Immunocytochemical localization of the 70 kDa peroxisomal membrane protein in connections between peroxisomes in rat liver: support for a reticular organization of peroxisomes maintained by the cytoskeleton.

Recently it has been shown that peroxisomes interact with microtubules which affect the structure and intracellular distribution of the organelle (Schrader, M., J. K. Burkhardt, E. Baumgart, G. Lüers, H. Spring, A. Völkl, H. D. Fahimi: Interaction of microtubules with peroxisomes. Tubular and spherical peroxisomes in HepG2 cells and their alterations induced by microtubule-active drugs. Eur. J. Cell Biol. 69, 24-35 (1996)). In the present work, we have applied immunological techniques to study the organization of peroxisomes within the rat liver cell. Antibodies to a pentadecapeptide corresponding to amino acid residues 403-417 of the 70 kDa integral peroxisomal membrane protein (Kamijo, K., S. Taketani, S. Yokota, T. Osumi, T. Hashimoto: The 70-kDa peroxisomal membrane protein is a member of the Mdr (P-glycoprotein)-related ATP-binding protein super family. J. Biol. Chem. 265, 4534-4540 (1990)) were raised in rabbits and affinity purified. This antibody was found to be highly specific for peroxisomes as determined by ELISA and Western blot analysis. Immunoelectron microscopy of tissue sections from rat liver revealed that peroxisomal membranes were labeled with this antibody and, in addition, labeling was found on tubular extensions often connecting peroxisomes. Antibodies to alpha-tubulin were used to locate the microtubular system. Microtubules were often found in close connection to peroxisomes, suggesting interaction between peroxisomes and the cytoskeleton. Double-labeling experiments for the 70 kDa integral peroxisomal membrane protein and alpha-tubulin demonstrated that the tubular structures connecting peroxisomes did not colocalize with microtubules. These results suggest that peroxisomes are organized in reticular structures within rat liver cells and that the structure and localization of these reticuli may be determined by their association to the microtubular network.