppresses nuclear translocation of TFE3, a master transcription factor for lysosomal biogenesis, via regulation of amino-acid-sensing Rag GTPases. However, the importance of this lysosomal regulation in mammalian physiology remains unclear. Following hematopoietic-lineage-specific Flcn deletion in mice, we found expansion of vacuolated phagocytes that accumulate glycogen in their cytoplasm, phenotypes reminiscent of lysosomal storage disorder (LSD). We report that TFE3 acts in a feedback loop to transcriptionally activate FLCN expression, and FLCN loss disrupts this loop, augmenting TFE3 activity. Tfe3 deletion in Flcn knockout mice reduces the number of phagocytes and ameliorates LSD-like phenotypes. We further reveal that TFE3 stimulates glycogenesis by promoting the expression of glycogenesis genes, including Gys1 and Gyg, upon loss of Flcn. Taken together, we propose that the FLCN-TFE3 feedback loop acts as a rheostat to control lysosome activity and prevents excessive glycogenesis and LSD-like phagocyte activation.

Murine neonatal ketogenesis preserves mitochondrial energetics by preventing protein hyperacetylation

Ketone bodies are generated in the liver and allow for the maintenance of systemic caloric and energy homeostasis during fasting and caloric restriction. It has previously been demonstrated that neonatal ketogenesis is activated independently of starvation. However, the role of ketogenesis during the perinatal period remains unclear. Here, we show that neonatal ketogenesis plays a protective role in mitochondrial function. We generated a mouse model of insufficient ketogenesis by disrupting the rate-limiting hydroxymethylglutaryl-CoA synthase 2 enzyme gene (Hmgcs2). Hmgcs2 knockout (KO) neonates develop microvesicular steatosis within a few days of birth. Electron microscopic analysis and metabolite profiling indicate a restricted energy production capacity and accumulation of acetyl-CoA in Hmgcs2 KO mice. Furthermore, acetylome analysis of Hmgcs2 KO cells revealed enhanced acetylation of mitochondrial proteins. These findings suggest that neonatal ketogenesis protects the energy-producing capacity of mitochondria by preventing the hyperacetylation of mitochondrial proteins.

Hematopoietic Stem Cell Metabolism during Development and Aging

Cellular metabolism in hematopoietic stem cells (HSCs) is an area of intense research interest, but the metabolic requirements of HSCs and their adaptations to their niches during development have remained largely unaddressed. Distinctive from other tissue stem cells, HSCs transition through multiple hematopoietic sites during development. This transition requires drastic metabolic shifts, insinuating the capacity of HSCs to meet the physiological demand of hematopoiesis. In this review, we highlight how mitochondrial metabolism determines HSC fate, and especially focus on the links between mitochondria, endoplasmic reticulum (ER), and lysosomes in HSC metabolism.

[Efficacy of thrombopoietin in bone marrow failure]

Thrombopoietin (Thpo) is a hematopoietic cytokine that regulates the production of megakaryocyte/platelet lineage cells and maintains hematopoietic stem and progenitor cells (HSPCs). While Thpo directly stimulates the proliferation of HSPCs, it also maintains HSCs in quiescence to form a reserve pool of HSCs in the bone marrow. Moreover, Thpo activates mitochondria and induces HSC differentiation to megakaryocyte/platelet lineage cells. Being void of instigating anti-Thpo antibody formation in vivo, the use of Thpo receptor agonists (Mpl agonists) transcends the use of recombinant Thpo in the treatment of immune thrombocytopenia. Since its invention, the therapeutic indication of Mpl agonists has extended to the treatment of bone marrow failure in aplastic anemia. As the clinical application of Mpl agonists expands, a detailed investigation of the function and effect of Mpl agonists on physiological HSCs and bone marrow failure is necessary.

