DIVERGENT EFFECT OF N,N-DIMETHYLFORMAMIDE ON THE EXPRESSION OF UROKINASE AND ITS RECEPTOR

The plasminogen activator (PA), urokinase, (UK) plays an important rol e in tissue remodelling by mediating the conversion of plasminogen int o the serine-protease, plasmin. UK can bind to a specific cell surface receptor which serves to accelerate plasminogen activation. The prese nt study was undertaken to determine the effect of the chemical agent N,N-dimethylformamide (DMF), on the expression of UK and its receptor in a colon cancer cell line, CBS. DMF increased radioactive UK binding to CBS in a dose-dependent fashion. A level of 0.75% (v/v) has a maxi mal effect in this regard producing a 150% increase in the amount of r adioligand bound. Crosslinking of a radioactive aminoterminal (ATF) of UK, corresponding to the receptor-binding sequence of the PA, to the surface of CBS cells indicated a radioactive complex of molecular mass 66 kDa. This binding could be abolished with an excess of unlabelled ATF. The amount of this 66 kDa complex increased over an identical con centration range used to elevate radioligand binding in the receptor a ssays. Augmented radioligand binding to CBS cells, treated with DMF, w as a consequence of an increase in the number of UK receptors from 7.6 x 10(3) to 19.9 X 10(3) as determined by Scatchard analysis. Northern blotting for UK receptor transcript revealed that this increase in th e amount of receptor binding protein was a consequence of a more abund ant transcript. In contrast to the inductive effect on UK receptor exp ression, DMF, over an identical concentration range, suppressed, by up to 80%, the level of steady-state mRNA encoding the PA. Maximal suppr ession of UK mRNA occurred after 4 days suggesting that this effect of DMF was not coordinated with the induction of UK receptor expression which required only a 24 h period. In conclusion, this is the first st udy to indicate a divergent effect of an agent, on the expression of U K and its receptor.