Phosphorylation of human interleukin-2 (IL-2)

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Human interleukin-2 (IL-2) is a lymphokine crucial for lymphocyte activation and T cell clone growth.
• Understanding post-translational modifications of IL-2 is important for its biological function.
• Recombinant IL-2 produced in E. coli and COS cells serves as a model for studying IL-2 modifications.

Purpose of the Study:

• To investigate the phosphorylation of recombinant human IL-2 by protein kinase C.
• To identify the specific site and characteristics of IL-2 phosphorylation.
• To assess the impact of phosphorylation on IL-2's biological activity.

Main Methods:

• Expression of recombinant human IL-2 in E. coli and COS cells.
• In vitro phosphorylation using protein kinase C and [gamma-32P] ATP.
• Analysis of phosphorylated IL-2 using SDS-PAGE, reverse-phase HPLC, and tryptic peptide mapping.
• Biological activity assessment via T cell growth assay.

Main Results:

• Recombinant human IL-2 is phosphorylated by protein kinase C.
• Phosphorylation occurs at serine residue 7 on the N-terminal fragment.
• No significant difference in biological activity was observed between phosphorylated and non-phosphorylated IL-2.
• 32P-labeled IL-2 can be synthesized with high specific radioactivity.

Conclusions:

• IL-2 phosphorylation by protein kinase C occurs at a specific site (Ser7) without altering its T cell growth-promoting activity.
• The physiological role of IL-2 phosphorylation remains to be elucidated.
• Biologically active, 32P-labeled IL-2 is a valuable tool for receptor-binding studies, particularly in cells with low phosphoprotein phosphatase levels.