Mammalian target of rapamycin: immunosuppressive drugs uncover a novel pathway of cytokine receptor signaling.

Recent findings have significantly advanced our understanding of the mechanism by which the potent immunosuppressive drug rapamycin inhibits cytokine-dependent lymphocyte proliferation. The protein targeted by the immunophilin-rapamycin complex is a member of a newly defined family of phosphoinositide-3-kinase-related kinases. The rapamycin target protein functions as a protein kinase in a signal transduction pathway that regulates the synthesis of proteins required for cell-cycle progression in both lymphoid and nonlymphoid cells.