A PP2A regulatory subunit positively regulates Ras-mediated signaling during Caenorhabditis elegans vulval induction

We describe evidence that a regulatory B subunit of protein phosphatase 2A (PP2A) positively regulates an RTK-Ras-MAP kinase signaling cascade during Caenorhabditis elegans vulval induction. Although reduction of sur-6 PP2A-B function causes few vulval induction defects in an otherwise wild-type bac kground, sur-6 PP2A-B mutations suppress the Multivulva phenotype of an act ivated as mutation and enhance the Vulvaless phenotype of mutations in lin- 45 raf, sur-8, or mpk-1. Double mutant analysis suggests that sur-G PP2A B acts downstream or in parallel to ras, but likely upstream of raf, and func tions with ksr-1 in a common pathway to positively regulate Ras signaling.