TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL REGULATION OF UROKINASE-TYPE PLASMINOGEN-ACTIVATOR EXPRESSION IN ENDOTHELIAL-CELLS BY BASIC FIBROBLAST GROWTH-FACTOR

The mechanism of induction of urokinase-type plasminogen activator (uP A) by basic fibroblast growth factor (bFGF) was explored in fetal bovi ne aortic endothelial GM 7373 cells. A three- to four-fold increase in the steady-state levels of uPA mRNA was observed after 6 h of incubat ion of the cell cultures with bFGF. Accordingly, nuclear run-on experi ments showed a 2-2.4-fold increase in the rate oi uPA gene transcripti on during the first 4 h of treatment with the growth factor. bFGF did not affect uPA mRNA stability, as evaluated by chase experiments with the mRNA synthesis inhibitor actinomycin D. Upregulation of uPA mRNA w as followed by a delayed increase in uPA protein synthesis paralleled by an increase in secreted and cell-associated uPA activity. Twelve h were required before accumulated uPA mRNA was translated into the corr esponding protein. During this time interval, the continuous presence of biologically active bFGF in the extracellular environment represent ed an absolute requirement for uPA mRNA translation. Substitution of r esidues Lys-27, Lys-30, and Arg-31 to glutamine residues in the bFGF m olecule resulted in a mutant (M1Q-bFGF) that caused uPA mRNA accumulat ion in the absence of a significant increase in cell-associated uPA ac tivity. M1Q-bFGF also induced an increase in cell-associated uPA activ ity only when added to the cell cultures in the presence of soluble he parin. These results provide evidence that bFGF can affect uPA express ion in endothelial CM 7373 cells both at transcriptional and posttrans criptional/translational levels. They also show the possibility to dis sociate upregulation of uPA mRNA from upregulation of uPA activity by mutagenesis of the bFGF molecule. (C) 1995 Wiley-Liss, Inc.