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 virus-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 cultured in CLC-free medium for 10 months without loss of resistance. All variants demonstrated 'typical' multidrug resistance. The parental cells contained actin in dispersed form, as determined by rhodamine-phalloidin staining. In contrast, already in 11- and 12.4-fold resistant sublines up to 30% of cells demonstrated restored stress fibers. Cultivation in CLC-free medium leads to the accumulation of cells with a partially restored actin cytoskeleton. Putative mechanisms of up-regulation of stress fiber assembly in cells with P-glycoprotein-mediated multidrug resistance are discussed.