Originally published as Genetics Published Articles Ahead of Print on November 17, 2008.

Genetics, Vol. 181, 119-128, January 2009, Copyright © 2009
doi:10.1534/genetics.108.093450

Alternative Processing of Sterol Regulatory Element Binding Protein During Larval Development in Drosophila melanogaster

Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046

2 Corresponding author: Department of Molecular Genetics, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9046.
E-mail: rob.rawson{at}utsouthwestern.edu

Sterol regulatory element binding protein (SREBP) is a major transcriptional regulator of lipid metabolism. Nuclear Drosophila SREBP (dSREBP) is essential for larval development in Drosophila melanogaster but dispensable in adults. dSREBP larvae die at second instar owing to loss of dSREBP-mediated transcription but survive to adulthood when fed fatty acids. Activation of SREBP requires two separate cleavages. Site-1 protease (S1P) cleaves in the luminal loop of the membrane-bound SREBP precursor, cutting it in two. The NH2- and COOH-terminal domains remain membrane bound owing to their single membrane-spanning helices. The NH2-terminal cleavage product is the substrate for site-2 protease (S2P), which cleaves within its membrane-spanning helix to release the transcription factor. In mice, loss of S1P is lethal but the consequences of loss of S2P in animals remain undefined. All known functions of SREBP require its cleavage by S2P. We isolated Drosophila mutants that eliminate all dS2P function (dS2P). Unexpectedly, larvae lacking dS2P are viable. They are deficient in transcription of some dSREBP target genes but less so than larvae lacking dSREBP. Despite loss of dS2P, dSREBP is processed in mutant larvae. Therefore, larvae have an alternative cleavage mechanism for producing transcriptionally active dSREBP, and this permits survival of dS2P mutants.




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B. Amarneh, K. A. Matthews, and R. B. Rawson
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