Cell adhesion to fibronectin induces mitomycin C resistance in bladder cancer cells.

OBJECTIVE

To investigate whether cell adhesion to fibronectin induces drug resistance in human bladder cancer cells, and to study the survival signalling pathway in cell adhesion to fibronectin-mediated chemotherapy resistance in vitro.

MATERIALS AND METHODS

T24 cells (human bladder cancer cell lines) were pre-coated with fibronectin, and treated with mitomycin C (MMC) and the specific phosphoinositide-3 kinase (PI3-K) inhibitor LY294002. The apoptosis and cell cycles were analysed. The activity of the caspase-8, -9 and apoptosis-inducing factor (AIF) apoptosis pathways were assessed using colorimetric assay, immunofluorescence, Western blot and flow cytometry. The expression of glycogen synthase kinase-3beta (GSK-3beta) and cyclin D1, as the key regulator of G1/S phase transition, were determined by Western blot. The expression of PI3-K, Akt, phospho-Akt and beta1-integrin were also examined by Western blot.

RESULTS

Apoptosis induced by MMC was significantly resisted by fibronectin adhesion in T24 cells, and this effect was through inhibition of the caspase-9 and AIF apoptosis pathways, but not the caspase-8 pathway. Fibronectin antagonized MMC-induced G0/G1-phase arrest by inactivating GSK-3beta to stabilize cyclin D1 expression in T24 cells. Furthermore, fibronectin-mediated protection of T24 cells was dependent on the activity of the PI3-K/Akt signalling pathway, and the protection could be abolished by the PI3-K inhibitor LY294002.

CONCLUSIONS

Fibronectin-mediated PI3-K/Akt activation protects T24 cells from MMC-induced cell death through inhibition of both caspase-9 and AIF-mediated apoptosis and GSK-3beta/cyclin D1 involved G0/G1-phase arrest.