Naoharu Takano

Hypoxia-inducible factor–dependent breast cancer–mesenchymal stem cell bidirectional signaling promotes metastasis

Metastasis involves critical interactions between cancer and stromal cells. Intratumoral hypoxia promotes metastasis through activation of hypoxia-inducible factors (HIFs). We demonstrate that HIFs mediate paracrine signaling between breast cancer cells (BCCs) and mesenchymal stem cells (MSCs) to promote metastasis. In a mouse orthotopic implantation model, MSCs were recruited to primary breast tumors and promoted BCC metastasis to LNs and lungs in a HIF-dependent manner. Coculture of MSCs with BCCs augmented HIF activity in BCCs. Additionally, coculture induced expression of the chemokine CXCL10 in MSCs and the cognate receptor CXCR3 in BCCs, which was augmented by hypoxia. CXCR3 expression was blocked in cocultures treated with neutralizing antibody against CXCL10. Conversely, CXCL10 expression was blocked in MSCs cocultured with BCCs that did not express CXCR3 or HIFs. MSC coculture did not enhance the metastasis of HIF-deficient BCCs. BCCs and MSCs expressed placental growth factor (PGF) and its cognate receptor VEGFR1, respectively, in a HIF-dependent manner, and CXCL10 expression by MSCs was dependent on PGF expression by BCCs. PGF promoted metastasis of BCCs and also facilitated homing of MSCs to tumors. Thus, HIFs mediate complex and bidirectional paracrine signaling between BCCs and MSCs that stimulates breast cancer metastasis.

Hypoxia-inducible factors and RAB22A mediate formation of microvesicles that stimulate breast cancer invasion and metastasis

Significance Cancer cells release from their cell surface membrane-lined microvesicles (MVs), which contain proteins, mRNAs, and microRNAs that can be taken up by other cells. We report that breast cancer cells exposed to decreased oxygen availability (hypoxia) increase their production of MVs, which stimulate invasion and metastasis by recipient breast cancer cells. Increased MV shedding by hypoxic cells requires expression of hypoxia-inducible factors (HIFs), which activate transcription of the RAB22A gene, and expression of the small GTPase RAB22A, which is a protein that localizes to budding MVs. Our results delineate a molecular mechanism by which hypoxia increases invasion and metastasis by stimulating MV shedding and provide further evidence that addition of HIF inhibitors to current treatment regimens may improve clinical outcome. Extracellular vesicles such as exosomes and microvesicles (MVs) are shed by cancer cells, are detected in the plasma of cancer patients, and promote cancer progression, but the molecular mechanisms regulating their production are not well understood. Intratumoral hypoxia is common in advanced breast cancers and is associated with an increased risk of metastasis and patient mortality that is mediated in part by the activation of hypoxia-inducible factors (HIFs). In this paper, we report that exposure of human breast cancer cells to hypoxia augments MV shedding that is mediated by the HIF-dependent expression of the small GTPase RAB22A, which colocalizes with budding MVs at the cell surface. Incubation of naïve breast cancer cells with MVs shed by hypoxic breast cancer cells promotes focal adhesion formation, invasion, and metastasis. In breast cancer patients, RAB22A mRNA overexpression in the primary tumor is associated with decreased overall and metastasis-free survival and, in an orthotopic mouse model, RAB22A knockdown impairs breast cancer metastasis.

Cystathionine β-synthase as a carbon monoxide–sensitive regulator of bile excretion†

Carbon monoxide (CO) is a stress‐inducible gas generated by heme oxygenase (HO) eliciting adaptive responses against toxicants; however, mechanisms for its reception remain unknown. Serendipitous observation in metabolome analysis in CO‐overproducing livers suggested roles of cystathionine β‐synthase (CBS) that rate‐limits transsulfuration pathway and H2S generation, for the gas‐responsive receptor. Studies using recombinant CBS indicated that CO binds to the prosthetic heme, stabilizing 6‐coordinated CO‐Fe(II)‐histidine complex to block the activity, whereas nitric oxide (NO) forms 5‐coordinated structure without inhibiting it. The CO‐overproducing livers down‐regulated H2S to stimulate HCO3−‐dependent choleresis: these responses were attenuated by blocking HO or by donating H2S. Livers of heterozygous CBS knockout mice neither down‐regulated H2S nor exhibited the choleresis while overproducing CO. In the mouse model of estradiol‐induced cholestasis, CO overproduction by inducing HO‐1 significantly improved the bile output through stimulating HCO3− excretion; such a choleretic response did not occur in the knockout mice. Conclusion: Results collected from metabolome analyses suggested that CBS serves as a CO‐sensitive modulator of H2S to support biliary excretion, shedding light on a putative role of the enzyme for stress‐elicited adaptive response against bile‐dependent detoxification processes. (HEPATOLOGY 2009;49:141‐150.)

