CD5 acts as a tyrosine kinase substrate within a receptor complex comprising T-cell receptor zeta chain/CD3 and protein-tyrosine kinases p56lck and p59fyn.
T-cell antigens including CD2, CD4, CD6, CD8, and CD28 serve as coreceptors with the T-cell receptor (TCR)/CD3 complex in control of T-cell growth. The molecular basis by which these antigens fulfill this role has remained a major issue. An initial clue to this question came with our finding that the sensitivity of in vitro kinase labeling (specifically using protein-tyrosine kinase p56lck) allowed detection of a physical association between CD4-p56lck and the TCR/CD3 complexes. Another T-cell antigen, CD5, is structurally related to the macrophage scavenger receptor family and, as such, can directly stimulate and/or potentiate T-cell proliferation. In this study, we reveal that in Brij 96-based cell lysates, anti-CD5 antibodies coprecipitated TCR zeta chain (TCR zeta)/CD3 subunits as well as the protein-tyrosine kinases p56lck and p59fyn. Conversely, anti-CD3 antibody coprecipitated CD5, p56lck, and p59fyn. Indeed, anti-CD5 and anti-CD3 gel patterns were virtually identical, except for a difference in relative intensity of polypeptides. Anti-CD4 coprecipitated p56lck, p32, and CD3/TCR zeta subunits but precipitated less CD5, suggesting the existence of CD4-TCR zeta/CD3 complexes distinct from the CD5-TCR zeta/CD3 complexes. Consistent with the formation of a multimeric CD5-TCR zeta/CD3 complex, anti-CD5 crosslinking induced tyrosine phosphorylation of numerous T-cell substrates, similar to those phosphorylated by TCR zeta/CD3 ligation. Significantly, as for TCR zeta, CD5 was found to act as a tyrosine kinase substrate induced by TCR/CD3 ligation. The kinetics of phosphorylation of CD5 (t1/2 = 20 sec) was among the earliest of activation events, more rapid than seen for TCR zeta (t1/2 = 1 min). CD5 represents a likely TCR/CD3-associated substrate for protein-tyrosine kinases (p56lck or p59fyn) and an alternative signaling pathway within a multimeric TCR complex.
Burgess
K E
KE
Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, MA 02115.
Yamamoto
M
M
Prasad
K V
KV
Rudd
C E
CE
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000378:metabolism*; D017252:CD3 Complex / Q000378:metabolism*; D018956:CD5 Antigens; D002460:Cell Line; D003432:Cross-Linking Reagents; D006801:Humans; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D013601:T-Lymphocytes / Q000276:immunology*
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D017252:CD3 Complex; D018956:CD5 Antigens; D003432:Cross-Linking Reagents; D009856:Oncogene Proteins, Viral; D011518:Proto-Oncogene Proteins; D011948:Receptors, Antigen, T-Cell; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051076:Proto-Oncogene Proteins c-fyn