BUTYRATE SPECIFICALLY STIMULATES TISSUE-TYPE PLASMINOGEN ACTIVATOR SYNTHESIS IN CULTURED HUMAN ENDOTHELIAL CELLS

In a search for compounds that can enhance tissue-type plasminogen activator (t-PA) synthesis in cultured human endothelial cells we found that dibutyryl cyclic AMP (at a concentration of 2 mM) led to a several-fold increase in t-PA production by endothelial cells over a 24 h incubation period. Further researchshowed that this stimulating effectcould be explained by the slow liberation of butyrate, as the effect could be reproduced by addition of free butyrate to the medium, but notby addition of 8-bromo cyclic AMP. With butyrate, an accelerated accumulation of t-PA antigen in the conditioned medium (CM) was observed after a lag period of about 6 h. Increasing amounts of butyrate caused anincreasingly stimulatory effect, reaching a plateau with 5 mM butyrate. The relative increase in t-PAproduction in thempresence of 5 mM butyrate varied among different endothelial cell cultures from 6 to 25-fold in 24 h CM. The butyrate-induced increase in t-PA production wasaccompanied by increased t-PA mRNAlevels.

Analysis of radiolabelled CM andcell extracts by SDS-PAGE and autoradiography indicated that the potent action of butyrate is restricted to a limited group of proteins. We found that theaccumulation of PA-inhibitor activity in CM from butyrate-treated cells increased only moderately.

In our study of the relationshipbetween structure and stimulatory activity we found that butyrate wasby far the most effective inducer oft-PA synthesis. Shortening or lengthening the carbon chain by one carbon atom decreased the stimulatory effect after 24 h of incubation by 50-70%. Further changes in the length of the carbon chain almost completely suppressed the stimulatory activity. Similarly, alterations of the aliphatic chain by introduction of functional groups, a double bond or a branched structure rendered butyrate ineffective in increasing t-PA synthesis. Thus, a straight-chain C⁴ monocarboxylate structure with a methyl group at one end and a carboxyl moiety at the other seems to be required for the rather specific induction of t-PA synthesis in cultured human endothelialcells.