Premium
An acidic extracellular pH disrupts adherens junctions in HepG2 cells by Src kinases‐dependent modification of E‐cadherin
Author(s) -
Chen Ying,
Chen ChiaHuei,
Tung PoYuan,
Huang ShihHorng,
Wang SeuMei
Publication year - 2009
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.22313
Subject(s) - adherens junction , cadherin , proto oncogene tyrosine protein kinase src , microbiology and biotechnology , phosphorylation , tyrosine phosphorylation , fyn , tyrosine protein kinase csk , chemistry , tyrosine , tyrosine kinase , kinase , biology , biochemistry , signal transduction , sh3 domain , cell
We have previously shown that culturing HepG2 cells in pH 6.6 culture medium increases the c‐Src‐dependent tyrosine phosphorylation of β‐catenin and induces disassembly of adherens junctions (AJs). Here, we investigated the upstream mechanism leading to this pH 6.6‐induced modification of E‐cadherin. In control cells cultured at pH 7.4, E‐cadherin staining was linear and continuous at cell–cell contact sites. Culturing cells at pH 6.6 was not cytotoxic, and resulted in weak and discontinuous junctional E‐cadherin staining, consistent with the decreased levels of E‐cadherin in membrane fractions. pH 6.6 treatment activated c‐Src and Fyn kinase and induced tyrosine phosphorylation of p120 catenin (p120ctn) and E‐cadherin. Inhibition of Src family kinases by PP2 attenuated the pH 6.6‐induced tyrosine phosphorylation of E‐cadherin and p120ctn, and prevented the loss of these proteins from AJs. In addition, E‐cadherin was bound to Hakai and ubiquitinated. Furthermore, pH 6.6‐induced detachment of E‐cadherin from AJs was blocked by pretreatment with MG132 or NH 4 Cl, indicating the involvement of ubiquitin‐proteasomal/lysosomal degradation of E‐cadherin. An early loss of p120ctn prior to E‐cadherin detachment from AJs was noted, concomitant with a decreased association between p120ctn and E‐cadherin at pH 6.6. PP2 pretreatment prevented the dissociation of these two proteins. In conclusion, pH 6.6 activated Src kinases, resulting in tyrosine phosphorylation of E‐cadherin and p120ctn and a weakening of the association of E‐cadherin with p120ctn and contributing to the instability of E‐cadherin at AJs. J. Cell. Biochem. 108: 851–859, 2009. © 2009 Wiley‐Liss, Inc.