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This Article Full Text (PDF) All Versions of this Article: 297/6/E1395    most recent ajpendo.00188.2009v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Liu, K. Articles by Smas, C. M. PubMed PubMed Citation Articles by Liu, K. Articles by Smas, C. M.

RESEARCH ARTICLE

Functional Analysis of FSP27 Protein Regions for Lipid Droplet Localization, Caspase-Dependent Apoptosis and Dimerization with CIDEA

¹University of Toledo Medical College ²Bowling Green State University

Submitted 20 March 2009 ; revised 10 September 2009 ; accepted in final form 13 October 2009

The adipocyte-specific protein FSP27 is one of three cell death-inducing DFF45-like effector (CIDE) proteins. The first known function for CIDEs was promotion of apoptosis upon ectopic expression in mammalian cells. Recent studies in endogenous settings demonstrated key roles for CIDEs in energy metabolism. FSP27 is a lipid droplet associated protein whose heterologous expression enhances formation of enlarged lipid droplets and is required for unilocular lipid droplets typical of white adipocytes in vivo. Here we delineate relationships between apoptotic function and lipid droplet localization of FSP27. We demonstrate ectopic expression of FSP27 induces enlarged lipid droplets in multiple human cell lines, indicative that its mechanism involves ubiquitously present, rather than adipocyte-specific, cellular machinery. Furthermore, promotion of lipid droplet formation in HeLa cells via culture in exogenous oleic acid offsets FSP27-mediated apoptosis. Using transient co-transfections and analysis of lipid droplets in HeLa cells stably expressing FSP27, we show FSP27 does not protect lipid droplets from action of ATGL lipase. Domain mapping with eGFP-FSP27 deletion constructs indicates lipid droplet localization of FSP27 requires amino acids 174-192 of its CIDE-C domain. The apoptotic mechanism of FSP27, which we show involves caspase-9 and mitochondrial cytochrome c, also requires this 19 AA region. Interaction assays determine the FSP27 CIDE-C domain complexes with CIDEA and Western blot reveals FSP27 protein levels are reduced by co-expression of CIDEA. Overall, our findings demonstrate the function of the FSP27 CIDE-C domain and/or regions thereof for apoptosis, lipid droplet localization and CIDEA interaction.

lipid droplet; adipocyte; obesity; cide; apoptosis