Molecular cloning, DNA sequence analysis, and biochemical characterization of a novel 65-kDa FK506-binding protein (FKBP65)

Profibrotic behavior of fibroblasts derived from patients that develop posttraumatic shoulder stiffness

Background and Aims

Arthrofibrosis is a severe scarring condition characterized by joint stiffness and pain. Fundamental to developing arthrofibrotic scars is the accelerated production of procollagen I, a precursor of collagen I molecules that form fibrotic deposits in affected joints. The procollagen I production mechanism comprises numerous elements, including enzymes, protein chaperones, and growth factors. This study aimed to elucidate the differences in the production of vital elements of this mechanism in surgical patients who developed significant posttraumatic arthrofibrosis and those who did not.

Methods

We studied a group of patients who underwent shoulder arthroscopic repair of the rotator cuff. Utilizing fibroblasts isolated from the patients' rotator intervals, we analyzed their responses to profibrotic stimulation with transforming growth factor β1 (TGFβ1). We compared TGFβ1-dependent changes in the production of procollagen I. We studied auxiliary proteins, prolyl 4-hydroxylase (P4H), and heat shock protein 47 (HSP47), that control procollagen stability and folding. A group of other proteins involved in excessive scar formation, including connective tissue growth factor (CTGF), α smooth muscle actin (αSMA), and fibronectin, was also analyzed.

Results

We observed robust TGFβ1-dependent increases in the production of CTGF, HSP47, αSMA, procollagen I, and fibronectin in fibroblasts from both groups of patients. In contrast, TGFβ1-dependent P4H production increased only in the stiff-shoulder-derived fibroblasts.

Conclusion

Results suggest P4H may serve as an element of a mechanism that modulates the fibrotic response after rotator cuff injury.

Penetrating Exploration of Prognostic Correlations of the FKBP Gene Family with Lung Adenocarcinoma

The complexity of lung adenocarcinoma (LUAD), the development of which involves many interacting biological processes, makes it difficult to find therapeutic biomarkers for treatment. FK506-binding proteins (FKBPs) are composed of 12 members classified as conservative intracellular immunophilin family proteins, which are often connected to cyclophilin structures by tetratricopeptide repeat domains and have peptidyl prolyl isomerase activity that catalyzes proline from residues and turns the trans form into the cis form. Since FKBPs belong to chaperone molecules and promote protein folding, previous studies demonstrated that FKBP family members significantly contribute to the degradation of damaged, misfolded, abnormal, and foreign proteins. However, transcript expressions of this gene family in LUAD still need to be more fully investigated. In this research, we adopted high-throughput bioinformatics technology to analyze FKBP family genes in LUAD to provide credible information to clinicians and promote the development of novel cancer target drugs in the future. The current data revealed that the messenger (m)RNA levels of FKBP2, FKBP3, FKBP4, FKBP10, FKBP11, and FKBP14 were overexpressed in LUAD, and FKBP10 had connections to poor prognoses among LUAD patients in an overall survival (OS) analysis. Based on the above results, we selected FKBP10 to further conduct a comprehensive analysis of the downstream pathway and network. Through a DAVID analysis, we found that FKBP10 was involved in mitochondrial electron transport, NADH to ubiquinone transport, mitochondrial respiratory chain complex I assembly, etc. The MetaCore pathway analysis also indicated that FKBP10 was involved in "Ubiquinone metabolism", "Translation_(L)-selenoaminoacid incorporation in proteins during translation", and "Transcription_Negative regulation of HIF1A function". Collectively, this study revealed that FKBP family members are both significant prognostic biomarkers for lung cancer progression and promising clinical therapeutic targets, thus providing new targets for treating LUAD patients.

Increasing of FKBP9 can predict poor prognosis in patients with prostate cancer

BACKGROUND

FK506 binding protein 9 (FKBP9) has been reported and identified for a long time, but its relationship with cancer is rarely studied. For example, the role of FK506 binding protein 9 in prostate cancer (PCa) is still unclear. Therefore, we decided to detect the expression level of FKBP9 in PCa and explore its clinical significance.

METHODS

The expression level of FKBP9 protein was detected by immunohistochemistry. In addition, it was demonstrated by high-throughput sequencing of mRNA levels in the TCGA (cancer genome atlas) dataset of 499 patients. Kaplan-meier analysis and Cox proportional hazard regression model were used to evaluate the relationship between FKBP9 expression and survival in prostate cancer patients.

RESULTS

The expression of FKBP9 was localized in the cytoplasm, which in normal prostate tissues was obviously lower than that in PCa tissues (P = 0.001). High expression of FKBP9 was related with lymph node metastasis (P = 0.022) and distant metastasis (P = 0.028). Kaplan-Meier survival analysis revealed that the BCR-free survival of PCa patients with high FKBP9 level was significantly shortened (P=0.041).

CONCLUSIONS

FKBP9 may be a cancer promoter that enhances PCa progression, and the level of FKBP9 may be used as an independent precursor of PCa patients.

Comprehensive evaluation of FKBP10 expression and its prognostic potential in gastric cancer

FK506 binding protein 10 (FKBP10) has been reported to be dysregulated in numerous types of cancer; however, few reports have investigated FKBP10 in gastric cancer (GC). The aim of the present study was to investigate FKBP10 expression in GC and to analyze its association with the prognosis of patients with GC. FKBP10 mRNA expression was evaluated using The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. The standardized mean differences of the meta‑analysis were comprehensively evaluated for FKBP10 expression from a series of GEO datasets. Kaplan‑Meier survival and Cox regression analyses were applied to predict the prognostic value of FKBP10 in patients with GC. Additionally, the protein expression levels of FKBP10 were validated by immunohistochemistry (IHC) in 40 GC and adjacent tissues. FKBP10 co‑expression network and bioinformatics analyses were then used to explore the potential functional mechanisms of FKBP10. The results revealed that the mRNA expression levels of FKBP10 were significantly increased in GC within the TCGA and GEO databases. Survival analysis revealed that high FKBP10 expression results in poorer overall survival and disease‑free survival (P<0.05). Multivariate cox regression analysis indicate FKBP10 as a dependent prognostic factor. The results of IHC indicated that the protein expression levels of FKBP10 were higher in GC tissues than in adjacent non‑GC tissues (P<0.001). Co‑expression networks and functional enrichment analysis suggested that FKBP10 may be involved in the development of GC via cell adhesion molecules and extracellular matrix‑receptor interaction pathways. Therefore, the findings of the present study indicated that FKBP10 is upregulated in GC tissues, and suggests its potential prognostic value. Therefore FKBP10 may be a potential therapeutic target for the treatment of GC.

