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Published online
doi:10.1083/jcb.200808041
The Journal of Cell Biology, Vol. 184, No. 6, 881-894
The Rockefeller University Press, 0021-9525 $30.00
© Eastman et al.
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Article

A role for ubiquitin ligases and Spartin/SPG20 in lipid droplet turnover



Scott W. Eastman1,2,3, Mina Yassaee1,2,3, and Paul D. Bieniasz1,2,3

1 Howard Hughes Medical Institute, 2 Aaron Diamond AIDS Research Center, and 3 Laboratory of Retrovirology, The Rockefeller University, New York, NY 10065

Correspondence to Paul D. Bieniasz: pbienias{at}adarc.org

HECT (homologous to the E6AP C terminus) ubiquitin ligases have diverse functions in eukaryotic cells. In screens for proteins that bind to the HECT ubiquitin ligase WWP1, we identified Spartin, which is also known as SPG20. This protein is truncated in a neurological disease, Troyer syndrome. In this study, we show that SPG20 associates with the surface of lipid droplets (LDs) and can regulate their size and number. SPG20 binds to another LD protein, TIP47, and both proteins compete with an additional LD protein, adipophilin/adipocyte differentiation-related protein, for occupancy of LDs. The mutant SPG20 present in Troyer syndrome does not possess these activities. Depletion of SPG20 using RNA interference increases the number and size of LDs when cells are fed with oleic acid. Binding of WWP1 to SPG20 and the consequent ubiquitin transfer remove SPG20 from LDs and reduce the levels of coexpressed SPG20. These experiments suggest functions for ubiquitin ligases and SPG20 in the regulation of LD turnover and potential pathological mechanisms in Troyer syndrome.

M. Yassaee's present address is University of Pennsylvania School of Medicine, Philadelphia, PA 19104.

Abbreviations used in this paper: ADRP, adipophilin/adipocyte differentiation-related protein; BODIPY, boron-dipyrromethene; ESCRT, endosomal sorting complex required for transport; HECT, homologous to the E6AP C terminus; LD, lipid droplet; MIT, microtubule interaction and trafficking; MLV, murine leukemia virus; NTE, neuropathy target esterase; OA, oleic acid; shRNA, short hairpin RNA; TAP, tandem affinity purification; TEV, tobacco etch virus.

© 2009 Eastman et al.
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