SKI-606 decreases growth and motility of colorectal cancer cells by preventing pp60(c-Src)-dependent tyrosine phosphorylation of beta-catenin and its nuclear signaling.
Inhibition of deregulated protein tyrosine kinases represents an attractive strategy for controlling cancer growth. However, target specificity is an essential aim of this strategy. In this report, pp60(c-Src) kinase and beta-catenin were found physically associated and constitutively activated on tyrosine residues in human colorectal cancer cells. The use of specific small-interfering RNAs (siRNA) validated pp60(c-Src) as the major kinase responsible for beta-catenin tyrosine phosphorylation in colorectal cancer. Src-dependent activation of beta-catenin was prevented by SKI-606, a novel Src family kinase inhibitor, which also abrogated beta-catenin nuclear function by impairing its binding to the TCF4 transcription factor and its trans-activating ability in colorectal cancer cells. These effects were seemingly specific, as cyclin D1, a crucial beta-catenin/TCF4 target gene, was also down-regulated by SKI-606 in a dose-dependent manner accounting, at least in part, for the reduced growth (IC50, 1.5-2.4 micromol/L) and clonogenic potential of colorectal cancer cells. Protein levels of beta-catenin remained substantially unchanged by SKI-606, which promoted instead a cytosolic/membranous retention of beta-catenin as judged by immunoblotting analysis of cytosolic/nuclear extracts and cell immunofluorescence staining. The SKI-606-mediated relocalization of beta-catenin increased its binding affinity to E-cadherin and adhesion of colorectal cancer cells, with ensuing reduced motility in a wound healing assay. Interestingly, the siRNA-driven knockdown of beta-catenin removed the effect of SKI-606 on cell-to-cell adhesion, which was associated with prolonged stability of E-cadherin protein in a pulse-chase experiment. Thus, our results show that SKI-606 operates a switch between the transcriptional and adhesive function of beta-catenin by inhibiting its pp60(c-Src)-dependent tyrosine phosphorylation; this could constitute a new therapeutic target in colorectal cancer.
Department of Experimental Oncology, National Cancer Institute, Milan, Italy.
Addolorata Maria Luce
AM
Coluccia
Daniela
D
Benati
Hafedh
H
Dekhil
Annamaria
A
De Filippo
Cathy
C
Lan
Carlo
C
Gambacorti-Passerini
D000814:Aniline Compounds / Q000494:pharmacology*; D015820:Cadherins / Q000378:metabolism; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007365:Intercellular Junctions / Q000187:drug effects; D009570:Nitriles / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011804:Quinolines / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D051820:TCF Transcription Factors / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D015533:Transcriptional Activation / Q000187:drug effects; D014443:Tyrosine / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism*
D000814:Aniline Compounds; D015820:Cadherins; D009570:Nitriles; D011804:Quinolines; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D058118:Transcription Factor 7-Like 2 Protein; D051176:beta Catenin; D014443:Tyrosine; C471992:bosutinib; D016392:Proto-Oncogene Proteins pp60(c-src)