PARTIAL RESTORATION OF THE ACTIN CYTOSKELETON IN TRANSFORMED SYRIAN-HAMSTER FIBROBLASTS SELECTED FOR LOW-LEVELS OF TYPICAL MULTIDRUG-RESISTANCE

Two independent colchicine (CLC)-resistant sublines of Rous sarcoma vi rus-transformed Syrian hamster fibroblasts were isolated. Each subline represented variants with 11- and 12.4-fold resistance, respectively, their 23- and 23.7-fold resistant descendants, as well as variants cu ltured in CLC-free medium for 10 months without loss of resistance. Al l variants demonstrated 'typical' multidrug resistance. The parental c ells contained actin in dispersed form, as determined by rhodamine-pha lloidin staining. In contrast, already in 11- and 12.4-fold resistant sublines up to 30% of cells demonstrated restored stress fibers. Culti vation in CLC-free medium leads to the accumulation of cells with a pa rtially restored actin cytoskeleton. Putative mechanisms of up-regulat ion of stress fiber assembly in cells with P-glycoprotein-mediated mul tidrug resistance are discussed.