Secreted Heat Shock Protein 90α (HSP90α) Induces Nuclear Factor-κB-mediated TCF12 Protein Expression to Down-regulate E-cadherin and to Enhance Colorectal Cancer Cell Migration and Invasion

Secreted levels of HSP90 alpha and overexpression of TCF12 have been associated with the enhancement of colorectal cancer (CRC) cell migration and invasion. In this study, we observed that CRC patients with tumor TCF12 overexpression exhibited both a higher rate of metastatic occurrence and a higher average serum HSP90 alpha level compared with patients without TCF12 overexpression. Therefore, we studied the relationship between the actions of secreted HSP90 alpha and TCF12. Like overexpressed TCF12, secreted HSP90 alpha or recombinant HSP90 alpha (rHSP90 alpha) induced fibronectin expression and repressed E-cadherin, connexin-26, connexin-43, and gap junction levels in CRC cells. Consistently, rHSP90 alpha stimulated invasive outgrowths of CRC cells from spherical structures during three-dimensional culture. rHSP90 alpha also induced TCF12 expression in CRC cells. Its effects on CRC cell epithelial-mesenchymal transition, migration, and invasion were drastically prevented when TCF12 was knocked down. This suggests that TCF12 expression is required for secreted HSP90 alpha to enhance CRC cell spreading. Through the cellular receptor CD91, rHSP90 alpha facilitated the complex formation of CD91 with I kappa B kinases (IKKs) alpha and beta and increased the levels of phosphorylated (active) IKK alpha/beta and NF-kappa B. Use of an IKK alpha/beta inhibitor or ectopic overexpression of dominant-negative I kappa B alpha efficiently repressed rHSP90 alpha-induced TCF12 expression. Moreover, kappa B motifs were recognized in the gene sequence of the TCF12 promoter, and a physical association between NF-kappa B and the TCF12 promoter was detected in rHSP90 alpha-treated CRC cells. Together, these results suggest that the CD91/IKK/NF-kappa B signaling cascade is involved in secreted HSP90 alpha-induced TCF12 expression, leading to E-cadherin down-regulation and enhanced CRC cell migration/invasion.