FKBP65-dependent peptidyl-prolyl isomerase activity potentiates the lysyl hydroxylase 2-driven collagen cross-link switch

Bruck Syndrome is a connective tissue disease associated with inactivating mutations in lysyl hydroxylase 2 (LH2/PLOD2) or FK506 binding protein 65 (FKBP65/FKBP10). However, the functional relationship between LH2 and FKBP65 remains unclear. Here, we postulated that peptidyl prolyl isomerase (PPIase) activity of FKBP65 positively modulates LH2 enzymatic activity and is critical for the formation of hydroxylysine-aldehyde derived intermolecular collagen cross-links (HLCCs). To test this hypothesis, we analyzed collagen cross-links in Fkbp10-null and –wild-type murine embryonic fibroblasts. Although LH2 protein levels did not change, FKBP65 deficiency significantly diminished HLCCs and increased the non-hydroxylated lysine-aldehyde–derived collagen cross-links (LCCs), a pattern consistent with loss of LH2 enzymatic activity. The HLCC-to-LCC ratio was rescued in FKBP65-deficient murine embryonic fibroblasts by reconstitution with wild-type but not mutant FKBP65 that lacks intact PPIase domains. Findings from co-immunoprecipitation, protein-fragment complementation, and co-immunofluorescence assays showed that LH2 and FKBP65 are part of a common protein complex. We conclude that FKBP65 regulates LH2-mediated collagen cross-linking. Because LH2 promotes fibrosis and cancer metastasis, our findings suggest that pharmacologic strategies to target FKBP65 and LH2 may have complementary therapeutic activities.

Novel mutations in FKBP10 in Chinese patients with osteogenesis imperfecta and their treatment with zoledronic acid

Osteogenesis imperfecta (OI) is a group of hereditary disorders characterized by decreased bone mass and increased fracture risk. The majority of OI cases have an autosomal dominant pattern of inheritance and are usually caused by mutations in genes encoding type I collagen. OI cases of autosomal recessive inheritance are rare, and OI type XI is attributable to mutation of the FKBP10 gene. Here, we used next-generation sequencing and Sanger sequencing to detect mutations in FKBP10 and to analyze their relation to the phenotypes of OI type XI in three Chinese patients. We also evaluated the efficacy of zoledronic acid treatment in these patients. Two of the affected patients had novel compound heterozygous mutations, one patient with c.343C>T (p.R115X) in exon 2 and c.1085delC (p.A362fsX1) in exon 7, and the other patient with c.879C>G (p.Y293X) in exon 5 and c.918-3C>G in intron 5. In the third proband, we identified a homozygous single base-pair duplication, c.831dupC (p.G278RfsX95) in exon 5. In conclusion, we report for the first time that these novel pathogenic mutations of FKBP10 can lead to the extremely rare type XI OI without contractures, which expands the genotypic spectrum of OI. The phenotypes of these patients are similar to patients with types III or IV OI, and zoledronic acid is effective in increasing BMD, inhibiting bone resorption biomarkers and reducing fractures of these patients.

Disentangling mechanisms involved in collagen pyridinoline cross-linking: The immunophilin FKBP65 is critical for dimerization of lysyl hydroxylase 2

Collagens are subjected to extensive posttranslational modifications, such as lysine hydroxylation. Bruck syndrome (BS) is a connective tissue disorder characterized at the molecular level by a loss of telopeptide lysine hydroxylation, resulting in reduced collagen pyridinoline cross-linking. BS results from mutations in the genes coding for lysyl hydroxylase (LH) 2 or peptidyl-prolyl cis-trans isomerase (PPIase) FKBP65. Given that the immunophilin FKBP65 does not exhibit LH activity, it is likely that LH2 activity is somehow dependent on FKPB65. In this report, we provide insights regarding the interplay between LH2 and FKBP65. We found that FKBP65 forms complexes with LH2 splice variants LH2A and LH2B but not with LH1 and LH3. Ablating the catalytic activity of FKBP65 or LH2 did not affect complex formation. Both depletion of FKBP65 and inhibition of FKBP65 PPIase activity reduced the dimeric (active) form of LH2 but did not affect the binding of monomeric (inactive) LH2 to procollagen Iα1. Furthermore, we show that LH2A and LH2B cannot form heterodimers with each other but are able to form heterodimers with LH1 and LH3. Collectively, our results indicate that FKBP65 is linked to pyridinoline cross-linking by specifically mediating the dimerization of LH2. Moreover, FKBP65 does not interact with LH1 and LH3, explaining why in BS triple-helical hydroxylysines are not affected. Our results provide a mechanistic link between FKBP65 and the loss of pyridinolines and may hold the key to future treatments for diseases related to collagen cross-linking anomalies, such as fibrosis and cancer.

FK506-Binding Protein 10, a Potential Novel Drug Target for Idiopathic Pulmonary Fibrosis

RATIONALE

Increased abundance and stiffness of the extracellular matrix, in particular collagens, is a hallmark of idiopathic pulmonary fibrosis (IPF). FK506-binding protein 10 (FKBP10) is a collagen chaperone, mutations of which have been indicated in the reduction of extracellular matrix stiffness (e.g., in osteogenesis imperfecta).

OBJECTIVES

To assess the expression and function of FKBP10 in IPF.

METHODS

We assessed FKBP10 expression in bleomycin-induced lung fibrosis (using quantitative reverse transcriptase-polymerase chain reaction, Western blot, and immunofluorescence), analyzed microarray data from 99 patients with IPF and 43 control subjects from a U.S. cohort, and performed Western blot analysis from 6 patients with IPF and 5 control subjects from a German cohort. Subcellular localization of FKBP10 was assessed by immunofluorescent stainings. The expression and function of FKBP10, as well as its regulation by endoplasmic reticulum stress or transforming growth factor-β1, was analyzed by small interfering RNA-mediated loss-of-function experiments, quantitative reverse transcriptase-polymerase chain reaction, Western blot, and quantification of secreted collagens in the lung and in primary human lung fibroblasts (phLF). Effects on collagen secretion were compared with those of the drugs nintedanib and pirfenidone, recently approved for IPF.

MEASUREMENTS AND MAIN RESULTS

FKBP10 expression was up-regulated in bleomycin-induced lung fibrosis and IPF. Immunofluorescent stainings demonstrated localization to interstitial (myo)fibroblasts and CD68(+) macrophages. Transforming growth factor-β1, but not endoplasmic reticulum stress, induced FKBP10 expression in phLF. The small interfering RNA-mediated knockdown of FKBP10 attenuated expression of profibrotic mediators and effectors, including collagens I and V and α-smooth muscle actin, on the transcript and protein level. Importantly, loss of FKBP10 expression significantly suppressed collagen secretion by phLF.

