The immunosuppressive action of the calcineurin inhibitor cyclosporine A (CsA) stems from the inhibition of nuclear factor of activated T cells (NFAT) signaling in T cells. CsA is also used for the treatment of proteinuric kidney diseases. As it stands, the antiproteinuric effect of CsA is attributed to its immunosuppressive action. Here we show that the beneficial effect of CsA on proteinuria is not dependent on NFAT inhibition in T cells, but rather results from the stabilization of the actin cytoskeleton in kidney podocytes. CsA blocks the calcineurin-mediated dephosphorylation of synaptopodin, a regulator of Rho GTPases in podocytes, thereby preserving the phosphorylation-dependent synaptopodin–14-3-3β interaction. Preservation of this interaction, in turn, protects synaptopodin from cathepsin L–mediated degradation. These results represent a new view of calcineurin signaling and shed further light on the treatment of proteinuric kidney diseases. Novel calcineurin substrates such as synaptopodin may provide promising starting points for antiproteinuric drugs that avoid the serious side effects of long-term CsA treatment.
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We thank C. Chiu and S. Ratner for excellent technical assistance and T. Reinheckel for the analysis of CatL cleavage sites. We thank the Mount Sinai School of Medicine Mouse Genetics Research Facility for performing pronuclear injections. We also thank J.B. Kopp (US National Institutes of Health) for providing the podocin-rtTA mice, H. Fu (Emory University) for yellow fluorescence protein–tagged difopein and E.N. Olson (The University of Texas Southwestern Medical Center at Dallas) for wild-type and constitutively active calcineurin cDNA constructs. Y.H.C. was supported by a research fellowship from the Albert Einstein College of Medicine, S.F. was supported by Karger Stiftung and J.D. was supported by the Deutsche Forschungsgemeinschaft. This work was supported by US National Institutes of Health grants DA18886, DK57683 and DK062472 and the George M. O'Brien Kidney Center grants DK064236 (to P.M.) and DK073495 (to J.R.).
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Faul, C., Donnelly, M., Merscher-Gomez, S. et al. The actin cytoskeleton of kidney podocytes is a direct target of the antiproteinuric effect of cyclosporine A. Nat Med 14, 931–938 (2008). https://doi.org/10.1038/nm.1857
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