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

A novel compound heterozygous variation in the FKBP10 gene causes Bruck syndrome without congenital contractures: A case report

Background

Bruck syndrome (BS) is an extremely rare autosomal-recessive connective tissue disorder mainly characterized by bone fragility, congenital joint contracture, and spinal deformity. It is also considered as a rare form of osteogenesis imperfecta (OI) due to features of osteopenia and fragility fractures. Its two forms, BS1 and BS2, are caused by pathogenic variations in FKBP10 and PLOD2, respectively.

Objective

We aimed to improve the clinical understanding of BS by presenting a case from China and to identify the genetic variants that led to this case.

Methods

OI was suspected in a Chinese boy with a history of recurrent long bone fractures, lumbar kyphosis, and dentinogenesis imperfecta (DI). Whole-exome sequencing (WES) was performed to identify pathogenic variations. Sanger sequencing was used to confirm the results of the WES. In silico analysis was used to predict the pathogenicity of genetic variants.

Results

WES and Sanger sequencing revealed a compound heterozygous variation in the FKBP10 gene (NM_021939, c.23dupG in exon 1, and c.825dupC in exon 5). Both variants resulted in a frameshift and premature stop codon. Of these two variants, c.23dupG has not been previously reported. The patient's parents were heterozygous carriers of one variant. In addition, zoledronic acid treatment improved the vertebral deformity and bone mineral density (BMD) significantly in this patient.

Conclusions

A novel compound heterozygous variation of FKBP10, c.23dupG/c.825dupC, was identified in a patient with moderately severe OI. Based on these findings, the patient was diagnosed with BS1 without congenital joint contractures or OI type XI. This study expands the spectrum of FKBP10 genetic variants that cause BS and OI.

Subcellular Expression Patterns of FKBP Prolyl Isomerase 10 (FKBP10) in Colorectal Cancer and Its Clinical Significance

FKBP10, a member of the FK506-binding protein (FKBP) family, has been implicated in cancer development, although its prognostic function remains controversial. In this study, we analyzed the expression of FKBP10 in tumor tissues using online databases (TCGA) as well as our CRC cohort, and investigated the relationship between its subcellular expression pattern and patient outcomes. Cox regression analysis was used to determine the associations between different subcellular expression patterns of FKBP10 and clinical features of patients. We also discussed the expression level of FKBP10 based on different subcellular expression patterns. Our results showed that FKBP10 was significantly elevated in CRC tissues and exhibited three different subcellular expression patterns which were defined as 'FKBP10-C' (concentrated), 'FKBP10-T' (transitional) and 'FKBP10-D' (dispersive). The FKBP10-D expression pattern was only found in tumor tissues and was associated with unfavorable disease-free survival in CRC patients. High expression levels of FKBP10-C predicted an unfavorable prognosis of recurrence of CRC, while FKBP10-D did not. Our findings suggest that the subcellular expression patterns and expression level of FKBP10 play crucial prognostic roles in CRC, which revealed that FKBP10 may be a viable prognostic and therapeutic target for the diagnosis and treatment of CRC.

FKBP52 in Neuronal Signaling and Neurodegenerative Diseases: A Microtubule Story

The FK506-binding protein 52 (FKBP52) belongs to a large family of ubiquitously expressed and highly conserved proteins (FKBPs) that share an FKBP domain and possess Peptidyl-Prolyl Isomerase (PPIase) activity. PPIase activity catalyzes the isomerization of Peptidyl-Prolyl bonds and therefore influences target protein folding and function. FKBP52 is particularly abundant in the nervous system and is partially associated with the microtubule network in different cell types suggesting its implication in microtubule function. Various studies have focused on FKBP52, highlighting its importance in several neuronal microtubule-dependent signaling pathways and its possible implication in neurodegenerative diseases such as tauopathies (i.e., Alzheimer disease) and alpha-synucleinopathies (i.e., Parkinson disease). This review summarizes our current understanding of FKBP52 actions in the microtubule environment, its implication in neuronal signaling and function, its interactions with other members of the FKBPs family and its involvement in neurodegenerative disease.

