Cloning and expression of a mouse cDNA encoding p59, an immunophilin that associates with the glucocorticoid receptor

Role of cellular FKBP52 protein in intracellular trafficking of recombinant adeno-associated virus 2 vectors

We have reported that tyrosine-phosphorylated forms of a cellular protein, FKBP52, inhibit the second-strand DNA synthesis of adeno-associated virus 2 (AAV), leading to inefficient transgene expression from recombinant AAV vectors. To further explore the role of FKBP52 in AAV-mediated transduction, we established murine embryo fibroblasts (MEFs) cultures from FKBP52 wild-type (WT), heterozygous (HE), and knockout (KO) mice. Conventional AAV vectors failed to transduce WT MEFs efficiently, and the transduction efficiency was not significantly increased in HE or KO MEFs. AAV vectors failed to traffic efficiently to the nucleus in these cells. Treatment with hydroxyurea (HU) increased the transduction efficiency of conventional AAV vectors by approximately 25-fold in WT MEFs, but only by approximately 4-fold in KO MEFs. The use of self-complementary AAV (scAAV) vectors, which bypass the requirement of viral second-strand DNA synthesis, revealed that HU treatment increased the transduction efficiency approximately 23-fold in WT MEFs, but only approximately 4-fold in KO MEFs, indicating that the lack of HU treatment-mediated increase in KO MEFs was not due to failure of AAV to undergo viral second-strand DNA synthesis. Following HU treatment, approximately 59% of AAV genomes were present in the nuclear fraction from WT MEFs, but only approximately 28% in KO MEFs, indicating that the pathway by which HU treatment mediates nuclear transport of AAV was impaired in KO MEFs. When KO MEFs were stably transfected with an FKBP52 expression plasmid, HU treatment-mediated increase in the transduction efficiency was restored in these cells, which correlated directly with improved intracellular trafficking. Intact AAV particles were also shown to interact with FKBP52 as well as with dynein, a known cellular protein involved in AAV trafficking. These studies suggest that FKBP52, being a cellular chaperone protein, facilitates intracellular trafficking of AAV, which has implications in the optimal use of recombinant AAV vectors in human gene therapy.

Organization of the human FK506-binding immunophilin FKBP52 protein gene (FKBP4)

FKBP52 is a widely expressed FK506-binding immunophilin that possesses peptidylprolyl isomerase activity and a tetratricopeptide repeat involved in protein-protein interaction. FKBP52 plays an important role in steroid receptor function and is implicated in other diverse processes, including regulation of transcription, cation channel activity, and gene transfer efficiency. Reported here is the genomic organization of the human FKBP52 gene (FKBP4), which shares all but one of the same exon-intron boundaries as the structurally related immunophilin FKBP51 gene (FKBP5). Approximately 3.5 kb of 5'-flanking DNA of FKBP4 was subcloned into a luciferase reporter vector and was found to exhibit robust activity in T-47D, MCF7, and COS-7 cells. Promoter constructs with only 143 bp of upstream sequence maintained high activity. This region contains a CAAT motif sequence and consensus binding sites for Sp1, heat-shock factor, and MYC-MAX, which are conserved in the rabbit FKBP4 promoter and, when deleted, dramatically reduced promoter activity in T-47D cells.

Calcium- and FK506-independent interaction between the immunophilin FKBP51 and calcineurin

