N-BUTYRATE INDUCES PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 MESSENGER-RNA IN CULTURED HEP G2 CELLS

n-Butyrate, a short-chain aliphatic carboxylic acid with pleiotropic a ctions, is present at high concentrations in the portal circulation an d thus may play an important role in the regulation of specific gene e xpression in the mammalian Liver. We report here that n-butyrate can i ncrease substantially the level of plasminogen activator inhibitor typ e 1 (PAI-1) messenger RNA (mRNA) in Rep G2 cells, up to eightfold abov e control cultures. Maximal effects occurred at a concentration of 3 m mol/L n-butyrate and with a treatment period of 8 to 12 hours. Increas es in PAI-1 mRNA were accompanied by modest increases (twofold) in the encoded protein as assessed by specific enzyme-linked immunosorbent a ssay and by [S-35]methionine incorporation into immunoprecipitable PAI -1 in the culture medium. Nuclear run on studies showed that the rate of transcription of the PAI-1 gene did not appear altered by treatment with 3 mmol/L n-butyrate for 6 hours. The increases in steady-state P AI-1 mRNA caused by exposure to n-butyrate can be blocked by cyclohexi mide. Enhanced stability of mature PAI-1 transcript could not be demon strated in Rep G2 cells treated with the carboxylic acid. We have repo rted previously that n-butyrate can reduce the level of beta-galactosi de alpha 2,6-sialyltransferase expression in Hep G2 cells. That effect was attenuated with inhibitors of protein and RNA synthesis and was m ediated at the posttranscriptional level. Thus, n-butyrate can influen ce the expression of multiple genes in this hepatoblastoma cell throug h its actions on events that appear to be posttranscriptional. These o bservations may be relevant to the normal physiology of the mammalian Liver because of the high concentrations of n-butyrate and related com pounds to which the organ is ordinarily exposed.