Ras-dependent, Ca2+-stimulated activation of nuclear factor of activated T cells by a constitutively active Cbl mutant in T cells.

T cell receptor (TCR) stimulation induces rapid tyrosine phosphorylation of cellular proteins, including Cbl, a protooncogene product whose function remains unclear. As a first step toward elucidating the function of Cbl in TCR-initiated signaling, we evaluated the ability of wild-type Cbl or a transforming Cbl mutant (70Z/3) to induce transcriptional ...
activation of a nuclear factor of activated T cells (NFAT) element derived from the interleukin 2 (IL2) promoter in transiently cotransfected Jurkat-TAg T cells. 70Z/3, but not Cbl, caused NFAT activation which was significantly enhanced by stimulation with calcium ionophore, and was drastically reduced by cyclosporin A pretreatment. A point mutation of a potential phosphatidylinositol 3-kinase (PI3-K) binding site (Y731EAM to Y731EAC) in 70Z/3 disrupted the association of PI3-K with 70Z/3, but did not reduce the induction of NFAT activity, suggesting that the interaction between Cbl and PI3-K is not required in the 70Z/3-mediated induction of NFAT. Additional mapping studies indicated that defined deletions of C-terminal 70Z/3 sequences affected to a variable degree its ability to stimulate NFAT activity. Strikingly, deletion of 346 C-terminal residues augmented this activity, whereas removal of 20 additional residues abolished it. Coexpression of dominant negative Ras abrogated the basal or ionomycin-stimulated, 70Z/3-mediated NFAT activation, suggesting a functional Ras is required for this activation. These results implicate Cbl in Ras-dependent signaling pathways which lead to NFAT activation.
Mesh Terms:
Animals, Calcineurin, Calcium, Calmodulin-Binding Proteins, DNA-Binding Proteins, Humans, Ionomycin, Lymphocyte Activation, Mice, NFATC Transcription Factors, Nuclear Proteins, Oncogene Protein v-cbl, Phosphatidylinositol 3-Kinases, Phosphoprotein Phosphatases, Phosphotransferases (Alcohol Group Acceptor), Proto-Oncogene Proteins, Proto-Oncogene Proteins c-cbl, Proto-Oncogene Proteins p21(ras), Retroviridae Proteins, Oncogenic, Sequence Deletion, Structure-Activity Relationship, T-Lymphocytes, Transcription Factors, Tumor Cells, Cultured, Ubiquitin-Protein Ligases
J. Biol. Chem.
Date: Jan. 03, 1997
Download Curated Data For This Publication
144288
Switch View:
  • Interactions 1