Fms is a growth factor receptor regulating monocyte/macrophage growth, development, survival, and function. It also plays a not-well-understood role in placenta development through expression in trophoblast cells. Abnormal Fms expression has been detected in both breast and ovarian tumors where it may play some role in tumor progression or metastases. Macrophage-colony stimulating factor (M-CSF) is the ligand for Fms and is produced by a limited number of cell types including the stromal cells of the bone marrow and uterine epithelial cells. The major aim of this proposed project is to further characterize the control of Fms functions through analysis of positive and negative regulatory signals that mediate and modulate Fms activity. This study will focus on the molecular mechanisms of Fms-induced signal transduction within the hematopoietic environment. One project will further characterize the Fms-specific signal transduction mechanism through analysis of a 150 kDa protein that is rapidly phosphorylated on tyrosine after M-CSF stimulation of Fms- expressing myeloid cells, and becomes associated with other signal transduction molecules (Shc and Grb2). The 150 kDa protein appears to be a unique myeloid cell specific protein unrelated to other known signal transduction proteins, and is not detectable in M-CSF stimulated fibroblast cells expressing Fms. A cDNA encoding the 150 kDa protein will be cloned and the role of this protein in growth and differentiation characterized. A second project will characterize an important negative regulatory mechanism for the control of macrophage development. TGF-beta1 inhibits macrophage development and specifically blocks the Fms-induced expression of the c-myc and bcl-2 genes, but does not affect expression of granulocyte macrophage colony stimulating factor (GM-CSF)-induced c-myc or bcl-2 expression in the same cells. This suggests that M-CSF and GM-CSF induced c-myc and bcl-2 by different mechanisms that could account for the selective growth inhibition of TGF-beta1 on M-CSF-stimulated cells. The molecular mechanism of this selective effect of TGF-beta1 on c-myc and bcl-2 expression will be analyzed using the c-myc promoter coupled to a reporter gene, and the signal transduction pathways from Fms, the GM-CSF receptor and TGF-beta1 receptor culminating in c-myc and bcl-2 induction will be analyzed. These results will help to understand normal hematopoiesis and the multiple steps leading to hematopoietic malignancies.
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