The sterol-sensing endoplasmic reticulum (ER) membrane protein TRC8 hampers ER to Golgi transport of sterol regulatory element-binding protein-2 (SREBP-2)/SREBP cleavage-activated protein and reduces SREBP-2 cleavage.
TRC8 (translocation in renal cancer from chromosome 8) is an intrinsic protein of the endoplasmic reticulum that contains a sterol-sensing domain and a RING finger motif encoding an E3 ubiquitin ligase. Here we show that TRC8 overexpression hinders sterol regulatory element-binding protein-2 (SREBP-2) processing, thereby reducing SREBP-2 target gene expression, TRC8 depletion has the opposite effect. Mutation analyses of TRC8 reveal that the ubiquitin ligase activity is dispensable for these effects. Activating transcription factor 6 (ATF6) is also processed in the Golgi by the same two proteases as those for SREBP, but ATF6 processing is not affected by TRC8. TRC8 is capable of binding both SREBP-2 and SREBP cleavage-activated protein (SCAP), thereby forming a TRC8.SREBP-2.SCAP complex. This complex formation hampers the interaction between SCAP and Sec24, one of the COPII proteins that are involved in SREBP-2 transport to the Golgi, thereby reducing SREBP-2 cleavage. TRC8 conjugated by ubiquitin is unstable, whereas the mutant TRC8, lacking the E3 ubiquitin ligase activity and only slightly modified by ubiquitin, is quite stable. TRC8 becomes stable when cells are cultured with a proteasome inhibitor or under a lipoprotein-depleted condition. Lipoprotein depletion impairs ubiquitination of TRC8. Taken together, TRC8 is a novel sterol-sensing endoplasmic reticulum membrane protein that hinders SREBP-2 processing through interaction with SREBP-2 and SCAP, regulating its own turnover rate by means of its E3 ubiquitin ligase activity.
Irisawa
Masato
M
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
Inoue
Jun
J
Ozawa
Nozomi
N
Mori
Kazutoshi
K
Sato
Ryuichiro
R
D000469:Alkaline Phosphatase / Q000378:metabolism; D001665:Binding Sites; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008074:Lipoproteins / Q000737:chemistry; D008565:Membrane Proteins / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D051782:Sterol Regulatory Element Binding Protein 2 / Q000378:metabolism*; D013261:Sterols / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism
D047908:Intracellular Signaling Peptides and Proteins; D008074:Lipoproteins; D008565:Membrane Proteins; D034741:RNA, Small Interfering; C114025:RNF139 protein, human; D011956:Receptors, Cell Surface; C530638:SEC24A protein, human; C102196:SREBP cleavage-activating protein; D051782:Sterol Regulatory Element Binding Protein 2; D013261:Sterols; D033921:Vesicular Transport Proteins; D044767:Ubiquitin-Protein Ligases; D000469:Alkaline Phosphatase
J Biol Chem. 1999 Dec 10;274(50):35832-9
10585467
J Biol Chem. 2003 Aug 15;278(33):31024-32
12782636
Mol Cell. 1998 Oct;2(4):505-14
9809072
J Biol Chem. 2001 Sep 28;276(39):36431-7
11477106
J Biol Chem. 2003 May 9;278(19):16809-19
12615929
Proc Natl Acad Sci U S A. 2002 Dec 24;99(26):16672-7
12482938
J Clin Invest. 2004 Apr;113(8):1168-75
15085196
J Biol Chem. 2009 Mar 20;284(12):7518-32
19158095
Oncogene. 2007 Apr 5;26(16):2263-71
17016439
J Biol Chem. 1996 Oct 25;271(43):26461-4
8900111
Genes Dev. 2001 May 15;15(10):1206-16
11358865
Cell. 2002 Aug 23;110(4):489-500
12202038
Cell Metab. 2005 Mar;1(3):179-89
16054061
J Biol Chem. 2004 Jul 2;279(27):28798-806
15090540
Oncogene. 2002 May 16;21(22):3507-16
12032852
Mol Cell. 2003 Jan;11(1):25-33
12535518
J Clin Invest. 2005 Sep;115(9):2489-98
16100574
J Biol Chem. 1997 Aug 8;272(32):20213-21
9242699
Mol Cell. 2005 Sep 16;19(6):829-40
16168377
Proc Natl Acad Sci U S A. 1999 Sep 28;96(20):11364-9
10500182
J Biol Chem. 2008 May 30;283(22):15224-31
18403372
Proc Natl Acad Sci U S A. 2007 Apr 17;104(16):6519-26
17428919
J Biol Chem. 1999 Aug 27;274(35):24714-20
10455139
J Biol Chem. 2000 Apr 28;275(17):12497-502
10777536
Proc Natl Acad Sci U S A. 1998 May 26;95(11):5987-92
9600904
Cell. 2006 Jan 13;124(1):35-46
16413480
Proc Natl Acad Sci U S A. 1999 Sep 28;96(20):11041-8
10500120
J Biochem. 1998 Jun;123(6):1191-8
9604010
Mol Biol Cell. 2004 Jun;15(6):2537-48
15020717
Proc Natl Acad Sci U S A. 2002 Sep 3;99(18):11694-9
12193656
Proc Natl Acad Sci U S A. 1998 Aug 4;95(16):9572-7
9689122
J Biol Chem. 2007 Apr 6;282(14):10290-8
17283069
Proc Natl Acad Sci U S A. 2003 Mar 18;100(6):3155-60
12624180
J Biol Chem. 1999 Oct 1;274(40):28549-56
10497220
J Biol Chem. 2005 Jul 15;280(28):26483-90
15899885