CONCLUSIONS

FKBP10 might be a novel drug target for IPF.

Calcineurin regulates coordinated outgrowth of zebrafish regenerating fins

Vertebrates develop organs and appendages in a proportionally coordinated manner, and animals that regenerate them do so to the same dimensions as the original structures. Coordinated proportional growth involves controlled regulation between allometric and isometric growth programs, but it is unclear what executes this control. We show that calcineurin inhibition results in continued allometric outgrowth of regenerating fins beyond their original dimensions. Calcineurin inhibition also maintains allometric growth of juvenile fins and induces it in adult fins. Furthermore, calcineurin activity is low when the regeneration rate is highest, and its activity increases as the rate decreases. Growth measurements and morphometric analysis of proximodistal asymmetry indicate that calcineurin inhibition shifts fin regeneration from a distal growth program to a proximal program. This shift is associated with the promotion of retinoic acid signaling. Thus, we identified a calcineurin-mediated mechanism that operates as a molecular switch between position-associated isometric and allometric growth programs.

FKBP10/FKBP65 expression in high-grade ovarian serous carcinoma and its association with patient outcome

The frequent loss of chromosome 17 in epithelial ovarian carcinomas (EOC), particularly high-grade serous carcinomas (HGSC), has been attributed to the disruption of TP53 (at 17p13.1) and other chromosome 17 genes suspected to play a role in tumour suppressor pathways. In a transcriptome analysis of HGSC, we showed underexpression of a number of chromosome 17 genes, which included FKBP10 (at 17q21.1) and collagen I α 1 (COL1A1; at 17q21.33). FKBP10 codes for the immunophilin FKBP65 and is suspected to act as a chaperone for COL1A1. We have investigated FKBP10 (gene) and FKBP65 (protein) expression in HGSC samples and EOC cell lines that differ in their tumourigenic potential. COL1A1 expression was also investigated given the purported function of FKBP65. RT-PCR analysis verified underexpression of FKBP10 and COL1A1 in HGSCs (n=14) and six tumourigenic EOC cell lines, relative to normal ovarian surface epithelial cells and a non-tumourigenic EOC cell line. Immunohistochemistry analyses of 196 HGSC samples using tissue microarrays revealed variable staining intensities in the epithelial tumour component where only 7.8% and 1.0% of samples stained intensely for FKBP65 and COL1A1, respectively. Variable staining intensities were also observed for the stromal component where 23.6% and 24.1% stained intensely for FKBP65 and COL1A1, respectively. There was no significant correlation of staining intensity of either protein with disease stage. Staining of FKBP65 was clearly visible in normal epithelial cells of the ovarian surface and fallopian tube. There was a significant correlation between absence of FKBP65 staining in the epithelial cell component of the tumour and prolonged overall survival (p<0.001). Our results suggest that underexpression of FKBP65 protein is characteristic of HGSCs and that this expression profile may be linked to molecular pathways associated with an unfavourable outcome in cancer patients.

Absence of FKBP10 in recessive type XI osteogenesis imperfecta leads to diminished collagen cross-linking and reduced collagen deposition in extracellular matrix

Recessive osteogenesis imperfecta (OI) is caused by defects in genes whose products interact with type I collagen for modification and/or folding. We identified a Palestinian pedigree with moderate and lethal forms of recessive OI caused by mutations in FKBP10 or PPIB, which encode endoplasmic reticulum resident chaperone/isomerases FKBP65 and CyPB, respectively. In one pedigree branch, both parents carry a deletion in PPIB (c.563_566delACAG), causing lethal type IX OI in their two children. In another branch, a child with moderate type XI OI has a homozygous FKBP10 mutation (c.1271_1272delCCinsA). Proband FKBP10 transcripts are 4% of control and FKBP65 protein is absent from proband cells. Proband collagen electrophoresis reveals slight band broadening, compatible with ≈10% over-modification. Normal chain incorporation, helix folding, and collagen T(m) support a minimal general collagen chaperone role for FKBP65. However, there is a dramatic decrease in collagen deposited in culture despite normal collagen secretion. Mass spectrometry reveals absence of hydroxylation of the collagen telopeptide lysine involved in cross-linking, suggesting that FKBP65 is required for lysyl hydroxylase activity or access to type I collagen telopeptide lysines, perhaps through its function as a peptidylprolyl isomerase. Proband collagen to organics ratio in matrix is approximately 30% of normal in Raman spectra. Immunofluorescence shows sparse, disorganized collagen fibrils in proband matrix.

Endoplasmic reticulum stress or mutation of an EF-hand Ca(2+)-binding domain directs the FKBP65 rotamase to an ERAD-based proteolysis

FKBP65 is an endoplasmic reticulum (ER)-localized chaperone and rotamase, with cargo proteins that include tropoelastin and collagen. In humans, mutations in FKBP65 have recently been shown to cause a form of osteogenesis imperfecta (OI), a brittle bone disease resulting from deficient secretion of mature type I collagen. In this work, we describe the rapid proteolysis of FKBP65 in response to ER stress signals that activate the release of ER Ca(2+) stores. A large-scale screen for stress-induced cellular changes revealed FKBP65 proteins to decrease within 6-12 h of stress activation. Inhibiting IP(3)R-mediated ER Ca(2+) release blocked this response. No other ER-localized chaperone and folding mediators assessed in the study displayed this phenomenon, indicating that this rapid proteolysis of folding mediator is distinctive. Imaging and cellular fractionation confirmed the localization of FKBP65 (72 kDa glycoprotein) to the ER of untreated cells, a rapid decrease in protein levels following ER stress, and the corresponding appearance of a 30-kDa fragment in the cytosol. Inhibition of the proteasome during ER stress revealed an accumulation of FKBP65 in the cytosol, consistent with retrotranslocation and a proteasome-based proteolysis. To assess the role of Ca(2+)-binding EF-hand domains in FKBP65 stability, a recombinant FKBP65-GFP construct was engineered to ablate Ca(2+) binding at each of two EF-hand domains. Cells transfected with the wild-type construct displayed ER localization of the FKBP65-GFP protein and a proteasome-dependent proteolysis in response to ER stress. Recombinant FKBP65-GFP carrying a defect in the EF1 Ca(2+)-binding domain displayed diminished protein in the ER when compared to wild-type FKBP65-GFP. Proteasome inhibition restored mutant protein to levels similar to that of the wild-type FKBP65-GFP. A similar mutation in EF2 did not confer FKBP65 proteolysis. This work supports a model in which stress-induced changes in ER Ca(2+) stores induce the rapid proteolysis of FKBP65, a chaperone and folding mediator of collagen and tropoelastin. The destruction of this protein may identify a cellular strategy for replacement of protein folding machinery following ER stress. The implications for stress-induced changes in the handling of aggregate-prone proteins in the ER-Golgi secretory pathway are discussed. This work was supported by grants from the National Institutes of Health (R15GM065139) and the National Science Foundation (DBI-0452587).

