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Mode of action of tacrolimus (FK506): molecular and cellular mechanisms
A W Thomson1, C A Bonham, A Zeevi
1Pittsburgh Transplantation Institute, University of Pittsburgh Medical Center, Pennsylvania 15213, USA.
Abstract:
Tacrolimus, formerly known as FK506, is a macrolide antibiotic with immunosuppressive properties. Although structurally unrelated to cyclosporin A (CsA), its mode of action is similar. It exerts its effects principally through impairment of gene expression in target cells. Tacrolimus bonds to an immunophilin, FK506 binding protein (FKBP). This complex inhibits calcineurin phosphatase. The drug inhibits calcium-dependent events, such as interleukin-2 gene transcription, nitric oxide synthase activation, cell degranulation, and apoptosis. Tacrolimus also potentiates the actions of glucocorticoids and progesterone by binding to FKBPs contained within the hormone receptor complex, preventing degradation. The agent may enhance expression of the transforming growth factor beta-1 gene in a fashion analogous to that demonstrated for CsA. T cell proliferation in response to ligation of the T cell receptor is inhibited by tacrolimus. Type 1 T helper cells appear to be preferentially suppressed compared with type 2 T helper cells. T cell-mediated cytotoxicity is impaired. B cell growth and antibody production are affected indirectly by the suppression of T cell-derived growth factors necessary for these functions. Antigen presentation appears to be spared. The molecular events affected by tacrolimus continue to be discovered.
Insights
Tacrolimus (FK506) is an immunosuppressant that inhibits T cell proliferation and function by blocking calcineurin phosphatase. This macrolide antibiotic impacts gene expression, T helper cell activity, and potentiates hormone receptor actions.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Tacrolimus (FK506) is a macrolide antibiotic with significant immunosuppressive properties.
- Its mechanism of action is similar to cyclosporin A (CsA) but structurally distinct.
- It primarily functions by impairing gene expression in target cells.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying tacrolimus's immunosuppressive effects.
- To understand how tacrolimus interacts with cellular components like FKBP and calcineurin.
- To investigate the impact of tacrolimus on various immune cell functions and signaling pathways.
Main Methods:
- Tacrolimus binds to FK506 binding protein (FKBP), forming a complex.
- This complex inhibits calcineurin phosphatase activity.
- The study examines the downstream effects on calcium-dependent signaling and gene transcription.
Main Results:
- Tacrolimus inhibits calcium-dependent events including IL-2 gene transcription and nitric oxide synthase activation.
- It preferentially suppresses Type 1 T helper cells over Type 2 T helper cells.
- Tacrolimus potentiates glucocorticoid and progesterone actions and may enhance TGF-β1 gene expression.
Conclusions:
- Tacrolimus effectively inhibits T cell proliferation, cytotoxicity, and indirectly affects B cell functions.
- The drug's mechanism involves calcineurin inhibition and modulation of gene expression.
- Further research is ongoing to discover all molecular events influenced by tacrolimus.