TRANSFORMING GROWTH-FACTOR-BETA-1 STIMULATES MACROPHAGE UROKINASE EXPRESSION AND RELEASE OF MATRIX-BOUND BASIC FIBROBLAST GROWTH-FACTOR

Macrophage expression of urokinase-type plasminogen activator (uPA) ap pears to play a role in their release of matrix-bound basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta). In experiments reported here, we have examined the potential regulator y effects of bFGF and TGF-beta1 on macrophage uPA expression. TGF-beta 1 stimulated in a dose- and time-dependent manner the expression of se creted membrane and intracellular uPA activities by a macrophage cell line (RAW264.7). When examined at similar concentrations, bFGF had lit tle effect, and interleukin-1alpha, tumor necrosis factor-alpha, and m onocyte colony stimulating factor had no effect on macrophage uPA expr ession. Exposure of macrophages to TGF-beta1 led to a rapid and sustai ned increase in the steady-state levels of uPA mRNA that was independe nt of de novo protein synthesis and was completely inhibited by actino mycin D. However, the TGF-beta1-induced increase in uPA mRNA was large ly unaffected by subsequent incubation of cells with actinomycin D. Th e protein kinase C inhibitior H7 markedly reduced the ability of TGF-b eta1 to stimulate expression of uPA activity. Likewise, okadaic acid a nd microcystin, inhibitors of serine/threonine phosphatases, potentiat ed the ability of TGF-beta1 to upregulate macrophage uPA expression. T GF-beta1 primed cells converted nearly all added plasminogen to plasmi n and expressed sixfold more membrane-bound plasmin than control cells . Preincubation of TGF-beta1 with either serum or methylamine-modified alpha2-macroglobulin did not affect its ability to induce macrophage uPA expression. When control and TGF-beta1-primed macrophages were cul tured on matrices containing bound I-125-bFGF, their release of I-125- bFGF was increased five and tenfold, respectively, in the presence of plasminogen. The ability of TGF-beta to induce macrophage uPA expressi on and the plasmin-dependent release of matrix-bound bFGF may provide an indirect mechanism by which TGF-beta stimulates angiogenesis.