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Claudin-4 controls the receptor tyrosine kinase EphA2 pro-oncogenic switch through β-catenin

  • Author(s): Shang, X
  • Lin, X
  • Howell, SB
  • et al.
Abstract

©2014 Shang et al.; licensee BioMed Central Ltd. Background: The EphA2 receptor, which is expressed in many types of cancer, is activated by two different mechanisms. Activation by engagement with one of its ephrin ligands is anti-oncogenic whereas phosphorylation of S897 by AKT increases migration, invasion and metastasis. Down-regulation of claudin-4 (CLDN4) produces a loss of E-cadherin and increased β-catenin signaling and a phenotype similar to that produced by oncogenic activation of EphA2, suggesting that CLDN4 may serve to restrain the pro-oncogenic signaling of EphA2. Results: We found that constitutive knockdown of CLDN4 was associated with a 4.5-fold increase in EphA2 mRNA and a 2.5-fold increase in EphA2 protein which was reversible by re-expression of CLDN4. Knockdown of EphA2 blocked the migratory phenotype induced by loss of CLDN4. Knockdown of CLDN4 resulted in a 5.8-fold increase in pEphA(S897), the oncogenic form of the receptor, as well as partial mislocalization of the excess EphA2 to the interior of the cell. Forced expression of E-cadherin did not reduce total EphA2 or pEphA(S897) whereas re-expression of CLDN4 restored localization and reduced EphA2 and pEphA(S897) even in cells not expressing E-cadherin. Transient siRNA-mediated knockdown of EphA2 and β-catenin, and inhibition of PI3K by LY294002, demonstrated that increased pEphA(S897) in the CLDN4 knockdown cells was attributable to an increase in the level of active dephospho-β-catenin upstream of PI3K and AKT. Conclusions: We conclude that CLDN4 serves to restrain pro-oncogenic signaling from EphA2 by limiting the activity of β-catenin and PI3K and preventing phosphorylation of EphA2 on S897 by AKT. This suggests that interventions directed at enhancing the level or functional activity of CLDN4may be of therapeutic interest.

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