Shigehiko Imagawa

Repression via the GATA box is essential for tissue-specific erythropoietin gene expression

In response to anemia, erythropoietin (Epo) gene transcription is markedly induced in the kidney and liver. To elucidate how Epo gene expression is regulated in vivo, we established transgenic mouse lines expressing green fluorescent protein (GFP) under the control of a 180-kb mouse Epo gene locus. GFP expression was induced by anemia or hypoxia specifically in peritubular interstitial cells of the kidney and hepatocytes surrounding the central vein. Surprisingly, renal Epo-producing cells had a neuronlike morphology and expressed neuronal marker genes. Furthermore, the regulatory mechanisms of Epo gene expression were explored using transgenes containing mutations in the GATA motif of the promoter region. A single nucleotide mutation in this motif resulted in constitutive ectopic expression of transgenic GFP in renal distal tubules, collecting ducts, and certain populations of epithelial cells in other tissues. Since both GATA-2 and GATA-3 bind to the GATA box in distal tubular cells, both factors are likely to repress constitutively ectopic Epo gene expression in these cells. Thus, GATA-based repression is essential for the inducible and cell type-specific expression of the Epo gene.

Enhanced erythropoiesis mediated by activation of the renin-angiotensin system via angiotensin II type 1a receptor

Although clinical and experimental studies have long suggested a role for the renin‐angiotensin system (RAS) in the regulation of erythropoiesis, the molecular basis of this role has not been well understood. We report here that transgenic mice carrying both the human renin and human angiotensinogen genes displayed persistent erythrocytosis as well as hypertension. To identify the receptor molecule responsible for this phenotype, we introduced both transgenes into the AT1a receptor null background and found that the hematocrit level in the compound mice was restored to the normal level. Angiotensin II has been shown to influence erythropoiesis by two means, up‐regulation of erythropoietin levels and direct stimulation of erythroid progenitor cells. Thus, we conducted bone marrow transplantation experiments and clarified that AT1a receptors on bone marrow‐derived cells were dispensable for RAS‐dependent erythrocytosis. Plasma erythropoietin levels and kidney erythropoietin mRNA expression in the double transgenic mice were significantly increased compared with those of the wild‐type control, while the elevated plasma erythropoietin levels were significantly attenuated in the compound mice. These results provide clear genetic evidence that activated RAS enhances erythropoiesis through the AT1a receptor of kidney cells and that this effect is mediated by the elevation of plasma erythropoietin levels in vivo.

Characterization of stage progression in chronic myeloid leukemia by DNA microarray with purified hematopoietic stem cells.

Chronic myeloid leukemia (CML) is characterized by the clonal expansion of hematopoietic stem cells (HSCs). Without effective treatment, individuals in the indolent, chronic phase (CP) of CML undergo blast crisis (BC), the prognosis for which is poor. It is therefore important to clarify the mechanism underlying stage progression in CML. DNA microarray is a versatile tool for such a purpose. However, simple comparison of bone marrow mononuclear cells from individuals at different disease stages is likely to result in the identification of pseudo-positive genes whose change in expression only reflects the different proportions of leukemic blasts in bone marrow. We have therefore compared with DNA microarray the expression profiles of 3456 genes in the purified HSC-like fractions that had been isolated from 13 CML patients and healthy volunteers. Interestingly, expression of the gene for PIASy, a potential inhibitor of STAT (signal transducer and activator of transcription) proteins, was down-regulated in association with stage progression in CML. Furthermore, forced expression of PIASy has induced apoptosis in a CML cell line. These data suggest that microarray analysis with background-matched samples is an efficient approach to identify molecular events underlying the stage progression in CML.

Overexpression of c-Maf Contributes to T-Cell Lymphoma in Both Mice and Human

c-Maf translocation or overexpression has been observed in human multiple myeloma. Although c-maf might function as an oncogene in multiple myeloma, a role for this gene in other cancers has not been shown. In this study, we have found that mice transgenic for c-Maf whose expression was direct to the T-cell compartment developed T-cell lymphoma. Moreover, we showed that cyclin D2, integrin beta(7), and ARK5 were up-regulated in c-Maf transgenic lymphoma cells. Furthermore, 60% of human T-cell lymphomas (11 of 18 cases), classified as angioimmunoblastic T-cell lymphoma, were found to express c-Maf. These results suggest that c-Maf might cause a type of T-cell lymphoma in both mice and humans and that ARK5, in addition to cyclin D2 and integrin beta(7), might be downstream target genes of c-Maf leading to malignant transformation.

c-Maf expression in angioimmunoblastic T-cell lymphoma.

