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. 2013 Dec 1;27(23):2531–2536. doi: 10.1101/gad.229195.113

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© 2013 Welcker et al.; Published by Cold Spring Harbor Laboratory Press

This article is distributed exclusively by Cold Spring Harbor Laboratory Press for the first six months after the full-issue publication date (see http://genesdev.cshlp.org/site/misc/terms.xhtml). After six months, it is available under a Creative Commons License (Attribution-NonCommercial 3.0 Unported), as described at http://creativecommons.org/licenses/by-nc/3.0/.

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Figure 4. — SREBP regulation requires Fbw7 dimers. (A) Cells in serum-free medium were treated with insulin as indicated and immunoblotted for nuclear SREBP1 and Cul1 (loading control). (B) SREBP1 half-life is prolonged in HCT116 ΔD cells. Cells were treated with cycloheximide and analyzed by Western blotting. (C) Active nuclear SREBP1 is nearly maximally stabilized in cells expressing Fbw7 monomers compared with Fbw7-null cells. (*) Background band/loading control. (D) Nuclear SREBP2 abundance in HCT116 cell lines was determined by immunoprecipitation-Western analysis. (E) Dimer-dependent SREBP binding. 293A cells were transfected as indicated, immunoprecipitated with Flag antibody (Fbw7), and Western-blotted. (S1) SREBP1; (S2) SREBP2. dnCul1 was coexpressed to prevent SREBP turnover by coexpressed Fbw7. (F) 293A cells were transfected and blotted as indicated (PCNA-loading control). Converting the central serine to a threonine in the SREBP2 degron (LMSPPAS and S432T) allows SREBP2 degradation by Fbw7 monomers. (G) Model for the SREBP–Fbw7 interaction.