FKBP51 is a member of the immunophilin family having intrinsic peptidyl-prolyl cis-trans-isomerase (PPIase) activity. Its enzymatic activity is inhibited by binding either immunosuppressive agent FK506 or rapamycin. Similar to FKBP12, but at higher concentrations of FK506, FKBP51 has been shown to inhibit the serine/threonine phosphatase activity of calcineurin in the presence of calcium and calmodulin. Here we show that a glutathione S-transferase (GST) fusion protein of FKBP51 on glutathione-Sepharose beads precipitated both purified calcineurin from bovine brain and calcineurin from murine T cell lysates. Surprisingly, the binding of GST-FKBP51 to calcineurin was FK506-independent and independent of a requirement for calcium or exogenous calmodulin. Unlike FKBP12, FKBP51 transiently expressed in COS-7 cells was precipitated by calcineurin bound to calmodulin-Sepharose beads in the absence of either FK506 or rapamycin. Unlike FKBP12, however, overexpression of FKBP51 in Jurkat T cells did not significantly affect the transcriptional activation of nuclear factor of activated T cells (NFAT) upon physiological stimulation, nor did it affect the ability of FK506 to inhibit NFAT-driven transcription. We generated a series of FKBP51 mutations to map the interaction of FKBP51 with calcineurin. Deletion of the aminoterminal, FKBP12-like domain of FKBP51 did not affect the ability of FKBP51 to bind to purified calcineurin, while deletion of the FKBP51 carboxyterminal domain abrogated the ability of FKBP51 to bind to calcineurin. Taken together, these results demonstrate a novel interaction between calcineurin and the immunophilin FKBP51 that is independent of calcium, calmodulin, and drug. The binding site on calcineurin for FKBP51 is separable from the immunophilin PPIase-active and drug-binding site.

Tacrolimus limits polymorphonuclear leucocyte accumulation and protects against myocardial ischaemia- reperfusion injury

Intercellular adhesion molecule-1 (ICAM-1) plays an important role in the pathogenesis of either human and experimental myocardial ischaemia. Tacrolimus, formerly known as FK506, has been previously shown to display cardioprotective effects on experimental ischaemia/reperfusion-induced myocardial damage. This study investigated whether cardioprotection induced by tacrolimus in myocardial ischaemia-reperfusion (MI/R) injury might be due to inhibition of the nuclear factor kappa B (NF- kappaB) that in turn causes reduced cardiac ICAM-1 expression and blunted polymorphonuclear leukocyte accumulation. Anaesthetized rats were subjected to total occlusion (45 min) of the left main coronary artery followed by 5 h reperfusion (MI/R). Sham myocardial ischaemia-reperfusion rats (Sham MI/R) were used as controls. Myocardial necrosis, myocardial myeloperoxidase activity, serum creatine kinase (CK) activity, cardiac mRNA for ICAM-1 reverse-transcriptase polymerase chain reaction, the inhibitory protein of NF- kappaB I kappaB alpha (Western blot analysis) in the myocardium-at-risk, and left ventricle d P/d t(max)were evaluated. Myocardial ischaemia plus reperfusion in untreated rats produced marked myocardial necrosis, increased serum CK activity and myeloperoxidase activity (MPO, a marker of leukocyte accumulation) both in the area at risk and in the necrotic area, and reduced the left ventricle dP/d t(max). Furthermore, inhibitory protein I kappaB alpha levels decreased, and cardiac mRNA for ICAM-1 increased, after 0.5 and 5 h of reperfusion, respectively. Administration of tacrolimus (25, 50 and 100microg/kg as an i.v. infusion 5 min after reperfusion) lowered myocardial necrosis and myeloperoxidase activity in the area at risk and in necrotic area, decreased serum CK activity, increased left ventricle dP/d t(max), reduced the loss the of inhibitory protein I kappaB alpha and blunted the message for ICAM-1. The present data suggest that tacrolimus blocks the early activation of the transcription factor NF- kappaB, suppresses ICAM-1 gene activation, reduces leukocyte accumulation and protects against myocardial ischaemia-reperfusion injury.

Tacrolimus suppresses tumour necrosis factor-alpha and protects against splanchnic artery occlusion shock

