Down-regulation of urokinase secretion from a human lymphoma cell line RC-K8 by dexamethasone without inducing plasminogen activator inhibitors

Abstract

The plasminogen activator (PA) activity in various cell lines is suppressed by glucocorticoids. These phenomena are attributed to either a suppression of PA biosynthesis, to an increase of PA inhibitor or to a combination of both. The regulation of urokinase (UK) production in a human pre-B cell lymphoma line, RC-K8, by dexamethasone (Dex) and phorbol myristate acetate (PMA) was investigated. RC-K8 is a cell line which is consistently producing a high molecular weight UK in the conditioned medium (Kubonishi, I., et al: Jpn. J. Cancer Res. 76 , 12–15, 1985). The cells were cultured in RPMI-1640 with Dex or PMA for 1–4 days. UK activity was measured using a chromogenic substrate S-2444 and the antigen by an ELISA kit. PAI-1 and PAI-2 antigens were also measured by ELISA kits and the complex between PA and PAI was examined by SDS-PAGE fibrin-zymography. The UK secretion in RC-K8 cells was inhibited by cycloheximide and actinomycin D. PMA at 0.16–1.6 uM up-regulated the UK activity approximately two-fold, parallel with the antigen, whereas Dex at 1–10 uM decreased the UK expression approximately half. These were verified by SDS-PAGE fibrin-zymography. Neither PAI-1, PAI-2 nor PA/PAI complex was detected in the conditioned medium and in the cell lysate. These data suggest that PMA up-regulates the UK secretion without inducing PAIs and the down-regulation of the UK secretion by Dex results from the inhibition of the expression of UK itself but not from the induction of PAIs.