FKBP10 Regulates Protein Translation to Sustain Lung Cancer Growth

Cancer therapy is limited, in part, by lack of specificity. Thus, identifying molecules that are selectively expressed by, and relevant for, cancer cells is of paramount medical importance. Here, we show that peptidyl-prolyl-cis-trans-isomerase (PPIase) FK506-binding protein 10 (FKBP10)-positive cells are present in cancer lesions but absent in the healthy parenchyma of human lung. FKBP10 expression negatively correlates with survival of lung cancer patients, and its downregulation causes a dramatic diminution of lung tumor burden in mice. Mechanistically, our results from gain- and loss-of-function assays show that FKBP10 boosts cancer growth and stemness via its PPIase activity. Also, FKBP10 interacts with ribosomes, and its downregulation leads to reduction of translation elongation at the beginning of open reading frames (ORFs), particularly upon insertion of proline residues. Thus, our data unveil FKBP10 as a cancer-selective molecule with a key role in translational reprogramming, stem-like traits, and growth of lung cancer.

Case Report: Exome Sequencing Identified a Novel Compound Heterozygous Variation in PLOD2 Causing Bruck Syndrome Type 2

Bruck Syndrome (BRKS) is a rare type of recessive osteogenesis imperfecta (OI) and consists of two subtypes, BRKS1 and BRKS2, which are caused by variations in FKBP10 and PLOD2 genes, respectively. In this study, a family that had experienced multiple miscarriages and recurrent fetal skeletal dysplasia was recruited for the purpose of a multiplatform laboratory investigation. Prenatal genetic testing with whole-exome sequencing (WES) identified a compound heterozygous variation in the PLOD2 gene with two variants, namely c.2038C>T (p.R680^*) and c.191_201+3 delATACTGTGAAGGTA (p.Y64Cfs^*12). The amino acids affected by the two variants maintained conserved across species. And the result of immunohistochemistry (IHC) indicated that the expression of PLOD2 protein in the proband's osteochondral tissue was significantly decreased. These findings in our study expanded the variation spectrum of PLOD2 gene, provided solid evidence for the family's counseling in regard to future pregnancies, strongly supported the application of WES in prenatal diagnosis, and might give insight into the understanding of PLOD2 function.

FKBP10 Acts as a New Biomarker for Prognosis and Lymph Node Metastasis of Gastric Cancer by Bioinformatics Analysis and in Vitro Experiments

Purpose

To explore the role of FKBP prolyl isomerase 10 (FKBP10) protein in the progression of gastric cancer.

Methods

Four independent gastric cancer databases (GSE27342, GSE29272, GSE54129 and TCGA-STAD) were used to identify differentially expressed genes (DEGs). Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was used to identify the abnormally active pathways in patients with gastric cancer. Univariate Cox regression analysis was used to identify genes with stable prognostic value in gastric cancer patients based on three independent gastric cancer databases (GSE15459, GSE62254, TCGA-STAD). Gene set enrichment analysis (GSEA) was used to explore the possible pathways related to FKBP10. The reverse transcription-polymerase chain reaction (RT-PCR) was employed to determine the expression of FKBP10 mRNA in the HGC-27 and MKN-7 cell lines. Adhesion assay was used to detect changes in cell adhesion ability. FKBP10, ITGA1, ITGA2, ITGA5, ITGAV, ITGA6, P-AKT₄₇₃, P-AKT₃₀₈, AKT, and β-actin were evaluated by Western blot (WB).

Results

We first performed differential expression genes (DEGs) screening of four independent GC databases (GSE27342, GSE29272, GSE54129 and TCGA-STAD). Eighty-nine genes showed consistent up-regulation in GC, the results of pathway analysis showed that they were related to “Focal adhesion”. The prognostic value of these 89 genes was tested in three independent GC databases GSE15459, GSE62254 and TCGA-STAD cohort. Finally, 12 genes, in which the expression of FKBP10 was prominently increased in patients with lymph node metastasis (LNM), showed stable prognostic value. The following gene set enrichment analysis (GSEA) also showed that FKBP10 is mainly involved in cell adhesion process, while adhesion experiments confirmed that cell adhesion was down-regulated after silencing FKBP10 in GC cells, and adhesion-related molecules integrin αV and α6 were down-regulated.