1. Tumour necrosis factor (TNF-alpha) is a pleiotropic cytokine which is deeply involved in the pathogenesis of splanchnic artery occlusion (SAO) shock. Tacrolimus, formerly known as FK506, is a macrolide antibiotic, that blocks the transcription of several proinflammatory cytokines including TNF-alpha. 2. Male anaesthetized rats were subjected to clamping of the splanchnic arteries for 45 min. This surgical procedure resulted in an irreversible state of shock (SAO shock). Sham operated animals were used as controls. SAO shocked rats had a decreased survival rate (0% at 4 h of reperfusion, while sham shocked rats survived more than 4 h), enhanced serum TNF-alpha concentrations (415+/-12 U ml(-1)), decreased mean arterial blood pressure (MAP), leukopenia and increased ileal leukocyte accumulation studied by means of myeloperoxidase activity (MPO=7.5+/-0.3 U g(-1) tissue). Moreover aortic rings from shocked rats showed a marked hyporeactivity to phenylephrine (PE, 1 nM - 10 microM), reduced responsiveness to acetylcholine (ACh, 10 nM - 10 microM) and increased staining for intercellular adhesion molecule-1 (ICAM-1). Furthermore increased mRNA for TNF-alpha was observed in peritoneal macrophages of SAO shocked rats. 3. Tacrolimus (100 microg kg(-1), 5 min after splanchnic arteries occlusion) increased survival rate (SAO + Tacrolimus = 100% at 4 h of reperfusion), reverted the marked hypotension, reduced serum TNF-alpha (15+/-3 U ml(-1)), ameliorated leukopenia, reduced ileal MPO (0.9+/-0.01 U g(-1) tissue), restored to control values the hyporeactivity to PE. improved the reduced responsiveness to ACh and blunted the enhanced immunostaining for ICAM-1 in the aorta. Finally tacrolimus suppressed cytokine mRNA levels in peritoneal macrophages. 4. The data suggest that tacrolimus may represent a new therapeutic approach in circulatory shock.

The function of steroid hormone receptors is inhibited by the hsp90-specific compound geldanamycin

The ansamycin antibiotic geldanamycin, which specifically interacts with the heat shock protein hsp90, was used to study the function of hsp90 in steroid hormone receptors. We observed inhibition of glucocorticoid-specific gene induction in several responsive cell systems. Hormone binding abilities of receptors for glucocorticoid, progestin, androgen, and estrogen were inhibited upon exposing intact cells to geldanamycin. Inhibition was only seen when geldanamycin was applied to cell cultures under growth conditions or was present during in vitro synthesis; presynthesized receptors in cell extracts were not affected. Upon withdrawal of geldanamycin, glucocorticoid binding ability was regained; this was partially independent of de novo protein synthesis. Geldanamycin caused decreased levels of immunoreactive glucocorticoid receptors in wild-type cells with enhanced degradation occurring through the ubiquitin-proteasome pathway. Analysis of receptors from treated cells revealed a heteromeric structure of normal size in which the receptor polypeptide is complexed with normal amounts of hsp90 and the immunophilin p59. These data support the view that hsp90 actively participates in steroid-induced signal transduction, and they suggest that geldanamycin affects receptor action without disrupting hsp90-containing heterocomplexes per se. Nevertheless, complexes synthesized and assembled in vitro in the presence of geldanamycin differ from receptors of cellular origin.

Steroid receptor interactions with heat shock protein and immunophilin chaperones

