Rapamycin inhibits p34cdc2 expression and arrests T lymphocyte proliferation at the G1/S transition.

Rapamycin, a potent immunosuppressant and antifungal agent, inhibits an evolutionarily conserved mechanism regulating cell cycle progression. In an interleukin-2 (IL-2) dependent murine T cell, we demonstrate that rapamycin arrested T cells prior to the entry into S-phase of the cell cycle and that rapamycin inhibited the IL-2-stimulated expression of p34cdc2, a serine/threonine kinase that is required for cells to progress through the cell cycle. The mechanism of action of rapamycin appeared specific since the structural analogue and immunosuppressant FK506 had no effect on the progression of the cells through S-phase or the expression of p34cdc2. These results demonstrate a rapamycin-sensitive IL-2-dependent signaling pathway in T cells and suggest that the immunosuppressive properties of rapamycin are mediated by impinging on the IL-2-induced T cell expression of p34cdc2.