Comparative analysis of different peptidyl-prolyl isomerases reveals FK506-binding protein 12 as the most potent enhancer of alpha-synuclein aggregation

FK506-binding proteins (FKBPs) are members of the immunophilins, enzymes that assist protein folding with their peptidyl-prolyl isomerase (PPIase) activity. Some non-immunosuppressive inhibitors of these enzymes have neuroregenerative and neuroprotective properties with an unknown mechanism of action. We have previously shown that FKBPs accelerate the aggregation of α-synuclein (α-SYN) in vitro and in a neuronal cell culture model for synucleinopathy. In this study we investigated whether acceleration of α-SYN aggregation is specific for the FKBP or even the PPIase family. Therefore, we studied the effect of several physiologically relevant PPIases, namely FKBP12, FKBP38, FKBP52, FKBP65, Pin1, and cyclophilin A, on α-SYN aggregation in vitro and in neuronal cell culture. Among all PPIases tested in vitro, FKBP12 accelerated α-SYN aggregation the most. Furthermore, only FKBP12 accelerated α-SYN fibril formation at subnanomolar concentrations, pointing toward an enzymatic effect. Although stable overexpression of various FKBPs enhanced the aggregation of α-SYN and cell death in cell culture, they were less potent than FKBP12. When FKBP38, FKBP52, and FKBP65 were overexpressed in a stable FKBP12 knockdown cell line, they could not fully restore the number of α-SYN inclusion-positive cells. Both in vitro and cell culture data provide strong evidence that FKBP12 is the most important PPIase modulating α-SYN aggregation and validate the protein as an interesting drug target for Parkinson disease.

Effect of FKBP65, a putative elastin chaperone, on the coacervation of tropoelastin in vitro

FKBP65 is a protein of the endoplasmic reticulum that is relatively abundant in elastin-producing cells and is associated with tropoelastin in the secretory pathway. To test an earlier suggestion by Davis and co-workers that FKBP65 could act as an intracellular chaperone for elastin, we obtained recombinant FKBP65 (rFKBP65) by expressing it in E. coli and examined its effect on the coacervation characteristics of chicken aorta tropoelastin (TE) using an in vitro turbidimetric assay. Our results reveal that rFKBP65 markedly promotes the initiation of coacervation of TE without significantly affecting the temperature of onset of coacervation. This effect shows saturation at a 1:2 molar ratio of TE to rFKBP65. By contrast, FKBP12, a peptidyl prolyl isomerase, has a negligible effect on TE coacervation. Moreover, the effect of rFKBP65 on TE coacervation is unaffected by the addition of rapamycin, an inhibitor of peptidyl prolyl isomerase (PPIase) activity. These observations rule out the involvement of the PPIase activity of rFKBP65 in modulating the coacervation of TE. Additional experiments using a polypeptide model of TE showed that rFKBP65, while promoting coacervation, may retard the maturation of this model polypeptide into larger aggregates. Based on these results, we suggest that FKBP65 may act as an elastin chaperone in vivo by controlling both the coacervation and the maturation stages of its self-assembly into fibrils.

Developmental regulation and coordinate reexpression of FKBP65 with extracellular matrix proteins after lung injury suggest a specialized function for this endoplasmic reticulum immunophilin

AFKBP65 (65-kDa FK506-binding protein) is an endoplasmic reticulum (ER)-localized peptidyl-prolyl cis-trans isomerase predicted to play a role in the folding and trafficking of secretory proteins. In previous studies, we have shown that FKBP65 is developmentally regulated and associates with the extracellular matrix protein, tropoelastin, during its maturation and transport through the ER. In this study, we show that FKBP65 is expressed in the lung with the same developmental pattern as tropoelastin and other matrix proteins. To test the hypothesis that FKBP65 is upregulated at times when extracellular matrix proteins are being actively synthesized and assembled, adult mice were treated with bleomycin to cause reinitiation of matrix protein production during the ensuing development of pulmonary fibrosis. After bleomycin instillation, FKBP65 expression was reactivated in the lung with a pattern similar to that observed for tropoelastin and type I collagen. Using human lung fibroblast cultures, we showed that FKBP65 does not undergo the unfolded protein response, a response associated with an upregulation of resident ER proteins that occurs after increased ER stress. When fibroblasts were treated with transforming growth factor (TGF)-beta1, which is upregulated during the development of pulmonary fibrosis and known to induce matrix production, FKBP65 expression and synthesis was also increased. Similar to type I collagen and tropoelastin, this response was completely inhibited in a dose-dependent manner by GGTI-298, a geranylgeranyl transferase I inhibitor. Treatment of fibroblasts with an inhibitor of ribonucleic acid (RNA) polymerase II after TGF-beta1 treatment showed that the effect of TGF-beta1 was not because of increased stabilization of the FKBP65 messenger RNA. In summary, we have shown that FKBP65 is highly expressed in lung development, downregulated in the adult, and can be reactivated in a coordinated manner with extracellular matrix proteins after lung injury. The expression pattern of FKBP65, which is atypical for general ER foldases, suggests that FKBP65 has a distinct set of developmentally regulated protein ligands. The response to injury, which may be in part a direct response to TGF-beta1, assures the presence of FKBP65 in the ER of cells actively producing components of the extracellular matrix.

ER stress and the unfolded protein response

Conformational diseases are caused by mutations altering the folding pathway or final conformation of a protein. Many conformational diseases are caused by mutations in secretory proteins and reach from metabolic diseases, e.g. diabetes, to developmental and neurological diseases, e.g. Alzheimer's disease. Expression of mutant proteins disrupts protein folding in the endoplasmic reticulum (ER), causes ER stress, and activates a signaling network called the unfolded protein response (UPR). The UPR increases the biosynthetic capacity of the secretory pathway through upregulation of ER chaperone and foldase expression. In addition, the UPR decreases the biosynthetic burden of the secretory pathway by downregulating expression of genes encoding secreted proteins. Here we review our current understanding of how an unfolded protein signal is generated, sensed, transmitted across the ER membrane, and how downstream events in this stress response are regulated. We propose a model in which the activity of UPR signaling pathways reflects the biosynthetic activity of the ER. We summarize data that shows that this information is integrated into control of cellular events, which were previously not considered to be under control of ER signaling pathways, e.g. execution of differentiation and starvation programs.

