UC Davis

Activation of EGF receptor (EGFR) triggers signaling pathways regulating various cellular events that contribute to tissue development and function. Aberrant activation of EGFR contributes to tumor progression as well as therapeutic resistance in patients with cancer. C-terminal tensin-like (CTEN; TNS4) is a focal adhesion molecule that is a member of the tensin family. Its expression is upregulated by EGF and elevated CTEN mediates EGF-induced cell migration. In the presence of CTEN, we found that EGF treatment elevated the level of EGFR protein but not mRNA. The extended half-life of activated EGFR sustained its signaling cascades. CTEN reduced ligand-induced EGFR degradation by binding to the E3 ubiquitin ligase c-Cbl and decreasing the ubiquitination of EGFR. The Src homology 2 domain of CTEN is not only required for binding to the phosphorylated tyrosine residue at codon 774 of c-Cbl, but is also essential for the tumorigenicity observed in the presence of CTEN. Public database analyses indicated that CTEN mRNA levels are elevated in breast, colon, lung, and pancreas cancers, but not correlated with EGFR mRNA levels in these cancers. In contrast, immunohistochemistry analyses of lung cancer specimens showed that CTEN and EGFR protein levels were positively associated, in support of our finding that CTEN regulates EGFR protein levels through a posttranslational mechanism. Overall, this work defines a function for CTEN in prolonging signaling from EGFR by reducing its ligand-induced degradation.