Figure 4. Mechanical induction ofβ-catenin tyrosine 654 phosphorylation in APC deficient colon is impaired by Src-family kinase inhibition.

Src is activated (Y418 phosphorylated) in restricted areas of uncompressed preneoplastic APC^1638N∕+ distal colon, and similarly when compressed for 40 min. pY418 Src expression is lost when compressed in the presence of PP1 (n=3), PP2 (n=3) or SU6656 (n=9) Src-family kinase inhibitors. pY654 β-catenin is absent in uncompressed APC deficient colon but can be mechanically induced to accumulate in the apical cytoplasm (green arrows; mesenchymal staining with the β-catenin antibody was variable but uncorrelated with epithelial cell staining or inhibitor treatment). Treatment with PP1 or PP2 blocks mechanical induction of Y654 phosphorylation, but treatment with SU6656 does not. Merged images of pY654 β-catenin (red) and DAPI nuclear counterstain (blue) are shown magnified below. Untreated tissues shown here have been compressed in the presence of an equivalent volume of DMSO (n=2), which is used as a vehicle for the kinase inhibitors, in order to control for possible side effects. The same result is obtained without DMSO (not shown).