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MBC in Press, published online ahead of print October 17, 2007
Mol. Biol. Cell 10.1091/mbc.E07-04-0330

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Submitted on April 12, 2007
Revised on September 21, 2007
Accepted on October 5, 2007

Endocytic Trafficking of Sphingomyelin Depends on Its Acyl Chain Length

Mirkka Koivusalo,*{dagger} Maurice Jansen,* Pentti Somerharju,{ddagger} and Elina Ikonen*

*Institute of Biomedicine/Anatomy and {ddagger}Institute of Biomedicine/Biochemistry, University of Helsinki, FIN-00014, Helsinki, Finland

Monitoring Editor: Howard Riezman

To study the principles of endocytic lipid trafficking, we introduced pyrene sphingomyelins (PyrSMs) with varying acyl chain lengths and domain partitioning properties into human fibroblasts or HeLa cells. We found that a long-chain, ordered-domain preferring PyrSM was targeted Hrs- and Tsg101-dependently to late endosomal compartments and recycled to the plasma membrane in an NPC1- and cholesterol- dependent manner. A short-chain, disordered domain preferring PyrSM recycled more effectively, using Hrs-, Tsg101- and NPC1-independent routing that was insensitive to cholesterol loading. Similar chain length-dependent recycling was observed for unlabeled SMs. The findings 1) establish acyl chain length as an important determinant in the endocytic trafficking of SMs, 2) implicate ESCRT complex proteins and NPC1 in the endocytic recycling of ordered domain lipids to the plasma membrane and 3) introduce long-chain PyrSM as the first fluorescent lipid tracing this pathway.

{dagger}Present address: Programme in Cell Biology, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, M5G 1X8, Canada.

Address correspondence to: Elina Ikonen (elina.ikonen{at}helsinki.fi)






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