REGULATION OF UROKINASE EXPRESSION IN THE DEVELOPING AVIAN HEART - A ROLE FOR THE ETS-2 TRANSCRIPTION FACTOR

During heart development, cells of the endocardial cushions undergo an epithelial-mesenchymal transformation and migrate into the surroundin g extracellular matrix. This event is required for the normal formatio n of valves and chamber septation. Coincident with this phenotypic cha nge is the expression of the serine protease urokinase by the mesenchy mal cells. This protease plays an important role in remodeling of the matrix, promotion of cell migration by regulating cell-matrix interact ions, and the activation of growth factors. To understand the mechanis ms underlying the expression of urokinase during heart development, st udies were designed to analyze the role of the Ets transcription facto rs in the regulation of the avian urokinase gene promoter. Deletion or mutagenesis of the Ets consensus sites significantly decreased the ac tivity of the promoter in isolated cushion tissue cells. Proteins were identified by electrophoretic mobility shift analysis and UV-crosslin king which bound to a specific region of the promoter shown to be requ ired for full transcriptional activity. Analyses based upon protein mo lecular weight and interaction with specific antibodies suggest a role for the Ets-2 protein in promoter binding and activity. The expressio n of Ets-2 in the cushion tissue cells was confirmed by RT PCR analysi s and in situ hybridization. The mRNA levels and the DNA binding activ ity of the Ets-2 protein were found to change during development paral leling the increase in urokinase activity. Overexpression of the full- length Ets-2 protein or a dominant-negative form of the protein altere d the activity of the promoter and significantly affected the producti on of urokinase in these cells. The results from these studies suggest an important role for the Ets-2 protein in heart development and may contribute to a better understanding of the inductive factors present in the heart which facilitate the normal morphogenesis of this organ. (C) 1997 Elsevier Science Ireland Ltd.