Induction of differentiation and apoptosis in cancer cells through ligands of nuclear hormone receptors (NHRs) is a novel and promising approach to cancer therapy. All-trans-retinoic acid (ATRA), an RA receptor-specific NHR ligand, is now used for selective cancers.

The CCAAT/enhancer binding protein ␣ (C/EBP␣) protein is essential for proper lung and liver function and granulocytic and adipose tissue differentation. It was hypothesized that abnormalties in C/EBP␣ function contribute to the development of malignancies in a variety of tissues. To test this, genomic DNA from 408 patient samples and 5 cell lines representing 11 different cancers was screened for mutations in the C/EBP␣ gene. Two silent polymorphisms termed P1 and P2 were present at frequencies of 13.5% and 2.2%, respectively. Of the12 mutations detected in 10 patients, silent changes were identified in one nonsmall cell lung cancer, one prostate cancer, and one acute myelog- IntroductionThe CCAAT/enhancer binding protein ␣ (C/EBP␣) belongs to a family of proteins that possess a bipartite DNA-binding domain composed of a positively charged basic (b) region that contacts the DNA and a leucine zipper (ZIP) in the C terminus that mediates dimerization. 1 The less-conserved N terminus contains regulatory and transactivation domains. 2-5 C/EBP␣ is expressed in a number of tissues, most prominently in the highly differentiated cells of the liver, white and brown adipose, lung, and myeloid-lineage cells. [6][7][8][9] It has also been detected in the adrenal gland, skin, pancreas, prostate, differentiated enterocytes in the intestine, and, during follicular development, the ovary. [9][10][11][12] C/EBP␣ is proposed to be a regulator of energy metabolism and transcriptionally activates the promoters of energy-related genes such as GLUT4 and PEPCK in hepatocytes and adipocytes. [13][14][15] In myeloid cells, C/EBP␣ transcriptionally activates the promoters of the myeloid-specific receptors for the growth factors macrophage colony-stimulating factor, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor. [16][17][18] Studies demonstrate that C/EBP␣ is critical for the process of terminal differentiation of adipocytes. C/EBP␣ is upregulated in adipocyte differentiation, and blocking its expression halts differentiation of preadipocytes into adipocytes, while overexpression induces differentiation and inhibits proliferation. [19][20][21][22][23] Also, overexpression of C/EBP␣ induces differentiation of myeloid leukemia cell lines and inhibits the proliferation of a number of cell lines and tumor cells. [24][25][26][27] The inhibition of proliferation is partly due to the ability of C/EBP␣ to activate transcription and induce posttranscriptional stabilization of the cyclin-dependent kinase inhibitor p21 (WAF-1). 28,29 These studies suggest a central role for C/EBP␣ in the regulation of cell proliferation and differentiation.Targeted inactivation of C/EBP␣ in mice demonstrates its importance in the proper development and function of liver, adipose, lung, and hematopoietic tissues. 8,30,31 Within 8 hours after birth, the mice die of impaired glucose metabolism, and adipose metabolism is altered with a failure of adipocytes to accumulate lipids. 30,31 The lung shows hyperproliferati...

Monosomy 7 and interstitial deletion of 7q (-7/7q-) are well-recognized nonrandom chromosomal abnormalities frequently found among patients with myelodysplastic syndromes (MDSs) and myeloid leukemias. We previously identified candidate myeloid tumor suppressor genes (SAMD9, SAMD9-like = SAMD9L, and Miki) in the 7q21.3 subband. We established SAMD9L-deficient mice and found that SAMD9L(+/-) mice as well as SAMD9L(-/-) mice develop myeloid diseases resembling human diseases associated with -7/7q-. SAMD9L-deficient hematopoietic stem cells showed enhanced colony formation potential and in vivo reconstitution ability. SAMD9L localizes in early endosomes. SAMD9L-deficient cells showed delays in homotypic endosome fusion, resulting in persistence of ligand-bound cytokine receptors. These findings suggest that haploinsufficiency of SAMD9L and/or SAMD9 gene(s) contributes to myeloid transformation.

Previous gene-targeting studies indicated that Bim, a BH3-only death activator, regulates total blood cell number. Cytokines contribute to this process by negatively regulating steady-state levels of Bim mRNA. Here we present a molecular mechanism for cytokine-mediated posttranscriptional regulation of Bim mRNA by heat-shock cognate protein 70 (Hsc70), which binds to AU-rich elements (AREs) in the 3'-untranslated region of specific mRNAs and enhances their stability. The RNA binding potential of Hsc70 is regulated by cochaperones including Bag-4 (also SODD), CHIP, Hip, and Hsp40. Cytokines regulate the expression or function of these cochaperones by activating Ras pathways. Thus, exposure of cells to cytokines ultimately leads to destabilization of Bim mRNA and promotion of cell survival. This unanticipated role of a chaperone/cochaperone complex in mRNA stability appears to be critical for hematopoiesis and leukemogenesis.

