Restoration of PEX2 peroxisome assembly defects by overexpression of PMP70

The mutant Chinese hamster ovary (CHO) cell line Z78/C has defective peroxisome assembly due to a missense mutation in PEX2, the gene which encodes the 35 kDa peroxisomal integral membrane protein. In humans, PEX2 mutations are responsible for complementation group 10 of the human peroxisome biogenesis disorders (PBD), a genetically heterogeneous group of lethal, autosomal recessive diseases including the Zellweger syndrome and related phenotypes. To develop additional cellular models for Zellweger syndrome, we produced a series of new mutant CHO cell clones in the same complementation group as Z78/C (Z2, Z7, Z22, and Z105). As expected, expression of human PEX2 restores peroxisomal biogenesis in all of these clones. Surprisingly, expression of the human 70 kDa peroxisomal membrane protein (PMP70) also restores peroxisome biogenesis in these same CHO cell clones. We confirmed this effect of PMP70 expression on peroxisome biogenesis by determining the subcellular latency of catalase, the immunohistochemical localization of catalase and the beta-oxidation of very long chain fatty acids (VLCFA). By contrast, expression of a mutant allele of PMP70 identified in a patient with Zellweger syndrome did not restore peroxisome biogenesis in the PEX2-deficient CHO cell clones. Our results indicate that overexpression of PMP70 suppresses the phenotype of PEX2 gene mutations. These observations suggest a functional interaction between PEX2 and PMP70 in the peroxisome membrane.