Figure 10.

Half-lives of occludin and ZO-1 in Ras-transformed MDCK cells with or without treatment with 50 μM PD98059 for 20 h. Cells were metabolically labeled for 18 h with 250 μCi of [³⁵S]methionine per plate and then chased with unlabeled methionine for 0, 6, 12, and 24 h. At the end of the chase, cell lysates were immunoprecipitated with anti-occludin (A) or anti-ZO-1 (C) antibodies. The data in A and C are quantitated by densitometry in B and D, respectively. The half-life (T_1/2) was 11.2 h for occludin without PD98059 treatment (Ras) and 24.1 h for occludin with PD98059 treatment (Ras+PD), whereas the half-life was 5.1 h for ZO-1 without PD98059 treatment (Ras) and 7.7 h for ZO-1 with PD98059 treatment (Ras+PD). These experiments were repeated three times. From all three experiments, the average half-life (±SE) for occludin was 10.5 ± 0.7 h (Ras) and 27 ± 2.9 h (Ras+PD), and the average half-life for ZO-1 was 5.6 ± 0.8 h (Ras) and 8.0 ± 1.4 h (Ras+PD).