The Caenorhabditis elegans EGL-15 Signaling Pathway Implicates a DOS-Like Multisubstrate Adaptor Protein in Fibroblast Growth Factor Signal Transduction

Abstract

EGL-15 is a fibroblast growth factor receptor in the nematodeCaenorhabditis elegans. Components that mediate EGL-15 signaling have been identified via mutations that confer a Clear (Clr) phenotype, indicative of hyperactivity of this pathway, or a suppressor-of-Clr (Soc) phenotype, indicative of reduced pathway activity. We have isolated a gain-of-function allele of let-60 ras that confers a Clr phenotype and implicated bothlet-60 ras and components of a mitogen-activated protein kinase cascade in EGL-15 signaling by their Soc phenotype. Epistasis analysis indicates that the gene soc-1 functions in EGL-15 signaling by acting either upstream of or independently of LET-60 RAS. soc-1 encodes a multisubstrate adaptor protein with an amino-terminal pleckstrin homology domain that is structurally similar to the DOS protein in Drosophilaand mammalian GAB1. DOS is known to act with the cytoplasmic tyrosine phosphatase Corkscrew (CSW) in signaling pathways in Drosophila. Similarly, the C. elegans CSW ortholog PTP-2 was found to be involved in EGL-15 signaling. Structure-function analysis of SOC-1 and phenotypic analysis of single and double mutants are consistent with a model in which SOC-1 and PTP-2 act together in a pathway downstream of EGL-15 and the Src homology domain 2 (SH2)/SH3-adaptor protein SEM-5/GRB2 contributes to SOC-1-independent activities of EGL-15.

ACKNOWLEDGMENTS

We thank Tom Duchesne for isolating let-60(ay75); Leslie DeLong for additional genetic mapping of soc-1, initial YAC rescue of soc-1, and help in characterization of let-60(ay75); Laura Selfors for restriction mapping of Y47D10 and assaying soc-1 rescue using cosmid pools; Peng Huang for assistance with soc-1site-directed mutagenesis; Tim Schedl for providing the ptp-2(op194); let-60(ga89) strain; Catherine Branda and Sandra Mayday for constructing clr-1(e1745ts); soc-1(n1789); sem-5(n1781); Alan Coulson for providing cosmids; and Anton Bennett and David Stern for advice. Some nematode strains used in this work were provided by the Caenorhabditis Genetics Center.

J. L. Schutzman and C. Z. Borland contributed equally to this paper.

The Caenorhabditis Genetics Center is funded by the NIH National Center for Research Resources (NCRR). This work was supported by American Cancer Society grant RPG-98-070-01-DDC. M. K. Robinson was supported by NRSA postdoctoral fellowship F32 CA76713.