Myeloma cells self-promote migration by regulating TAB1-driven TIMP-1 expression in mesenchymal stem cells

Multiple myeloma (MM) is an intractable hematological malignancy characterized by abnormal plasma cells in the bone marrow (BM) and increased osteolytic lesions. Within the BM niche, mesenchymal stem cells (MSCs) have been proposed to contribute to functionally important MM-MSC interactions. However, despite various studies on MM pathology, the impact of MM on MSCs during the early stages of malignancy has not been adequately addressed. We previously identified tissue inhibitor of matrix metalloproteinase 1 (TIMP-1) as a cytokine that is modulated in vivo within the MM BM niche, and highlighted its potential relevance in MM. Given the role of TIMP-1 in preventing migration of breast cancer cells, this study aimed to investigate the relationship between MSC-secreted TIMP-1 and MM progression. Here, we examined the effect of MSC-derived TIMP-1 on MM cell migration, and found that TIMP-1 secreted by human MSCs play a role in preventing migration of MM cells by reducing the levels of MM cell-derived MMP-9. We also investigated how MM cells regulate expression of TIMP-1 in MSCs. Using a knockdown approach in MSCs, we implicated TGF-B activated kinase 1 binding protein 1 (TAB1) as an upstream effector of TIMP-1 that was downregulated in the presence of MM cells, which resulted in reduced TIMP-1 secretion. Overall, our findings uncover how MSCs in the MM BM niche are modulated to promote MM progression, and unravel a previously unreported role of the TAB1-TIMP-1 axis in the context of the MM BM niche.

Comprehensive assessment of multiple tryptophan metabolites as potential biomarkers for immune checkpoint inhibitors in patients with non-small cell lung cancer

Purpose

Tryptophan metabolites have immunomodulatory functions, suggesting possible roles in cancer immunity.

Methods

Plasma tryptophan metabolites were measured using liquid chromatography/mass spectrometry before immune checkpoint inhibitors (ICIs) in patients with non-small cell lung cancer (NSCLC).

Results

The 19 patients with NSCLC had significantly lower levels of tryptophan (p = 0.002) and xanthurenic acid (p = 0.032), and a significantly higher level of 3-hydroxyanthranilic acid (3-HAA) (p = 0.028) compared with the 10 healthy volunteers. The patients achieving objective responses had significantly lower levels of 3-HAA than those who did not (p = 0.045). Receiver operating characteristic analyses determined that the cutoff value of 3-HAA for objective response was 35.4 pmol/mL (sensitivity: 87.5% and specificity: 83.3%). The patients with 3-HAA < 35.4 pmol/mL had significantly longer median progression-free survival (7.0 months) than those without (1.6 months, p = 0.022).

Conclusions

Tryptophan metabolites may have a potential for predicting the efficacy of ICIs.

Registration number

University Hospital Medical Information Network Clinical Trial Registry 000026140.

Electronic supplementary material

The online version of this article (10.1007/s12094-020-02421-8) contains supplementary material, which is available to authorized users.

PRMT5 Modulates Splicing for Genome Integrity and Preserves Proteostasis of Hematopoietic Stem Cells

Protein arginine methyltransferase 5 (PRMT5) is essential for hematopoiesis, while PRMT5 inhibition remains a promising therapeutic strategy against various cancers. Here, we demonstrate that hematopoietic stem cell (HSC) quiescence and viability are severely perturbed upon PRMT5 depletion, which also increases HSC size, PI3K/AKT/mechanistic target of rapamycin (mTOR) pathway activity, and protein synthesis rate. We uncover a critical role for PRMT5 in maintaining HSC genomic integrity by modulating splicing of genes involved in DNA repair. We found that reducing PRMT5 activity upregulates exon skipping and intron retention events that impair gene expression. Genes across multiple DNA repair pathways are affected, several of which mediate interstrand crosslink repair and homologous recombination. Consequently, loss of PRMT5 activity leads to endogenous DNA damage that triggers p53 activation, induces apoptosis, and culminates in rapid HSC exhaustion, which is significantly delayed by p53 depletion. Collectively, these findings establish the importance of cell-intrinsic PRMT5 activity in HSCs.