Submitted to: Journal of Lipid Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2012
Publication Date: 3/1/2013
Citation: Ueno, M., Shen, W., Patel, S., Greenberg, A.S., Azhar, S., Kraemer, F.B. 2013. Fat-specific protein 27 modulates nuclear factor of activated T cells 5 and the cellular response to stress. Journal of Lipid Research. 54(3):734-743. Interpretive Summary: In this publication we investigated how the amount of a protein called fat specific protein 27 (FSP27) that coats stored fat within fat cells regulates the production of factors that control inflammation. In obesity, reductions in FSP27 are associated with increased recruitment of cells into fat tissues that are part of the inflammatory process. It is thought that increased numbers of immune cells in fat tissue of obese people promotes the release of factors into the blood that contribute to the development of diabetes and hyperlipidemia. Our research demonstrated that in fat cells, FSP27 binds tightly to a protein called nuclear factor of activated T-cells 5 (NFAT5). Furthermore we demonstrated that a reduction in FSP27 releases NFAT5 to bind to DNA in the cell. When NFAT5 binds to the DNA of the cell, the cell produces and secretes proteins that recruit immune cells. These studies demonstrate that levels of FSP27 within fat cells binds to and inhibits the actions of a protein that recruits immune cells and detrimentally alter fat tissue. As a result reductions in FSP27 protein expression may contribute to the development of diabetes and hyperlipidemia.
Technical Abstract: Fat-specific protein 27 (FSP27), a member of the cell death-inducing DNA fragmentation factor a-like effector (Cide) family, is highly expressed in adipose tissues and is a lipid droplet (LD)-associated protein that induces the accumulation of LDs. Using a yeast two-hybrid system to examine potential interactions of FSP27 with other proteins, a direct interaction with the N-terminal region of nuclear factor of activated T cells 5 (NFAT5) was identified. NFAT5 is a transcription factor that induces osmoprotective and inflammatory genes after its translocation to the nucleus. The interaction between FSP27 and NFAT5 was confirmed by bimolecular fluorescence complementation and coimmunoprecipitation. Using immunocytochemistry, NFAT5 is detected in the cytoplasm and in the nucleus under isotonic conditions; however, overexpression of FSP27 inhibited the hypertonic-induced nuclear translocation of NFAT5. Consistent with the suppression of NFAT5 nuclear translocation, in cells transfected with a reporter construct containing the NFAT5 response element from the monocyte chemoattractant protein 1 (MCP1) promoter, FSP27 overexpression repressed hypertonic-induced luciferase activity and the expression of NFAT5 target genes. Knockdown of FSP27 in differentiated 3T3-L1 adipocytes increased the NFAT5-mediated rise in MCP1. These results suggest that FSP27 not only modulates LD homeostasis but also modulates the response to osmotic stress via a physical interaction with NFAT5 at the LD surface.