Immunolabeling for Detection of Endogenous and Overexpressed Peroxisomal Proteins in Mammalian Cells

Peroxisomes are dynamic subcellular organelles in mammals, playing essential roles in cellular lipid metabolism and redox homeostasis. They perform a wide spectrum of functions in human health and disease, with new roles, mechanisms, and regulatory pathways still being discovered. Recently elucidated biological roles of peroxisomes include as antiviral defense hubs, intracellular signaling platforms, immunomodulators, and protective organelles in sensory cells. Furthermore, peroxisomes are part of a complex inter-organelle interaction network, which involves metabolic cooperation and cross talk via membrane contacts. The detection of endogenous and/or overexpressed proteins within a cell by immunolabelling informs us about the organellar and even sub-organellar localization of both known and putative peroxisomal proteins. In turn, this can be exploited to characterize the effects of experimental manipulations on the morphology, distribution, and/or number of peroxisomes in a cell, which are key properties controlling peroxisome function. Here, we present a protocol used successfully in our laboratory for the immunolabelling of peroxisomal proteins in cultured mammalian cells. We present immunofluorescence and transfection techniques as well as reagents to determine the localization of endogenous and overexpressed peroxisomal proteins.