Human FK506 binding protein 65 is associated with colorectal cancer

We initiated the present study to identify new genes associated with colorectal cancer. In a previously published microarray study an EST (W80763), later identified as the gene hFKBP10 (NM_021939), was found to be strongly expressed in tumors while absent in the normal mucosa. Here we describe this gene hFKBP10 together with its encoded protein hFKBP65 as a novel marker associated with colorectal cancer. Analysis of 31 colorectal adenocarcinomas and 14 normal colorectal mucosa by RealTime PCR for hFKBP10 showed a significant up-regulation in tumors, when compared with normal mucosa. Immunohistochemical analysis of 26 adenocarcinomas and matching normal mucosa, as well as benign hyperplastic polyps and adenomas, using a monoclonal anti-hFKBP65 antibody, showed that the protein was not present in normal colorectal epithelial cells, but strongly expressed in the tumor cells of colorectal cancer. The protein was also expressed in fibroblasts of both normal mucosa and tumor tissue. Western blot analysis of matched tumors and normal mucosa supported the finding of increased hFKBP65 expression in tumors compared with normal mucosa, in addition to identifying the molecular mass of hFKBP65 to approximately 72 kDa. Cellular localization and glycosylation studies revealed the hFKBP65 protein to be localized in the endoplasmic reticulum, and to be N-glycosylated. In conclusion, the protein hFKBP65 is associated with colorectal cancer, and we hypothesize the protein to be involved in fibroblast and transformed epithelial cell-specific protein synthesis in the endoplasmic reticulum.

Review on testicular development, structure, function, and regulation in common marmoset

BACKGROUND

The common marmoset (Callithrix jacchus) is a New World primate that has been used increasingly in toxicological evaluations including testing for testicular toxicity of pharmaceutical and environmental chemicals. Information on structural and functional characteristics of the testis in common marmosets ("marmoset" in this review) is critical for designing experiments, interpreting data collected, and determining relevance to humans in risk assessment.

METHODS

This study provides a comprehensive review on testicular development, structure, function, and regulation in common marmosets.

RESULTS

There is little information regarding testicular formation and development during gestation. Based on the overall pattern of embryonic development in marmosets, it is postulated that gonadal formation and testicular differentiation most likely takes place during gestational Week 6-12. After birth, the neonatal period of the first 2-3 weeks and the pubertal period from Months 6-12 are critical for establishment of spermatogenesis in the adult. In the adult, a nine-stage model has been used to describe the organization of seminiferous epithelium and multiple stages per tubular cross-section have been observed. Seminiferous epithelium is organized in a wave or partial-wave manner. There are on average two stages per cross-section of seminiferous tubules in adult marmoset testis. Sertoli cells in the marmoset have a uniform morphology. Marmoset spermatogenesis has a high efficiency. The prime determinant of germ cell production is proliferation and survival of spermatogonia. Sertoli cell proliferation during the neonatal period is regulated by follicle-stimulating hormone (FSH), but chorionic gonadotropin (CG), instead of luteinizing hormone (LH), is the only gonadotropin with luteinizing function in marmoset. The receptor gene for CG in marmoset is unique in that it does not have exon 10. Marmosets have a "generalized steroid hormone resistance," i.e., relatively high levels of steroid hormones in circulation and relatively low response to exogenous steroids. Blockage of FSH, CG, and testosterone production during the first 3 months after birth does not cause permanent damage to the male reproductive system. Initiation of spermatogenesis in the marmoset requires unique factors that are probably not present in other mammals. Normal male marmosets respond to estradiol injection positively (increased LH or CG levels), a pattern seen in normal females or castrated males, but not usually in normal males of other mammalian species.

CONCLUSIONS

It seems that the endocrine system including the testis in marmosets has some unique features that have not been observed in rodents, Old World primates, and humans, but detailed comparison in these features among these species will be presented in another review. Based on the data available, marmoset seems to be an interesting model for comparative studies. However, interpretation of experimental findings on the testicular effects in marmosets should be made with serious caution. Depending on potential mode of testicular actions of the chemical under investigation, marmoset may have very limited value in predicting potential testicular or steroid hormone-related endocrine effects of test chemicals in humans.

Candidate target genes for loss of heterozygosity on human chromosome 17q21

Loss of heterozygosity (LOH) on chromosome 17q21 has been detected in 30% of primary human breast tumours. The smallest common region deleted occurred in an interval between the D17S746 and D17S846 polymorphic sequences tagged sites that are located on two recombinant P1-bacteriophage clones of chromosome 17q21: 122F4 and 50H1, respectively. To identify the target gene for LOH, we defined a map of this chromosomal region. We found the following genes: JUP, FK506BP10, SC65, Gastrin (GAS) and HAP1. Of the genes that have been identified in this study, only JUP is located between D17S746 and D17S846. This was of interest since earlier studies have shown that JUP expression is altered in breast, lung and thyroid tumours as well as cell lines having LOH in chromosome 17q21. However, no mutations were detected in JUP using single-strand conformation polymorphism analysis of primary breast tumour DNAs having LOH at 17q21. We could find no evidence that the transcription promoter for JUP is methylated in tumour DNAs having LOH at 17q21. We suspect that the target gene for LOH in primary human breast tumours on chromosome 17q21 is either JUP and results in a haploinsufficiency for expression or may be an unidentified gene located in the interval between D17S846 and JUP.

Changes in peptidyl-prolyl cis/trans isomerase activity and FK506 binding protein expression following neuroprotection by FK506 in the ischemic rat brain

