Influence of phosphotyrosine kinase inhibitors on adhesive properties of highly and poorly metastatic HT-29 colon carcinoma cells to collagen

Organ-specific sites of metastastic lesions are determined in part by integrin-mediated adhesion to extracellular matrix (ECM) components. Using poorly (HT-29P) and highly liver-metastatic (HT-29LMM) colon carcinoma cells we previously found different integrin-mediated adhesion to various ECM components, but similar inte-grin expression of both cell lines. These HT-29 cell lines were used to study adhesion to collagen I (C I) and possible intracellular signaling mechanisms that could explain different adhesive properties. HT-29LMM cells had significantly poorer rates of adhesion to C I (P<0.05) than HT-29P cells. For examination of the integrin subunits involved in adhesion to C I, cells were treated with various anti-integrin antibodies. These results demonstrated that adhesion of HT-29 cells to C I is mediated in part by the α2β1 integrin. Using immunoprecipitation and Western blotting, both cell lines expressed similar patterns of integrins (α2, α3, α6, and β1). Weaker signals were found for the expression of αv and β5 integrins. Although poorly and highly metastatic cells possessed different patterns of adhesion to C I, these differences were not caused by different expression of integrin subunits. For investigation of the involvement of phosphotyrosine kinases in adhesion, cells were pretreated with the Erbstatin analog, Genistein, or Herbimycin A. Genistein transiently stimulated the adhesive properties of both cell lines. In contrast, Herbimycin A had biphasic effects. At lower concentrations of Herbimycin A stimulation of adhesion was found after 30 and 90 min. However, higher concentrations inhibited adhesive properties. The stimulatory effect was more pronounced in poorly metastatic HT-29P cells. The Erbstatin analog had no effect, probably because of the lack of epidermal growth factor receptor expression in both cell lines. The results suggest that adhesion of tumor cells to ECM components may be dependent on signal transduction into the cell, and tyrosine phosphorylation appears to be involved.