title: CD81 promotes both the degradation of transferrin receptor 2 (TfR2) and the Tfr2-mediated maintenance of hepcidin expression.
abstract: Mutations in transferrin receptor 2 (TfR2) cause a rare form of the hereditary hemochromatosis, resulting in iron overload predominantly in the liver. TfR2 is primarily expressed in hepatocytes and is hypothesized to sense iron levels in the blood to positively regulate the expression of hepcidin through activation of the BMP signaling pathway. Hepcidin is a peptide hormone that negatively regulates iron egress from cells and thus limits intestinal iron uptake. In this study, a yeast two-hybrid approach using the cytoplasmic domain of TfR2 identified CD81 as an interacting protein. CD81 is an abundant tetraspanin in the liver. Co-precipitations of CD81 with different TfR2 constructs demonstrated that both the cytoplasmic and ecto-transmembrane domains of TfR2 interact with CD81. Knockdown of CD81 using siRNA significantly increased TfR2 levels by increasing the half-life of TfR2, indicating that CD81 promotes degradation of TfR2. Previous studies showed that CD81 is targeted for degradation by GRAIL, an ubiquitin E3 ligase. Knockdown of GRAIL in Hep3B-TfR2 cells increased TfR2 levels, consistent with inhibition of CD81 ubiquitination. These results suggest that down-regulation of CD81 by GRAIL targets TfR2 for degradation. Surprisingly, knockdown of CD81 decreased hepcidin expression, implying that the TfR2/CD81 complex is involved in the maintenance of hepcidin mRNA. Moreover, knockdown of CD81 did not affect the stimulation of hepcidin expression by BMP6 but increased both the expression of ID1 and SMAD7, direct targets of BMP signaling pathway, and the phosphorylation of ERK1/2, indicating that the CD81 regulates hepcidin expression differently from the BMP and ERK1/2 signaling pathways.
authors: From the Department of Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, Oregon 97239.
authors: Juxing
authors: J
authors: Chen
authors: From the Department of Cell, Developmental and Cancer Biology, Oregon Health & Science University, Portland, Oregon 97239 ennsca@ohsu.edu.
authors: Caroline A
authors: CA
authors: Enns
mesh_terms: D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D064451:Hepcidins / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D011990:Receptors, Transferrin / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D060225:Tetraspanin 28 / Q000502:physiology*
chemical_list: C554798:CD81 protein, human; D017931:DNA Primers; D064451:Hepcidins; D011990:Receptors, Transferrin; C503640:TFR2 protein, human; D060225:Tetraspanin 28
keywords: E3 Ubiquitin Ligase; Iron; Iron Metabolism; Protein Degradation; Tetraspanin
references: Nat Genet. 2000 May;25(1):14-5
references: 10802645
references: Mol Biol Cell. 2007 Mar;18(3):743-54
references: 17182845
references: Cell. 2002 Jan 25;108(2):261-9
references: 11832215
references: Blood. 2002 Jul 15;100(2):692-4
references: 12091366
references: Blood. 2002 Nov 15;100(10):3776-81
references: 12393428
references: Nat Genet. 2003 Jan;33(1):21-2
references: 12469120
references: Annu Rev Biochem. 1979;48:193-216
references: 382984
references: Endocrinology. 1986 Jan;118(1):413-23
references: 3484450
references: J Cell Biol. 1986 Jan;102(1):24-36
references: 3001101
references: J Cell Biol. 1986 Feb;102(2):500-9
references: 2868013
references: Brain Res. 1993 Sep 17;622(1-2):9-16
references: 8242389
references: Nat Genet. 1996 Aug;13(4):399-408
references: 8696333
references: Curr Opin Cell Biol. 1996 Aug;8(4):549-56
references: 8791448
references: Science. 1996 Dec 20;274(5295):2086-9
references: 8953040
references: Annu Rev Immunol. 1998;16:89-109
references: 9597125
references: Blood. 2004 Dec 15;104(13):4294-9
references: 15319276
references: Blood. 2004 Dec 15;104(13):4287-93
references: 15319290
references: Science. 2004 Dec 17;306(5704):2090-3
references: 15514116
references: Nat Rev Immunol. 2005 Feb;5(2):136-48
references: 15688041
references: Blood. 2005 Feb 15;105(4):1803-6
references: 15486069
references: Gut. 2005 Jul;54(7):980-6
references: 15951546
references: Cell Metab. 2005 Dec;2(6):399-409
references: 16330325
references: Nat Genet. 2006 May;38(5):531-9
references: 16604073
references: Blood Cells Mol Dis. 2002 Nov-Dec;29(3):361-6
references: 12547226
references: Blood. 2003 Mar 1;101(5):2008-14
references: 12406888
references: Lancet. 2003 Feb 22;361(9358):669-73
references: 12606179
references: J Cell Sci. 2006 Nov 1;119(Pt 21):4486-98
references: 17046995
references: J Clin Invest. 2007 Jul;117(7):1933-9
references: 17607365
references: Hepatology. 2008 Feb;47(2):418-27
references: 18085708
references: J Mol Med (Berl). 2008 May;86(5):531-40
references: 18421430
references: J Biol Chem. 2008 Oct 17;283(42):28497-505
references: 18713730
references: Blood. 2009 Jan 15;113(3):688-95
references: 18997172
references: J Mol Endocrinol. 2009 Feb;42(2):161-9
references: 19060180
references: Haematologica. 2009 Jun;94(6):765-72
references: 19454495
references: Traffic. 2009 Oct;10(10):1488-501
references: 19682329
references: Hepatology. 2009 Dec;50(6):1992-2000
references: 19824072
references: Blood. 2010 Apr 22;115(16):3374-81
references: 20177050
references: Br J Pharmacol. 2010 May;160(2):191-203
references: 20423334
references: Blood. 2010 May 6;115(18):3686-94
references: 20223923
references: Haematologica. 2010 Nov;95(11):1832-40
references: 20634490
references: Gastroenterology. 2011 Nov;141(5):1907-14
references: 21745449
references: Mol Cell Biol. 2013 Sep;33(18):3644-58
references: 23858057
references: Viruses. 2014 Feb;6(2):875-92
references: 24553110
references: Science. 1999 Oct 22;286(5440):779-82
references: 10531064
references: Nature. 2000 Feb 17;403(6771):776-81
references: 10693807
references: Immunity. 2003 Apr;18(4):535-47
references: 12705856
references: Biochem Soc Trans. 2003 Dec;31(Pt 6):1191-7
references: 14641024
references: Nat Genet. 2004 Jan;36(1):77-82
references: 14647275
references: Oncogene. 2004 Feb 26;23(8):1566-74
references: 14676841
references: Nature. 1970 Aug 15;227(5259):680-5
references: 5432063
references: J Biol Chem. 1975 Jun 10;250(11):4297-304
references: 1126952
references: J Biol Chem. 2007 Mar 2;282(9):6201-9
references: 17202145
references: Proc Natl Acad Sci U S A. 1978 Oct;75(10):5025-9
references: 311005
references: J Biol Chem. 2001 Mar 16;276(11):7811-9
references: 11113132