FK506 is an immunosuppressant also showing neuroprotection following cerebral ischemia. FK506 binds to intracellular proteins (FKBP) which have a wide range of functions but have in common the peptidyl-prolyl cis/trans isomerase activity. Following transient focal ischemia, we have analyzed the expression of FKBP12, 52 and 65 and the total FKBP enzyme activity. Furthermore, we have investigated the effect of FK506 on signal transduction in neurons and perfusion changes in the infarct area. After 90 min of transient middle cerebral artery occlusion in male rats the expression of FKBP12, 52 and 65 was analyzed by Western blot in FK506-treated and control animals and the peptidyl-prolyl cis/trans isomerase activity was determined. Magnetic resonance imaging was used to measure tissue perfusion, development of vasogenic edema and infarct size. To investigate the neuronal stress signal cascade, activating transcription factor 2 (ATF-2), Fas-ligand (Fas-L) and c-Jun expression and phosphorylation were analyzed by immunohistochemistry. FK506 decreased the cerebral infarct volume by 53% and reduced the cytotoxic edema. The total FKBP enzymatic activity in the infarct area was increased and blocked dose dependently by FK506. FKBP expression was selectively up-regulated by cerebral ischemia. FK506 treatment does not influence the expression patterns. c-Jun phosphorylation in neurons of the peri-infarct area and Fas-L expression was reduced by FK506 treatment whereas ATF-2 expression was preserved. Cerebral ischemic damage to the brain was reduced by FK506. It was shown for the first time that neuroprotection by FK506 also included the suppression of the cerebral peptidyl-prolyl cis/trans isomerase activity of FKBP in vivo whereas the expression levels of FKBP12, 52 and 65 following ischemia changed slightly and FK506 treatment does not suppress the expression patterns. However, changes of FKBP enzymatic activity result in suppression of the stress cell body response in the peri-infarct area as observed by suppression of c-Jun phosphorylation and Fas-L expression.

Heart-selective expression of the chicken FK506-binding protein (FKBP) 12.6 gene during embryonic development

FKBP12.6, a member of the family of FK506-binding proteins, selectively associates with the cardiac isoform of the ryanodine receptor and thereby stabilizes this Ca(2+) release channel. A chicken FKBP12.6 (chFKBP12.6) cDNA was cloned and shown to encode a protein of 108 amino acids. The deduced amino acid sequence of chFKBP12.6 is 91-92% identical to those of mammalian FKBP12.6 proteins. Northern blot analysis revealed that chFKBP12.6 mRNA is largely restricted to the heart during embryonic development and that the abundance of this mRNA in the heart decreases, and it becomes restricted to the atrium during cardiogenesis. In situ hybridization revealed that chFKBP12.6 mRNA is localized to the precardiac mesoderm before formation of the primitive heart tube. Expression of the chFKBP12.6 gene was initially apparent throughout the developing multichambered heart but became restricted to the atria before hatching. Reverse transcription and polymerase chain reaction analysis demonstrated that chFKBP12.6 mRNA is present in the embryo from early gastrulation and is most abundant immediately after the onset of the heartbeat. These observations suggest that the chFKBP12.6 gene is expressed before heart morphogenesis to play a role in excitation-contraction coupling in cardiomyocytes and that the function of the encoded protein becomes increasingly restricted to the atrium during embryonic development.

Genomic organization of mouse and human 65 kDa FK506-binding protein genes and evolution of the FKBP multigene family

FK506-binding proteins (FKBPs) are peptidyl-prolyl cis/trans isomerases PPIases) that bind the immunosuppressive drug FK506. Of the many eukaryotic FKBPs that have been identified, FKBP65 is an endoplasmic reticulum-localized protein that associates with tropoelastin in the secretory pathway. Unlike any other FKBP characterized so far, FKBP65 is developmentally regulated and may be intimately involved in organogenesis. Here, we report the isolation, sequencing, and genomic organization of the mouse FKBP65 gene (Fkbp10) and provide a comparison with the human ortholog. Mouse Fkbp10 contains 10 exons and 9 introns encompassing 8.5 kb. The exon-intron organization of Fkbp10 displays a pattern of repetition that reflects the coding sequence of the four PPIase, or FK506-binding, domains present in the mature protein. The exon organization of the PPIase domains differs from that of the other FKBP family members. The evolution of the FKBP65 gene and other members of the FKBP multigene family were therefore investigated from a taxonomically diverse array of prokaryotic and eukaryotic taxa. These analyses suggest that the FKBP multigene family emerged early in the evolutionary history of eukaryotes, and during that time some members, including the FKBP65 gene, have experienced gene elongation by means of PPIase domain duplication.

Neuroimmunophilin ligands exert neuroregeneration and neuroprotection in midbrain dopaminergic neurons

Immunosuppressant drugs, like FK506, and nonimmunosuppressant compounds like, GPI1046 and L685818, are immunophilin ligands that specifically bind to immunophilins, like FK506 binding protein 12 (FKBP12). Several lines of evidence show that these ligands exert neurotrophic properties in neural injury models and in PC12 cells. However, the mechanism of the neurotrophic function of the immunophilin ligands is poorly known. In the present study, we use MPP+ and 6-OHDA toxicity models to examine both neuroprotective and neuroregenerative effects of immunophilin ligands on primary cultures of midbrain dopaminergic neurons. We find that FK506, GPI1046 and L685818 at concentrations from 0.01 to 1 microM partially, but significantly, protect dopaminergic neurons against both MPP+ and 6-OHDA toxicity. By Western blot analysis, we also find that all three compounds prevent tyrosine hydroxylase (TH) loss induced by MPP+ and 6-OHDA treatments. Morphologic analysis of dopaminergic neurons, by immunocytochemistry, shows that MPP+ and 6-OHDA cause the retraction and loss of neuronal processes, while FK506, GPI1046 and L685818 promote regeneration of these processes as indicated by increases in process number and length. To examine if FKBP12 is required for neurotrophic effects of immunophilin ligands, we cultured dopaminergic neurons from FKBP12 knockout mice and find that FK506 still protects dopaminergic neurons against MPP+ toxicity. These results suggest that FKBP12 is not essential for the neurotrophic properties of immunophilin ligands, and immunophilin ligands are a new class of neuroprotective and neuroregenerative agents that may have therapeutic potential in a variety of neurological disorders.

Neuroimmunophilins: novel neuroprotective and neuroregenerative targets

Cyclosporin A (CsA) and FK506 (tacrolimus) are immunosuppresants that are widely used in organ transplantation. CsA is an 11-member cyclic peptide, whereas FK506 is a macrolide antibiotic. Recently, these powerful and useful compounds have become of great interest to neuroscientists for their unique neuroprotective and neuroregenerative effects. These drugs and nonimmunosuppressive analogs protect neurons from the effects of glutamate excitotoxicity, focal ischemia, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic cell death. They also stimulate functional recovery of neurons in a variety of neurologic injury paradigms. These drugs exert their effects via immunophilins, the protein receptors for these agents. The immunophilin ligands show particular promise as a novel class of neuroprotective and neuroregenerative agents that have the potential to treat a variety of neurologic disorders.

