PTP1BΔ6 protects L-428 cells against cytotoxic agents. (A) Proliferation of the different stable L-428 cell clones treated with the indicated concentrations of gemcitabine for 24 hours, determined by MTS assay. (B) Proliferation of the different stable L-428 cell clones treated with the indicated concentrations of etoposide for 24 hours determined by MTS assay. Proliferation of solvent-treated L-428 cell clones was set to 1 arbitrarily. Depicted is the relative proliferation of the gemcitabine-treated cells. All treatments were performed in triplicates. Mean values and SEM are depicted. Significances are calculated in comparison with the empty vector values. *P ≤ .05; **P ≤ .01; ***P ≤ .001.