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First published online March 8, 2006
doi: 10.1242/10.1242/jcs02866
Cell Science at a Glance |
Johns Hopkins University School of Medicine, 725 N. Wolfe Street, Baltimore, MA 21205, USA
e-mail: peter.espenshade{at}jhmi.edu
| Introduction |
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| Sterol regulatory element binding proteins |
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1150 residues): SREBP-1a, SREBP-1c/ADD1 and SREBP-2 (Tontonoz et al., 1993| Regulation of SREBPs |
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| Scap |
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Interestingly, HMG-CoA reductase, which catalyzes the first committed step in sterol synthesis, also contains a sterol-sensing domain and is negatively regulated by binding to Insig (Sever et al., 2003
). However, in the case of HMG-CoA reductase, sterol-regulated binding to Insig accelerates ubiquitylation and proteasomal degradation of the enzyme (Song et al., 2005
). Sterol-sensing domains are also found in other proteins, such as the Neimann-Pick type C disease gene NPC1 and the Hedgehog receptor Patched. However, the role of Insig in regulation of these proteins remains to be tested (Kuwabara and Labouesse, 2002
).
| Insig |
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| S1P and S2P |
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| SREBP transcriptional regulation |
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| Regulation of SREBP activity |
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One function of the liver is to convert excess carbohydrates to fatty acids for storage as triglycerides. Insulin stimulates this fatty acid synthesis in response to excess carbohydrate (Horton et al., 2002
). Importantly, these lipogenic effects of insulin in the liver are mediated by SREBP-1c (Eberle et al., 2004
). Insulin increases SREBP-1c mRNA levels and SREBP-1c target gene expression in both the liver and tissue culture cells (Shimomura et al., 1999
; Foretz et al., 1999
). Although a complete description of insulin action on SREBP-1c requires further experimentation, a recent study suggests that control of SREBP-1c transcription by insulin is mediated by RXR-LXR (Chen et al., 2004
). Interestingly, polyunsaturated fatty acids (PUFA) inhibit SREBP-1c and fatty acid synthesis activity by antagonizing LXR-dependent activation of SREBP-1c. LXR may thus integrate these two dietary signals (Ou et al., 2001
).
| Control of protein degradation |
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| SREBP in non-mammalian systems |
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| Outlook |
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| Acknowledgments |
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| References |
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