Rearrangement of the F-actin cytoskeleton in estradiol-treated MCF-7 breast carcinoma cells.

In response to treatment with 17beta-estradiol, MCF-7 human breast carcinoma cells undergo a marked rearrangement of the F-actin cytoskeleton. The most conspicuous aspect of this rearrangement is the formation of an extensive array of lamellipodial structures which are situated beneath cell clusters. Treatment of cells with 17beta-estradiol in the presence of the anti-estrogen ICI182,780 suppressed the development of the lamellipodial structures, indicating that this cytoskeletal rearrangement is mediated by the estrogen receptor. Time-lapse, video-enhanced, differential interference contrast microscopy reveals that the lamellipodial structures are actively motile beneath cell clusters. Furthermore, the lamellipodial structures form few focal contacts with the underlying substrate of the coverslip, as evidenced by either interference reflection microscopy or staining for the focal contact protein talin, indicating that these structures are not strongly adhered to the substratum. Immunofluorescence localization of E-cadherin indicates that this cell-cell adhesion receptor is present within these structures as either adhesion plaque- or point contact-like depositions. These findings implicate the cadherin-based cell-cell adhesion system in supporting tumor cell motility over adjacent cell surfaces via discrete adhesive structures which are associated with motile lamellipodia.