A novel leukemic cell line with an 8;21 chromosome translocation, designated as Kasumi-1, was established from the peripheral blood of a 7-year-old boy suffering from acute myeloid leukemia (AML). The Kasumi- 1 cells were positive for myeloperoxidase showing a morphology of myeloid maturation. The response in proliferation assay was observed in the culture with interleukin-3 (IL-3), IL-6, granulocyte colony- stimulating factor (G-CSF), and granulocytemacrophage CSF (GM-CSF), but not with IL-1 or IL-5. Neither granulocytic nor eosinophilic maturation was observed in the liquid culture by the addition of dimethyl sulfoxide, G-CSF, or IL-5, respectively. In contrast, induction of macrophagelike cells was seen by the addition of phorbol ester. This is the first report of a human AML cell line with t(8;21) that has characteristics of myeloid and macrophage lineages. The cell line could be a useful tool for elucidating the pathophysiology of AML with t(8;21).

Monosomy 7 and interstitial deletions in the long arm of chromosome 7 (-7/7q-) is a common nonrandom chromosomal abnormality found frequently in myeloid disorders including acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and juvenile myelomonocytic leukemia (JMML). Using a short probe-based microarray comparative genomic hybridization (mCGH) technology, we identified a common microdeletion cluster in 7q21.3 subband, which is adjacent to 'hot deletion region' thus far identified by conventional methods. This common microdeletion cluster contains three poorly characterized genes; Samd9, Samd9L, and a putative gene LOC253012, which we named Miki. Gene copy number assessment of three genes by real-time PCR revealed heterozygous deletion of these three genes in adult patients with AML and MDS at high frequency, in addition to JMML patients. Miki locates to mitotic spindles and centrosomes and downregulation of Miki by RNA interference induced abnormalities in mitosis and nuclear morphology, similar to myelodysplasia. In addition, a recent report indicated Samd9 as a tumor suppressor. These findings indicate the usefulness of the short probe-based CGH to detect microdeletions. The three genes located to 7q21.3 would be candidates for myeloid tumor-suppressor genes on 7q.

During prometaphase, dense microtubule nucleation sites at centrosomes form robust spindles that align chromosomes promptly. Failure of centrosome maturation leaves chromosomes scattered, as seen routinely in cancer cells, including myelodysplastic syndrome (MDS). We previously reported that the Miki (LOC253012) gene is frequently deleted in MDS patients, and that low levels of Miki are associated with abnormal mitosis. Here we demonstrate that Miki localizes to the Golgi apparatus and is poly(ADP-ribosyl)ated by tankyrase-1 during late G2 and prophase. PARsylated Miki then translocates to mitotic centrosomes and anchors CG-NAP, a large scaffold protein of the γ-tubulin ring complex. Due to impairment of microtubule aster formation, cells in which tankyrase-1, Miki, or CG-NAP expression is downregulated all show prometaphase disturbances, including scattered and lagging chromosomes. Our data suggest that PARsylation of Miki by tankyrase-1 is a key initial event promoting prometaphase.

Structural alterations occur in the long arm of chromosome 3 in approximately 2% of patients with acute myelogenous leukemia (AML) or myelodysplastic syndrome (MDS). The major alterations are inv(3)(q21q26) and t(3:3)(q21;q26) and are often classified as the 3q21q26 syndrome. We previously reported that the EVI1 gene is transcriptionally activated in AMLs with t(3;3)(q21;q26) and inv(3)(q21q26) and that the chromosomal breakpoints at 3q26 in the translocations were 5′ of the EVI1 gene, whereas the breakpoints in the inversion cases were 3′ of the gene. In these studies, four additional cases of AML with inv(3)(q21q26) are shown to express the EVI1 gene and to have breakpoints 3′ of the gene. To characterize the 3q21 breakpoint region, cosmid and phage clones were isolated that cover approximately 100 kb. At 3q21, the breakpoints for both AMLs with t(3;3)(q21;q26) and inv(3)(q21q26) were found to cluster over a region of approximately 50 kb downstream of the Ribophorin I gene. The results indicate a common mechanism for the translocations and inversions and support the hypothesis that the transcriptional activation of the EVI1 gene is mediated by enhancer elements associated with the Ribophorin I gene.