The origin and maintenance of mammalian peroxisomes involves a de novo PEX16-dependent pathway from the ER

Peter K Kim,Uwe Schumann,Jennifer Lippincott-Schwartz,Robert T Mullen

doi:10.1083/jcb.200601036

Abstract

Peroxisomes are ubiquitous organelles that proliferate under different physiological conditions and can form de novo in cells that lack them. The endoplasmic reticulum (ER) has been shown to be the source of peroxisomes in yeast and plant cells. It remains unclear, however, whether the ER has a similar role in mammalian cells and whether peroxisome division or outgrowth from the ER maintains peroxisomes in growing cells. We use a new in cellula pulse-chase imaging protocol with photoactivatable GFP to investigate the mechanism underlying the biogenesis of mammalian peroxisomes. We provide direct evidence that peroxisomes can arise de novo from the ER in both normal and peroxisome-less mutant cells. We further show that PEX16 regulates this process by being cotranslationally inserted into the ER and serving to recruit other peroxisomal membrane proteins to membranes. Finally, we demonstrate that the increase in peroxisome number in growing wild-type cells results primarily from new peroxisomes derived from the ER rather than by division of preexisting peroxisomes.

Highlights

Peroxisomes are small membrane-bound organelles that function in cellular metabolism in diverse ways, including the β- and α-oxidation of fatty acids, the oxidation of bile acids and cholesterol, and conversion of hydrogen peroxide to nontoxic forms
When PEX16 tagged with GFP (PEX16-GFP) was expressed in COS-7 cells, complete colocalization was observed between PEX16-GFP and a coexpressed peroxisomal reporter molecule consisting of the red fluorescent protein (RFP) tagged to type 1 peroxisomal matrix targeting signal, SKL-COOH (RFP-SKL; Fig. 1 A)
We provide evidence based on live cell imaging approaches that peroxisomes in mammalian cells can arise de novo from the endoplasmic reticulum (ER)

Summary

Introduction

Peroxisomes are small membrane-bound organelles that function in cellular metabolism in diverse ways, including the β- and α-oxidation of fatty acids, the oxidation of bile acids and cholesterol, and conversion of hydrogen peroxide to nontoxic forms. Genetic and proteomic studies in yeast and mammalian cell systems have led to the identification of up to 32 proteins (collectively called peroxins or PEX) involved in peroxisome biogenesis Of these peroxins, three in mammalian cells— PEX3, PEX16, and PEX19—and two in yeast cells—Pex3p and Pex19p—are involved in peroxisomal membrane protein (PMP) import (Schliebs and Kunau, 2004; for review see Heiland and Erdmann, 2005). Three in mammalian cells— PEX3, PEX16, and PEX19—and two in yeast cells—Pex3p and Pex19p—are involved in peroxisomal membrane protein (PMP) import (Schliebs and Kunau, 2004; for review see Heiland and Erdmann, 2005) When any of these proteins are absent or mutated in cells, peroxisomes disappear. PEX16, an integral membrane protein absent in most yeast, is thought to serve as a receptor for PEX3 or as a component of the membrane translocator (Honsho et al, 2002; Fang et al, 2004)

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