Assignment of the human homologue of the Drosophila Cut homeobox gene (CUTL1) to band 7q22 by fluorescence in situ hybridization

-7/7q- syndrome in myeloid-lineage hematopoietic malignancies: attempts to understand this complex disease entity

The recurrence of chromosomal abnormalities in a specific subtype of cancer strongly suggests that dysregulated gene expression in the corresponding region has a critical role in disease pathogenesis. -7/7q-, defined as the entire loss of chromosome 7 and partial deletion of its long arm, is among the most frequently observed chromosomal aberrations in myeloid-lineage hematopoietic malignancies such as myelodysplastic syndrome and acute myeloid leukemia, particularly in patients treated with cytotoxic agents and/or irradiation. Tremendous efforts have been made to clarify the molecular mechanisms underlying the disease development, and several possible candidate genes have been cloned. However, the study is still underway, and the entire nature of this syndrome is not completely understood. In this review, we focus on the attempts to identify commonly deleted regions in patients with -7/7q-; isolate the candidate genes responsible for disease development, cooperative genes and the factors affecting disease prognosis; and determine effective and potent therapeutic approaches. We also refer to the possibility that the accumulation of multiple gene haploinsufficiency, rather than the loss of a single tumor suppressor gene, may contribute to the development of diseases with large chromosomal deletions such as -7/7q-.

Cutl1: a potential target for cancer therapy

CDP, a key transcription regulator encoded by Cutl1 gene, has been demonstrated to be involved in repressing or promoting expression of target genes through its specific DNA-binding, meanwhile, the activity of CDP was influenced by some types of modifications including transcriptional, posttranscriptional, translational and posttranslational modifications. In this review, we systematically analyzed the role of CDP in normal development and tumor progression, and then emphasized its interactors and downstream molecules. Eventually, we concluded that Cut1 could promote cancer progression and its down-regulating expression will be a promising strategy for cancer therapy.

The multiple roles of CUX1: insights from mouse models and cell-based assays

Cux (Cut homeobox) genes are present in all metazoans. Early reports described many phenotypes caused by cut mutations in Drosophila melanogaster. In vertebrates, CUX1 was originally characterized as the CCAAT-displacement protein (CDP). Another line of investigation revealed the presence of CUX1 within a multi-protein complex called the histone nuclear factor D (HiNF-D). Recent studies led to the identification of several CUX1 isoforms with distinct DNA binding and transcriptional properties. While the CCAAT-displacement activity was implicated in the transcriptional repression of several genes, some CUX1 isoforms were found to participate in the transcriptional activation of some genes. The expression and activity of CUX1 was shown to be regulated through the cell cycle and to be a target of TGF-beta signaling. Mechanisms of regulation include alternative transcription initiation, proteolytic processing, phosphorylation and acetylation. Cell-based assays have established a role for CUX1 in the control of cell cycle progression, cell motility and invasion. In the mouse, gene inactivation as well as over-expression in transgenic mice has revealed phenotypes in multiple organs and cell types. While some phenotypes could be explained by the presumed functions of CUX1 in the affected cells, other phenotypes invoked non-cell-autonomous effects that suggest regulatory functions with an impact on cell-cell interactions. The implication of CUX1 in cancer was suggested first from its over-expression in primary tumors and cancer cell lines and was later confirmed in mouse models.

Addressing nonlinearity in the exposure-response relationship for a genotoxic carcinogen: cancer potency estimates for ethylene oxide

Ethylene oxide (EO) has been identified as a carcinogen in laboratory animals. Although the precise mechanism of action is not known, tumors in animals exposed to EO are presumed to result from its genotoxicity. The overall weight of evidence for carcinogenicity from a large body of epidemiological data in the published literature remains limited. There is some evidence for an association between EO exposure and lympho/hematopoietic cancer mortality. Of these cancers, the evidence provided by two large cohorts with the longest follow-up is most consistent for leukemia. Together with what is known about human leukemia and EO at the molecular level, there is a body of evidence that supports a plausible mode of action for EO as a potential leukemogen. Based on a consideration of the mode of action, the events leading from EO exposure to the development of leukemia (and therefore risk) are expected to be proportional to the square of the dose. In support of this hypothesis, a quadratic dose-response model provided the best overall fit to the epidemiology data in the range of observation. Cancer dose-response assessments based on human and animal data are presented using three different assumptions for extrapolating to low doses: (1) risk is linearly proportionate to dose; (2) there is no appreciable risk at low doses (margin-of-exposure or reference dose approach); and (3) risk below the point of departure continues to be proportionate to the square of the dose. The weight of evidence for EO supports the use of a nonlinear assessment. Therefore, exposures to concentrations below 37 microg/m3 are not likely to pose an appreciable risk of leukemia in human populations. However, if quantitative estimates of risk at low doses are desired and the mode of action for EO is considered, these risks are best quantified using the quadratic estimates of cancer potency, which are approximately 3.2- to 32-fold lower, using alternative points of departure, than the linear estimates of cancer potency for EO. An approach is described for linking the selection of an appropriate point of departure to the confidence in the proposed mode of action. Despite high confidence in the proposed mode of action, a small linear component for the dose-response relationship at low concentrations cannot be ruled out conclusively. Accordingly, a unit risk value of 4.5 x 10(-8) (microg/m3)(-1) was derived for EO, with a range of unit risk values of 1.4 x 10(-8) to 1.4 x 10(-7) (microg/m3)(-1) reflecting the uncertainty associated with a theoretical linear term at low concentrations.

