Sanglifehrin A, a Novel Cyclophilin-Binding Immunosuppressant, Inhibits IL-2-Dependent T Cell Proliferation at the G1 Phase of the Cell Cycle

Abstract

Sanglifehrin A (SFA) is a novel immunosuppressive natural product that binds to cyclophilin but is structurally distinct from cyclosporin A (CsA). We have investigated the cellular and molecular mechanisms of the action of SFA in T lymphocytes. We show that SFA inhibits T cell proliferation induced by IL-2 with an IC50 of 200 nM. Distinct from CsA, which also binds to cyclophilin, SFA does not affect calcium-dependent IL-2 production, although SFA enhanced IL-2 gene transcription in the same cells. SFA blocks T cell proliferation induced by IL-2 in G1 with no appreciable effect on IL-2 receptor expression in a manner similar to that of the immunosuppressant rapamycin. Unlike rapamycin, however, SFA has no effect on the phosphorylation or enzymatic activity of p70s6k kinase, distinguishing SFA from rapamycin in their mode of action. SFA inhibits hyperphosphorylation of Rb and the activity of cyclin E-cyclin-dependent kinase 2 on IL-2 signaling. These results suggest that SFA has a novel mode of action in comparison with CsA, FK506, and rapamycin, and that its use as a molecular probe may lead to the discovery of a novel target involved in T cell activation.