Current Genomics - Volume 1, Issue 2, 2000

One of the most recent and exciting approaches in cancer gene therapy is the ability to target the developing blood supply of the tumor. An appealing feature of antiangiogenic gene therapy is that the tumor vasculature is a readily accessible target, particularly when the carrier and its gene are administered systemically. This is in contrast to several other gene therapy approaches in which the tumor vasculature represents a major obstacle to achieving high levels of transfection of the tumor cells. Several gene-based viral or non-viral therapies that target tumor angiogenesis have shown efficacy in pre-clinical models. Genes that encode antiangiogenic polypeptides such as angiostatin and endostatin have significantly inhibited tumor growth, inducing a microscopic dormant state. The products of these genes are thought to act extracellularly to inhibit angiogenesis. An alternative approach that investigators have used successfully in tumor-bearing mice is to target angiogenic growth factors or their receptors that are essential for tumor growth. Levels of angiogenic factors such as vascular endothelial growth factor (VEGF) have been reduced by either antisense methods or the use of genes encoding truncated angiogenic decoy receptors. Despite these promising findings of tumor reduction with antiangiogenic gene therapy, advances in the viral and or non-viral delivery systems are essential for this therapy to have clinical utility. In this review, we will discuss the mechanisms of angiogenesis antiangiogenesis, and the current status and future directions of antiangiogenic gene therapy.

Although structurally related to other steroid thyroid hormone nuclear receptors, Nur77, Nurr1 and NOR-1 represent a distinct subfamily of nuclear receptors, the Nur77 receptor subfamily. In addition to very strong structural homologies among these three nuclear receptors, all can be rapidly induced as immediate early genes. Furthermore, they have similar DNA binding and transactivation properties, and can function in the absence of a not yet known ligand(s). The present review addresses the properties of the Nur77 receptor subfamily, including gene structure, promotor elements, regulation of expression, DNA binding and transactivation properties, and potential physiological and developmental roles. The functions of all three receptors in negative selection of T-cells, the regulation of the hypothalamus-pituitary-adrenal axis and the potential functional redundancy are discussed. Also reviewed is the role of Nurr1 in the differentiation and function of midbrain dopaminergic neurons, as demonstrated by the ablation of Nurr1 function in mice, and the potential implications for Nurr1 in Parkinsons disease and or schizophrenia. Although similar in many structural and functional aspects, subtle differences in certain properties, regulation and expression patterns of the different receptors may result in different physiological roles of these proteins, while similarities may account for a redundancy of function. Much has been described about the regulation of these proteins, however, future research will need to focus on the identification of potential ligands and the target genes that are regulated by this unique class of transcription factors.

Single autosomal trisomy is a common numerical cytogenetic abnormality in hematological malignancies, and shows a predilection for myeloid disorders. While the strong morphologic correlation as for chromosomal translocations is lacking, phenotypic associations are observed for the trisomies. Trisomy 10 is associated with aberrant CD7 expression in acute myeloid leukemia (AML), and trisomy 13 is associated with immature subtypes of AML having hand-mirror blast morphology. Cytogenetic abnormalities have been shown to be the most valuable prognostic determinant in AML and myelodysplastic syndrome (MDS). Trisomy 8, the commonest of the trisomies in myeloid disorders, is associated with an intermediate prognosis, while poor clinical outcome has been described in AML with trisomy 11 and trisomy 13. Additionally, the presence of a trisomy allows the application of fluorescence in situ hybridization (FISH) techniques in monitoring therapy response, detection of minimal residual disease and determination of lineage involvement. The role of trisomy in pathogenesis remains to be defined and a gene dosage effect has been suspected. The recent finding of MLL gene duplication in association with trisomy 11 represents the first documented gene rearrangement in this setting. Finally, whether single autosomal trisomy is a primary or secondary cytogenetic abnormality is presently unclear. Evidence in favor of a secondary change includes frequent association with well-defined structural changes and translocations, and appearance of trisomy with disease evolution. In this respect, it is interesting to note that trisomy may be a cytogenetic marker for an underlying cryptic gene rearrangement, for example trisomy 22 and CBFbeeta MYH11 fusion in AML. This review will summarize the current understanding of single autosomal trisomy in myeloid disorders.

