Figure 2.

Shedding accelerated by PMA and stress but not by receptor activation depends on protein kinase C activity. NMuMG cells were incubated (A and B) for 30 min with PMA or 4αPDD (0.5 μM). NMuMG cells were incubated (C and D) for 2 h with or without the following: 700 mOsm NaCl, or (E and F) 100 μM ceramide, or (G and H) 10 ng/ml EGF, or 100 μM TRAP. Each agonist was assayed in the absence or presence of bisindolylmaleimide I (Bis., 1 μM). Conditioned media were assayed for syndecan-1 (A, C, E, and G) and syndecan-4 (B, D, F, and H) ectodomains by dot blot analysis as in Fig. 1. Quantitation was done as in Fig. 1, and each point represents the mean ± SD (n = 3). For each shedding agonist assayed, incubation with inhibitor alone had no effect on the level of shedding compared with the untreated control.