HuR regulates gap junctional intercellular communication by controlling beta-catenin levels and adherens junction integrity.
Gap junctional intercellular communication (GJIC) plays a critical role in the regulation of tissue homeostasis and carcinogenesis and is modulated by the levels, subcellular localization, and posttranslational modification of gap junction proteins, the connexins (Cx). Here, using oval cell-like rat liver epithelial cells, we demonstrate that the RNA-binding protein HuR promotes GJIC through two mechanisms. First, HuR silencing lowered the levels of Cx43 protein and Cx43 messenger RNA (mRNA), and decreased Cx43 mRNA half-life. This regulation was likely due to the direct stabilization of Cx43 mRNA by HuR, because HuR associated directly with Cx43 mRNA, a transcript that bears signature adenylate-uridylate-rich (AU-rich) and uridylate-rich (U-rich) sequences in its 3'-untranslated region. Second, HuR silencing reduced both half-life and the levels of beta-catenin mRNA, also a target of HuR; accordingly, HuR silencing lowered the levels of whole-cell and membrane-associated beta-catenin. Coimmunoprecipitation experiments showed a direct interaction between beta-catenin and Cx43. Small interfering RNA (siRNA)-mediated depletion of beta-catenin recapitulated the effects of decreasing HuR levels: it attenuated GJIC, decreased Cx43 levels, and redistributed Cx43 to the cytoplasm, suggesting that depletion of beta-catenin in HuR-silenced cells contributed to lowering Cx43 levels at the membrane. Finally, HuR was demonstrated to support GJIC after exposure to a genotoxic agent, doxorubicin, or an inducer of differentiation processes, retinoic acid, thus pointing to a crucial role of HuR in the cellular response to stress and in physiological processes modulated by GJIC.


CONCLUSIONS
HuR promotes gap junctional intercellular communication in rat liver epithelial cells through two related regulatory processes, by enhancing the expression of Cx43 and by increasing the expression of beta-catenin, which, in turn, interacts with Cx43 and is required for proper positioning of Cx43 at the plasma membrane.
Ale-Agha
Niloofar
N
Institut für umweltmedizinische Forschung (IUF) an der Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany.
Galban
Stefanie
S
Sobieroy
Christiane
C
Abdelmohsen
Kotb
K
Gorospe
Myriam
M
Sies
Helmut
H
Klotz
Lars-Oliver
LO
D022005:Adherens Junctions / Q000378:metabolism*; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism*; D000970:Antineoplastic Agents; D002450:Cell Communication / Q000502:physiology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D023421:Models, Animal; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D014212:Tretinoin / Q000494:pharmacology; D051176:beta Catenin / Q000378:metabolism*
D000954:Antigens, Surface; D000970:Antineoplastic Agents; D018031:Connexin 43; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D051176:beta Catenin; D014212:Tretinoin; D004317:Doxorubicin
EMBO J. 2004 Aug 4;23(15):3092-102
15257295
Genes Dev. 2008 Jul 1;22(13):1804-15
18593881
Antioxid Redox Signal. 2009 Feb;11(2):297-307
18834329
Front Biosci. 1998 Feb 15;3:d208-36
9458335
Mol Cell. 2007 Feb 23;25(4):543-57
17317627
Biochem Biophys Res Commun. 2005 Feb 25;327(4):1016-23
15652497
Mol Cell Biol. 1995 Apr;15(4):2219-30
7891716
Carcinogenesis. 1992 Feb;13(2):199-203
1310904
Oncogene. 2003 Oct 16;22(46):7146-54
14562043
Biochem Biophys Res Commun. 2007 Dec 14;364(2):313-7
17945186
Mol Cell Biol. 2000 Feb;20(3):760-9
10629032
Mol Carcinog. 1994 Aug;10(4):226-36
8068183
Blood Cells Mol Dis. 2001 May-Jun;27(3):590-600
11482872
Methods Enzymol. 2004;378:258-72
15038974
Science. 2008 Dec 5;322(5907):1490-4
19056973
Arch Biochem Biophys. 2000 Dec 15;384(2):205-15
11368307
Mol Biol Cell. 1992 Aug;3(8):865-74
1327298
Am J Pathol. 1997 Aug;151(2):353-9
9250149
FEBS Lett. 1997 Dec 15;419(2-3):268-70
9428648
Mol Cell Biol. 2007 Aug;27(15):5365-80
17548472
Biochem Pharmacol. 1999 Apr 1;57(7):727-41
10075079
Biol Chem. 2005 Mar;386(3):217-23
15843167
Biol Chem. 2008 Mar;389(3):243-55
18177264
Carcinogenesis. 1997 Jan;18(1):37-42
9054587
Cell Mol Life Sci. 2001 Feb;58(2):266-77
11289308
Hepatology. 2002 Sep;36(3):631-40
12198655
Cell. 2007 Feb 9;128(3):547-60
17289573
Biochim Biophys Acta. 2005 Dec 20;1719(1-2):6-23
16359940
Biochem Biophys Res Commun. 2007 Jan 12;352(2):410-7
17118341
J Clin Invest. 2000 Jan;105(2):161-71
10642594
Cancer Res. 2002 Sep 1;62(17):4922-8
12208742
Biochem J. 2006 Mar 15;394(Pt 3):527-43
16492141
J Cell Biol. 1991 Aug;114(3):545-55
1650371
Mol Cell Biol. 1994 Dec;14(12):7984-95
7969138
Cell Signal. 2008 Dec;20(12):2165-73
18585896
Biol Chem. 2002 May;383(5):725-37
12108537
Exp Cell Res. 1984 Sep;154(1):38-52
6468534
J Biol Chem. 2005 May 20;280(20):19925-36
15741167
Am J Pathol. 1993 May;142(5):1373-82
8494041
RNA Biol. 2005 Jan;2(1):11-3
17132932
Cell Mol Life Sci. 2008 Oct;65(20):3168-81
18581050
Cell Mol Life Sci. 2002 Oct;59(10):1758-65
12475186
Hepatology. 2008 Jan;47(1):288-95
17929301
Gastroenterology. 2005 Feb;128(2):433-48
15685554
Cell Adhes Commun. 1996 Nov;4(4-5):223-35
9117343