Reduced methylation of PFKFB3 in cancer cells shunts glucose towards the pentose phosphate pathway.

Haem oxygenase (HO)-1/carbon monoxide (CO) protects cancer cells from oxidative stress, but the gas-responsive signalling mechanisms remain unknown. Here we show using metabolomics that CO-sensitive methylation of PFKFB3, an enzyme producing fructose 2,6-bisphosphate (F-2,6-BP), serves as a switch to activate phosphofructokinase-1, a rate-limiting glycolytic enzyme. In human leukaemia U937 cells, PFKFB3 is asymmetrically di-methylated at R131 and R134 through modification by protein arginine methyltransferase 1. HO-1 induction or CO results in reduced methylation of PFKFB3 in varied cancer cells to suppress F-2,6-BP, shifting glucose utilization from glycolysis toward the pentose phosphate pathway. Loss of PFKFB3 methylation depends on the inhibitory effects of CO on haem-containing cystathionine β-synthase (CBS). CBS modulates remethylation metabolism, and increases NADPH to supply reduced glutathione, protecting cells from oxidative stress and anti-cancer reagents. Once the methylation of PFKFB3 is reduced, the protein undergoes polyubiquitination and is degraded in the proteasome. These results suggest that the CO/CBS-dependent regulation of PFKFB3 methylation determines directional glucose utilization to ensure resistance against oxidative stress for cancer cell survival.

Hypoxia-inducible factor-dependent signaling between triple-negative breast cancer cells and mesenchymal stem cells promotes macrophage recruitment.

Significance The recruitment of host stromal cells, such as macrophages and mesenchymal stem cells (MSCs), to the primary tumor is a critical step toward cancer malignancy. We have identified signals that are exchanged between breast cancer cells (BCCs) and MSCs. This signaling increases the recruitment of both MSCs and macrophages to primary tumors and increases metastasis of BCCs to lymph nodes and lungs. Reduced oxygen levels (hypoxia) in breast cancers are associated with increased risk of metastasis and decreased patient survival. We show that hypoxia stimulates signaling between BCCs and MSCs due to the activity of hypoxia-inducible factors (HIFs). Drugs that block HIF activity prevent signaling and macrophage recruitment, which suggests that they may be useful additions to breast cancer therapy. Intratumoral hypoxia induces the recruitment of stromal cells, such as macrophages and mesenchymal stem cells (MSCs), which stimulate invasion and metastasis by breast cancer cells (BCCs). Production of macrophage colony-stimulating factor 1 (CSF1) by BCCs is required for macrophage recruitment, but the mechanisms underlying CSF1 expression have not been delineated. Triple-negative breast cancers have increased expression of genes regulated by hypoxia-inducible factors (HIFs). In this study, we delineate two feed-forward signaling loops between human MDA-MB-231 triple-negative BCCs and human MSCs that drive stromal cell recruitment to primary breast tumors. The first loop, in which BCCs secrete chemokine (C-X-C motif) ligand 16 (CXCL16) that binds to C-X-C chemokine receptor type 6 (CXCR6) on MSCs and MSCs secrete chemokine CXCL10 that binds to receptor CXCR3 on BCCs, drives recruitment of MSCs. The second loop, in which MSCs secrete chemokine (C-C motif) ligand 5 that binds to C-C chemokine receptor type 5 on BCCs and BCCs secrete cytokine CSF1 that binds to the CSF1 receptor on MSCs, drives recruitment of tumor-associated macrophages and myeloid-derived suppressor cells. These two signaling loops operate independent of each other, but both are dependent on the transcriptional activity of HIFs, with hypoxia serving as a pathophysiological signal that synergizes with chemokine signals from MSCs to trigger CSF1 gene transcription in triple-negative BCCs.