Role of the multifunctional CDP/Cut/Cux homeodomain transcription factor in regulating differentiation, cell growth and development

CDP/Cux/Cut proteins are an evolutionarily conserved family of proteins containing several DNA binding domains: one Cut homeodomain and one, two or three Cut repeats. In Drosophila melanogaster, genetic studies indicated that Cut functions as a determinant of cell-type specification in several tissues, notably in the peripheral nervous system, the wing margin and the Malpighian tubule. Moreover, Cut was found to be a target and an effector of the Notch signaling pathway. In vertebrates, the same functions appear to be fulfilled by two cut-related genes with distinct patterns of expression. Cloning of the cDNA for the CCAAT-displacement protein (CDP) revealed that it was the human homologue of Drosophila Cut. CDP was later found be the DNA binding protein of the previously characterized histone nuclear factor D (HiNF-D). CDP and its mouse counterpart, Cux, were also reported to interact with regulatory elements from a large number of genes, including matrix attachment regions (MARs). CDP/Cut proteins were found generally to function as transcriptional repressors, although a participation in transcriptional activation is suggested by some data. Repression by CDP/Cut involves competition for binding site occupancy and active repression via the recruitment of a histone deacetylase activity. Various combinations of Cut repeats and the Cut homeodomains can generate distinct DNA binding activities. These activities are elevated in proliferating cells and decrease during terminal differentiation. One activity, involving the Cut homeodomain, is upregulated in S phase. CDP/Cut function is regulated by several post-translational modification events including phosphorylation, dephosphorylation, and acetylation. The CUTL1 gene in human was mapped to 7q22, a chromosomal region that is frequently rearranged in various cancers.

The del(7q) subgroup in uterine leiomyomata: genetic and biologic characteristics. Further evidence for the secondary nature of cytogenetic abnormalities in the pathobiology of uterine leiomyomata

Rearrangement of 7q represents one of the major cytogenetic subgroups in uterine leiomyomata, the most common tumors arising in females. Herein we report cytogenetic analysis on a series of 22 cases of uterine leiomyomata with 7q abnormalities, and describe observations regarding tumor size and maintenance of the tumor cells in culture. We discuss the frequent finding of mosaic tumors containing both cells with the 7q rearrangement and karyotypically normal cells. Clonality studies of three mosaic cases reveal nonrandom X chromosome inactivation substantiating prior findings suggesting the secondary nature of chromosome aberrations in these tumors. Genes mapped in 7q22 and those identified in the pathobiology of other uterine leiomyomata subgroups are discussed in addition to a perspective on the role of the 7q22 leiomyomata gene.

Cux/CDP homeodomain protein binds to an enhancer in the rat c-mos locus and represses its activity

The c-mos gene is transcribed in male and female germ cells, in differentiating myoblasts and in 3T3 cells from cell-specific promoters. We characterized the rat testis promoter, which contains a TATA-box and one binding site for a testis-specific transcription factor TTF-D, as well as a region which can act as enhancer, which is located approx. 2 kb upstream of the c-mos AUG start codon. It binds three factors at sites I, II and III as determined in DNAse I footprint assays. We demonstrated that a member of the NF-1/CTF family of transcription factors binds site II. Here we report the cloning of the protein that binds to enhancer site III. This protein is the rat homolog of human hCut/CDP, mouse Cux/CDP and canine Clox. hCut/Cux/CDP/Clox (hereafter called Cux/CDP), a 160 kDa protein containing multiple repeats and a homeodomain, negatively regulates the mammalian c-myc, gp91-phox and N-Cam genes. Using bacterially produced murine GST-Cux fusion proteins and GST-Cux deletion mutants, we find that Cux repeat CR3 and the homeodomain are both required for efficient binding to enhancer site III. Mouse lung and testis nuclear Cux/CDP bind to site III as determined in electrophoretic gel mobility supershift assays using two different anti-hCut specific monoclonal antibodies. Transfections of CAT constructs containing the enhancer fragment linked to a minimal promoter demonstrated that Cux/CDP represses c-mos enhancer activity.

Checklist: vertebrate homeobox genes

Up to now around 170 different homeobox genes have been cloned from vertebrate genomes. A compilation of the various isolates from mouse, chick, frog, fish and man is presented in the form of a concise checklist, including the designations from the original publications. Putative homologs from different species are aligned, and key characteristics of embryonic or adult expression domains, as well as mutant phenotypes are briefly indicated.