Transcription of the human urokinase type plasminogen activator (uPA) gene in HeLa cells is induced by phorbol myristate acetate (PMA), interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha). The response to these factors is rapid, independent of new protein synthesis and amplified in the presence of an inhibitor of protein synthesis, indicating the presence of a labile repressor. A DNA element, similar to the binding site for the transcription factor NFkB, is located around--1865 with respect to the start site of transcription in the uPA promoter and confers superinducibility by these agents in the presence of cycloheximide (CHX). A synthetic copy of this element confers superinducibility on a minimal uPA gene promoter and on the thymidine kinase (TK) gene promoter linked to the chloramphenicol acetyl transferase (CAT) gene. CHX alone does not increase transcription from these constructs in HeLa cells, although it superinduces the effects of PMA, IL-1 and TNF alpha. A second NFkB-like binding site located at around--1835 is not capable of conferring transcriptional activation under the same conditions. Our results suggest that maximal transcriptional activation of the uPA gene by PMA, IL-1 and TNF alpha requires the induction of NFkB activity and the decay of a short lived repressor protein, possibly IkB.