Biochemical characterization of human kallikrein 8 and its possible involvement in the degradation of extracellular matrix proteins

Human kallikrein 8 (KLK8) is a member of the human kallikrein gene family of serine proteases, and its protein, hK8, has recently been suggested to serve as a new ovarian cancer marker. To gain insights into the physiological role of hK8, the active recombinant enzyme was obtained in a pure state for biochemical and enzymatic characterizations. hK8 had trypsin‐like activity with a strong preference for Arg over Lys in the P1 position, and its activity was inhibited by typical serine protease inhibitors. The protease degraded casein, fibronectin, gelatin, collagen type IV, fibrinogen, and high‐molecular‐weight kininogen. hK8 also converted human single‐chain tissue‐type plasminogen activator (65 kDa) to its two‐chain form (32 and 33 kDa) by specifically cleaving the peptide bond Arg275–Ile276. This conversion resulted in a drastic increase in the activity of the activator toward the fluorogenic substrate Pyr‐Gly‐Arg‐MCA and plasminogen in the absence of fibrin. Our findings suggest that hK8 may be implicated in ECM protein degradation in the area surrounding hK8‐producing cells.

Ganetespib blocks HIF-1 activity and inhibits tumor growth, vascularization, stem cell maintenance, invasion, and metastasis in orthotopic mouse models of triple-negative breast cancer

Targeted therapy against triple-negative breast cancers, which lack expression of the estrogen, progesterone, and HER2 receptors, is not available and the overall response to cytotoxic chemotherapy is poor. One of the molecular hallmarks of triple-negative breast cancers is increased expression of genes that are transcriptionally activated by hypoxia-inducible factors (HIFs), which are implicated in many critical aspects of cancer progression including metabolism, angiogenesis, invasion, metastasis, and stem cell maintenance. Ganetespib is a second-generation inhibitor of heat shock protein 90 (HSP90), a molecular chaperone that is essential for the stability and function of multiple client proteins in cancer cells including HIF-1α. In this study, human MDA-MB-231 and MDA-MB-435 triple-negative breast cancer cells were injected into the mammary fat pad of immunodeficient mice that received weekly intravenous injections of ganetespib or vehicle following the development of palpable tumors. Ganetespib treatment markedly impaired primary tumor growth and vascularization, and eliminated local tissue invasion and distant metastasis to regional lymph nodes and lungs. Ganetespib treatment also significantly reduced the number of Aldefluor-positive cancer stem cells in the primary tumor. Primary tumors of ganetespib-treated mice had significantly reduced levels of HIF-1α (but not HIF-2α) protein and of HIF-1 target gene mRNAs encoding proteins that play key roles in angiogenesis, metabolism, invasion, and metastasis, thereby providing a molecular basis for observed effects of the drug on the growth and metastasis of triple-negative breast cancer.Key MessagesTriple-negative breast cancers (TNBCs) respond poorly to available chemotherapy.TNBCs overexpress genes regulated by hypoxia-inducible factors (HIFs).Ganetespib induces degradation of HSP90 client proteins, including HIF-1α.Ganetespib inhibited TNBC orthotopic tumor growth, invasion, and metastasis.Ganetespib inhibited expression of HIF-1 target genes involved in TNBC progression.

Methionine excess in diet induces acute lethal hepatitis in mice lacking cystathionine γ-lyase, an animal model of cystathioninuria.

