The immunosuppressive macrolides FK-506 and rapamycin act as reciprocal antagonists in murine T cells.

The structurally related immunosuppressive macrolides FK-506 and rapamycin (RAP) were previously shown to inhibit T cell stimulation through different mechanisms. FK-506 acts similarly to cyclosporin A (CsA) and prevents IL-2 production and IL-2R expression. RAP has little or no effect on these events but markedly impedes the response to IL-2. The present study was initiated to examine the possibility of a complementation between the immunosuppressive actions of RAP and FK-506 or CsA on various murine T cell responses. RAP potentiated the effect of CsA on proliferation and IL-2R expression in T cells stimulated with ionomycin + PMA. However, in the same system, RAP acted as a potent antagonist of FK-506 suppression. RAP also blocked FK-506- but not CsA-mediated inhibition of IL-2 mRNA induction. By using model systems sensitive to inhibition by RAP but not FK-506 we further demonstrated that FK-506 reciprocally behaves as an antagonist of RAP. In one such model, the stimulation of splenic T cells with IL-2 + PMA, FK-506, but not CsA, reversed the suppressive effect of RAP on proliferation. FK-506 also antagonized RAP-mediated inhibition with respect to the induction of Ly-6E Ag expression by IFN in YAC cells. To explore further the competition between the two macrolides at the cellular level, we performed binding experiments with a radiolabeled derivative of FK-506. Both FK-506 and RAP, but not CsA, inhibited the binding of this probe in YAC cells. Taken together, these data demonstrate that FK-506 and RAP antagonize each other's biologic activity and physically interact with a common receptor site(s) in T cells. Moreover, CsA acts at a site distinct from the cellular target(s) of FK-506 or RAP.     

Distinct mechanisms of suppression of murine T cell activation by the related macrolides FK-506 and rapamycin.

FK-506 and the structurally related macrolide rapamycin (RAP) were investigated in comparison with cyclosporin A (CsA) for their immunosuppressive effects on murine T cells. All three agents suppressed the proliferation of splenic T cells triggered by lectins or antibodies to CD3 and Ly-6C. FK-506 or CsA also inhibited proliferation, IL-2 production, and IL-2R expression in splenic T cells activated with ionomycin + PMA. However, RAP minimally affected IL-2 production and IL-2R expression in these cells, although it reduced proliferation. Similarly, FK-506 and CsA, but not RAP, suppressed IL-2 production by activated DO.11.10 T hybridoma cells. In such a system, as well as in normal T cells stimulated with high ionomycin concentrations, FK-506 and CsA enhanced proliferation, indicating that they both abrogate negative signals associated with T cell activation. On the contrary, RAP diminished the autonomous proliferation of hybridoma cells, whereas FK-506 and CsA had little effect. The proliferative response induced in D10.G4 cells by IL-1 + ionomycin but not that induced by IL-1 + PMA was sensitive to inhibition by FK-506 and CsA. In contrast, RAP inhibited equally well both types of stimulation. Finally, T cell proliferation driven by IL-2 or IL-4 was found to be relatively resistant to FK-506 or CsA but sensitive to RAP. Altogether, these data demonstrate that FK-506 and CsA alter similar calcium-associated events of T cell activation and block T cell proliferation primarily by suppressing lymphokine production. RAP interferes with a different set of events and inhibits T cells by impairing their response to growth-promoting lymphokines.     

FK-506, a potent novel immunosuppressive agent, binds to a cytosolic protein which is distinct from the cyclosporin A-binding protein, cyclophilin

A novel macrolide antibiotic, FK-506, isolated from Streptomyces tsukubaensis, has been shown to be a potent immunosuppressive agent in vivo and in vitro. FK-506 shares a number of immunosuppressive properties with the cyclic peptide, cyclosporin A (CsA), although 10 to 100 times more potent in this regard. These similarities suggest that both agents may share a similar mechanism(s) of action at the biochemical level. We have identified a cytoplasmic binding protein for FK-506 in the human T cell line, JURKAT, using [3H]FK-506. The FK-506 binding protein has a mr of 10 to 12 kDa (as determined by gel filtration), is heat stable and does not bind CsA. This contrasts with the CsA binding protein, cyclophilin, in that cyclophilin is heat labile and has a mr of 15 to 17 kDa. Our data suggest that FK-506 binds to a low m.w. protein(s) in JURKAT cells, which is distinct from cyclophilin. This protein may mediate the immunosuppressive effects of FK-506 in T cells. In addition, our results suggest that the immunosuppressive activity of FK-506, as with CsA, is mediated by an intracellular mechanism.     

