Reduced Cbl phosphorylation and degradation of the zeta-chain of the T-cell receptor/CD3 complex in T cells with low Lck levels.
T cells with short interfering RNA-mediated Lck-knockdown (kd) display paradoxical hyper-responsiveness upon TCR ligation. We have previously reported a possible mechanism for T-cell activation in cells with low levels of Lck depending on Grb2-SOS1 recruitment to the zeta-chain of TCR/CD3 (Methi et al., Eur. J. Immunol. 2007, 37: 2539-2548). Here, we show that short interfering RNA-mediated targeting of Lck caused a dramatic reduction in c-Cbl phosphorylation and a general reduction in protein ubiquitination after TCR stimulation. Specifically, this resulted in reduced ubiquitination of the zeta-chain, yet internalization of TCR/CD3 appeared to be normal after receptor engagement. However, zeta-chain levels were elevated in Lck-kd cells, and confocal microscopy revealed reduced colocalization of CD3-containing vesicles with endosomal and lysosomal compartments. We hypothesize that prolonged stability of internalized T-cell receptor complex may result in extended signaling in T cells with low Lck levels.
Methi
Trond
T
The Biotechnology Centre of Oslo and Centre for Molecular Medicine Norway, Nordic EMBL Partnership, University of Oslo, Oslo, Norway.
Berge
Torunn
T
Torgersen
Knut Martin
KM
Taskén
Kjetil
K
D006801:Humans; D019169:Jurkat Cells; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism*; D050778:NFATC Transcription Factors / Q000378:metabolism; D010766:Phosphorylation; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism; D054875:Ubiquitination
D050778:NFATC Transcription Factors; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D011948:Receptors, Antigen, T-Cell; D018808:Transcription Factor AP-1; C054979:antigen T cell receptor, zeta chain; D050721:Proto-Oncogene Proteins c-cbl; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); C067419:CBL protein, human