CELLULAR ACTIVATION OF MESANGIAL GELATINASE-A BY CYTOCHALASIN-D IS ACCOMPANIED BY ENHANCED MESSENGER-RNA EXPRESSION OF BOTH GELATINASE-A AND ITS MEMBRANE-ASSOCIATED GELATINASE-A-ACTIVATOR (MT-MMP)

Activation of gelatinase A represents a crucial regulatory step in the control of its enzymic activity. Rat kidney mesangial cells secrete p redominantly latent gelatinase A that can be activated following treat ment with cytochalasin D. In the present paper we provide new evidence , using reverse transcription-PCR, that treatment of rat mesangial cel ls with cytochalasin D enhances the steady-state level of mRNA of the membrane-type matrix metalloproteinase (MT-MMP), as well as of gelatin ase A, with no change in the level of tissue inhibitor of metalloprote inases-2 (TIMP-2) mRNA. Since the TIMP-2 protein level is reduced in c onditioned medium from cytochalasin D-treated cells, the results of th e present study are consistent with a model in which the action of cyt ochalasin D is to cause extracellular gelatinase A and TIMP-2 to be se questered at the plasma membrane, forming a heterotrimeric complex wit h MT-MMP. In this manner, TIMP-2 may assume a bifunctional role causin g: (i) inhibition of gelatinase A in the extracellular compartment; an d (ii) guiding gelatinase A to activation through a membrane associati on with MT-MMP.