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Sirolimus (rapamycin), a new immunosuppressive drug, inhibits proliferation of a wide spectrum of T and B cells. The immunosuppressive mechanism of sirolimus is still unclear. We recently isolated a membrane associated protein with an apparent molecular weight of 210 kDa, p210, from cultured Molt 4 cells and BJAB cells and from normal human T cells using an affinity matrix method. The p210 binds to sirolimus:FKBP12 complex, but only at background levels to FKBP12 alone, to FK506:FKBP12 complex, or sirolimus-biotin alone. Among the sirolimus analogs tested, the binding ability of p210 to drug:FKBP12 complexes correlates with the immunosuppressive activity of the drugs, suggesting that p210 is the sirolimus effector protein.
Chen et al. (Mon,) studied this question.