Developmental regulation of FKBP65. An ER-localized extracellular matrix binding-protein

FKBP65 (65-kDa FK506-binding protein) is a member of the highly conserved family of intracellular receptors called immunophilins. All have the property of peptidyl-prolyl cis-trans isomerization, and most have been implicated in folding and trafficking events. In an earlier study, we identified that FKBP65 associates with the extracellular matrix protein tropoelastin during its transport through the cell. In the present study, we have carried out a detailed investigation of the subcellular localization of FKBP65 and its relationship to tropoelastin. Using subcellular fractionation, Triton X-114 phase separation, protease protection assays, and immunofluorescence microscopy (IF), we have identified that FKBP65 is contained within the lumen of the endoplasmic reticulum (ER). Subsequent IF studies colocalized FKBP65 with tropoelastin and showed that the two proteins dissociate before reaching the Golgi apparatus. Immunohistochemical localization of FKBP65 in developing lung showed strong staining of vascular and airway smooth muscle cells. Similar areas stained positive for the presence of elastic fibers in the extracellular matrix. The expression of FKBP65 was investigated during development as tropoelastin is not expressed in adult tissues. Tissue-specific expression of FKBP65 was observed in 12-d old mouse tissues; however, the pattern of expression of FKBP65 was not restricted to those tissues expressing tropoelastin. This suggests that additional ligands for FKBP65 likely exist within the ER. Remarkably, in the adult tissues examined, FKBP65 expression was absent or barely detectable. Taken together, these results support an ER-localized FKBP65-tropoelastin interaction that occurs specifically during growth and development of tissues.

Mammalian FKBP-25 and its associated proteins

Soluble proteins from porcine brain were divided into two packs: (1) proteins which pass freely through CM52-cellulose, and (2) proteins retained on CM52. Each of these two packs of proteins was fractionated on preparative flat-bed isoelectrofocusing gel in the range of pH 2-12. Native FKBP-25 and its truncated forms were found among other proteins retained on CM52-cellulose. Immunoblotting with anti-FKBP-25 showed two bands in the range 27-30 kDa, one due to unmodified FKBP-25 and other due to FKBP-25 mixed with high-mobility group II protein (HMG-II). Selective immunostaining with anti-FKBP-25 antibodies of proteins which were not retained on CM52-cellulose showed several bands within the range of pI 7-5 and mass of 23 +/- 2 kDa. These fractions of proteins were next resolved on two-dimensional gels and immunostained with anti-FKBP-25 antibodies. Six proteins in the pI range 7-5 were detected. Edman degradation of alpha-chymotrypsin digests of the major spot suggests that it contains the GTP-binding protein Rab5 co-migrating with guanylyl kinase, whereas MALDI-TOF showed that a residual content of FKBP-25 may be also associated with these two proteins. A residual quantity of FKBP-25 was also associated with the phosphatidylethanolamine-binding protein which is abundant in the brain.

Sequence diversification of the FK506-binding proteins in several different genomes

Sequences of FK506-binding proteins (FKBPs) from four genomes of the following organisms were compared: the prokaryote Escherichia coli, the lower eukaryote Saccharomyces cerevisiae, the plant Arabidopsis thaliana, the nematode Caenorhabditis elegans and a composite of 14 unique FKBPs from two mammalian organisms Homo sapiens (man) and Mus musculus (domestic mouse). A singular FK506-like binding domain (FKBD) has about 12 kDa and occurs in the form of archetypal FKBP-12 and as a part of different proteins ranging in size from 13 to 135 kDa. Some organisms may contain a variable number of proteins which consist from two to four consecutively fused FKBDs. In the 12-kDa subgroup of archetypal FKBPs sequence identity (ID) varies from 100 to 83% (mammalian FKBPs-12), 75-50% in mammalian vs. invertebrate FKBPs-12, and fall to about 30% for pairwise sequence comparisons of mammalian and bacterial FKBPs-12 which suggests that their sequences are divergent. Multiple sequence alignment of FKBPs from the four genomes and a set of unique mammalian FKBPs does not contain any explicit consensus sequence but certain sequence positions have conserved physico-chemical characteristics. Variations of hydrophobicity and bulkiness in the multiple sequence alignment are nonsymmetrical because the physico-chemical properties of the aligned sequences changed during evolution. These variations at the sequence positions which are crucial for binding the immunosuppressive macrolide FK506 and peptidyl-prolyl cis/trans isomerase (PPIase) activity are small.

Xenopus FK 506-binding protein, a novel immunophilin expressed during early development

FK 506-binding proteins (FKBPs) are a family of cytosolic proteins identified by virtue of their ability to bind the immunosuppressants FK 506 and rapamycin. While their function has been extensively studied in the immune system, little is known about their role during early embryonic development. Here we describe the cloning and expression of a new Xenopus FKBP (xFKBP). xFKBP encodes a 63-kDa protein that shares high sequence homology with mouse FKBP65. It is expressed maternally and becomes restricted after the gastrula stage to dorsal mesoderm and notochord. At the tailbud stage expression persists in the notochord and begins to accumulate in epidermis, branchial arches and developing somites. In adults, xFKBP mRNA is confined to the testis.

Protein folding in the ER

The endoplasmic reticulum (ER) is a major protein folding compartment for secreted, plasma membrane and organelle proteins. Each of these newly-synthesized polypeptides folds in a deterministic process, affected by the unique conditions that exist in the ER. An understanding of protein folding in the ER is a fundamental biomolecular challenge at two levels. The first level addresses how the amino acid sequence programs that polypeptide to efficiently arrive at a particular fold out of a multitude of alternatives, and how different sequences obtain similar folds. At the second level are the issues introduced by folding not in the cytosol, but in the ER, including the risk of aggregation in a molecularly crowded environment, accommodation of post-translational modifications and the compatibility with subsequent intracellular trafficking. This review discusses both the physicochemical and cell biological constraints of folding, which are the challenges that the ER molecular chaperones help overcome.

Biochemical analysis of mouse FKBP60, a novel member of the FKPB family

We have identified mouse and human FKBP60, a new member of the FKBP gene family. FKBP60 shares strongest homology with FKBP65 and SMAP. FKBP60 contains a hydrophobic signal peptide at the N-terminus, 4 peptidyl-prolyl cis/trans isomerase (PPIase) domains and an endoplasmic reticulum retention motif (HDEL) at the C-terminus. Immunodetection of HA-tagged FKBP60 in NIH-3T3 cells suggests that FKBP60 is segregated to the endoplasmic reticulum. Northern blot analysis shows that FKBP60 is predominantly expressed in heart, skeletal muscle, lung, liver and kidney. With N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate, recombinant GST-FKBP60 is shown to accelerate effectively the isomerization of the peptidyl-prolyl bond. This isomerization activity is inhibited by FK506. mFKBP60 binds Ca2+ in vitro, presumably by its C-terminal EF-hand Ca2+ binding motif, and is phosphorylated in vivo. hFKBP60 has been mapped to 7p12 and/or 7p14 by fluorescence in situ hybridization (FISH).

