| 研究実績の概要 |
Dysregulated metabolism is a common feature in cancer. HSP90 is a crucial target of cancer therapy. However, its role in lipid metabolism is unclear.
Using HSP90 inhibitor and siRNA, we found that HSP90 inhibition in vitro and in mice substantially reduced proteins of SCAP-SREBP. This led to a downregulation of SREBP-target genes, resulting in a decrease in lipid biosynthesis.
Mechanistically, we show that HSP90 binds to and acts as a chaperone of SCAP-SREBP complex, where inhibition of HSP90 accelerated complex degradation. This phenomenon was not altered by presence or absence of sterols.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
We elucidated the role of HSP90 in lipid metabolism, and we investigated the interaction sites in HSP90-SREBP-SCAP complex.
Using truncated or point-mutated SCAP, we located the SREBP-binding domain of SCAP in the 4th and the 5th WD40 domains. In addition, we identified 8 positively charged amino acid residues, R984, K1018, R1019, H1118, D1162, L1178, R1187, and R1248, that are critical to SCAP-SREBP interaction.
On the other hand, to examine the SCAP-binding domain of SREBP, we designed truncated SREBP1 based on its sequence similarity between SREBP2. Our preliminary results suggest that SREBP1 and SREBP2 may bind to SCAP using a highly similar domain (90% in sequence similarity). In addition, we found evidence suggesting that SREBP-SCAP binding may involve multiple domains from both sides.
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| 今後の研究の推進方策 |
To further elucidate the protein-protein interactions in HSP90-SCAP-SREBP complex and to exclude interference of endogenous proteins, SCAP-null cell line, SRD-13A, will be used for IP experiments. In addition, in vitro binding assays may also be used to confirm direct protein-protein interaction.
On the other hand, we set out to search for E3 ligase that regulates SCAP-SREBP and discovered RNF5 as an SCAP-binding E3 ligase. Intriguingly, while RNF5 mediates ubiquitination of SCAP, it did not altered protein stability of SCAP. Moreover, Our preliminary data suggests that RNF5 is involved in de novo lipogenesis, which may link to integrative antiviral response.
Therefore, we will continue to investigate the role of RNF5 in SCAP-SREBP-mediated lipid metabolism in the context of virus infection.
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