Role of Peroxisomes in Isoprenoid Biosynthesis

Abstract

Our group and others have recently demonstrated that peroxisomes contain a number of enzymes involved in cholesterol biosynthesis that previously were considered to be cytosolic or located in the endoplasmic reticulum (ER). Peroxisomes have been shown to contain HMG-CoA reductase, mevalonate kinase, phosphomevalonate kinase, phosphomevalonate decarboxylase, isopentenyl diphosphate isomerase, and FPP synthase. Four of the five enzymes required for the conversion of mevalonate to FPP contain a conserved putative PTS1 or PTS2, supporting the concept of targeted transport into peroxisomes. To date, no information is available regarding the function of the peroxisomal HMG-CoA reductase in cholesterol/isoprenoid metabolism, and the structure of the peroxisomal HMG-CoA reductase has yet to be determined. We have identified a mammalian cell line that expresses only one HMG-CoA reductase protein, and which is localized exclusively to peroxisomes, to facilitate our studies on the function, regulation, and structure of the peroxisomal HMG-CoA reductase. This cell line was obtained by growing UT2 cells (which lack the ER HMG-CoA reductase) in the absence of mevalonate. The surviving cells exhibited a marked increase in a 90-kD HMG-CoA reductase that was localized exclusively to peroxisomes. The wild-type CHO cells contain two HMG-CoA reductase proteins, the well-characterized 97-kD protein localized in the ER, and a 90-kD protein localized in peroxisomes. We have also identified the mutations in the UT2 cells responsible for the lack of the 97-kD protein. In addition, peroxisomal-deficient Pex2 CHO cell mutants display reduced HMG-CoA reductase levels and have reduced rates of sterol and nonsterol biosynthesis. These data further support the proposal that peroxisomes play an essential role in isoprenoid biosynthesis.

Effects of WY-14643 on Peroxisomal Enzyme Activity and Hormone Secretion in Immortalized Human Trophoblast Cells

“…Peroxisomes participate in fatty acid b-oxidation and the mevalonate pathway. 36,37) Acetyl-CoA derived from b-oxidation may be used for cholesterol synthesis in peroxisomes. Prognenolone is synthesized from cholesterol by cytochrome P450scc and is used for progesterone synthesis.…”

Subcellular Localization of Arabidopsis 3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase

“…These observations led to the suggestion that these organelles contained the various HMGR isoforms. In liver, CHO, and brain cells, HMGR was found in ER and peroxisomes (Keller et al, 1985;Appelkvist and Kalen, 1989;Aboushadi et al, 1999;Kovacs et al, 2001), suggesting an essential role of peroxisomes in isoprenoid biosynthesis (Gupta et al, 1999). Animal peroxisomes apparently are a major site of cholesterol biosynthesis since they contain all of the cholesterogenic enzymes involved in the conversion of mevalonate into farnesyl diphosphate (e.g.…”

Loss of Compartmentalization Causes Misregulation of Lysine Biosynthesis in Peroxisome-Deficient Yeast Cells

“…Enzymes of these supplemental pathways are usually absent or localized in nonperoxisomal compartments in most eukaryotes, and their peroxisomal localization is a specialization of relatively few species. Examples of facultative peroxisomal pathways are glycolysis and purine salvage (in the peroxisomes of kinetoplastids, such as Trypanosoma and Leishmania [23]), isoprenoid biosynthesis (in vertebrates [1]), ether phospholipid biosynthesis (in kinetoplastids and animals [15,33]), and the glyoxylate cycle, which channels the products of beta-oxidation into gluconeogenesis in plants, yeasts, and Caenorhabditis elegans (7).…”