FIG. 1.

PKC activation suppresses growth factor activation of Ral but not Erk. Cells were pretreated with buffer, PDA, or PDA plus the PKC inhibitor GF109230X for 30 min. The cells were then stimulated for various amounts of time with growth factors, and the active state of either RalB (A and B) or Erk (C and D) was measured. (A) PC12 cells were stimulated with NGF with and without PMA and PKC inhibitor GF109230X, and active GTP-RalB was purified with the Ral binding domain of RalBP1. Total RalB in cell lysates is shown below. To quantify the difference in the amount of RalB-GTP between stimulated and unstimulated samples, serial dilutions of both samples were compared (data not shown). (B) COS-7 cells were stimulated with EGF and processed as for panel A. (C) PC12 cells were stimulated with NGF, and active Erk was measured in immunoblots using phospho-specific Erk antibodies. (D) COS-7 cells were stimulated with EGF and processed as described for panel C. Data are representative of at least three independent experiments.