We have provided a historical perspective on a body of steroid receptor research dealing with the structure and physiological significance of the untransformed 9S receptor that has often confused both novice and expert investigators. The frequent controversies and equivocations of earlier studies were due to the fact that the native, hormone-free state of these receptors is a large multiprotein complex that resisted description for many years because of its unstable and dynamic nature. The untransformed 9S state of the steroid and dioxin receptors has provided a unique system for studying the function of the ubiquitous, abundant, and conserved heat shock protein, hsp90. The hormonal control of receptor association with hsp90 provided a method of manipulating the receptor heterocomplex in a manner that was physiologically meaningful. For several steroid receptors, binding to hsp90 was required for the receptor to be in a native hormone-binding state, and for all of the receptors, hormone binding promoted dissociation of the receptor from hsp90 and conversion of the receptor to the DNA-binding state. Although the complexes between tyrosine kinases and hsp90 were discovered earlier, the hormonal regulation or steroid receptor association with hsp90 permitted much more rapid and facile study of hsp90 function. The observations that hsp90 binds to the receptors through their HBDs and that these domains can be fused to structurally different proteins bringing their function under hormonal control provided a powerful linkage between the hormonal regulation of receptor binding to hsp90 and the initial step in steroid hormone action. Because the 9S receptor hsp90 heterocomplexes could be physically stabilized by molybdate, their protein composition could be readily studied, and it became clear that these complexes are multiprotein structures containing a number of unique proteins, such as FKBP51, FKBP52, CyP-40, and p23, that were discovered because of their presence in these structures. Further analysis showed that hsp90 itself exists in a variety of native multiprotein heterocomplexes independent of steroid receptors and other 'substrate' proteins. Cell-free systems can now be used to study the formation of receptor heterocomplexes. As we outlined in the scheme of Fig. 1, the multicomponent receptor-hsp90 heterocomplex assembly system is being reconstituted, and the importance of individual proteins, such as hsp70, p60, and p23, in the assembly process is becoming recognized. It should be noted that our understanding of the mechanism and purpose of steroid receptor heterocomplex assembly is still at an early stage. We can now speculate on the roles of receptor-associated proteins in receptor action, both as individuals and as a group, but their actual functions are still vague or unknown. We can make realistic models about the chaperoning and trafficking of steroid receptors, but we don't yet know how these processes occur, we don't know where chaperoning occurs in the cell (e.g. Is it limited to the cytoplasm? Is it a diffuse process or does chaperoning occur in association with structural elements?), and, with the exception of the requirement for hormone binding, we don't know the extent to which the hsp90-based chaperone system impacts on steroid hormone action. It is not yet clear how far the discovery of this hsp90 heterocomplex assembly system will be extended to the development of a general understanding of protein processing in the cell. Because this assembly system is apparently present in all eukaryotic cells, it probably performs an essential function for many proteins. The bacterial homolog of hsp90 is not an essential protein, but hsp90 is essential in eukaryotes, and recent studies indicate that the development of the cell nucleus from prokaryotic progenitors was accompanied by the duplication of genes for hsp90 and hsp70 (698). (ABSTRACT TRUNCATED)

The role of the hsp90-based chaperone system in signal transduction by nuclear receptors and receptors signaling via MAP kinase

The multicomponent heat-shock protein (hsp) 90-based chaperone system is an ubiquitous protein-folding system in the cytoplasm of eukaryotes. Several signal transduction systems utilize an interaction with hsp90 as an essential component of the signaling pathway. The steroid and dioxin receptors are bound to hsp90 through their hormone-binding domains, and several of them must be bound to hsp90 in order to have a ligand-binding site. The binding of ligands to these receptors promotes their dissociation from hsp90, an event that is the first step in their signaling pathways. Several protein kinases, including the Src and Raf components of the MAP kinase system, are also bound to hsp90. Genetic studies in yeast have demonstrated that hsp90 is required for normal signaling via steroid and dioxin receptors and for the activity of Src in vivo. The hsp90-based chaperone system has been reconstituted from purified components, permitting detailed analysis of the molecular basis of the chaperone's role in signal transduction.

A model of protein targeting mediated by immunophilins and other proteins that bind to hsp90 via tetratricopeptide repeat domains

We have shown recently that the immunophilins CyP-40 and FKBP52/hsp56 bind to a common site on hsp90 and that they exist in separate heterocomplexes with the glucocorticoid receptor (GR). FKBP52/hsp56 binds to hsp90 via its tetratricopeptide repeat (TPR) domains, it is not required for GR.hsp90 heterocomplex assembly, and it is thought to play a role in targeted movement of the GR. In this work we examine the hsp90 binding of four proteins (FKBP52/hsp56, CyP-40, p50, Mas70p) thought to be involved in targeted protein trafficking. FKBP52/hsp56 and CyP-40 (each with three TPRs), localize to the nucleus and nucleoli, respectively, and form relatively weak complexes with hsp90 that are competed by a CyP-40 fragment containing its three TPRs. The p50 component of the Src.hsp90 and Raf.hsp90 heterocomplexes localizes to cytoskeletal fibers extending from the perinuclear region to the plasma membrane and forming a rim under the plasma membrane of endothelial cells. p50, Mas70p (seven TPRs), which is a receptor for mitochondrial import, and the p60 (six to eight TPRs) component of the steroid receptor.hsp90 heterocomplex assembly system bind very tightly to hsp90 in a manner that is not competed by the CyP-40 fragment. However, bacterially expressed p60 blocks the binding of p50, Mas70p, FKBP52/hsp56, and CyP-40 to purified hsp90. The data are consistent with binding of all of these proteins to a site on hsp90 that is a general TPR domain acceptor. Our localization and binding data are used to develop a model in which proteins that are chaperoned by hsp90 move as dynamic complexes to their cellular sites of action, with the TPR-containing protein participating in targeting the movement of the complexes.

