Fig. 8.

MTX protects cells from DHFR degradation by NADPS. DHFR protein levels were determined by Western blotting in DG44-(DHFR-EGFP) cells. (A and B) DG44 DHFR-EGFP cells or DG44 DHFRS118AEGFP cells were treated with 10 nM MTX alone, 10 μM NADPS alone, and the simultaneously addition of 10 nM MTX and 10 μM NAPDS for 24 and 48 hours. DHFR-EGFP and DHFRS118AEGFP protein were detected by a monoclonal anti-EGFP antibody. GAPDH was used as a loading control. Quantification of DHFR levels (shown at the bottom of gels) was measured by the Image J program (provided by NIH).