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R Ono, H Kumagai,
H Nakajima,
A Hishiya,
T Taki,
K Horikawa,
K Takatsu,
T Satoh,
Y Hayashi,
T Kitamura,
T Nosaka
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ABSTRACT: Mixed-lineage-leukemia (MLL) fusion oncogenes are closely involved in infant acute leukemia, which is frequently accompanied by mutations or overexpression of FMS-like receptor tyrosine kinase 3 (FLT3). Earlier studies have shown that MLL fusion proteins induced acute leukemia together with another mutation, such as an FLT3 mutant, in mouse models. However, little has hitherto been elucidated regarding the molecular mechanism of the cooperativity in leukemogenesis. Using murine model systems of the MLL-fusion-mediated leukemogenesis leading to oncogenic transformation in vitro and acute leukemia in vivo, this study characterized the molecular network in the cooperative leukemogenesis. This research revealed that MLL fusion proteins cooperated with activation of Ras in vivo, which was substitutable for Raf in vitro, synergistically, but not with activation of signal transducer and activator of transcription 5 (STAT5), to induce acute leukemia in vivo as well as oncogenic transformation in vitro. Furthermore, Hoxa9, one of the MLL-targeted critical molecules, and activation of Ras in vivo, which was replaceable with Raf in vitro, were identified as fundamental components sufficient for mimicking MLL-fusion-mediated leukemogenesis. These findings suggest that the molecular crosstalk between aberrant expression of Hox molecule(s) and activated Raf may have a key role in the MLL-fusion-mediated-leukemogenesis, and may thus help develop the novel molecularly targeted therapy against MLL-related leukemia.
Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 09/2009; 23(12):2197-209. · 8.30 Impact Factor
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Y Lu,
J Kitaura,
T Oki,
Y Komeno,
K Ozaki,
M Kiyono, H Kumagai,
H Nakajima,
T Nosaka,
H Aburatani,
T Kitamura
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ABSTRACT: Transforming growth factor-beta (TGF-beta)-stimulated clone-22 (TSC-22) was originally isolated as a TGF-beta-inducible gene. In this study, we identified TSC-22 as a potential leukemia suppressor. Two types of FMS-like tyrosine kinase-3 (Flt3) mutations are frequently found in acute myeloid leukemia: Flt3-ITD harboring an internal tandem duplication in the juxtamembrane domain associated with poor prognosis and Flt3-TKD harboring a point mutation in the kinase domain. Comparison of gene expression profiles between Flt3-ITD- and Flt3-TKD-transduced Ba/F3 cells revealed that constitutive activation of Flt3 by Flt3-TKD, but not Flt3-ITD, upregulated the expression of TSC-22. Importantly, treatment with an Flt3 inhibitor PKC412 or an Flt3 small interfering RNA decreased the expression level of TSC-22 in Flt3-TKD-transduced cells. Forced expression of TSC-22 suppressed the growth and accelerated the differentiation of several leukemia cell lines into monocytes, in particular, in combination with differentiation-inducing reagents. On the other hand, a dominant-negative form of TSC-22 accelerated the growth of Flt3-TKD-transduced 32Dcl.3 cells. Collectively, these results suggest that TSC-22 is a possible target of leukemia therapy.