Conclusion

FKBP10 may be used as a marker for lymph node metastasis of GC and could be used as a potential target for future treatment of GC.

Elastic fiber ultrastructure and assembly

Studies over the years have described a filamentous structure to mature elastin that suggests a complicated packing arrangement of tropoelastin subunits. The currently accepted mechanism for tropoelastin assembly requires microfibrils to serve as a physical extracellular scaffold for alignment of tropoelastin monomers during and before crosslinking. However, recent evidence suggests that the initial stages of tropoelastin assembly occur within the cell or at unique assembly sites on the plasma membrane where tropoelastin self assembles to form elastin aggregates. Outside the cell, elastin aggregates transfer to growing elastic fibers in the extracellular matrix where tensional forces on microfibrils generated through cell movement help shape the growing fiber. Overall, these observations challenge the widely held idea that interaction between monomeric tropoelastin and microfibrils is a requirement for elastin assembly, and point to self-assembly of tropoelastin as a driving force in elastin maturation.

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.

Fkbp10 Deletion in Osteoblasts Leads to Qualitative Defects in Bone

Osteogenesis imperfecta (OI), also known as brittle bone disease, displays a spectrum of clinical severity from mild (OI type I) to severe early lethality (OI type II), with clinical features including low bone mass, fractures, and deformities. Mutations in the FK506 Binding Protein 10 (FKBP10), gene encoding the 65-kDa protein FKBP65, cause a recessive form of OI and Bruck syndrome, the latter being characterized by joint contractures in addition to low bone mass. We previously showed that Fkbp10 expression is limited to bone, tendon, and ligaments in postnatal tissues. Furthermore, in both patients and Fkbp10 knockout mice, collagen telopeptide hydroxylysine crosslinking is dramatically reduced. To further characterize the bone specific contributions of Fkbp10, we conditionally ablated FKBP65 in Fkbp10fl/fl mice (Mus musculus; C57BL/6) using the osteoblast-specific Col1a1 2.3-kb Cre recombinase. Using μCT, histomorphometry and quantitative backscattered electron imaging, we found minimal alterations in the quantity of bone and no differences in the degree of bone matrix mineralization in this model. However, mass spectroscopy (MS) of bone collagen demonstrated a decrease in mature, hydroxylysine-aldehyde crosslinking. Furthermore, bone of mutant mice exhibits a reduction in mineral-to-matrix ratio and in crystal size as shown by Raman spectroscopy and small-angle X-ray scattering, respectively. Importantly, abnormalities in bone quality were associated with impaired bone biomechanical strength in mutant femurs compared with those of wild-type littermates. Taken together, these data suggest that the altered collagen crosslinking through Fkbp10 ablation in osteoblasts primarily leads to a qualitative defect in the skeleton. © 2017 American Society for Bone and Mineral Research.

Regulation of mitochondrial calcium in plants versus animals

Ca(2+) acts as an important cellular second messenger in eukaryotes. In both plants and animals, a wide variety of environmental and developmental stimuli trigger Ca(2+) transients of a specific signature that can modulate gene expression and metabolism. In animals, mitochondrial energy metabolism has long been considered a hotspot of Ca(2+) regulation, with a range of pathophysiology linked to altered Ca(2+) control. Recently, several molecular players involved in mitochondrial Ca(2+) signalling have been identified, including those of the mitochondrial Ca(2+) uniporter. Despite strong evidence for sophisticated Ca(2+) regulation in plant mitochondria, the picture has remained much less clear. This is currently changing aided by live imaging and genetic approaches which allow dissection of subcellular Ca(2+) dynamics and identification of the proteins involved. We provide an update on our current understanding in the regulation of mitochondrial Ca(2+) and signalling by comparing work in plants and animals. The significance of mitochondrial Ca(2+) control is discussed in the light of the specific metabolic and energetic needs of plant and animal cells.

