The ecotropic viral integration site‐1 ( Evi1 ) is an oncogenic transcription factor in murine and human myeloid leukemia. We herein show that Evi1 is predominantly expressed in hematopoietic stem cells (HSCs) in embryos and adult bone marrows, suggesting a physiological role of Evi1 in HSCs. We therefore investigate the role and authentic target genes of Evi1 in hematopoiesis using Evi1 −/− mice, which die at embryonic day 10.5. HSCs in Evi1 −/− embryos are markedly decreased in numbers in vivo with defective self‐renewing proliferation and repopulating capacity. Notably, expression rate of GATA‐2 mRNA, which is essential for proliferation of definitive HSCs, is profoundly reduced in HSCs of Evi1 −/− embryos. Restoration of the Evi1 or GATA‐2 expression in Evi1 −/− HSCs could prevent the failure of in vitro maintenance and proliferation of HSC through upregulation of GATA‐2 expression. An analysis of the GATA‐2 promoter region revealed that Evi1 directly binds to GATA‐2 promoter as an enhancer. Our results reveal that GATA‐2 is presumably one of critical targets for Evi1 and that transcription factors regulate the HSC pool hierarchically.

Constitutive phosphatidylinositol 3-kinase (PI3K)-AKT activation has a causal role in adult T-cell leukaemia-lymphoma (ATLL) and other cancers. ATLL cells do not harbour genetic alterations in PTEN and PI3KCA but express high levels of PTEN that is highly phosphorylated at its C-terminal tail. Here we report a mechanism for the N-myc downstream-regulated gene 2 (NDRG2)-dependent regulation of PTEN phosphatase activity via the dephosphorylation of PTEN at the Ser380, Thr382 and Thr383 cluster within the C-terminal tail. We show that NDRG2 is a PTEN-binding protein that recruits protein phosphatase 2A (PP2A) to PTEN. The expression of NDRG2 is frequently downregulated in ATLL, resulting in enhanced phosphorylation of PTEN at the Ser380/Thr382/Thr383 cluster and enhanced activation of the PI3K-AKT pathway. Given the high incidence of T-cell lymphoma and other cancers in NDRG2-deficient mice, PI3K-AKT activation via enhanced PTEN phosphorylation may be critical for the development of cancer.

Acute myeloid leukemia with high ecotropic viral integration site-1 expression (EVI1^high AML) is classified as a refractory type of leukemia with a poor prognosis. To provide new insights into the prevention and treatment of this disease, we identified the high expression of EVI1-regulated G protein-coupled receptor 56 (GPR56), and the association of high cell adhesion and antiapoptotic activities in EVI1^high AML cells. Knockdown of GPR56 expression decreased the cellular adhesion ability through inactivation of RhoA signaling, resulting in a reduction of cellular growth rates and enhanced apoptosis. Moreover, in Gpr56^−/− mice, the number of hematopoietic stem cells (HSCs) was significantly decreased in the bone marrow (BM) and, conversely, was increased in the spleen, liver and peripheral blood. The number of Gpr56^−/− HSC progenitors in the G0/G1-phase was significantly reduced and was associated with impaired cellular adhesion. Finally, the loss of GPR56 function resulted in a reduction of the in vivo repopulating ability of the HSCs. In conclusion, GPR56 may represent an important GPCR for the maintenance of HSCs by acting as a co-ordinator of interactions with the BM osteosteal niche; furthermore, this receptor has the potential to become a novel molecular target in EVI1^high leukemia.

The development of oral squamous cell carcinoma (OSCC) is a multistep process that requires the accumulation of genetic alterations. To identify genes responsible for OSCC development, we performed high‐density single nucleotide polymorphism array analysis and genome‐wide gene expression profiling on OSCC tumors. These analyses indicated that the absent in melanoma 2 (AIM2) gene and the interferon‐inducible gene 16 (IFI16) mapped to the hematopoietic interferon‐inducible nuclear proteins. The 200‐amino‐acid repeat gene cluster in the amplified region of chromosome 1q23 is overexpressed in OSCC. Both AIM2 and IFI16 are cytoplasmic double‐stranded DNA sensors for innate immunity and act as tumor suppressors in several human cancers. Knockdown of AIM2 or IFI16 in OSCC cells results in the suppression of cell growth and apoptosis, accompanied by the downregulation of nuclear factor kappa‐light‐chain‐enhancer of activated B cells activation. Because all OSCC cell lines have reduced p53 activity, wild‐type p53 was introduced in p53‐deficient OSCC cells. The expression of wild‐type p53 suppressed cell growth and induced apoptosis via suppression of nuclear factor kappa‐light‐chain‐enhancer of activated B cells activity. Finally, the co‐expression of AIM2 and IFI16 significantly enhanced cell growth in p53‐deficient cells; in contrast, the expression of AIM2 and/or IFI16 in cells bearing wild‐type p53 suppressed cell growth. Moreover, AIM2 and IFI16 synergistically enhanced nuclear factor kappa‐light‐chain‐enhancer of activated B cells signaling in p53‐deficient cells. Thus, expression of AIM2 and IFI16 may have oncogenic activities in the OSCC cells that have inactivated the p53 system. (Cancer Sci 2012; 103: 782–790)

Zinc-finger E-box binding homeobox 1 (ZEB1) is a candidate tumor-suppressor gene in adult T-cell leukemia/lymphoma (ATLL). ZEB1 binds phosphorylated Smad2/3 to enhance transforming growth factor-β1 (TGF-β1) signaling. In addition to downregulation of ZEB1 mRNA, we found overexpression of inhibitory Smad, Smad7, in resistance of ATLL cells to growth suppression by TGF-β1. A protein complex of Smad7 and histone deacetylase constantly bound to the promoter region of TGF-β1 responsive genes with the Smad-responsive element (SRE) to inhibit TGF-β1 signaling; however, ectopic expression of ZEB1 reactivated TGF-β1 signaling by binding to Smad7 and recruiting the Smad3/p300 histone acetyltransferase complex to the promoter after TGF-β1 stimulation in ATLL. Conversely, because ZEB1 mRNA was detected in the late stages of T-cell development, we used CTLL2 cells with ZEB1 expression, a murine peripheral T-cell lymphoma, and found that a complex of Smad3, Smad7 and ZEB1 was bound to the SRE of the p21^CDKN1A promoter after the induction of Smad7 by TGF-β1 treatment. Because the duration of TGF-β1-induced transcriptional activation of PAI-1 and p21 was shortened in shZEB1-expressing CTLL2 cells, ZEB1 may have a role in enhancing TGF-β1 signaling by binding not only to Smad3 but also to Smad7 in the nucleus. Altogether, these results suggest that both ZEB1 downregulation and Smad7 overexpression contribute to resistance to TGF-β1-mediated growth suppression in ATLL.

Adult T-cell leukemia (ATL) is associated with human T-cell leukemia virus type 1 infection. The tumor suppressor lung cancer 1 (TSLC1) gene was previously identified as a novel cell surface marker for ATL, and this study demonstrated the involvement of TSLC1 expression in tumor growth and organ infiltration of ATL cells. In experiments using NOD/SCID/gamma c(null) mice, both leukemia cell lines and primary ATL cells with high TSLC1 expression caused more tumor formation and aggressive infiltration of various organs of mice. Our results suggest that TSLC1 expression in ATL cells plays an important role in the growth and organ infiltration of ATL cells.