Fig. 10. MDCK P2₁R (MDCK/P2₁R) cells display increased expression levels of the endogenous EGFR. (A) Ectopic expression of P2Y₁R increases EGFR levels. Immunoblots of total cell extracts, densitometrically quantified in four independent experiments and normalized with respect to actin show a threefold increased level of EGFR in MDCK P2Y1R cells. (B) Ectopic expression of P2Y₁R increases EGFR biosynthesis. Newly synthesized EGFR was immunoprecipitated from cells metabolically labeled for 2 hours with [³⁵S]Met/Cys (200 µCi/ml). Graph shows twofold increase in synthesis in MDCK P2Y1R cells (n=3). For A and B, values are the means ± s.e.m. ^***P<0.001; paired t-test compared with wild-type cells. (C) Increased EGFR expression in MDCK P2Y1R cells depends on EGFR and PKC activity. Cells were treated with either 100 nM AG1478 or 10 nM Ro318220 for 6-18 hours before and during the metabolic labeling. Graph show the densitometric quantification of three independent experiments. Values are the means ± s.e.m. ^*P<0.05, ^**P<0.01; Dunnett's test compared with untreated cells.