Physiological roles of the transsulfuration pathway have been recognized by its contribution to the synthesis of cytoprotective cysteine metabolites, such as glutathione, taurine/hypotaurine, and hydrogen sulfide (H(2)S), whereas its roles in protecting against methionine toxicity remained to be clarified. This study aimed at revealing these roles by analyzing high-methionine diet-fed transsulfuration-defective cystathionine γ-lyase-deficient (Cth(-/-)) mice. Wild-type and Cth(-/-) mice were fed a standard diet (1 × Met: 0.44%) or a high-methionine diet (3 × Met or 6 × Met), and hepatic conditions were monitored by serum biochemistry and histology. Metabolome analysis was performed for methionine derivatives using capillary electrophoresis- or liquid chromatography-mass spectrometry and sulfur-detecting gas chromatography. The 6 × Met-fed Cth(-/-) (not 1 × Met-fed Cth(-/-) or 6 × Met-fed wild type) mice displayed acute hepatitis, which was characterized by markedly elevated levels of serum alanine/aspartate aminotransferases and serum/hepatic lipid peroxidation, inflammatory cell infiltration, and hepatocyte ballooning; thereafter, they died of gastrointestinal bleeding due to coagulation factor deficiency. After 1 week on 6 × Met, blood levels of ammonia/homocysteine and hepatic levels of methanethiol/3-methylthiopropionate (a methionine transamination product/methanethiol precursor) became significantly higher in Cth(-/-) mice than in wild-type mice. Although hepatic levels of methionine sulfoxide became higher in 6 × Met-fed wild-type mice and Cth(-/-) mice, those of glutathione, taurine/hypotaurine, and H(2)S became lower and serum levels of homocysteine became much higher in 6 × Met-fed Cth(-/-) mice than in wild-type mice. Thus, transsulfuration plays a critical role in the detoxification of excessive methionine by circumventing aberrant accumulation of its toxic transamination metabolites, including ammonia, methanethiol, and 3-methylthiopropionate, in addition to synthesizing cysteine-derived antioxidants to counteract accumulated pro-oxidants such as methionine sulfoxide and homocysteine.

Carbon monoxide stimulates global protein methylation via its inhibitory action on cystathionine β-synthase

Although carbon monoxide derived from heme oxygenase has been reported to exert diverse biological actions in mammals, macromolecules responsible for its direct reception and functional outcomes of the gas binding remain largely unknown. Based on our previous results in vivo suggesting carbon monoxide serves as an inhibitor of cystathionine β-synthase that rate-limits transsulfuration pathway for generation of hydrogen sulfide, we have herein hypothesized that the gas might serve as a regulator of protein methylation through accelerating turnover of remethylation cycle residing at the upstream of the enzyme. Metabolomic analysis in human monoblastic leukemia U937 cells in culture revealed that application of carbon monoxide-releasing molecules caused increases in methionine and S-adenosylmethionine and a decrease in cystathionine in the cells, suggesting the cystathionine β-synthase inhibition by carbon monoxide. Under these circumstances, the cells exhibited global protein arginine methylation: this event was also reproduced by the cell treatment with hemin, a heme oxygenase-1 inducer. The protein arginine methylation elicited by carbon monoxide was attenuated by knocking down cystathionine β-synthase with its small interfering RNA or by blocking S-adenosylhomocysteine hydrolase with adenosine dialdehyde, suggesting remethylation cycling is necessary to trigger the methylation processing. Furthermore, proteins undergoing the carbon monoxide-induced arginine methylation involved histone H3 proteins, suggesting chromatin modification by the gas. Collectively with our studies in vivo showing its inhibitory action on endogenous hydrogen sulfide production, the current results suggest that not only inhibition of transsulfuration pathway for H2S generation but also activation of protein methylation accounts for notable biological actions of carbon monoxide via the cystathionine β-synthase inhibition.

Decreased Expression of Cystathionine β-Synthase Promotes Glioma Tumorigenesis

Cystathionine β-synthase (CBS) catalyzes metabolic reactions that convert homocysteine to cystathionine. To assess the role of CBS in human glioma, cells were stably transfected with lentiviral vectors encoding shRNA targeting CBS or a nontargeting control shRNA, and subclones were injected into immunodeficient mice. Interestingly, decreased CBS expression did not affect proliferation in vitro but decreased the latency period before rapid tumor xenograft growth after subcutaneous injection and increased tumor incidence and volume following orthotopic implantation into the caudate–putamen. In soft-agar colony formation assays, CBS knockdown subclones displayed increased anchorage-independent growth. Molecular analysis revealed that CBS knockdown subclones expressed higher basal levels of the transcriptional activator hypoxia-inducible factor 2α (HIF2α/EPAS1). HIF2α knockdown counteracted the effect of CBS knockdown on anchorage-independent growth. Bioinformatic analysis of mRNA expression data from human glioma specimens revealed a significant association between low expression of CBS mRNA and high expression of angiopoietin-like 4 (ANGPTL4) and VEGF transcripts, which are HIF2 target gene products that were also increased in CBS knockdown subclones. These results suggest that decreased CBS expression in glioma increases HIF2α protein levels and HIF2 target gene expression, which promotes glioma tumor formation. Implications: CBS loss-of-function promotes glioma growth. Mol Cancer Res; 12(10); 1398–406. ©2014 AACR.