Dr. Staudt's laboratory is currently focused on understanding the molecular pathogenesis of human leukemias and lymphomas. A major area of interest is in diffuse large cell lymphoma caused by the BCL-6 oncogene. Diffuse large cell lymphoma is a malignancy of mature B lymphocytes that accounts for roughly 40% of cases of non-Hodgkin's lymphoma. The BCL-6 gene is translocated in approximately 32% of diffuse large cell lymphomas and 70-80% have mutations in a presumptive 5' regulatory region of the gene. BCL-6 is also frequently rearranged in other non-Hodgkin's lymphoma sub-types and in AIDS-associated diffuse lymphomas. The coding region of BCL-6 remains unmutated in the lymphomas suggesting that dysregulation of gene expression underlies the lymphomagenesis. The laboratory has previously shown that the BCL-6 protein is a zinc finger transcriptional repressor protein which is expressed at highest levels in germinal center B cells and a subset of T cells. """"""""To gain insight into the normal biological function of BCL-6, the gene was mutated in the mouse germ line using homologous recombination in embryonic stem cells. Mice homozygous for the mutant BCL-6 allele are born normally but display growth retardation shortly after birth and frequently die within 1 to 4 weeks. Upon immunization with a T cell-dependent antigen, the BCL-6 mutant mice fail to generate germinal centers and do not mount an IgG immune response. The second characteristic phenotype of BCL-6 mutant mice is a severe inflammatory disease consisting of myocarditis and pulmonary vasculitis. These data show that BCL-6 is required to initiate a germinal center immune response and further is required to prevent undesired inflammatory responses, thus demonstrating that BCL-6 governs the outcome of the immune response."""""""" """"""""The inflammatory disease in BCL-6 mutant mice involves helper T cells that produce a Th2 pattern of cytokines (IL-4, IL-5, IL-13). Consistent with this pattern of lymphokine production, the inflammatory lesions display marked eosinophilia and the BCL-6 mutant mice produce elevated titers of IgE following immunization. Differentiation of naive T cells to Th2 cells in vitro requires IL-4 signaling through the Stat6 transcription factor. In this regard, it is intriguing that the consensus BCL-6 DNA binding site is homologous to the binding motifs of the Stat transcription factors. In fact, BCL-6 could block IL-4 induced, Stat6-dependent transcriptional activation, thus demonstrating the ability of BCL-6 to modulate the outcome of cytokine signaling. Thus, BCL-6 may normally repress transcription of critical cytokine-responsive genes, some of which may regulate Th2 differentiation and, consequently, inflammatory responses. To understand the role of BCL-6 in regulating Th2 differentiation in vivo, the BCL-6 mutant mice were bred with animals deficient in IL-4 or Stat6. Surprisingly, neither IL-4 nor Stat6 were required for BCL-6 mutant mice to manifest the Th2 inflammatory phenotype. These data demonstrate that BCL-6 regulates a previously unsuspected, mechanistically distinct pathway to Th2 differentiation. A further understanding of the contribution of BCL-6 translocations to the pathogenesis of diffuse large cell lymphomas should come from detailed knowledge of the role of BCL-6 in cytokine signaling and in the germinal center reaction."""""""" """"""""A major new initiative of the laboratory uses functional genomics to characterize gene expression patterns in normal and malignant lymphocytes. Recently, a new technology utilizing cDNA microarrays has emerged that permits the simultaneous quantitation of the expression of thousands of genes. In brief, this technique relies on robotic spotting of cDNAs for defined genes in an ordered microscopic array on a glass slide. Fluorescently labeled cDNA probes are then prepared from total cellular mRNA derived from the cell of interest and hybridized at high concentration to this microarray. The extent of hybridization of the probes to each cDNA on the microarray is then quantitated using a modified confocal microscope. Two different cell types can be directly compared with each other on the same microarray by labeling the cDNA from each cell with a different fluorochrome. Genomic-scale knowledge of gene expression in a malignant lymphoid cell should allow us to determine which normal lymphocyte subset gives rise to a particular subtype of lymphoid malignancy, which signaling pathways are altered in the malignant cells, and the molecular basis for responsiveness or resistance of lymphomas and leukemias to therapy."""""""" """"""""Dr. Staudt's laboratory has designed a specialized cDNA microarray, termed the """"""""""""""""Lymphochip"""""""""""""""", that is enriched in genes which are selectively expressed in lymphocytes and genes which regulate lymphocyte function. Since the majority of human lymphomas appear to represent malignant transformation of the germinal center B lymphocyte, a cDNA library was created from germinal center B lymphocytes that were purified by flow sorting from human tonsils. 50,000 sequences were obtained from this library, over 10% of which had not been observed previously in other libraries. This rich source of novel genes formed the basis of the Lymphochip microarray that currently contains over 15,000 clones.""""""""
Showing the most recent 10 out of 25 publications
