Specific oncogenic activity of the Src-family tyrosine kinase c-Yes in colon carcinoma cells.

c-Yes, a member of the Src tyrosine kinase family, is found highly activated in colon carcinoma but its importance relative to c-Src has remained unclear. Here we show that, in HT29 colon carcinoma cells, silencing of c-Yes, but not of c-Src, selectively leads to an increase of cell clustering associated with a localisation of ß-catenin at cell membranes and a reduction of expression of ß-catenin target genes. c-Yes silencing induced an increase in apoptosis, inhibition of growth in soft-agar and in mouse xenografts, inhibition of cell migration and loss of the capacity to generate liver metastases in mice. Re-introduction of c-Yes, but not c -Src, restores transforming properties of c-Yes depleted cells. Moreover, we found that c-Yes kinase activity is required for its role in ß-catenin localisation and growth in soft agar, whereas kinase activity is dispensable for its role in cell migration. We conclude that c-Yes regulates specific oncogenic signalling pathways important for colon cancer progression that is not shared with c-Src.

A novel non-phosphorylated potential antitumoral peptide inhibits STAT3 biological activity.

STAT3 (Signal Transducer and Activator of Transcription 3) is an SH2 (Src Homology 2)-domain containing transcription factor that plays a key role in cancer, by regulating as a dimer the expression of genes implicated in the main processes of the tumorigenesis. Therefore, STAT3 and more particularly its dimeric form has emerged as promising targets for cancer therapy. STAT3 dimerization occurs through reciprocal interaction between the SH2 domain of one monomer and the phosphorylated tyrosine residue of a second one. One strategy to design small inhibitors of STAT3 dimerization, consists in using phosphotyrosine-based peptidomimetics targeted to the SH2 domain. We have tested whether a high affinity phosphotyrosyl peptide ligand P1 (AYRNRY( *)RRQYRY) (K(d) = 0.34 microM), issued from combinatorial chemistry, could inhibit STAT3 dimerization and biological activity. This ligand was found to disrupt dimerization with an IC(50) of 9 microM. Further biological evaluation using a STAT3-dependent cell line demonstrated that its Antennapedia-vectorized form P1a interacted with STAT3 within the cell, resulting in a significant effect on cell proliferation and expression of cell cycle and apoptosis regulators controlled by STAT3. More importantly, these studies identified unexpectedly a non-phosphorylated vectorized peptide P2a, as another potent inhibitor of STAT3 biological activity and thus give further insight for the development of novel inhibitors.