Effect of oncogenic ras expression on p70S6 kinase in myeloma cells.

Expression of oncogenic ras results in constitutive phosphorylation of p70S6 kinase in myeloma cells. (A) Control (C; empty vector–transfected), mutant N-ras (N), or K-ras (K) cells depleted of IL-6 for 0, 48, or 72 hours and immunoblot assay performed for total p70S6 kinase (bottom panel) or p70 phosphorylated on serine 411 (Ser411), threonine 389 (Thr389), or threonine 421/serine 424 (Thr421/Ser424). (B) Control cells (wild-type) depleted of IL-6 for 48 hours and then re-treated with or without IL-6 (100 U/mL) for 15 minutes. Immunoblot assay was then performed with the same antibodies as in panel A. (C) Mutant N-ras or K-ras cells were depleted of IL-6 for 48 hours and treated with or without LY294002 (10 μM for 2 hours), rapamycin (10 nM for 6 hours), or PD98059 (10 μM for 2 hours); then immunoblot assay was performed with same antibodies as in panels A and B.