title: Dual regulation of T cell receptor-mediated signaling by oncogenic Cbl mutant 70Z.
abstract: We previously showed that an oncogenic Cbl mutant (70Z) is constitutively active in transcriptional activation of nuclear factor at activated T cells (NFAT). However, the mechanism underlying this effect remains unclear. Here we analyzed the effects of 70Z mutations at an amino-terminal loss of function site (Gly-306) and at carboxyl-terminal potential tyrosine or serine phosphorylation sites on association with signaling proteins and on NFAT activation. Mutation at Gly-306 of 70Z disrupted its association with Zap-70 and almost completely abolished its ability to induce NFAT activation under basal and ionomycin-stimulated conditions. However, mutations at potential tyrosine or serine phosphorylation sites had little effect. In fact, expression of 70Z with Tyr-700, Tyr-731, or Tyr-774 mutated to Phe increased NFAT activity in comparison with unmutated 70Z. These findings suggest that an amino terminus-mediated interaction of 70Z with Zap-70 plays a positive role and that a carboxyl terminus-mediated, phosphotyrosine-dependent interaction with their binding proteins plays a negative role in 70Z-mediated NFAT activation. In support of this notion are the observations that 70Z reduced T cell receptor-induced NFAT activation and that wild-type Cbl further inhibited this event, suggesting that both 70Z and wild-type Cbl employ a similar mechanism by which Cbl proteins dually regulate T cell receptor-mediated signaling.
authors.affiliation: Division of Cell Biology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: C
authors.initials: C
authors.lastname: Elly
authors.forename: A
authors.initials: A
authors.lastname: Altman
authors.forename: Y C
authors.initials: YC
authors.lastname: Liu
mesh_terms: D048948:14-3-3 Proteins; D004268:DNA-Binding Proteins / Q000235:genetics; D006801:Humans; D019169:Jurkat Cells; D009154:Mutation; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D050722:Oncogene Protein v-cbl; D010766:Phosphorylation; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics; D014446:Tyrosine 3-Monooxygenase