Chloroplast immunophilins

Immunophilins occur in almost all living organisms. They are ubiquitously expressed proteins including cyclophilins, FK506/rapamycin-binding proteins, and parvulins. Their functional significance in vascular plants is mostly related to plant developmental processes, signalling, and regulation of photosynthesis. Enzymatically active immunophilins catalyse isomerization of proline imidic peptide bonds and assist in rapid folding of nascent proline-containing polypeptides. They also participate in protein trafficking and assembly of supramolecular protein complexes. Complex immunophilins possess various additional functional domains associated with a multitude of molecular interactions. A considerable number of immunophilins act as auxiliary and/or regulatory proteins in highly specialized cellular compartments, such as lumen of thylakoids. In this review, we present a comprehensive overview of so far identified chloroplast immunophilins that assist in specific assembly/repair processes necessary for the maintenance of efficient photosynthetic energy conversion.

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.

Microbial peptidyl-prolyl cis/trans isomerases (PPIases): virulence factors and potential alternative drug targets

Initially discovered in the context of immunomodulation, peptidyl-prolyl cis/trans isomerases (PPIases) were soon identified as enzymes catalyzing the rate-limiting protein folding step at peptidyl bonds preceding proline residues. Intense searches revealed that PPIases are a superfamily of proteins consisting of three structurally distinguishable families with representatives in every described species of prokaryote and eukaryote and, recently, even in some giant viruses. Despite the clear-cut enzymatic activity and ubiquitous distribution of PPIases, reports on solely PPIase-dependent biological roles remain scarce. Nevertheless, they have been found to be involved in a plethora of biological processes, such as gene expression, signal transduction, protein secretion, development, and tissue regeneration, underscoring their general importance. Hence, it is not surprising that PPIases have also been identified as virulence-associated proteins. The extent of contribution to virulence is highly variable and dependent on the pleiotropic roles of a single PPIase in the respective pathogen. The main objective of this review is to discuss this variety in virulence-related bacterial and protozoan PPIases as well as the involvement of host PPIases in infectious processes. Moreover, a special focus is given to Legionella pneumophila macrophage infectivity potentiator (Mip) and Mip-like PPIases of other pathogens, as the best-characterized virulence-related representatives of this family. Finally, the potential of PPIases as alternative drug targets and first tangible results are highlighted.

Ziploc-ing the structure: Triple helix formation is coordinated by rough endoplasmic reticulum resident PPIases

BACKGROUND

Protein folding is crucial for proteins' specific functions and is facilitated by various types of enzymes and molecular chaperones. The peptidyl prolyl cis/trans isomerases (PPIase) are one of these families of enzymes. They ubiquitously exist inside the cell and there are eight PPIases in the rough endoplasmic reticulum (rER), a compartment where the folding of most secreted proteins occurs.

SCOPE OF REVIEW

We review the functional and structural aspects of individual rER resident PPIases. Furthermore, we specifically discuss the role of these PPIases during collagen biosynthesis, since collagen is the most abundant protein in humans, is synthesized in the rER, and contains a proportionally high number of proline residues.

MAJOR CONCLUSIONS

The rER resident PPIases recognize different sets of substrates and facilitate their folding. Although they are clearly catalysts for protein folding, they also have more broad and multifaceted functions. We propose that PPIases coordinate collagen biosynthesis in the rER.

GENERAL SIGNIFICANCE

This review expands our understanding of collagen biosynthesis by explaining the influence of novel indirect mechanisms of regulating folding and this is also explored for PPIases. We also suggest future directions of research to obtain a better understanding of collagen biosynthesis and functions of PPIases in the rER. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

Diet-induced unresolved ER stress hinders KRAS-driven lung tumorigenesis

Dietary effects on tumor biology can be exploited to unravel cancer vulnerabilities. Here, we present surprising evidence for anti-proliferative action of high-calorie-diet (HCD) feeding on KRAS-driven lung tumors. Tumors of mice that commenced HCD feeding before tumor onset displayed defective unfolded protein response (UPR) and unresolved endoplasmic reticulum (ER) stress. Unresolved ER stress and reduced proliferation are reversed by chemical chaperone treatment. Whole-genome transcriptional analyses revealed FKBP10 as one of the most downregulated chaperones in tumors of the HCD-pre-tumor-onset group. FKBP10 downregulation dampens tumor growth in vitro and in vivo. Providing translational value to these results, we report that FKBP10 is expressed in human KRAS-positive and -negative lung cancers, but not in healthy parenchyma. Collectively, our data shed light on an unexpected anti-tumor action of HCD imposed before tumor onset and identify FKBP10 as a putative therapeutic target to selectively hinder lung cancer.