Expression of housekeeping genes is essential and necessary for cell proliferation. The products of housekeeping genes have been strongly conserved during evolution, an indication that they are essential for living organisms. Human MAZ (Myc-associated zinc finger protein) and its mouse homolog, Pur-1 (purine binding factor-1), are transcription factors that bind to the GA box (GGGAGGG). We have characterized the gene structures, patterns of expression, and promoters of both the human gene for MAZ andthe mouse gene for Pur-1. We have also shown that the genes for MAZ and Pur-1 are typical housekeeping genes. One unusual feature of the promoter of the MAZ gene is that it is almost composed of G and C (G+C content, 88.4percent). MAZ and Pur-1 regulate a number of target genes, including the c-myc gene, the gene for complement 2, genes for insulin I and II, the gene for serotonin receptor, the gene for CD4, the gene for nitric-oxide synthase, and the gene for adenovirus major late protein. MAZ and Pur-1 have roles in both the initiation and termination of transcription, and they appear to be involved in the etiology of some diseases, such as insulin-dependent diabetes mellitus and chronic myelogenous leukemia. SAF, the rabbit homolog of MAZ, was isolated recently. It is an activator of the gene for serum amyloid A, which is involved in several chronic inflammatory diseases. The multiple functional roles of MAZ and Pur-1 indicate that their housekeeping functions are concerned mainly with the regulation of gene expression.

The progress in genome-scale approaches to human diseases will soon require to understand the function of a large number of genes as potentially interesting therapeutic targets. The determination of their biological role needs to be accelerated in order to select valid therapeutic targets and streamline the drug discovery process. The sequencing of the human genome, as well as a number of model organisms, provides a strong framework to achieve this goal. Several methods among which gene expression profiling and protein interaction mapping are being used on a large-scale basis and constitute useful entry points to identify pathways involved in disease mechanisms. The resulting information is however limited. Other methods rely on the genetic manipulation of well-characterized and simple model organisms (SMOs) to reconstruct human disease-associated pathways and pinpoint biologically-valid therapeutic targets on the basis of function-based datasets generated in vivo. SMOs are strongly complementary to well-established complex mammalian models, and multiple ways exist to integrate SMOs into the early stage of the drug discovery process. In this review, we attempt to highlight some of the general criteria and essential methodological components associated with the use of SMO technologies for rapid functional genomics. Examples are provided to illustrate the utility of C. elegans and Drososphila for the validation of targets for central nervous system drugs.

Several families of functionally and structurally distinct ion channels have been identified throughout the last decade, resulting in a growing complexity in our understanding of ion transport across biological membranes. Here, we introduce a novel family of putative chloride channel proteins with nine bovine, murine, and human homologs identified to date. The gene family has been termed CLCA family (chloride channels, calcium-activated) based on observations that heterologous expression of several family members is associated with the appearance of a novel anion channel activity that depends on the concentration of intracellular calcium. The family members identified so far are the bovine calcium-activated chloride channel (CaCC or bCLCA1), the bovine lung endothelial cell adhesion molecule-1 (LuECAM-1), the murine calcium-activated chloride channels mCLCA1, mCLCA2, and mCLCA3 (previously termed gob-5), and four human homologs (hCLCA1, hCLCA2, hCLCA3, and hCaCC2). Each of these homologs is characterized by a unique cellular and tissue expression pattern with most consistent expression in secretory epithelia of the digestive, respiratory, and reproductive organs. Of special interest is the observation that several of these molecules seem to combine cell-cell adhesion properties with ion channel function. Structural analyses have revealed that a four- or five-transmembrane topography is conserved throughout the family. Their functional features as well as the cellular coexpression of several CLCA homologs with the cystic fibrosis transmembrane conductance regulator (CFTR) in numerous tissues raises the question whether CLCA family members may participate in the complex ion channel disorder of cystic fibrosis.