A phosphorylation cascade controls the degradation of active SREBP1
2009 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 284, no 9, 5885-5895 p.Article in journal (Refereed) Published
Sterol regulatory element-binding proteins (SREBPs) are a family of transcription factors that regulates cholesterol and lipid metabolism. The active forms of these transcription factors are targeted by a number of post-translational modifications, including phosphorylation. Phosphorylation of Thr-426 and Ser-430 in SREBP1a creates a docking site for the ubiquitin ligase Fbw7, resulting in the degradation of the transcription factor. Here, we identify a novel phosphorylation site in SREBP1a, Ser-434, which regulates the Fbw7-dependent degradation of SREBP1. We demonstrate that both SREBP1a and SREBP1c are phosphorylated on this residue (Ser-410 in SREBP1c). Importantly, we demonstrate that the mature form of endogenous SREBP1 is phosphorylated on Ser-434. Glycogen synthase kinase-3 phosphorylates Ser-434, and the phosphorylation of this residue is attenuated in response to insulin signaling. Interestingly, phosphorylation of Ser-434 promotes the glycogen synthase kinase-3-dependent phosphorylation of Thr-426 and Ser-430 and destabilizes SREBP1. Consequently, mutation of Ser-434 blocks the interaction between SREBP1 and Fbw7 and attenuates Fbw7-dependent degradation of SREBP1. Importantly, insulin fails to enhance the levels of mature SREBP1 in cells lacking Fbw7. Thus, the degradation of mature SREBP1 is controlled by cross-talk between multiple phosphorylated residues in its C-terminal domain and the phosphorylation of Ser-434 could function as a molecular switch to control these processes.
Place, publisher, year, edition, pages
The American Society for Biochemistry and Molecular Biology, Inc. , 2009. Vol. 284, no 9, 5885-5895 p.
Medical and Health Sciences
IdentifiersURN: urn:nbn:se:uu:diva-105258DOI: 10.1074/jbc.M807906200ISI: 000263560600052PubMedID: 19126544OAI: oai:DiVA.org:uu-105258DiVA: diva2:220842