PRETRANSLATIONAL REGULATION OF CYTOCHROME P4504A1 BY FREE FATTY-ACIDSIN PRIMARY CULTURES OF RAT HEPATOCYTES

The effect of different fatty acids on cytochrome p4504A1 mRNA levels was studied in primary cultures of rat hepatocytes, using a solution h ybridization assay. All fatty acids tested induced P4504A1 mRNA levels in a dose- and time-dependent manner. Most potent were docosahexaenoi c acid (22:6) and arachidonic acid (20:4), both of which gave a 6-fold increase in mRNA levels at 300 mu M, followed by linolenic acid (18:3 ) and lauric acid (12:0). The effect of three different sulfur-substit uted fatty acids was investigated. Tetradecylthioacetic acid, which is blocked for beta-oxidation by sulfur substitution of the beta-carbon, induced P4504A1 mRNA levels 8-fold at 300 mu M concentration, whereas tetradecylthiopropionic acid, which can undergo one round of beta-oxi dation, only gave a 2-fold increase at the same concentration. The mos t pronounced effect was seen with 3,14-dithiahexadecanedioic acid, a d icarboxylic acid with both beta-carbons blocked for beta-oxidation, wh ich gave a 31-fold induction of mRNA levels at 300 mu M. In time-cours e studies the effect of docosahexaenoic acid, 3,14-dithiahexadecanedio ic acid and the potent peroxisomal proliferator Wy 14,643 on P4504A1 m RNA levels was already detectable after 2 h and maximal after 48 h of treatment, which was reflected in increased levels of P4504A1 protein. Taken together, these results show that endogenous fatty acids, such as docosahexaenoic acid and arachidonic acid, act as pretranslational regulators of P4504A1 when added to primary cultures of rat hepatocyte s. Blocking their metabolism (beta-oxidation) leads to significant enh ancement of their activity.