Purification of an interleukin-1β converting enzyme-related cysteine protease that cleaves sterol regulatory element-binding proteins between the leucine zipper and transmembrane domains

X. Wang, J. T. Pai, E. A. Wiedenfeld, J. C. Medina, C. A. Slaughter, J. L. Goldstein, M. S. Brown

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Abstract

We describe the characterization and purification of a protease that cleaves sterol regulatory element-binding protein-1 (SREBP-1) and SREBP-2 in vitro. Cleavage occurs between the basic helix-loop-helix-leucine zipper and the first transmembrane domain of each SREBP. This is the region in which the SREBPs are cleaved physiologically by a sterol-regulated protease that releases an NH2-terminal fragment that activates transcription of the genes for the low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl CoA synthase. The cleavage enzyme, designated SREBP cleavage activity (SCA), belongs to a new class of cysteine proteases of the interleukin-1β- converting enzyme (ICE) family, all of which cleave at aspartic acid residues. Like ICE, SCA was inactive in cytosol, and it was activated in vitro by incubation at 30 °C. SCA was resistant to inhibitors of serine, aspartyl, and metalloproteases, but it was sensitive to N-ethylmaleimide. The enzyme cleaved SREBP-1 and SREBP-2 between the Asp and Ser of a conserved sequence (S/DEPDSP). The activity was blocked by a tetrapeptide aldehyde, Ac- Asp-Glu-Ala-Asp-aldehyde (Ac-DEAD-CHO). A purified preparation of SCA from hamster liver contained a prominent 20-kDa polypeptide that could be labeled with [14C]iodoacetic acid. Labeling was blocked by Ac-DEAD-CHO. Partial amino acid sequence of this polypeptide revealed that it was the hamster equivalent of human CPP32, a putative protease whose cDNA was recently identified by virtue of sequence homology to ICE. CPP32 and ICE have been implicated in apoptosis in animal cells. Whether SCA/CPP32 participates in vivo in the sterol-regulated activation of SREBP, or whether it activates SREBPs during apoptosis, remains to be determined.

Original languageEnglish (US)
Pages (from-to)18044-18050
Number of pages7
JournalJournal of Biological Chemistry
Volume270
Issue number30
DOIs
StatePublished - Jan 1 1995
Externally publishedYes

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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