Expression of chimeric integrins alters cell-cell interactions and capacity for FNMA. Phase contrast and immunofluorescence images of MLL, MLL-X5C2, and MLL-X5C5 cells show that, whereas untransfected MLL cells tend to form loose colonies with very low capacity for FNMA, MLL-X5C2 cells form tighter colonies and acquire a limited capacity for matrix assembly. In contrast, MLL-X5C5 cells tend to aggregate into spheroids that lift off the surface of the culture dish. These cells also appear to assemble a rich fibronectin matrix. DAPI staining was used to demonstrate equal cell density (A). Biochemical analysis of FNMA by chimeric integrin-expressing cells. The assembly of high molecular weight fibronectin multimers (HMWFM) by MLL, MLL-X5C2, and MLL-X5C5 cells was assessed using DOC differential solubilization assay. DOC-soluble and insoluble fractions were separated by SDS-PAGE and analyzed by immunoblotting using an anti-fibronectin antibody. Actin in the soluble fraction was used as a loading control. The presence of HMWFM is highest in MLL-X5C5 cells (B).