Correlation of anionic residue mobility at the filopodial plasma membranes with multilayer formation in transformed 3T3 cells.

Simian virus 40-transformed 3T3 (SV40-3T3) cells formed multilayers on a Falcon dish and had numerous filopodial projections, some of which intertwined with those of adjacent cells, in contrast to the few projections of their nontransformed counterparts. When these cells were incubated with polycationic ferritin (0.5 mg/ml), ferritin particles, representative of anionic sites, were spread widely on their surfaces at 4 degrees C, while they formed clusters at 37 degrees C, especially on filopodial surface areas opposing adjacent projections in SV40-3T3 cells. These findings demonstrate an increase in the mobility of molecules with anionic residues on filopodial plasma membranes in SV40-3T3 cells, thus suggesting a role for these projections in the formation of multilayered cell aggregates.