Leukemia 12/2007; 21(11):2246-57. · 9.56 Impact Factor
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T Kawashima,
K Murata,
S Akira,
Y Tonozuka,
Y Minoshima,
S Feng, H Kumagai,
H Tsuruga,
Y Ikeda,
S Asano,
T Nosaka,
T Kitamura
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ABSTRACT: We recently demonstrated that STAT5 can induce a variety of biological functions in mouse IL-3-dependent Ba/F3 cells; STAT5-induced expression of pim-1, p21(WAF/Cip1), and suppressor of cytokine signaling-1/STAT-induced STAT inhibitor-1/Janus kinase binding protein is responsible for induction of proliferation, differentiation, and apoptosis, respectively. In the present study, using a constitutively active STAT5A (STAT5A1*6), we show that STAT5 induces macrophage differentiation of mouse leukemic M1 cells through a distinct mechanism, autocrine production of IL-6. The supernatant of STAT5A1*6-transduced cells contained sufficient concentrations of IL-6 to induce macrophage differentiation of parental M1 cells, and STAT3 was phosphorylated on their tyrosine residues in these cells. Treatment of the cells with anti-IL-6 blocking Abs profoundly inhibited the differentiation. We also found that the STAT5A1*6 transactivated the IL-6 promoter, which was mediated by the enhanced binding of NF-kappaB p65 (RelA) to the promoter region of IL-6. These findings indicate that STAT5A cooperates with Rel/NF-kappaB to induce production of IL-6, thereby inducing macrophage differentiation of M1 cells in an autocrine manner. In summary, we have shown a novel mechanism by which STAT5 induces its pleiotropic functions. Cytokines
The Journal of Immunology 11/2001; 167(7):3652-60. · 5.79 Impact Factor
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ABSTRACT: A member of sterol regulatory element-binding protein (SREBP) family, SREBP-1, is a key regulator of adipocyte differentiation. Expression of the SREBP-1 gene is induced during adipocyte differentiation, but proteolytic activation of the synthesized precursor form of SREBP-1 has not been well analyzed. The proteolytic processing of SREBPs is severely suppressed in sterol loaded culture cells. Here we report that a splicing isoform, SREBP-1a, is predominantly expressed in 3T3-L1 preadipocytes and adipocytes, and that the nuclear active form of SREBP-1 protein increases in adipocyte differentiation. We further show that the amount of nuclear SREBP-2 protein also increases despite no increase in SREBP-2 mRNA, suggesting that proteolytic cleavage of SREBPs is induced in lipid loaded adipocytes. Northern blot analyses reveal that mRNA levels for SREBP cleavage-activating protein (SCAP), Site-1 protease (S1P), and Site-2 protease (S2P), which participate in the proteolytic processing of SREBPs, are relatively unaffected in adipogenesis. These results demonstrate that SREBP-2 appears to promote adipocyte differentiation as well as SREBP-1 and that the proteolytic activation of SREBPs may be induced by an as-yet unidentified mechanism in lipid loaded adipocytes.
Biochemical and Biophysical Research Communications 06/2001; 283(5):1157-61. · 2.48 Impact Factor
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T Sugiyama, H Kumagai,
Y Morikawa,
Y Wada,
A Sugiyama,
K Yasuda,
N Yokoi,
S Tamura,
T Kojima,
T Nosaka,
E Senba,
S Kimura,
T Kadowaki,
T Kodama,
T Kitamura
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ABSTRACT: We report here the identification of a novel member of the low-density lipoprotein receptor (the LDL receptor) family through signal sequence trap screening of a mouse lymphocyte cDNA library. The protein was termed LDL receptor-related protein 9 (LRP9). LRP9 is a type I membrane protein predicted to contain 696 amino acids with a calculated molecular mass of 74 764 Da. The NH(2)-terminal half of LRP9 contains two CUB domains separated by a single ligand-binding repeat. The second CUB domain is followed by a cluster of three additional ligand-binding repeats and a transmembrane domain. The COOH-terminal intracellular region contains a proline-rich region. LRP9 mRNA was expressed in the liver, kidney, lung, and heart at high levels, and in the spleen and brain at low levels. In situ hybridization analysis of mouse liver, kidney, and brain detected LRP9 transcripts in hepatocytes, sinusoidal lining cells, peritubular capillaries, choroid plexus, ependyma of the third ventricle, pia matter, and hippocampus. In particular, high levels of expression were observed in the vascular walls. Apolipoprotein E (apoE)-enriched beta-VLDL stimulated cellular cholesteryl ester formation in ldl-A7/LRP9. These results raise the possibility that this newly identified receptor, which is expressed in the liver, may play a physiological role in the uptake of apoE-containing lipoproteins.
Biochemistry 01/2001; 39(51):15817-25. · 3.42 Impact Factor
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ABSTRACT: Adipose tissue is the largest organ in the body that secretes soluble proteins such as cytokines. A preadipocyte cell line 3T3-L1 has been widely used for investigations of mechanisms of adipocyte differentiation. 3T3-L1 cells convert to adipocytes in the presence of 1-methyl-3-isobutylxanthine, dexamethasone, and insulin. We screened a cDNA library derived from differentiated 3T3-L1 cells, using the SST-REX method (signal sequence trap by retrovirus-mediated expression screening method). Screening of 4 x 10(5) clones gave rise to 63 known and 8 novel clones. The known clones represented 28 independent proteins, 21 of which were secreted proteins and 7 were membrane proteins. The novel clones represented 7 independent proteins, 5 of which had no similarity to known proteins. Interestingly, most of these novel genes showed differentiation- and tissue-specific expression. The present results indicate that adipocytes specific genes or adipocyte differentiation-related genes encoding membrane and secreted proteins can be readily identified if signal sequence trap screening of differentiated adipocyte-derived cDNAs is done.
Biochemical and Biophysical Research Communications 06/2000; 272(1):293-7. · 2.48 Impact Factor
