The Bcl-2 Regulator FKBP38-Calmodulin-Ca2+ Is Inhibited by Hsp90

Abstract

FKBP38 is a negative effector of the anti-apoptotic Bcl-2 protein in neuroblastoma cells. The interaction with Bcl-2 and the enzyme activity of FKBP38 depend on prior binding of calmodulin-Ca 2؉ (CaM-Ca 2؉ ) at high Ca 2؉ concentrations. The FKBP38 protein structure contains three tetratricopeptide repeat (TPR) motifs corresponding to the Hsp90 interaction sites of other immunophilins. In this study we show that the TPR domain of FKBP38 interacts with the C-terminal domain of Hsp90, but only if the FKBP38-CaM-Ca 2؉ complex is preformed. Hence, FKBP38 is the first example of a TPR-containing immunophilin that interacts cofactor-dependently with Hsp90. In the ternary Hsp90-FKBP38-CaM-Ca 2؉ complex the active site of FKBP38 is blocked, thus preventing interactions with Bcl-2. The dual control of the active site cleft of FKBP38 by CaM-Ca 2؉ and Hsp90 highlights the importance of the enzyme activity of the FKBP38-CaM-Ca 2؉ complex in the regulation of programmed cell death.The human FKBP38 (FK506-binding protein 38), the product of the FKBP8 gene, belongs to the enzyme class of peptidylprolyl cis/trans isomerases (PPIases, 2 EC 5.2.1.8) that assist protein folding by catalyzing the slow interconversion of cis and trans isomers of the peptide bond preceding proline in polypeptide chains. This isomerization reaction is involved in both de novo protein folding and regulation of biological activity of native proteins. The accelerated isomerization catalyzed by PPIases is essential in signal transduction pathways (1, 2).FKBP38 was found to play an important role in the apoptosis regulation of neuroblastoma cells by inhibiting interactions of Bcl-2 with its cellular targets, such as calcineurin and Bad (3, 4). The negative regulation of Bcl-2 by FKBP38 depends on functional integrity of the FKBP domain, which is controlled by the cellular Ca 2ϩ concentration and the interaction with the Ca 2ϩ sensor CaM, characterizing FKBP38 as the first cofactor-regulated PPIase (3). Potent neuroprotective and neuroregenerative effects of specific low molecular weight FKBP38 inhibitors and FKBP38 short interfering RNA constructs in neuroblastoma cells outline the importance of FKBP38 activity in the control of neuronal apoptosis. Furthermore, the administration of N-(NЈ,NЈ-dimethylcarboxamidomethyl)-cycloheximide, a low molecular weight FKBP38 inhibitor, to an endothelin-1-induced middle cerebral artery occlusion stroke model in the rat brain demonstrated the potency of FKBP38 inhibition for neuroregeneration and neuroprotection in rat brain tissue (5). The crucial role of FKBP38 in the control of neuronal apoptosis is indicated as well by a pronounced FKBP38 expression in neuronal cells (5, 6). Additionally, FKBP38 is also involved in the apoptosis control of other cell types, as recently shown by the anti-apoptotic effect resulting from the interaction of FKBP38 and the NS5A protein of the hepatitis C virus in hepatoma cells (7,8). The FKBP38 ortholog in mice was described to be involved in the regulation of neuronal development by aff...

FK506 Binding Protein 8 Peptidylprolyl Isomerase Activity Manages a Late Stage of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Folding and Stability

“…FKBP8 is able to bind to Hsp90 through its tripartite TPR motif (47), consistent with what has been shown for related family members, such as FKBP51 and -52 (48 -51). However, unlike what is seen with FKBP51 and -52, which facilitate delivery of client proteins through their ability to bind Hsp90 and client simultaneously, Hsp90 binding prevents the ability of FKBP8 to interact with client proteins (47). This raises the possibility that FKBP8 has an additional independent role in the PN.…”

“…1) would suggest a common cellular function, a difference in their ability to interact with client proteins suggests otherwise. Whereas FKBP52 can only bind to the SHR receptor in the presence of Hsp90 (77)(78)(79)(80)(81), the binding of FKBP8 to a client, Bcl-2, is abolished upon Hsp90 recruitment (47). One possibility is that FKBP8 delivers client proteins to Hsp90, an event requiring client release upon binding of the TPR domain of FKBP8 to the C terminus of Hsp90.…”

Hsp40 Chaperones Promote Degradation of the hERG Potassium Channel

“…Hop binding would recruit Hsp90 to the complex and cause Hsc70 to dissociate. Hop may then be replaced by FKBP38, because these co-chaperones are thought to compete for Hsp90 binding (46,47). The activities of Hsp90 and FKBP38, which are known to promote proper hERG folding (23), may constitute a final chaperone-mediated folding step before export.…”

HSP90 regulates cell survival via inositol hexakisphosphate kinase-2

“…FKBP38 is a peptidylprolyl cis-trans isomerase that promotes apoptosis by inhibiting interactions of Bcl-2 with calcineurin and Bad. Binding of HSP90 to FKBP38 inhibits FKBP38 catalytic activity and blocks FKBP38-Bcl-2 binding, thus preventing apoptosis (44). Like IP6K2, FKBP38 interacts with the C terminus of HSP90 in a geldanamycin-insensitive manner.…”