INITIATION OF THE COAGULATION CASCADE BY VASCULAR CELLS

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A complex pattern of transcriptional control, mRNA stability and post-translational events has been implicated in the control of tissue factor (TF) expression. The goal of this study is to elucidate the multiple molecular mechanisms that bring about the cell-surface expression of this molecule which is responsible for "initiation" of the coagulation protease cascade by vascular cells (i.e., the monocyte and the endothelial cell). Sequence analysis of the newly isolated human TF gene has identified regions postulated to possess promoter and enhancer activity, including a number of predicted transcription factor binding sites. The cis- acting regulatory regions of the TF gene responsible for transcriptional control, including cell-type-specificity and inducibility by specific agonists, will be mapped by transfection and site-directed mutagenesis. Transfection experiments with unmodified DNA may not reflect all levels of TF gene control; a postulated role for DNA methylation (within and flanking the "HTF island" region) in the regulation of TF gene activity will also be investigated. Post-transcriptional control will be investigated at the level of TF mRNA turnover. Involvement of protein processing, transit and degradation is hypothesized in regulating the appearance of active TF molecules on the cell surface; these processes will be explored. Understanding how TF expression is regulated in the vascular compartment will be a crucial contribution to understanding normal physiologic regulation of the coagulation system as well as the pathogenesis of intravascular coagulation, the thrombogenic state, and secondary inflammatory responses.