Cloning the gene encoding Schistosoma mansoni p50, an immunophilin

A 2.2-kb fragment of genomic DNA encoding Schistosoma mansoni immunophilin p50 (Smp50) was identified on a 14-kb genomic clone. The sequence of Smp50 reveals seven exons interrupted by six small introns ranging from 28-35 bp in size. The transcription start point, defined by primer extension analysis of schistosome RNA, begins at 30 bp upstream from the start AUG codon. Smp50 lacks a TATA box and appears to be a single-copy gene.

Identification and characterization of an immunophilin expressed during the clonal expansion phase of adipocyte differentiation

Mouse 3T3-L1 cells differentiate into fat-laden adipocytes in response to a cocktail of adipogenic hormones. This conversion process occurs in two discrete steps. During an early clonal expansion phase, confluent 3T3-L1 cells proliferate and express the products of the beta and delta members of the CCAAT/enhancer binding protein (C/EBP) family of transcription factors. The cells subsequently arrest mitotic growth, induce the expression of the alpha form of C/EBP, and acquire the morphology of fully differentiated adipocytes. Many of the genes induced during the terminal phase of adipocyte conversion are directly activated by C/EBP alpha, and gratuitous expression of this transcription factor is capable of catalyzing adipose conversion in a number of different cultured cell lines. The genetic program undertaken during the clonal expansion phase of 3T3-L1 differentiation, controlled in part by C/EBP beta and C/EBP delta, is less clearly understood. To study the molecular events occurring during clonal expansion, we have identified mRNAs that selectively accumulate during this phase of adipocyte conversion. One such mRNA encodes an immunophilin hereby designated FKBP51. In this report we provide the initial molecular characterization of FKBP51.

FKBP51, a novel T-cell-specific immunophilin capable of calcineurin inhibition

The immunosuppressive drugs FK506 and cyclosporin A block T-lymphocyte proliferation by inhibiting calcineurin, a critical signaling molecule for activation. Multiple intracellular receptors (immunophilins) for these drugs that specifically bind either FK506 and rapamycin (FK506-binding proteins [FKBPs]) or cyclosporin A (cyclophilins) have been identified. We report the cloning and characterization of a new 51-kDa member of the FKBP family from murine T cells. The novel immunophilin, FKBP51, is distinct from the previously isolated and sequenced 52-kDa murine FKBP, demonstrating 53% identity overall. Importantly, Western blot (immunoblot) analysis showed that unlike all other FKBPs characterized to date, FKBP51 expression was largely restricted to T cells. Drug binding to recombinant FKBP51 was demonstrated by inhibition of peptidyl prolyl isomerase activity. As judged from peptidyl prolyl isomerase activity, FKBP51 had a slightly higher affinity for rapamycin than for FK520, an FK506 analog. FKBP51, when complexed with FK520, was capable of inhibiting calcineurin phosphatase activity in an in vitro assay system. Inhibition of calcineurin phosphatase activity has been implicated both in the mechanism of immunosuppression and in the observed toxic side effects of FK506 in nonlymphoid cells. Identification of a new FKBP that can mediate calcineurin inhibition and is restricted in its expression to T cells suggests that new immunosuppressive drugs may be identified that, by virtue of their specific interaction with FKBP51, would be targeted in their site of action.