A substrate preference for the rough endoplasmic reticulum resident protein FKBP22 during collagen biosynthesis

The biosynthesis of collagens occurs in the rough endoplasmic reticulum and requires a large numbers of molecular chaperones, foldases, and post-translational modification enzymes. Collagens contain a large number of proline residues that are post-translationally modified to 3-hydroxyproline or 4-hydroxyproline, and the rate-limiting step in formation of the triple helix is the cis-trans isomerization of peptidyl-proline bonds. This step is catalyzed by peptidyl-prolyl cis-trans isomerases. There are seven peptidyl-prolyl cis-trans isomerases in the rER, and so far, two of these enzymes, cyclophilin B and FKBP65, have been shown to be involved in collagen biosynthesis. The absence of either cyclophilin B or FKBP65 leads to a recessive form of osteogenesis imperfecta. The absence of FKBP22 leads to a kyphoscoliotic type of Ehlers-Danlos syndrome (EDS), and this type of EDS is classified as EDS type VI, which can also be caused by a deficiency in lysyl-hydroxylase 1. However, the lack of FKBP22 shows a wider spectrum of clinical phenotypes than the absence of lysyl-hydroxylase 1 and additionally includes myopathy, hearing loss, and aortic rupture. Here we show that FKBP22 catalyzes the folding of type III collagen and interacts with type III collagen, type VI collagen, and type X collagen, but not with type I collagen, type II collagen, or type V collagen. These restrictive interactions might help explain the broader phenotype observed in patients that lack FKBP22.

Connective tissue alterations in Fkbp10-/- mice

Osteogenesis imperfecta (OI) is an inherited brittle bone disorder characterized by bone fragility and low bone mass. Loss of function mutations in FK506-binding protein 10 (FKBP10), encoding the FKBP65 protein, result in recessive OI and Bruck syndrome, of which the latter is additionally characterized by joint contractures. FKBP65 is thought to act as a collagen chaperone, but it is unknown how loss of FKBP65 affects collagen synthesis and extracellular matrix formation. We evaluated the developmental and postnatal expression of Fkbp10 and analyzed the consequences of its generalized loss of function. Fkbp10 is expressed at low levels in E13.5 mouse embryos, particularly in skeletal tissues, and steadily increases through E17.5 with expression in not only skeletal tissues, but also in visceral tissues. Postnatally, expression is limited to developing bone and ligaments. In contrast to humans, with complete loss of function mutations, Fkbp10(-/-) mice do not survive birth, and embryos present with growth delay and tissue fragility. Type I calvarial collagen isolated from these mice showed reduced stable crosslink formation at telopeptide lysines. Furthermore, Fkbp10(-/-) mouse embryonic fibroblasts show retention of procollagen in the cell layer and associated dilated endoplasmic reticulum. These data suggest a requirement for FKBP65 function during embryonic connective tissue development in mice, but the restricted expression postnatally in bone, ligaments and tendons correlates with the bone fragility and contracture phenotype in humans.

Structure of human peptidyl-prolyl cis-trans isomerase FKBP22 containing two EF-hand motifs

