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Proteolytic Activation of SREBPs during Adipocyte Differentiation

Authors
  • Inoue, Jun
  • Kumagai, Hidetoshi
  • Terada, Tomoyuki
  • Maeda, Masatomo
  • Shimizu, Makoto
  • Sato, Ryuichiro
Type
Published Article
Journal
Biochemical and Biophysical Research Communications
Publication Date
Jan 01, 2001
Volume
283
Issue
5
Pages
1157–1161
Identifiers
DOI: 10.1006/bbrc.2001.4915
Source
Elsevier
Keywords
License
Unknown

Abstract

A member of sterol regulatory element-binding protein (SREBP) family, SREBP-1, is a key regulator of adipocyte differentiation. Expression of the SREBP-1 gene is induced during adipocyte differentiation, but proteolytic activation of the synthesized precursor form of SREBP-1 has not been well analyzed. The proteolytic processing of SREBPs is severely suppressed in sterol loaded culture cells. Here we report that a splicing isoform, SREBP-1a, is predominantly expressed in 3T3-L1 preadipocytes and adipocytes, and that the nuclear active form of SREBP-1 protein increases in adipocyte differentiation. We further show that the amount of nuclear SREBP-2 protein also increases despite no increase in SREBP-2 mRNA, suggesting that proteolytic cleavage of SREBPs is induced in lipid loaded adipocytes. Northern blot analyses reveal that mRNA levels for SREBP cleavage-activating protein (SCAP), Site-1 protease (S1P), and Site-2 protease (S2P), which participate in the proteolytic processing of SREBPs, are relatively unaffected in adipogenesis. These results demonstrate that SREBP-2 appears to promote adipocyte differentiation as well as SREBP-1 and that the proteolytic activation of SREBPs may be induced by an as-yet unidentified mechanism in lipid loaded adipocytes.

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