Stability of IL-2 mRNA in T lymphocytes is controlled by a protein kinase C-regulated mechanism.

The rate of the degradation of interleukin 2 (IL-2) mRNA produced in stimulated human tonsillar lymphocytes was found to be significantly decreased in cells continuously stimulated with a calcium ionophore, A23187, and a phorbol ester, phorbol 12, 13-dibutylate (PDB) as compared with that in unstimulated cells. When the lymphocytes were stimulated with A23187 and PDB, IL-2 mRNA reached a maximum level at 8 h and gradually decreased to almost the base line by 27 h. IL-2 mRNA produced was rapidly degraded when the stimulants were washed out at 12 h and the cells further cultured in the presence of actinomycin D, which stops mRNA synthesis. However, the stability of IL-2 mRNA was increased by the addition of PDB or A23187. A maximal effect was observed when both were added. The effect of PDB was dose-dependent and inhibited by the inhibitors of protein kinase C (PKC), staurosporine, and K252a, suggesting the involvement of PKC in the control of IL-2 mRNA stability. The involvement of protein phosphorylation in the regulating mechanism of IL-2 mRNA stability was supported by the fact that the addition of okadaic acid, which inhibits serine/threonine protein phosphatases, resulted in an increase in the stability of IL-2 mRNA. Further study demonstrated that the rate of degradation of 32P-labeled IL-2 mRNA, which was prepared by cell-free transcription of IL-2 cDNA, in the polysomal fraction obtained from PDB-stimulated lymphocytes was decreased compared with that obtained from unstimulated lymphocytes. These results indicate the presence of a mechanism controlling the stability of IL-2 mRNA that is regulated by PKC.