Adhesion of U937 cells to FN decreased topo II activity and nuclear topo IIβ protein levels.

(A) Nuclear extracts were obtained, and 1 μg nuclear extract from cells in suspension and FN-adhered cells were incubated with 0.4 μg tritium-kDNA for the times indicated. The amount of cleaved kDNA was reduced by approximately 20% to 30% in FN-adhered cells compared with cells grown in suspension (results were identical for 2 independent experiments, and the figure represents results from one experiment). (B) Western blot analysis of 1.0-M NaCl nuclear extracts showed a 66% reduction (mean value from 3 independent experiments) in nuclear topo IIβ protein levels when cells were adhered to FN. (C) Topo IIα protein levels were unchanged when cells were adhered to FN. (D) Topo I levels were unchanged when cells were adhered to FN.