Investigating the role of Batf in the differentiation of murine myeloid cells using in vitro and in vivo model systems
Abstract
Batf is a basic leucine zipper transcription factor belonging to the activator protein-1 superfamily. Batf is expressed in hematopoietic cells and is up-regulated following the stimulation of cells derived from both the lymphoid and myeloid lineages. When treated with leukemia inhibitory factor, mouse M1 myeloid leukemia cells commit to a macrophage differentiation program that is dependent on Stat3 and involves the induction of Batf gene transcription via the binding of Stat3 to the Batf promoter. M1 cells with reduced Batf activity fail to growth arrest or terminally differentiate. Using retrovirus-mediated gene transfer to restore Batf expression, the differentiation-defective phenotype of the cells is reversed, but the cells also display signs of spontaneous differentiation in the absence of stimulation. A comparative analysis of gene expression in M1 cells expressing a control small interfering RNA and a small interfering RNA specific for Batf was performed to define genetic targets of the Batf transcription factor. This study resulted in the identification of c-myb as a potential Batf target. c-Myb is encoded by a proto-oncogene and is known to promote blood cell proliferation and to inhibit the differentiation of M1 cells. An examination of the interaction of Batf with the c-myb promoter revealed the direct binding of Batf to an AP-1 motif within the c-myb promoter. These results suggest that suppression of c-myb transcription by Batf might account for the spontaneous differentiation observed when exogenous Batf is constitutively expressed in M1 cells. They also support a role for Batf as an AP-1 component functioning to restrict M1 cell growth and negatively regulate genes like c-myb whose repression is required for the differentiation of these cells. To test if Batf functions in a similar manner to regulate the development of myeloid cell lineages in mice, the ability of Batf deficient bone marrow precursor cells to differentiate in vitro was analyzed. Results of this study revealed a compromised development of bone marrow derived macrophages. Although these Batf deficient macrophages displayed a similar responsiveness to interleukin-4 or -10 stimulation, they produced increased levels of pro-inflammatory cytokines in response to lipopolysaccharide stimulation. This suggests a novel role for Batf in macrophage functionality. By combining the results obtained from the studies of M1 cells and macrophages, this work provides strong evidence that Batf functions as a critical regulator in the signal transduction pathways controlling cellular responses important to the differentiation and function of cells of myeloid lineage.
Degree
Ph.D.
Advisors
Taparowsky, Purdue University.
Subject Area
Molecular biology|Cellular biology
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