| Research Abstract |
We demonstrated that IL-2 rapidly induced protein phosphorylation of a 67-kDa (pp67) and four 63 kDa (pp63s) cellular proteins in various t cells, and the IL-2-stimulated phosphorylation was mediated by th IL-2R -chain composed of the high affinity IL-2R. In addition, various phorbol esters and tumor promoters. which activate PKC, were also demonstrated to induce the phosphorylation of a pp67 and pp63s in these T cell lines. Therefore, the present study suggests that IL-2/IL-2R -chain interaction triggers the phosphorylation of pp67 and pp63s, where the PKC may have an important role.
On the other hand, a selected clone from an IL-2-dependent human T-cell line was persistently propagate in the presence of phorbol esters with the ability to activate protein kinase C (PKC), such as 12-0-tetradecanoylphorbol-13-acetate (TPA) or phorbol-12,13-dibutylate (PDBu). Thus, a TPA(PDBu)-dependent T-cell line, designated TPA-Mat, was established from an IL-2-dependent T cell line, ILT-Mat. The TPA-d
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ependency of TPA-Mat was not lost during cultivation for more than a year in the presence of TPA, and TPA-Mat cells still showed IL-2-dependent growth. However, the TPA(PDBu)-dependent growth of TPA-Mat did not seem to be mediate by an autocrine mechanism of IL-2 or by any other growth factor production, because these factors were not detected in TPA-Mat cell supernatants. Therefore, the phorbol esters substituted for IL-2 and may be directly involved in transduction of growth signals in TPA-Mat cells. Furthermore, the growth of TPA-Mat cells was stimulated not only by phorbol esters but also by nonphorbol ester tumor promoters with the ability to activate PKC. These observations suggest that the sustained activation of PKC by the phorbol esters could induce continuous growth of the IL-2-dependent TPA-Mat cells. Furthermore, we demonstrated that the PDBu-dependent growth of TPA-Mat cells was inhibited up to 90% by adenosine 3',5'-cyclic monophosphate (cAMP) raising agents such as forskolin, cholera toxin and 1-methl-3-isobutyl-xanthine, and cAMP analogues, whereas the IL-2-stimulated TPA-Mat growth was slightly inhibited. These findings suggest that the signal transduction pathway of PDBu-induced growth, which should involve activation of protein kinase C, is sensitive to cAMP, and that it cannot be exactly identical to the signal transdution pathway of IL-2-induced growth in TPA-Mat cells. Less
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