The FK506-binding protein (FKBP) family consists of proteins with a variety of protein-protein interaction domains and versatile cellular functions. It is assumed that all members are peptidyl-prolyl cis-trans isomerases with the enzymatic function attributed to the FKBP domain. Six members of this family localize to the mammalian endoplasmic reticulum (ER). Four of them, FKBP22 (encoded by the FKBP14 gene), FKBP23 (FKBP7), FKBP60 (FKBP9), and FKBP65 (FKBP10), are unique among all FKBPs as they contain the EF-hand motifs. Little is known about the biological roles of these proteins, but emerging genetics studies are attracting great interest to the ER resident FKBPs, as mutations in genes encoding FKBP10 and FKBP14 were shown to cause a variety of matrix disorders. Although the structural organization of the FKBP-type domain as well as of the EF-hand motif has been known for a while, it is difficult to conclude how these structures are combined and how it affects the protein functionality. We have determined a unique 1.9 Å resolution crystal structure for human FKBP22, which can serve as a prototype for other EF hand-containing FKBPs. The EF-hand motifs of two FKBP22 molecules form a dimeric complex with an elongated and predominantly hydrophobic cavity that can potentially be occupied by an aliphatic ligand. The FKBP-type domains are separated by a cleft and their putative active sites can catalyze isomerazation of two bonds within a polypeptide chain in extended conformation. These structural results are of prime interest for understanding biological functions of ER resident FKBPs containing EF-hand motifs.

Kuskokwim syndrome, a recessive congenital contracture disorder, extends the phenotype of FKBP10 mutations

Recessive mutations in FKBP10 at 17q21.2, encoding FKBP65, cause both osteogenesis imperfecta (OI) and Bruck syndrome (OI plus congenital contractures). Contractures are a variable manifestation of null/missense FKBP10 mutations. Kuskokwim syndrome (KS) is an autosomal recessive congenital contracture disorder found among Yup'ik Eskimos. Linkage mapping of KS to chromosome 17q21, together with contractures as a feature of FKBP10 mutations, made FKBP10 a candidate gene. We identified a homozygous three-nucleotide deletion in FKBP10 (c.877_879delTAC) in multiple Kuskokwim pedigrees; 3% of regional controls are carriers. The mutation deletes the highly conserved p.Tyr293 residue in FKBP65's third peptidyl-prolyl cis-trans isomerase domain. FKBP10 transcripts are normal, but mutant FKBP65 is destabilized to a residual 5%. Collagen synthesized by KS fibroblasts has substantially decreased hydroxylation of the telopeptide lysine crucial for collagen cross-linking, with 2%-10% hydroxylation in probands versus 60% in controls. Matrix deposited by KS fibroblasts has marked reduction in maturely cross-linked collagen. KS collagen is disorganized in matrix, and fibrils formed in vitro had subtle loosening of monomer packing. Our results imply that FKBP10 mutations affect collagen indirectly, by ablating FKBP65 support for collagen telopeptide hydroxylation by lysyl hydroxylase 2, thus decreasing collagen cross-links in tendon and bone matrix. FKBP10 mutations may also underlie other arthrogryposis syndromes.

Molecular subtyping of primary prostate cancer reveals specific and shared target genes of different ETS rearrangements

This work aimed to evaluate whether ETS transcription factors frequently involved in rearrangements in prostate carcinomas (PCa), namely ERG and ETV1, regulate specific or shared target genes. We performed differential expression analysis on nine normal prostate tissues and 50 PCa enriched for different ETS rearrangements using exon-level expression microarrays, followed by in vitro validation using cell line models. We found specific deregulation of 57 genes in ERG-positive PCa and 15 genes in ETV1-positive PCa, whereas deregulation of 27 genes was shared in both tumor subtypes. We further showed that the expression of seven tumor-associated ERG target genes (PLA1A, CACNA1D, ATP8A2, HLA-DMB, PDE3B, TDRD1, and TMBIM1) and two tumor-associated ETV1 target genes (FKBP10 and GLYATL2) was significantly affected by specific ETS silencing in VCaP and LNCaP cell line models, respectively, whereas the expression of three candidate ERG and ETV1 shared targets (GRPR, KCNH8, and TMEM45B) was significantly affected by silencing of either ETS. Interestingly, we demonstrate that the expression of TDRD1, the topmost overexpressed gene of our list of ERG-specific candidate targets, is inversely correlated with the methylation levels of a CpG island found at -66 bp of the transcription start site in PCa and that TDRD1 expression is regulated by direct binding of ERG to the CpG island in VCaP cells. We conclude that ETS transcription factors regulate specific and shared target genes and that TDRD1, FKBP10, and GRPR are promising therapeutic targets and can serve as diagnostic markers for molecular subtypes of PCa harboring specific fusion gene rearrangements.

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.

