Inhibition of Cell Cycle Progression by the Novel Cyclophilin Ligand Sanglifehrin A Is Mediated through the NFκB-dependent Activation of p53

Abstract

Sanglifehrin A belongs to a novel family of immunophilin-binding ligands. Sanglifehrin A is similar to cyclosporin A in that it binds to cyclophilins. Unlike cyclosporin A, however, the cyclophilin-sanglifehrin A complex has no effect on the calcium-dependent protein phosphatase calcineurin. It has been previously shown that sanglifehrin A specifically blocks T cell proliferation in response to interleukin 2 by inhibiting the appearance of cell cycle kinase activity cyclinE-Cdk2. How sanglifehrin A treatment leads to the cell cycle blockade has remained unknown. We report that sanglifehrin A is capable of activating the tumor suppressor gene p53 at the transcription level, leading to up-regulation of p21 that then binds and inhibits the cylcinE-Cdk2 complex. Further analysis of different elements in the p53 promoter showed that sanglifehrin A activates p53 transcription primarily through the activation of the transcription factor NFB by activating IB kinase in a manner that is similar to several genotoxic agents. Unlike other genotoxic drugs, sanglifehrin A does not cause DNA damage, making it a unique natural product that is capable of activating the NFB signaling pathway without affecting DNA.The immunosuppressive drugs cyclosporin A, FK506, and rapamycin constitute a unique family of natural products that work by an unusual mechanism (1-8). They serve as natural dimerizers that bring together two proteins, suppressing the function of both proteins as a consequence. Thus, CsA 1 is known to bind to the cyclophilin family of proteins (9) while FK506 and rapamycin are known to bind to the FKBP family of proteins (10, 11). Each of the immunophilin-drug complexes specifically interacts with and inhibits the function of their ultimate target. The CsA-cyclophilin and the FKBP-FK506 complexes specifically inhibit the protein phosphatase calcineurin (12, 13) while the FKBP-rapamycin complex specifically inhibits the function of the protein known as FRAP/RAFT/ TOR (14 -18). Inhibition of the phosphatase activity of calcineurin prevents the dephosphorylation of a critical transcription factor, NFAT, thereby blocking the transcription of a number of cytokine genes (5, 8). The binding of FKBP-rapamycin to RRAP/RAFT/TOR interferes with the function of TOR, leading to a blockade of cell cycle at the G 1 phase of the cell cycle.Sanglifehrin A (SFA) is a new member of the immunophilin ligand superfamily. It was discovered through a screen for novel cyclophilin ligands that block T cell activation (19,20). Similar to CsA, SFA binds to cyclophilin with high affinity. Unlike CsA, however, the cyclophilin-SFA complex has no effect on the phosphatase activity of calcineurin (21). Although SFA was shown to inhibit mouse and human mixed lymphocyte reactions (19), we and others have recently found that SFA does not affect T cell receptor-mediated signal transduction pathways leading to the production of cytokines such as IL-2 (21, 22). Instead, SFA inhibits IL-2-dependent T cell proliferation, similar to rapamycin (23, 24). Moreover, ...

Sanglifehrin A Acts as a Potent Inhibitor of the Mitochondrial Permeability Transition and Reperfusion Injury of the Heart by Binding to Cyclophilin-D at a Different Site from Cyclosporin A

“…It thus represents an important new specific tool for exploring the role of the MPTP in cell death, which may have advantages over CsA analogues as a protective agent against reperfusion injury and other cellular stresses that cause cell death through MPTP opening. The immunosuppressant activity of SfA is exerted by blocking T cell proliferation in response to interleukin 2, through a mechanism involving an NFB-mediated increase in the expression of the tumor suppressor genes p53 and p21, with the latter binding to and inhibiting the appearance of cell cycle kinase activity cyclin E-Cdk2 (14,16,17). Whether this action of SfA on the cell cycle will have any detrimental effects when the drug is used to inhibit reperfusion injury is unknown, although the relatively short time scales involved in reperfusion after ischemia would suggest not.…”

“…However, unlike the CyPA⅐CsA complex, the CyP-A⅐SfA complex does not inhibit calcineurin (14,15). Rather, SfA specifically blocks T cell proliferation in response to interleukin 2 through a mechanism involving an NFB-mediated increase in the expression of the tumor suppressor genes p53 and p21, with the latter binding to and inhibiting the appearance of cell cycle kinase activity cyclin E-Cdk2 (14,16,17). If SfA were able to bind tightly to CyP-D and inhibit its PPIase activity and the opening of the MPTP, its lack of effect on calcineurin might make it an alternative to N-Me-Ala-6-cyclosporin A and N-Me-Val-4-cyclosporin A in studying the role of the MPTP in cell death.…”

Cutting Edge: Sanglifehrin A, a Novel Cyclophilin-Binding Immunosuppressant Blocks Bioactive IL-12 Production by Human Dendritic Cells

“…Similar to Rapa, SFA has been shown to inhibit cell cycle progression of T cells at the G 1 phase (7). However, in contrast to Rapa, inhibition of cell cycle progression by SFA was suggested to be related to NF-B-dependent activation of p53 (6). Unlike the calcineurin inhibitors CsA and FK506, SFA does not suppress IL-2 transcription (5, 6), nor does it inhibit IL-2 receptor expression (6).…”

“…Studies of the immunosuppressive effects of SFA have been focused on T and B lymphocytes (5,6). Thus, SFA inhibits IL-2-induced T cell proliferation and mitogen-induced B cell proliferation (5,6). Similar to Rapa, SFA has been shown to inhibit cell cycle progression of T cells at the G 1 phase (7).…”

“…SFA has been reported to exhibit lower immunosuppressive activity in the MLR when compared with CsA (1,5). Studies of the immunosuppressive effects of SFA have been focused on T and B lymphocytes (5,6). Thus, SFA inhibits IL-2-induced T cell proliferation and mitogen-induced B cell proliferation (5,6).…”