Role of peroxisomes in isoprenoid biosynthesis

Our group has demonstrated that all the enzymes required for the biosynthesis of farnesyl diphosphate (FPP) from mevalonate are localized to peroxisomes. FPP is the precursor of critical isoprenoids, thus, its regulation and metabolism are crucial. In rat liver, an allyl pyrophosphatase (FPPase) converts FPP to free farnesol. Farnesol is then oxidized to prenyl aldehyde by alcohol dehydrogenase (ADH) or it is converted to FPP by phosphorylation reactions. In this study, we identified a specific FPP kinase activity in rat liver. We also determined the subcellular localization of the FPPase, ADK and FPP kinase activities in whole liver homogenates. Regulation studies demonstrated that FPP kinase activity but not FPPase responded to modulation in FPP levels.; The rate-limiting enzyme in isoprenoid biosynthesis, 3-Hydroxy-3-methylglutaryl (HMG)-CoA reductase has been localized to peroxisomes and endoplasmic reticulum (ER). No information is available regarding the regulation or function of the peroxisomal reductase in isoprenoid metabolism. To facilitate the regulation studies of the peroxisomal reductase, we utilized a mammalian cell line (UT2*) that expresses only one reductase protein of 90 kDa that is localized exclusively in peroxisomes. Comparison of the regulation of the two reductases revealed major differences between the two proteins. The peroxisomal reductase is not the rate-limiting enzyme for cholesterol biosynthesis. The peroxisomal protein is not phosphorylated and its activity is not altered in the presence of cellular phosphatases. Its rate of degradation is not accelerated by mevalonate. Moreover, the degradation process is not blocked by the cysteine protease/proteosome inhibitor, N-acetyl-Leu-Leu-norleucinal (ALLN). Finally, the peroxisomal protein is more resistant to statin inhibition. These data suggest that the peroxisomal protein is functionally and structurally different from the ER reductase.; We also showed that peroxisomal-deficient PEX2-- Chinese hamster ovary (CHO) cells display reduced levels of peroxisomal. isoprenoid enzymes and show reduced rates of isoprenoid biosynthesis. We showed that the deficiency in the peroxisomal enzymes was due to acceleration in the rate of degradation of the proteins, and a decrease in the mRNA levels and rate of synthesis of these proteins.; Taken together, the data presented in this study emphasize the indispensable role of peroxisomes in isoprenoid biosynthesis.