Catalase-less peroxisomes - Implication in the milder forms of peroxisome biogenesis disorder

We established a Chinese hamster ovary cell line having a temperature-sensi tive phenotype in peroxisome biogenesis. This mutant (65TS) was produced by transforming a PEX2-defective mutant, Z65, with a mutant PEX2 gene, pEX2(E 55K), derived from a patient with infantile Refsum disease, a milder form o f peroxisome biogenesis disorder. In 65TS, catalase was found in the cytoso l at a nonpermissive temperature (39 degreesC), but upon the shift to a per missive temperature (33 degreesC), catalase gradually localized to the stru ctures containing a 70-kDa peroxisomal membrane protein, PMP70. In contrast to catalase, other matrix proteins containing typical peroxisome targeting signals, acyl-CoA oxidase and peroxisomal 3-ketoacyl-CoA thiolase, were co -localized with PMP70 in most cells, even at 39 degreesC. We found that the se structures are partially functional peroxisomes and named them "catalase -less peroxisomes.'' Catalase-less peroxisomes were also observed in human fibroblasts from patients with milder forms of peroxisome biogenesis disord er, including the one from which the mutant PEX2 gene was derived. We sugge st that these structures are the causes of the milder phenotypes of the pat ients. Temperature-dependent restoration of the peroxisomes in 65TS occurre d even in the presence of cycloheximide, a protein synthesis inhibitor. Thu s, we conclude that in 65TS, catalase-less peroxisomes are the direct precu rsors of peroxisomes.