FK-506 binding protein from Tolypocladium inflatum: resistance of FKBP/FK-506 complex against proteolysis.

A 12-kDa peptidyl-prolyl-cis/trans-isomerase was purified 225-fold to homogeneity from the cyclosporin producing fungus Tolypocladium inflatum. The enzyme is highly sensitive to the immunosuppressant FK-506 but not to cyclosporin and thus belongs to the class of FK-506 binding proteins (FKBP). Interestingly the FKBP/FK-506 complex is resistant against proteolytic digestion by the endoproteases GluC and LysC, in contrast to the free FKBP, which is readily cleaved by these proteases. This protection may play a role in the effects of FK-506 in the living cell.     

FK-506 and cyclosporin A inhibit highly similar signal transduction pathways in human T lymphocytes.

This report compares the ability of cyclosporin A and FK-506 to inhibit human T cell activation triggered via cell surface molecules that utilize different intracellular processes. We stimulated highly purified peripheral blood T lymphocytes with mitogens (Con A and PHA), ionomycin + PMA, or monoclonal antibodies specific for cell surface antigens involved in activation (CD2, CD3, CD28) either in combination with each other or in conjunction with PMA. Using measurements of the proliferative response, IL-2 production, and changes in intracellular Ca2+ ([Ca2+]i), we demonstrate that FK-506 exerts its inhibitory effect on early events of T-cell activation in a manner indistinguishable from that of CsA. An important finding in this study is the strict correlation between those activation pathways that are inhibited by FK-506 and CsA and the requirement that the sensitive pathways induce a measurable rise in [Ca2+]i. This correlation held even for the CD28/CD2 pathway which was previously shown to be calcium-independent; however by employing FACS analysis of [Ca2+]i within individual cells, a subset of cells activated via CD28/CD2 was found to respond with a measurable rise in [Ca2+]i. We also noted that the proliferative response induced by certain stimuli, such as ionomycin + PMA and PHA + PMA, was partially resistant to FK-506 and CsA, while IL-2 production was completely suppressed. The partial FK-506/CsA-resistance of these responses was shown to be determined by the amount of PMA added to the cultures. We conclude from our investigations that FK-506 and CsA inhibit highly similar signal transduction pathways in human T lymphocytes.     

Antifungal properties of the immunosuppressant FK-506: identification of an FK-506-responsive yeast gene distinct from FKB1.

FK-506 is a novel and potent antagonist of T-cell activation and an inhibitor of fungal growth. Its immunosuppressive activity can be antagonized by the structurally related antibiotic rapamycin, and both compounds interact with cytoplasmic FK-506-binding proteins (FKBPs) in T cells and yeast cells. In this paper, we show that FK-506 and two analogs inhibit vegetative growth of Saccharomyces cerevisiae in a fashion that parallels the immunosuppressive activity of these compounds. Yeast mutants resistant to FK-506 were isolated, and at least three complementation groups (fkr1, fkr2, and fkr3) were defined. These fkr mutants show no alteration in their levels of FK-506-binding activity. Likewise, strains carrying null alleles of FKB1 (the yeast gene coding for the FKBP) remain FK-506 sensitive, indicating that depletion of yeast FKBP is not sufficient to confer an FK-506 resistance phenotype, although fkb1 null mutants are resistant to rapamycin. FKB1 does not map to the three fkr loci defined here. These results suggest that yeast FKBP mediates the inhibitory effect of rapamycin but that at least one other protein is directly involved in mediating the activity of FK-506. Interestingly, the ability of FK-506 to rescue a temperature-sensitive growth defect of the fkr3 mutant suggests that the FKR3 gene may define such a protein.     

针对NFAT信号途径的新型免疫抑制剂

免疫抑制剂cyclosporin A和FK-506通过抑制依赖钙调蛋白的磷酸酶calcineurin(CaN)的活性,阻断了活化T细胞核因子(NFAT)的活化,最终抑制了机体的免疫应答.然而,这种直接对CaN酶活性的破坏,使得这类药物具有严重的临床毒副作用.随着对NFAT调节机制的研究深入,近年来,人们运用各种试验方法、手段筛选了一些天然的以及合成的抑制剂,它们针对NFAT信号通路的下游靶点发挥作用,从而选择性更强,毒性更小,为临床抗移植排斥反应、自身免疫性疾病的治疗奠定了基础.本文综述了这方面的进展,并就这些抑制剂的特点进行了简单的分析,另提出了一些新的有治疗潜力的靶点.