Formation of peroxisomes from peroxisomal ghosts in a peroxisome-deficientmammalian cell mutant upon complementation by protein microinjection

Most mammalian cell strains genetically deficient in peroxisome biogenesis have abnormal membrane structures called ghosts, containing integral peroxi somal membrane protein, PMP70, but lacking the peroxisomal matrix proteins. Upon genetic complementation, these mutants regain the ability of peroxiso me biogenesis. It is postulated that, in this process, the ghosts act as th e precursors of peroxisomes, but there has been no evidence to support this . In the present study, we investigated this issue by protein microinjectio n to a mutant Chinese hamster ovary cell line defective of PEX5, encoding a peroxisome-targeting signal receptor. When recombinant Pex5p and green flu orescent protein (GFP) carrying a peroxisome-targeting signal were co-injec ted into the mutant cells, the GFP fluorescence gathered over time to parti culate structures where PMP70 was co-localized. This process was dependent on both Pex5p and the targeting signal, and, most importantly, occurred eve n in the presence of cycloheximide, a protein synthesis inhibitor, These fi ndings suggest that the ghosts act as accepters of matrix proteins in the p eroxisome recovery process at least in the PEX5 mutant, and support the vie w that peroxisomes can grow by incorporating newly synthesized matrix prote ins.