The understanding of complex human disease and the development of therapeutic approaches are some of the great challenges of molecular medicine. The transport of molecules into and out of the cell is one of the most critical functions of living organisms. A large reason for the failure of chemotherapy in many cases is drug resistance. Pumps that remove toxins from cells are critically important in the resistance of tumors. In addition a number of genetic diseases are caused by defects in transport proteins. The ATP-binding cassette (ABC) gene family codes for transporter proteins pumping a variety of compounds across the membranes of cells and tissues. Overexpression of ABC transporters is an important cause of multidrug resistance to chemotherapy agents and these genes are mutated in diverse human diseases. Complement genes and Age-Related Macular Degeneration By studying variants in the complement B and C2 (<I>CFH</I>, <I>C2</I>) genes we have identified predisposing and protective variants in patients with age-related macular degeneration (AMD). AMD is the leading cause of blindness in the elderly and is estimated to effect as many as of 10 million Americans. By examining the genetic variants in the <I>BF</I>and <I>C2</I>genes significantly protective haplotypes were identified. The alternative complement pathway is important in the response to pathogens causative for cancer and inflammation. Further study of this arm of the innate immune response will lead to insights into human disease. we identified a deletion that removes the <I>CFHR1</I>gene adjacent to <I>CFH</I>is highly protective for AMD. We obtained over 3000 DNAs from subjects in the Age-Related Eye Disease Study, and typed them for the associated markers, confirming the associations of the major alleles and demonstrating that the CFH and CFB alleles mainly affect progression to early stages of disease (large drusen) and that the HTRA1 and CFHR1/3 deletion affect progression to late stage outcomes (neovascularization, geographic atrophy). Through the analysis of Affymetrix 6.0 chip data we have been able to genotype heterozygous deletion patients and identify an additional deletion that disrupts or deletes the CFHR4 gene. Further characterization of these deletions are likely to reveal more about the function of this immunoregulatory gene cluster. Recently published data implicated the Toll-like receptor 3 (TLR3) gene in AMD. However we have typed this variant in the AREDS cohort, and along with data from 7 other centers failed to replicate this association. ABC genes in Cancer Stem Cells Several ABC genes are expressed in cancer stem cells allowing for an innate resistance to cancer therapy. <I>ABCG2</I>is an important drug resistance gene and we have screened for and identified new inhibitors to the protein encoded by this gene. One of these is a new class of compounds known as botrylamides. The botrylamides are found in marine sponges and are simple enough chemically that derivatives can be synthesized and a structure/function relationship determined. <I>ABCG2</I>is an important marker and resistance factor in cancer stem cells. Several of these compounds can be shown to inhibit substrate binding and/or ATPase activity of the protein. The ABCB5 gene has been shown to be a marker for melanoma stem cells. We have performed evolutionary analysis of this gene and demonstrated that it evolved as a full-transporter. In addition we have validated and applied genotyping assays for several variants in the gene to demonstrate that variation in this gene is widely distributed and significantly different in distinct human populations. Metabolomics to study ABC gene Function To understand the function of the <I>ABCC6</I>gene causing pseudoxanthoma elasticum we have initiated a metabolomics study. Urine from male patients has been used to generate metabolite profiles. We have also performed studies of serum and urine from <I>Abcc6</I>-/- mice and from yeast cell deficient in an ABCC subfamily gene. These studies reveal a number of small molecules differentially present in these samples and provide important candidate substrates for further testing. In addition we have characterized the complement of ABC genes in the planktic crustacean Daphnia a globally distributed organism of central importance for the ecology of lakes and ponds. Daphnia is not only the first crustacean, but also the first non-insect arthropod to have its genome sequence determined. TRIM5 and HIV Infection A regulatory