InterAKTions with FKBPs - Mutational and Pharmacological Exploration

Abstract

The FK506-binding protein 51 (FKBP51) is an Hsp90-associated co-chaperone which regulates steroid receptors and kinases. In pancreatic cancer cell lines, FKBP51 was shown to recruit the phosphatase PHLPP to facilitate dephosphorylation of the kinase Akt, which was associated with reduced chemoresistance. Here we show that in addition to FKBP51 several other members of the FKBP family bind directly to Akt. FKBP51 can also form complexes with other AGC kinases and mapping studies revealed that FKBP51 interacts with Akt via multiple domains independent of their activation or phosphorylation status. The FKBP51-Akt1 interaction was not affected by FK506 analogs or Akt active site inhibitors, but was abolished by the allosteric Akt inhibitor VIII. None of the FKBP51 inhibitors affected AktS473 phosphorylation or downstream targets of Akt. In summary, we show that FKBP51 binds to Akt directly as well as via Hsp90. The FKBP51-Akt interaction is sensitive to the conformation of Akt1, but does not depend on the FK506-binding pocket of FKBP51. Therefore, FKBP inhibitors are unlikely to inhibit the Akt-FKBP-PHLPP network.

FKBPs and the Akt/mTOR pathway

“…32,33 In addition, FKBP51 associates with numerous kinases. 34,35 Notably, FKBP51 was found to act as a scaffolding protein to facilitate the dephosphorylation of Akt by the phosphatase PHLPP. 36,37 In cells, the interaction of FKBP51 with Akt was in part mediated by Hsp90 (FKBP51 binds to Hsp90 via its TPR domain and Akt is an established Hsp90 client).…”

“…36,37 In cells, the interaction of FKBP51 with Akt was in part mediated by Hsp90 (FKBP51 binds to Hsp90 via its TPR domain and Akt is an established Hsp90 client). 35 However, FKBP51 could also interact with Akt directly. Importantly, the Akt-FKBP51 interaction was unaffected by FK506, rapamycin or synthetic analogs thereof.…”

Coupling of Conformational Transitions in the N-terminal Domain of the 51-kDa FK506-binding Protein (FKBP51) Near Its Site of Interaction with the Steroid Receptor Proteins

“…Presumably acting via the glucocorticoid receptor, single nucleotide polymorphisms in the fkbp5 gene exhibit a strong correlation with recurrence of depressive episodes, the rate of response to antidepressant therapies, and in psychological stress disorders (9,10). As a necessary chaperone for the Akt-specific phosphatase PHLPP (11,12), FKBP51 also provides indirect feedback regulation by inhibiting glucocorticoid receptor phosphorylation via the Aktp38 kinase pathway (13,14).…”

“…The FK1 domain mediates the selectivity of interaction for steroid receptor binding exchange (15,16), dynein binding (6), and inhibition of the Akt kinase (12). The peptidylprolyl isomerase activity of this domain is not required for receptor binding exchange (16) or Akt kinase inhibition (12).…”

“…The peptidylprolyl isomerase activity of this domain is not required for receptor binding exchange (16) or Akt kinase inhibition (12). Using both * This work was supported, in whole or in part, by National Institutes of Health Grant GM 088214 (to G. H.).…”