Unraveling the role of peptidyl-prolyl isomerases in neurodegeneration

Immunophilins are a family of highly conserved proteins with a peptidyl-prolyl isomerase activity that binds immunosuppressive drugs such as FK506, cyclosporin A, and rapamycin. Immunophilins can be divided into two subfamilies, the cyclophilins, and the FK506 binding proteins (FKBPs). Next to the immunophilins, a third group of peptidyl-prolyl isomerases exist, the parvulins, which do not influence the immune system. The beneficial role of immunophilin ligands in neurodegenerative disease models has been known for more than a decade but remains largely unexplained in terms of molecular mechanisms. In this review, we summarize reported effects of parvulins, immunophilins, and their ligands in the context of neurodegeneration. We focus on the role of FKBP12 in Parkinson's disease and propose it as a novel drug target for therapy of Parkinson's disease.

The hyperthermia-enhanced association between tropoelastin and its 67-kDa chaperone results in better deposition of elastic fibers

The results of our in vitro experiments indicate that exposing cultured human aortic smooth muscle cells and dermal fibroblasts to 39 to 41 °C induces a significant up-regulation in the net deposition of elastic fibers, but not of collagen I or fibronectin, and also decreases the deposition of chondroitin sulfate-containing moieties. We further demonstrate that mild hyperthermia also rectifies the insufficient elastogenesis notable in cultures of fibroblasts derived from the stretch-marked skin of adult patients and in cultures of dermal fibroblasts from children with Costello syndrome, which is characterized by the accumulation of chondroitin 6-sulfate glycosaminoglycans that induce shedding and inactivation of the 67-kDa elastin-binding protein. We have previously established that this protein serves as a reusable chaperone for tropoelastin and that its recycling is essential for the normal deposition of elastic fibers. We now report that hyperthermia not only inhibits deposition of chondroitin 6-sulfate moieties and the consequent preservation of elastin-binding protein molecules but also induces their faster recycling. This, in turn, triggers a more efficient preservation of tropoelastin, enhancement of its secretion and extracellular assembly into elastic fibers. The presented results encourage using mild hyperthermia to restore elastic fiber production in damaged adult skin and to enhance elastogenesis in children with genetic elastinopathies.

Identification and comparative analysis of the peptidyl-prolyl cis/trans isomerase repertoires of H. sapiens, D. melanogaster, C. elegans, S. cerevisiae and Sz. pombe

The peptidyl-prolyl cis/trans isomerase (PPIase) class of proteins comprises three member families that are found throughout nature and are present in all the major compartments of the cell. Their numbers appear to be linked to the number of genes in their respective genomes, although we have found the human repertoire to be smaller than expected due to a reduced cyclophilin repertoire. We show here that whilst the members of the cyclophilin family (which are predominantly found in the nucleus and cytoplasm) and the parvulin family (which are predominantly nuclear) are largely conserved between different repertoires, the FKBPs (which are predominantly found in the cytoplasm and endoplasmic reticulum) are not. It therefore appears that the cyclophilins and parvulins have evolved to perform conserved functions, while the FKBPs have evolved to fill ever-changing niches within the constantly evolving organisms. Many orthologous subgroups within the different PPIase families appear to have evolved from a distinct common ancestor, whereas others, such as the mitochondrial cyclophilins, appear to have evolved independently of one another. We have also identified a novel parvulin within Drosophila melanogaster that is unique to the fruit fly, indicating a recent evolutionary emergence. Interestingly, the fission yeast repertoire, which contains no unique cyclophilins and parvulins, shares no PPIases solely with the budding yeast but it does share a majority with the higher eukaryotes in this study, unlike the budding yeast. It therefore appears that, in comparison with Schizosaccharomyces pombe, Saccharomyces cerevisiae is a poor representation of the higher eukaryotes for the study of PPIases.