protein, TRIM5-alpha, has been implicated in the transmission of HIV-1 and other retroviruses. We identified that approximately four percent of Baka pygmies in Cameroon have a mutation in the gene, R332X that is a null allele, with partial dominant negative activity. Genetic factors such as this, along with the high frequency of exposure to chimpanzee body fluids, may have predisposed population in this region to the initial cross-species transmission of HIV. Discovery of a new variant of ERBB4 gene, a candidate gene for schizophrenia. In collaboration with Dr. Amanda Law and Dr. Daniel Weinberger at the National Institute of Mental Health, NIH, we searched for splice variants of the human ERBB4 gene, which encodes a receptor for neuregulin 1 gene. We found that a novel ERBB4 exon 3-skipping transcript variant was expressed in the human fetal brain, and that this splice variant was present preferentially in the ERBB4 JM-b/CYT-2 isoform. In addition, a 45-nt sequence encoding 14 amino acids, characteristic of the JM-b isoform, is located in the intron 15 of the ERBB4 gene. We have for the first time shown that the ERBB4 exon 3 is an alternative exon. In contrast, both exon E15a and exon 16 are mutually exclusive. Therefore, we have clarified that there are currently four alternative exons (exons 3, 15a, 16 and 26) in human ERBB4 gene, which should consist of 29 exons instead of 28 exons. Detection of an Infectious Retrovirus, XMRV, in Patients with Chronic Fatigue Syndrome Chronic fatigue syndrome (CFS) is a debilitating disease of unknown etiology that is estimated to affect 17 million people worldwide. Studying peripheral blood mononuclear cells (PBMC) from CFS patients, our colleagues identified DNA from a human gammaretrovirus, xenotropic murine leukemia virus-related virus (XMRV), in 68 of 101 patients (67%) compared to 8 of 218 (3.7%) healthy controls. We genotyped the RNASEL gene in these samples, a gene previously implicated in XMRV infection of prostate cancer patients. There was no association with RNASEL genotype and either CFS or XMRV positivity. These findings raise the possibility that XMRV may be a contributing factor in the pathogenesis of CFS. Genetics and function of Schnyder Corneal Dystrophy Schnyder Corneal Dystrophy (SCD) is an inherited disease affecting vision due to abnormal deposition of cholesterol and lipid in the cornea. In addition, many SCD patients exhibit systemic hypercholesterolemia and apparent disregulation of an unknown aspect of cholesterol and/or HDL metabolism. Mutations in a novel gene (UBIAD1) were identified cause this disorder. Continued genetic analysis of SCD may allow a greater understanding of the role of the UBIAD1 protein in maintaining cholesterol and HDL homeostasis and may clarify the effect of mutations causing SCD on protein function. Sequencing of the gene in addition [summary truncated at 7800 characters]
| Allikmets, Rando; Bergen, Arthur A; Dean, Michael et al. (2009) Geographic atrophy in age-related macular degeneration and TLR3. N Engl J Med 360:2252-4; author reply 2255-6 |
| Polgar, Orsolya; Ediriwickrema, Lilangi S; Robey, Robert W et al. (2009) Arginine 383 is a crucial residue in ABCG2 biogenesis. Biochim Biophys Acta 1788:1434-43 |
| Dean, Michael (2009) ABC transporters, drug resistance, and cancer stem cells. J Mammary Gland Biol Neoplasia 14:3-9 |
| Torimiro, Judith N; Javanbakht, Hassan; Diaz-Griffero, Felipe et al. (2009) A rare null allele potentially encoding a dominant-negative TRIM5alpha protein in Baka pygmies. Virology 391:140-7 |
| Sturm, Armin; Cunningham, Phil; Dean, Michael (2009) The ABC transporter gene family of Daphnia pulex. BMC Genomics 10:170 |
| Bergeron-Sawitzke, Julie; Gold, Bert; Olsh, Adam et al. (2009) Multilocus analysis of age-related macular degeneration. Eur J Hum Genet 17:1190-9 |
| Robey, Robert W; To, Kenneth K K; Polgar, Orsolya et al. (2009) ABCG2: a perspective. Adv Drug Deliv Rev 61:3-13 |
| Meyer-Lindenberg, A; Kolachana, B; Gold, B et al. (2009) Genetic variants in AVPR1A linked to autism predict amygdala activation and personality traits in healthy humans. Mol Psychiatry 14:968-75 |
| Allikmets, Rando; Dean, Michael (2008) Bringing age-related macular degeneration into focus. Nat Genet 40:820-1 |
| Potocnik, Uros; Glavac, Damjan; Dean, Michael (2008) Common germline MDR1/ABCB1 functional polymorphisms and haplotypes modify susceptibility to colorectal cancers with high microsatellite instability. Cancer Genet Cytogenet 183:28-34 |
