FK506, an Immunosuppressive Drug, Induces Autophagy by Binding to the V‑ATPase Catalytic Subunit A in Neuronal Cells

The drug FK506 (tacrolimus, fujimycin)
exerts its immunosuppressive
effects by regulating the nuclear factor of the activated T-cell (NFAT)
family of transcription factors. However, FK506 also exhibits neuroprotective
effects, but its direct target proteins that mediate these effects
have not been determined. To identify the target proteins responsible
for FK506’s neuroprotective effects, the drug affinity responsive
target stability (DARTS) method was performed using label-free FK506,
and LC–MS/MS analysis of the FK506-treated proteome was also
performed. Using DARTS and LC–MS/MS analyses in combination
with reference studies, V-ATPase catalytic subunit A (ATP6V1A) was
identified as a new target protein of FK506. The biological relevance
of ATP6V1A in mediating the neuroprotective effects of FK506 was validated
by analyzing FK506 activity with respect to autophagy via acridine
orange staining and transcription factor EB (TFEB) translocation assay.
These analyses demonstrated that the binding of FK506 with ATP6V1A
induces autophagy by activating the translocation of TFEB from the
cytosol into the nucleus. Because autophagy has been identified as
a mechanism for treating neurodegenerative diseases and because we
have demonstrated that FK506 induces autophagy, this study demonstrates
that FK506 is a possible new therapy for treating neurodegenerative
diseases.