Swiss 3T3 fibroblasts were treated with the microtubule-disrupting age
nt colchicine to study any interaction between microtubule dynamics an
d actin polymerization. Colchicine increased the amount of filamentous
actin (F-actin), in a dose- and time-dependent manner with a signific
ant increase at 1 h by about 130% over control level. Confocal microsc
opic observation showed that colchicine increased F-actin contents by
stress fiber formation without inducing membrane ruffling. Colchicine
did not activate phospholipase C and phospholipase D, whereas lysophos
phatidic acid did, indicating that colchicine may have a different mec
hanism of actin polymerization regulation from LPA. A variety of micro
tubule-disrupting agents stimulated actin polymerization in Swiss 3T3
and Rat-2 fibroblasts as did colchicine, but the microtubule-stabilizi
ng agent taxol inhibited actin polymerization induced by the above mic
rotubule-disrupting agents. In addition, colchicine-induced actin poly
merization was blocked by two protein phosphatase inhibitors, okadaic
acid and calyculin A. These results suggest that microtubule depolymer
ization activates stress fiber formation by serine/threonine dephospho
rylation in fibroblasts.