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The phosphatidylinositol phosphatase PTEN is under control of costimulation and regulates proliferation in human T cells

The phosphatidylinositol phosphatase gene PTEN is a dualspecific phosphatase acting on phospho amino acids but also on three phosphorylated inositol phospholipids. Present results demonstrate that PTEN is inducible by costimulatory signals in human CD4+ T cells. PTEN expression was up‐regulated on RNA and protein level in freshly isolated human CD4+ T cells following stimulation with CD28 or CD2. In contrast, PTEN expression was high but remained CD28 and CD2 unresponsive in lymphoma cells. Intracellular staining revealed PTEN expression in CD4+ T cell populations stimulated with anti‐CD28 or anti‐CD28 / anti‐CD3. Stimulation with anti‐CD3 alone did not induce PTEN expression. Inhibition of PTEN expression by antisense oligonucleotides in CD4+ T cells stimulated with non‐mitogenic anti‐CD28 resulted in massively increased proliferation, which was sensitive to the phosphatidylinositol 3‐kinase (PI3 K) inhibitor wortmannin. Although CD28 and CD2 induce PI3 K signal transduction, wortmannin did not block PTEN up‐regulation by CD28 or CD2 indicating that PTEN gene expression is PI3 K independent. These results demonstrate that PTEN negativelycontrols costimulatory signals by antagonizing PI3 K activity in the absence of TCR engagement.