The oncogene c-Maf was recently found to be overexpressed in approximately 50% of multiple myeloma cases, and a role for c-Maf in promoting cyclin D2 expression has been postulated. We previously examined c-Maf expression in various T-cell lymphomas by reverse-transcription polymerase chain reaction and found extremely elevated c-Maf levels in angioimmunoblastic T-cell lymphoma (AILT). In this study, we examined T-cell lymphomas for c-Maf and cyclin expression immunohistochemically. Of 93 cases of T-cell lymphomas we investigated in the current study, c-Maf expression was seen in 23 out of 31 cases of AILT, 3 out of 11 of adult T-cell leukemia/lymphoma, 4 out of 19 of peripheral T-cell lymphoma, unspecified [PTCL(U)], and 0 out of 11 cases of mycosis fungoides, 0 out of 11 of anaplastic large cell lymphoma, and 1 out of 10 of extranodal NK/T-cell lymphoma, nasal type. Double immunostaining in AILT revealed that the majority of c-Maf–positive cells were also positive for CD43 (MT1), CD45RO (UCHL-1), and CD4 but were negative for CD20 (L26). Additionally, cyclins D1 and D2, which stimulate cell cycle progression, were overexpressed in a large number of the c-Maf–positive AILT samples. Quantitative reverse-transcription polymerase chain reaction analysis also showed that c-Maf was overexpressed in 8/31 cases of AILT, 0/19 cases of PTCL(U), 0/11 cases of anaplastic large cell lymphoma, 0/10 cases of extranodal NK/T-cell lymphoma, nasal type, and 2/8 cases of multiple myeloma, presenting significant difference between AILT and PTCL(U) (P=0.016, χ2 test).These findings strongly suggest that CD4-positive neoplastic T cells in AILT show c-Maf expression and provide new insight into the pathogenesis of AILT suggesting c-Maf to be a useful diagnostic marker for AILT.

Caffeine and taurine enhance endurance performance.

Caffeine enhances endurance performance; however, its effect on accumulated lactate remains unclear. Conversely, taurine, which also enhances endurance performance, decreases accumulated lactate. In this study, the effect of combination of caffeine and taurine on endurance performance was assessed. Mice ran on a treadmill, and the accumulated lactate was measured. In addition, muscle fibers from the gastrocnemius muscle of the mice were stained with ATPase and analyzed. The use of caffeine and taurine over a 2 week period enhanced endurance performance. Moreover, taurine significantly decreased the accumulated concentration of lactate over long running distances. However, the diameter of the cross-sections and ratios of Types I, IIA, and IIB muscle fibers were not affected.

Antitumor effects of 2‐oxoglutarate through inhibition of angiogenesis in a murine tumor model

Hypoxia‐inducible factor 1 (HIF‐1) plays essential roles in tumor angiogenesis and growth by regulating the transcription of several key genes in response to hypoxic stress and growth factors. HIF‐1 is a heterodimeric transcriptional activator consisting of inducible α and constitutive β subunits. In oxygenated cells, proteins containing the prolyl hydroxylase domain (PHD) directly sense intracellular oxygen concentrations. PHDs tag HIF‐1α subunits for polyubiquitination and proteasomal degradation by prolyl hydroxylation using 2‐oxoglutarate (2‐OX) and dioxygen. Our recent studies showed that 2‐OX reduces HIF‐1α, erythropoietin, and vascular endothelial growth factor (VEGF) expression in the hepatoma cell line Hep3B when under hypoxic conditions in vitro. Here, we report that similar results were obtained in Lewis lung cancer (LLC) cells in in vitro studies. Furthermore, 2‐OX showed potent antitumor effects in a mouse dorsal air sac assay and a murine tumor xenograft model. In the dorsal air sac assay, 2‐OX reduced the numbers of newly formed vessels induced by LLC cells. In a murine tumor xenograft model, intraperitoneal injection of 2‐OX significantly inhibited tumor growth and angiogenesis in tumor tissues. Moreover, 5‐fluorouracil combined with 2‐OX significantly inhibited tumor growth in this model, which was accompanied by reduction of Vegf gene expression and inhibited angiogenesis in tumor tissues. These results suggest that 2‐OX is a promising anti‐angiogenic therapeutic agent. (Cancer Sci 2009; 100: 1639–1647)