Rapamycin inhibits didemnin B-induced apoptosis in human HL-60 cells: evidence for the possible involvement of FK506-binding protein 25

In the present paper we show that the immunosuppressant rapamycin inhibits the induction of apoptosis by didemnin B in human promyeloid HL-60 cells. The mechanism of this inhibition is investigated using FK506, which competes with rapamycin for binding to their common target FK506-binding protein (FKBP)12. The lack of competition for rapamycin-mediated inhibition of didemnin B-induced apoptosis by FK506 suggests that rapamycin inhibits apoptosis through some mechanism other than inhibition of p70 S6 kinase activation. The lack of inhibition of didemnin B-induced apoptosis by inhibitors of phosphatidylinositol 3-kinase and mitogen-activated protein (MAP) kinase kinase further supports the conclusion that rapamycin does not inhibit didemnin B-induced apoptosis through inhibition of the MAP kinase pathway. Furthermore, didemnin B-induced apoptosis is not inhibited by the inhibitors of cyclin-dependent kinase, roscovitine and olomoucine. This indicates that rapamycin does not act through inhibition of cyclin-dependent kinases. Together with the lack of competition for the effect of rapamycin by FK506, our data suggest the possible involvement of the FK506-binding protein, FKBP25, which is localized in the nucleus. This interpretation of our data gains support from the fact that didemnin B does not induce apoptosis in enucleated HL-60 cells, which supports the possible involvement of FKBP25 in the inhibition of apoptosis by rapamycin.

Molecular cloning, characterization, and chromosomal localization of FKBP23, a novel FK506-binding protein with Ca2+-binding ability

We have identified and characterized a cDNA encoding a novel FK506-binding protein (FKBP), named FKBP23, from mouse heart by the signal sequence trap method. The deduced amino acid sequence has significant homology to other FKBP family members around the peptidylprolyl cis-trans-isomerase motifs. FKBP23 also has two Ca2+-binding (EF-hand) motifs, and purified FKBP23 protein was shown to have Ca2+-binding ability. This is the first report of a Ca2+-binding FKBP. FKBP23 is a glycoprotein retained in the endoplasmic reticulum by its carboxyl-terminal tetrapeptide His-Asp-Glu-Leu, as demonstrated by immunostaining, retention, and deglycosylation assays. FKBP23 mRNA is expressed most strongly in heart, lung, and testis, beginning at day 8.5 of embryonic development. The FKBP23 gene was mapped to mouse chromosome 2.

Chicken FK506-binding protein, FKBP65, a member of the FKBP family of peptidylprolyl cis-trans isomerases, is only partially inhibited by FK506

The chicken FK506-binding protein FKBP65, a peptidylprolyl cis-trans isomerase, is a rough endoplasmic reticulum protein that contains four domains homologous to FKBP13, another rough endoplasmic reticulum PPIase. Analytical ultracentrifugation suggests that in FKBP65 these four domains are arranged in a linear extended structure with a length of about 26 nm and a diameter of about 3 nm. All four domains are therefore expected to be accessible to substrates. The specificity of FKBP65 towards a number of peptide substrates was determined. The specific activity of FKBP65 is generally lower than that of FKBP12 when expressed as a per domain activity. The substrate specificity of FKBP65 also differs from that of FKBP12. Inhibition studies show that only one of the four domains can be inhibited by FK506, a powerful inhibitor of all other known FKBPs. Furthermore, the same domain seems to be susceptible to inhibition by cyclosporin A. No other FKBPs were shown to be inhibited by cyclosporin A. It is also shown that FKBP65 can catalyse the re-folding of type III collagen in vitro with a kcat/Km = 4.3 x 10(3) M-1.s-1.

Identification of tropoelastin as a ligand for the 65-kD FK506-binding protein, FKBP65, in the secretory pathway

The folding and trafficking of tropoelastin is thought to be mediated by intracellular chaperones, although the identity and role of any tropoelastin chaperone remain to be determined. To identify proteins that are associated with tropoelastin intracellularly, bifunctional chemical cross-linkers were used to covalently stabilize interactions between tropoelastin and associated proteins in the secretory pathway in intact fetal bovine auricular chondrocytes. Immunoprecipitation of tropoelastin from cell lysates after cross-linking and analysis by SDS-PAGE showed the presence of two proteins of approximately 74 kD (p74) and 78 kD (p78) that coimmunoprecipitated with tropoelastin. Microsequencing of peptide fragments from a cyanogen bromide digest of p78 identified this protein as BiP and sequence analysis identified p74 as the peptidyl-prolyl cis-trans isomerase, FKPB65. The appearance of BiP and FKBP65 in the immunoprecipitations could be enhanced by the addition of brefeldin A (BFA) and N-acetyl-leu-leu-norleucinal (ALLN) to the culture medium for the final 4 h of labeling. Tropoelastin accumulates in the fused ER/Golgi compartment in the presence of BFA if its degradation is inhibited by ALLN (Davis, E.C., and R.P. Mecham. 1996. J. Biol. Chem. 271:3787-3794). The use of BFA and other secretion-disrupting agents suggests that the association of tropoelastin with FKBP65 occurs in the ER. Results from this study provide the first identification of a ligand for an FKBP in the secretory pathway and suggest that the prolyl cis-trans isomerase activity of FKBP65 may be important for the proper folding of the proline-rich tropoelastin molecule before secretion.

A novel plant peptidyl-prolyl-cis-trans-isomerase (PPIase): cDNA cloning, structural analysis, enzymatic activity and expression

A novel cDNA encoding for a peptidyl-prolyl-cis-trans-isomerase (PPIase) belonging to the FK506-binding protein (FKBP) family was isolated from wheat. It contains an open reading frame of 559 amino acids and it represents the first plant FKBP-PPIase to be cloned. It possesses a unique sequence which is composed of three FKPB-like domains, in addition to a putative tetratricopeptide repeat (TPR) motif and a calmodulin-binding site. The recombinant FKBP-PPIase expressed in and purified from Escherichia coli exhibits PPIase activity that is efficiently inhibited by the immunosuppressive drugs FK506 and rapamycin. Northern blot analysis showed that wheat FKBP was found mainly in young tissues. Polyclonal antibodies revealed the presence of cross-reacting proteins in embryos, roots and shoots. The unique structural features, the enzymatic activity and the presence of putative isoforms in wheat tissues indicate the possibility of the involvement of wheat PPIase in essential biological functions, similar to other members of the FKBP gene family.