A Novel Role for the Immunophilin FKBP52 in Copper Transport

Abstract

FK506-binding protein 52 (FKBP52) is an immunophilin that possesses peptidylprolyl cis/trans-isomerase(PPIase) activity and is a component of a subclass of steroid hormone receptor complexes. Several recent studies indicate that immunophilins can regulate neuronal survival and nerve regeneration although the molecular mechanisms are poorly understood. To investigate the function of FKBP52 in the nervous system, we employed a yeast two-hybrid strategy using the PPIase domain (domain I) as bait to screen a neonatal rat dorsal root ganglia cDNA expression library. We identified an interaction between FKBP52 domain I and Atox1, a copper-binding metallochaperone. Atox1 interacts with Menkes disease protein and Wilson disease protein (WD) and functions in copper efflux. The interaction between FKBP52 and Atox1 was observed in both glutathione S-transferase pull-down experiments and when proteins were ectopically expressed in human embryonic kidney (HEK) 293T cells and was sensitive to FK506. Interestingly, the FKBP52/Atox1 interaction was enhanced when HEK 293T cells were cultured in copper-supplemented medium and decreased in the presence of the copper chelator, bathocuproine disulfate, suggesting that the interaction is regulated in part by intracellular copper. Overexpression of FKBP52 increased rapid copper efflux in 64 Cu-loaded cells, as did the overexpression of WD transporter. Taken together, our present findings suggest that FKBP52 is a component of the copper efflux machinery, and in so, may also promote neuroprotection from copper toxicity. FKBP521 is a high molecular weight FK506-binding immunophilin first identified as a component of steroid hormone receptor heterocomplexes (1). Analysis of mRNA and protein levels has demonstrated that FKBP52 is widely expressed in mammalian tissues but particularly abundant in the nervous system (2, 3). Structurally, FKBP52 contains an N-terminal peptidylprolyl cis-trans-isomerase (PPIase) domain (domain I), a FKBP-like pseudo domain (domain II), three tetratricopeptide repeat (TPR) domains (domain III) that mediate proteinprotein interactions with HSP90, and a C-terminal domain calmodulin-binding site (domain IV) (4, 5).FKBP52 has been shown to play important roles in a diverse number of intracellular processes, but much research has focused on its involvement in steroid hormone regulation. FKBP52 regulates the maturation of steroid hormone receptor complexes through interactions between its TPR domain and HSP90 chaperones, which act as scaffolds for receptor assembly and are thought to enhance the affinity of estrogen receptor and the glucocorticoid receptor toward their ligands (1, 6). The PPIase domain of FKBP52 facilitates translocation of the activated steroid receptors to the nucleus by binding to cytoplasmic dynein (7). FKBP52 serves as a transcriptional regulator by repressing the activity of interferon regulatory factor-4 in immune cells (8) and heat-shock factor-1 in HeLa cells (9). FKBP52 has been implicated in the cardiotrophic effect of cardiotrophin-1 (10...

The Role of Complex Formation between the Escherichia coli Hydrogenase Accessory Factors HypB and SlyD

“…For example, FKBP52 binds to Atox1, a metallochaperone that plays a role in delivering copper for export by the Wilson and Menkes proteins, and overexpression of FKBP52 enhances copper release in a cell culture model system (49). There are other proteins that are involved in metal homeostasis and that have polyhistidine regions.…”

A Role for SlyD in the Escherichia coli Hydrogenase Biosynthetic Pathway

“…None of the other known members of the FKBP family has a metal-binding domain similar to the C-terminal sequence of SlyD, but several have been implicated in metal homeostasis pathways. For example, a recent study demonstrated that FKBP52 interacts with the copper metallochaperone Atox1 and has a role in copper efflux (42). Mouse FKBP23 contains two Ca(II)-binding EF-hand motifs, and the ER-localized protein may act as a Ca(II)-dependent chaperone (43).…”

Biochemical basis of regulation of human copper-transporting ATPases

“…It may be that the process of copper transfer by Atox1 is further facilitated by some other proteins or by protein modifications. Recent yeast two-hybrid and immunoprecipitation studies demonstrated interaction between immunophilin FKBP52 and Atox1 that was enhanced in a copper-supplemented medium (82). Furthermore, over-expression of FKBP52 in HEK293 cells increased copper efflux similarly to over-expression of ATP7B.…”