FK506

Calcineurin Inhibitor and Autophagy Inducer

Calcineurin inhibition by FK506

FK506 (also known as Tacrolimus), a commonly used immunosuppressant, is a potent calcineurin inhibitor. Calcineurin is a calcium-dependent enzyme that activates the cytoplasmic nuclear factor of activated T cell (NFAT) by dephosphorylating it. The activated NFAT is then translocated into the nucleus, where it upregulates the expression of cytokines such as interleukin 2 (IL-2), which, in turn, stimulates the growth and differentiation of the T cell response.

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Mode of action:

Similar to cyclosporin A, FK506 blocks the activation of calcineurin through the formation of complexes with immunophilins. FK506 binds to an immunophilin called FK506 binding protein 12 (FKBP12), unlike cyclosporin A which binds to a different immunophilin [1]. The FK506–FKBP12 complex suppresses the activation of the calcineurin-dependent NFAT pathway and the subsequent expression of cytokines, such as IL-2. It has been demonstrated that FK506 also suppresses the calcineurin-independent activation pathway for JNK and p38 [2, 3].
Of note,  FK506 has been reported to be an activator of autophagy [4].

Key features:

• A potent calcineurin inhibitor
• An autophagy inducer
• InvitroFit™ grade: each lot is functionally tested

Read our review on Autophagy and Innate Immunity

References:

1. Powell J.D. & Zheng Y., 2006. Dissecting the mechanism of T-cell anergy with immunophilin ligands. Curr Opin Investig Drugs. 7(11):1002-7.
2. Matsuda S. et al., 2000. Two distinct action mechanisms of immunophilin-ligand complexes for the blockade of T-cell activation. EMBO Rep. 1(5):428-34.
3. Vafadari R. et al., 2012. Inhibitory Effect of Tacrolimus on p38 Mitogen-Activated Protein Kinase Signaling in Kidney Transplant Recipients Measured by Whole-Blood Phosphospecific Flow Cytometry. Transplantation. 93(12):1245-51.
4. Kim D. et al., 2017. FK506, an immunosuppressive drug, induces autophagy by binding to the V-ATPase catalytic subunit A in neuronal cells. J. Proteome Res. 16, 55–64. 

Figures

FK506 is a potent inhibitor of calcineurin signaling pathways.
Jurkat-Lucia™ NFAT cells were incubated overnight at 37°C in the presence of increasing concentrations of FK506 together with 10 μg/ml of ionomycin and 50 ng/ml of PMA. The next day, the inhibitory activity of FK506 was determined by measuring the reduction of Lucia luciferase production in the supernatant using the QUANTI-Luc™ detection reagent. Data are shown as percentage (%) inhibition.

Specifications

Synonym: Tacrolimus, FK-506

CAS number: 104987-11-3

Formula: C₄₄H₆₉NO₁₂

Molecular weight: 804.02 g/mol

Solubility: 100 mg/ml in DMSO

Working concentration: 1 - 100 nM

Quality control:

• The inhibitory activity has been validated using cellular assays.
• The absence of bacterial contamination (e.g. lipoproteins and endotoxins) has been confirmed using HEK-Blue™ TLR2 and HEK-Blue™ TLR4 cells.

Contents

FK506 is provided as a translucent film.

• 10 mg FK506

FK506 is shipped at room temperature.

Upon receipt, store at -20 °C.

Details

Calcineurin

Calcineurin, also known as protein phosphatase 2B, is a calcium-dependent serine/threonine protein phosphatase that is involved in many numerous cell signaling pathways [1]. It is activated by increases in intracellular calcium concentrations, a process that requires the binding of the calcium-sensing protein calmodulin to a recognition region within calcineurin's regulatory domain.

Calcineurin has the ability to dephosphorylate a broad range of proteins. Notably, calcineurin induces transcription factors (NFATs) that are important in the transcription of IL-2 genes. IL-2 activates T-helper lymphocytes and induces the production of other cytokines. In this way, it governs the action of cytotoxic lymphocytes [1]. Other transcription factor substrates regulated by dephosphorylation by calcineurin include the forkhead transcription factors (FOXO), myocyte-specific enhancer factor 2 (MEF2), and transcription factor EB (TFEB) [2-4]. These transcription factors regulate a wide variety of processes including metabolism and autophagy.

References:

1. Baksh S. et al., 2000. The role of calcineurin in lymphocyte activation. Semin Immunol. 12(4):405-15.
2. Li H. et al., 2011. Interaction of calcineurin with substrates and targeting proteins. Trends Cell Biol. 21(2):91-103.
3. Shimizu H. et al., 2017. The Calcineurin-FoxO-MuRF1 signaling pathway regulates myofibril integrity in cardiomyocytes. Elife. 6:e27955.
4. Li J. et al., 2013. Regulation of MEF2 transcriptional activity by calcineurin/mAKAP complexes. Exp Cell Res. 319(4):447-54.

Chemical structure of FK506: