A 135,000 molecular weight plasma membrane glycoprotein involved in fibronectin-mediated cell adhesion. Immunofluorescence localization in normal and RSV-transformed fibroblasts

Abstract

Monospecific antibodies to GP135, a plasma membrane glycoprotein involved in cell attachment and spreading on fibronectin-coated substratum (Giancotti et al., Exp cell res 156 (1985) 182), were affinity-purified from a broad-spectrum antiserum using the GP135 molecule immobilized on nitrocellulose filters. The purified antibodies specifically inhibited attachment and spreading of normal as well as RSV-transformed fibroblasts on fibronectin-coated dishes indicating that GP135 is involved in adhesion of both normal and transformed cells. Immunofluorescence experiments showed that GP135 has a discrete distribution on control 3T3 fibroblasts. On cells in the process of spreading GP135 was concentrated in 'close contact' sites, while on fully spread cells the glycoprotein was concentrated in 'adhesion plaques' and in streaks co-aligning with portions of stress fibres. In RSV-transformed cells the discrete distribution of GP135 was lost. The protein appeared in a diffuse distribution at the plasma membrane and was not concentrated in the dot- or rosette-shaped substratum contacts sites peculiar to these cells. It is concluded that GP135 mediates adhesion of both normal and RSV-transformed fibroblasts to fibronectin. While in normal cells this glycoprotein participates in the organization of specialized adhesion structures, in RSV-transformed fibroblasts recruiting of GP135 molecules within cell-substratum contact sites is perturbed.