Fig. 5. ERK, JNK/SAPK and PI-3-K, but not p38, are required for ET-1-induced mesangial cell hypertrophy. PP2B is also required for optimal ET-1-induced hypertrophy. (A) Mesangial cells were pre- treated with the indicated inhibitor compounds for 30 min, at which time vehicle or ET-1 was added and the incubation continued for an additional 48 h. Hypertrophy was measured as in Materials and methods. (B) Efficacy of the indicated inhibitors. A portion of the cells in (A) was lysed and the lysates subjected to analysis with phospho-specific antibodies. (C) FK506 blocks mesangial cell hypertrophy. Mesangial cells were pre-treated with 100 nM FK506 and treated with ET-1 as in (A). ET-1 triggers a significant increase in leucine incorporation (indicated by *, as determined by t-test; P < 0.05, n = 3); however, FK506 pre-treatment reduces leucine incorporation to insignificant levels (indicated by **, as determined by t-test; P > 0.05, n = 3).