Cyclic AMP sensitive signalling by the CD28 marker requires concomitant stimulation by the T-cell antigen receptor (TCR/CD3) complex.
We have previously demonstrated that activation of cAMP-dependent protein kinase (cAK) type I (cAKI, RI alpha 2-C beta 2) mediates the inhibitory effects of cAMP on T-cell replication induced through the TCR/CD3 complex. In the present study we have investigated the effect of cAMP on T-cell DNA synthesis, tyrosine phosphorylation of a 100 kDa protein (pp100) and IL2 mRNA expression, induced through stimulation of the TCR/CD3- and/or the CD28 molecules. Our results demonstrate that tyrosine phosphorylation of pp100 stimulated by anti-CD3 is inhibited by cAMP both in the presence and absence of the phorbol ester PMA, and reflects the changes seen in IL2 mRNA expression and T-cell replication. Combined stimulation with anti-CD3 and anti-CD28, which gives a synergistic response in T-cell replication, gave pp100 phosphorylation and IL2 mRNA expression sensitive to cAMP-dependent inhibition. When PMA was added in addition to anti-CD3 and anti-CD28, the inhibitory effect of cAMP on both T-cell replication and pp100 phosphorylation was completely abolished. The fact that pp100 phosphorylation in response to TCR/CD3-, CD28- and PMA stimulation and cAMP mediated inhibition are identical to the effects of the same stimuli on T-cell proliferation, makes this protein an interesting candidate in downstream signalling from these receptors. In addition, our results are compatible with a model where cAMP, through activation of cAKI, eliminates both the PTK and PKC activating capability of the T-cell receptor at a site(s) proximal to PKC activation. Furthermore, the CD28 molecule which activates PTKs, enters the PTK cascade at a point distal to the target(s) for cAKI action. Therefore, during CD28 signalling PKC activation can be achieved either by TCR/CD3 stimulation (inhibited by cAMP), or directly by PMA (not inhibited by cAMP).
Skålhegg
B S
BS
Institute of Medical Biochemistry, University of Oslo, Norway.
Rasmussen
A M
AM
Taskén
K
K
Hansson
V
V
Jahnsen
T
T
Lea
T
T
D018106:CD28 Antigens / Q000276:immunology / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D008213:Lymphocyte Activation / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D017260:Receptor-CD3 Complex, Antigen, T-Cell / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D018106:CD28 Antigens; D007376:Interleukin-2; D017260:Receptor-CD3 Complex, Antigen, T-Cell; D000242:Cyclic AMP; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate