alpha V integrins on HT-29 colon carcinoma cells: Adhesion to fibronectin is mediated solely by small amounts of alpha V beta 6, and alpha V beta 5 is codistributed with actin fibers

HT-29 colon carcinoma cells form liver metastases upon intrasplenic injection, and adhesion to fibronectin under the liver microvascular liver endothelium is likely to be important for metastasis formation. We have therefore studied the integrins involved in fibronectin adhesion, This was not affected by blocking antibodies against the beta 1, alpha 3, and alpha 5 integrin subunits, but it was blocked by an BOB-containing peptide, indicating involvement of BOB-dependent non-beta 1 alpha V integrins. Both alpha V beta 5 and alpha V beta 6 were detected on HT-29 cells, Blocking mAb against alpha V, but not against alpha V beta 5, abolished adhesion. From a HT-29 cell lysate, only alpha V beta 6 bound to a fibronectin-Sepharose column. Thus, alpha V beta 6 is the main fibronectin receptor on HT-29 cells, despite the very low levels of alpha V beta 6 and the much higher levels of alpha V beta 5. The HT29 cells did not spread on fibronectin in the absence of serum, not even after a three- to fourfold increase in alpha V beta 6 levels, induced by interleukin 4. The cells did spread on vitronectin. Using immunofluorescence we observed that both on vitronectin and on fibronectin alpha V beta 5 was arranged in a striped pattern, aligned with actin fibers, and not in focal adhesions, On fibronectin, but not on vitronectin, alpha V beta 6 was concentrated in a punctate pattern at the periphery of cell islands. (C) 1997 Academic Press.