THP-1 MACROPHAGE MEMBRANE-BOUND PLASMIN ACTIVITY IS UP-REGULATED BY TRANSFORMING GROWTH-FACTOR-BETA-1 VIA INCREASED EXPRESSION OF UROKINASEAND THE UROKINASE RECEPTOR

Receptors for urokinase (uPA) and plasminogen provide a mechanism to d irect the cellular activation of plasminogen. The regulation of these receptors is important for several macrophage functions. In these stud ies, the effect of transforming growth factor-beta 1 (TGF-beta 1) on u PA, uPA receptor, and plasminogen receptor expression by human THP-1 m acrophage was examined. TGF-beta 1 induction of uPA expression by THP- I cells was differentiation dependent. Suspension and adherent culture s expressed similar constitutive levels of uPA. Exposure of adherent c ells to TGF-beta 1 led to a dose- and time-dependent increase in uPA a ctivity which was paralleled by an increase in uPA antigen and uPA mRN A. In contrast, uPA expression by suspension cultures was unresponsive to TGF-beta 1. The differential response exhibited by suspension and adherent THP-1 cells may reflect differences in their expression of TG F-beta 1 receptors, since when assayed by crosslinking techniques, sus pension cells primarily expressed a 65 kDa receptor; whereas, the adhe rent cells expressed 65 and 100 kDa receptors. TGF-beta 1-induced alte rations in uPA receptor expression by adherent THP-1 cells were examin ed by quantitating membrane-bound uPA activity. Membrane-bound uPA act ivity increased three-fold when cells were incubated with TGF-beta 1. The increase in membrane-uPA activity expressed by TGF-beta 1-treated cells was not due to increased uPA receptor occupancy since incubation of either control or TGF-beta 1 primed cells with exogenous uPA did n ot lead to an increase in membrane-bound uPA activity. Furthermore, im munoreactive uPA receptor was increased in TGF-beta 1-treated cells. F ollowing incubation with plasminogen, membrane-bound plasmin activity increased three-fold in TGF-beta 1-treated cells. However, no change i n immunoreactive membrane-bound plasmin(ogen) was observed. In additio n, binding of I-125-Lys-plasminogen to THP-1 cells was not affected by TGF-beta 1 treatment. We conclude that TGF-beta 1 stimulates membrane -bound plasmin activity, without affecting plasminogen receptor expres sion, through the up-regulation of uPA and the uPA receptor expression . (C) 1995 Wiley-Liss, Inc.