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Defining the Roles of FSP27 in Lipid Droplet Formation and Apoptosis

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2010, Doctor of Philosophy in Biomedical Sciences (Ph.D.), University of Toledo, College of Medicine.
The adipocyte-specific protein fat-specific protein 27 (FSP27) is one of the three cell death-inducing DNA fragmentation factor 45 (DFF45)-like effector (CIDE) proteins. The other two CIDE proteins are CIDEA and CIDEB. CIDE proteins consist of two domains. The CIDE-N domain shares a homology to the CIDE-N domain of DFF45, and the CIDE-C domain is highly conserved across the three family members (Inohara et al., 1998). FSP27 expression is restricted to adipose tissues. Expression of FSP27 is significantly induced during adipogenesis. Insulin, a key lipogenic hormone, enhances FSP27 transcript expression in adipocytes, whereas the lipolytic agent TNF-α diminishes its expression. The first known function for CIDEs was the promotion of apoptosis upon ectopic expression in mammalian cells. FSP27 leads to a dose- and time-dependent apoptosis in all non-adipose cell lines tested to date. This is mediated through the intrinsic apoptosis pathway involving the release of cytochrome c from the mitochondria, activation of caspases and cleavage of their substrates. The apoptosis induced by FSP27 can be inhibited by the pan-caspase inhibitor Z-VAD-FMK or in the presence of a dominant-negative caspase-9. In addition to its role in apoptosis, FSP27 is also demonstrated to be a lipid droplet associated protein whose expression enhances formation of enlarged lipid droplets and which is required for the unilocular lipid droplets typical of white adipocytes in vivo. Here I delineate relationships between lipid droplet localization and apoptotic function of FSP27. I demonstrate that ectopic expression of FSP27 induces enlarged lipid droplets in multiple human cell lines, indicating that its mechanism involves ubiquitously present, rather than adipocyte-specific, cellular machinery. Furthermore, promotion of lipid droplet formation in HeLa cells by culturing in exogenous oleic acid offsets FSP27-mediated apoptosis. Using transient co-transfections and analysis of lipid droplets in HeLa cells stably expressing FSP27, I show that the FSP27 protein does not protect lipid droplets from the action of ATGL lipase. Using domain mapping with eGFP-FSP27 deletion constructs, I found that lipid droplet localization of FSP27 requires amino acids 173 to 191 of its CIDE-C domain, which is also essential for FSP27 to execute its apoptotic function. In addition, FSP27 interacts with another CIDE family protein, CIDEA. Overall, my findings demonstrate the function of the FSP27 CIDE-C domain and its subregions in apoptosis, lipid droplet localization and interaction with CIDEA.
Cynthia Smas (Committee Chair)
William Maltese (Committee Member)
Kevin Pan (Committee Member)
Randall Ruch (Committee Member)
Dorothea Sawicki (Committee Member)
Xiaodong Wang (Committee Member)
240 p.

Recommended Citations

Citations

  • LIU, K. (2010). Defining the Roles of FSP27 in Lipid Droplet Formation and Apoptosis [Doctoral dissertation, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=mco1277820858

    APA Style (7th edition)

  • LIU, KUN. Defining the Roles of FSP27 in Lipid Droplet Formation and Apoptosis. 2010. University of Toledo, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=mco1277820858.

    MLA Style (8th edition)

  • LIU, KUN. "Defining the Roles of FSP27 in Lipid Droplet Formation and Apoptosis." Doctoral dissertation, University of Toledo, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=mco1277820858

    Chicago Manual of Style (17th edition)