Proteolysis and sterol regulation.
The mammalian cell continuously adjusts its sterol content by regulating levels of key sterol synthetic enzymes and levels of LDL receptors that mediate uptake of cholesterol-laden particles. Control is brought about by sterol-regulated transcription of relevant genes and by regulated degradation of the committed step enzyme HMG-CoA reductase (HMGR). Current work has revealed that proteolysis is at the heart of each of these mechanistically distinct axes. Transcriptional control is effected by regulated cleavage of the membrane-bound transcription factor sterol regulatory element binding protein (SREBP), and HMGR degradation is brought about by ubiquitin-mediated degradation. In each case, ongoing cell biological processes are being harnessed to bring about regulation. The secretory pathway plays a central role in allowing sterol-mediated control of transcription. The constitutively active endoplasmic reticulum (ER) quality control apparatus is employed to bring about regulated destruction of HMGR. This review describes the methods and results of various studies to understand the mechanisms and molecules involved in these distinct but interrelated aspects of sterol regulation and the intriguing similarities that appear to exist at the levels of protein sequence and cell biology.
Hampton
Randolph Y
RY
Section of Cell and Developmental Biology, Division of Biology, University of California, San Diego, La Jolla 92093-0347, USA. rhampton@ucsd.edu
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005057:Eukaryotic Cells / Q000378:metabolism*; D005809:Genes, Regulator / Q000502:physiology; D006801:Humans; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D051780:Sterol Regulatory Element Binding Protein 1; D013261:Sterols / Q000378:metabolism*; D014157:Transcription Factors; D025801:Ubiquitin / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1; D013261:Sterols; D014157:Transcription Factors; D025801:Ubiquitin; D006903:Hydroxymethylglutaryl CoA Reductases; D010447:Peptide Hydrolases