Requirements of multiple domains of SLI-1, a Caenorhabditis elegans homologue of c-Cbl, and an inhibitory tyrosine in LET-23 in regulating vulval differentiation.
SLI-1, a Caenorhabditis elegans homologue of the proto-oncogene product c-Cbl, is a negative regulator of LET-23-mediated vulval differentiation. Lack of SLI-1 activity can compensate for decreased function of the LET-23 epidermal growth factor receptor, the SEM-5 adaptor, but not the LET-60 RAS, suggesting that SLI-1 acts before RAS activation. SLI-1 and c-Cbl comprise an N-terminal region (termed SLI-1:N/Cbl-N, containing a four-helix bundle, an EF hand calcium-binding domain, and a divergent SH2 domain) followed by a RING finger domain and a proline-rich C-terminus. In a transgenic functional assay, the proline-rich C-terminal domain is not essential for sli-1(+) function. A protein lacking the SH2 and RING finger domains has no activity, but a chimeric protein with the SH2 and RING finger domains of SLI-1 replaced by the equivalent domains of c-Cbl has activity. The RING finger domain of c-Cbl has been shown recently to enhance ubiquitination of active RTKs by acting as an E3 ubiquitin-protein ligase. We find that the RING finger domain of SLI-1 is partially dispensable. Further, we identify an inhibitory tyrosine of LET-23 requiring sli-1(+) for its effects: removal of this tyrosine closely mimics the loss of sli-1 but not of another negative regulator, ark-1. Thus, we suggest that this inhibitory tyrosine mediates its effects through SLI-1, which in turn inhibits signaling upstream of LET-60 RAS in a manner not wholly dependent on the ubiquitin-ligase domain.
Yoon
C H
CH
Howard Hughes Medical Institute and Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.
Chang
C
C
Hopper
N A
NA
Lesa
G M
GM
Sternberg
P W
PW
D020816:Amino Acid Motifs; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins; D002454:Cell Differentiation / Q000235:genetics*; D017124:Conserved Sequence; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D015801:Helminth Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D013489:Suppression, Genetic; D014443:Tyrosine; D044767:Ubiquitin-Protein Ligases; D014844:Vulva / Q000166:cytology* / Q000502:physiology; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism; D018909:src Homology Domains
D029742:Caenorhabditis elegans Proteins; C108739:GAP-1 protein, C elegans; D015801:Helminth Proteins; D011518:Proto-Oncogene Proteins; C085751:Sem-5 protein, C elegans; C095237:Sli-1 protein, C elegans; D020703:ras GTPase-Activating Proteins; C066646:let-60 protein, C elegans; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D066246:ErbB Receptors; D020794:Receptor Protein-Tyrosine Kinases; C085873:let-23 protein, C elegans; D018631:ras Proteins