2-oxoglutarate downregulates expression of vascular endothelial growth factor and erythropoietin through decreasing hypoxia-inducible factor-1α and inhibits angiogenesis

In oxygenated cells, hypoxia‐inducible factor‐1 (HIF‐1) α subunits are rapidly degraded by a mechanism that involves ubiquitination by the von Hippel–Lindau tumor suppressor E3 ligase complex using 2‐oxoglutarate as a substrate. We examined the effect of 2‐oxoglutarate on the production of erythropoietin and vascular endothelial growth factor (VEGF). The expression of erythropoietin and VEGF protein were dose‐dependently downregulated in Hep3B cells by the addition of 2‐oxoglutarate. The promoter activity of VEGF‐luciferase was dose‐dependently downregulated by the addition of 2‐oxoglutarate. Gel mobility shift assays revealed that the addition of 2‐oxoglutarate dose‐dependently inhibited HIF‐1 binding activity, but did not affect GATA binding activity. Western blot analysis revealed that 2‐oxoglutarate dose‐dependently inhibited the HIF‐1α protein level in Hep3B cells in hypoxic conditions. However, MG132 (the proteasome inhibitor) rescued the inhibition of HIF‐1α protein expression by 2‐oxoglutarate. Furthermore, under hypoxic conditions, 2‐oxoglutarate dose‐dependently inhibited tube formation in in vitro angiogenesis assays. These results indicate that 2‐oxoglutarate treatment may be useful for the inhibition of angiogenesis. J. Cell. Physiol. 209: 333–340, 2006.

GATA Suppresses Erythropoietin Gene Expression through GATA Site in Mouse Erythropoietin Gene Promoter

The promoter and enhancer elements of the mouse erythropoietin (mEpo) gene, which have high homology with those of the human erythropoietin (hEpo) gene, were fused withluciferase. The construct was transfected into erythropoietin-producing hepatoma cell line (Hep3B) cells by lipofectin with lacZ as an internal standard. The wild type (TGATA) showed a 39.5-fold increase in induction by hypoxia. Mouse GATA-2 inhibited the hypoxic induction of the wild-type (m3), promoter-luciferase construct but not the hypoxic induction of the mutant (m4, 5) promoter-luciferase constructs. NG-monomethyl L-arginine (L-NMMA) inhibited the hypoxic induction of the m3 promoter-luciferase construct, but this inhibition was recovered by L-arginine. H2O2 also inhibited the hypoxic induction of the m3 promoter-luciferase construct, but this inhibition was recovered by catalase. Gel shift assays performed on nuclear extracts of 293 cells overexpressing mGATA-1, -2, and -3 revealed that mGATA-1, -2, and -3 bind to the TGATA element of the mEpo promoter. These results indicate that mGATA binds to the TGATA site of the mEpo promoter and negatively regulates mEpo gene expression. Negative regulation of mEpo gene by GATA transcriptional factors is discussed.

Transgenic rabbits with increased VEGF expression develop hemangiomas in the liver: a new model for Kasabach-Merritt syndrome.

Clinical studies have provided ample evidence that high (either systemic or local) levels of vascular endothelial growth factor (VEGF) are associated with several pathophysiological disorders, including hemangiomas. To investigate whether elevated VEGF expression could directly affect these disorders, we created a transgenic (Tg) rabbit model with increased hepatic expression of the human VEGF165 transgene under the control of the human α-antitrypsin promoter. Tg rabbits exhibited marked hepatomegaly, with livers 2.5-fold heavier than those of control rabbits. Histological analysis revealed that the livers of Tg rabbits showed prominent dilation of the sinusoids and formed various-sized blood vessel networks, a feature of diffuse hemangiomas. Immunohistochemical staining revealed that the hepatocytes produced VEGF165, whereas plasma VEGF165 was not detected. Furthermore, Tg rabbits suffered from hemolytic anemia, thrombocytopenia and splenomegaly, which was associated with marked extramedullary hematopoiesis. The manifestations of Tg rabbits mimic many of the features of hemangiomatous disorders in humans such as the Kasabach–Merritt syndrome, and therefore this model may be potentially useful for the study of the pathogenesis and complications of hemangiomas as well as the investigation of angiogenesis inhibitors.