Mutations in the gene encoding the RER protein FKBP65 cause autosomal-recessive osteogenesis imperfecta

Osteogenesis imperfecta is a clinically and genetically heterogeneous brittle bone disorder that results from defects in the synthesis, structure, or posttranslational modification of type I procollagen. Dominant forms of OI result from mutations in COL1A1 or COL1A2, which encode the chains of the type I procollagen heterotrimer. The mildest form of OI typically results from diminished synthesis of structurally normal type I procollagen, whereas moderately severe to lethal forms of OI usually result from structural defects in one of the type I procollagen chains. Recessively inherited OI, usually phenotypically severe, has recently been shown to result from defects in the prolyl-3-hydroxylase complex that lead to the absence of a single 3-hydroxyproline at residue 986 of the alpha1(I) triple helical domain. We studied a cohort of five consanguineous Turkish families, originating from the Black Sea region of Turkey, with moderately severe recessively inherited OI and identified a novel locus for OI on chromosome 17. In these families, and in a Mexican-American family, homozygosity for mutations in FKBP10, which encodes FKBP65, a chaperone that participates in type I procollagen folding, was identified. Further, we determined that FKBP10 mutations affect type I procollagen secretion. These findings identify a previously unrecognized mechanism in the pathogenesis of OI.

Inhibition of FK506 binding proteins reduces alpha-synuclein aggregation and Parkinson's disease-like pathology

alpha-Synuclein (alpha-SYN) is a key player in the pathogenesis of Parkinson's disease (PD). In pathological conditions, the protein is present in a fibrillar, aggregated form inside cytoplasmic inclusions called Lewy bodies. Members of the FK506 binding protein (FKBP) family are peptidyl-prolyl isomerases that were shown recently to accelerate the aggregation of alpha-SYN in vitro. We now established a neuronal cell culture model for synucleinopathy based on oxidative stress-induced alpha-SYN aggregation and apoptosis. Using high-content analysis, we examined the role of FKBPs in aggregation and apoptotic cell death. FK506, a specific inhibitor of this family of proteins, inhibited alpha-SYN aggregation and neuronal cell death in this synucleinopathy model dose dependently. Knockdown of FKBP12 or FKBP52 reduced the number of alpha-SYN aggregates and protected against cell death, whereas overexpression of FKBP12 or FKBP52 accelerated both aggregation of alpha-SYN and cell death. Thus, FK506 likely targets FKBP members in the cell culture model. Furthermore, oral administration of FK506 after viral vector-mediated overexpression of alpha-SYN in adult mouse brain significantly reduced alpha-SYN aggregate formation and neuronal cell death. Our data explain previously described neuroregenerative and neuroprotective effects of immunophilin ligands and validate FKBPs as a novel drug target for the causative treatment of PD.

Role of immunophilins in recovery of erectile function after cavernous nerve injury

INTRODUCTION

Immunophilin ligands provide potentially new alternatives for the treatment of erectile dysfunction (ED), which occurs after injury of the cavernous nerves (CNs).

AIM

To review and update current knowledge of the neurotrophic effects and likely mechanism of action of immunophilin proteins with emphasis on the FK506-binding protein (FKBP) subfamily and the role of immunophilin ligands for the treatment of CN injury-induced ED.

METHODS

Review of available reports of studies investigating the effects and neurotrophic mechanisms of immunophilin ligands involved in erectile function recovery in rodent models of CN injury.

MAIN OUTCOME MEASURES

Erection parameters and molecular correlations associated with CN injury and functional recovery.

RESULTS

Treatment with prototype immunosuppressive immunophilin ligands FK506 (FK) and rapamycin (Rapa) improve erectile function in animal models of CN injury. Similarly, non-immunosuppressive analogs such as GPI-1046 and FK1706 are effective in recovery of erections after CN injury. Neuronal nitric oxide may influence the erection recovery effects of immunophilin ligands after CN injury. FKBPs 38 and 65 expression changes in the penis and its innervation coincide with the neurotrophic effects of immunophilin ligands. Antioxidative actions of immunophilin ligands contribute to their neurotrophic effects. Immunophilins are localized to nerves coursing in human prostate and penile tissue.

CONCLUSIONS

The findings support the hypothesis that immunophilin ligands, working through specific receptor mechanisms that are specific to injured CN, are potentially useful to sustain erectile function in men following radical prostatectomy.

Leveraging existing biological knowledge in the identification of candidate genes for facial dysmorphology

Background

In response to the frequently overwhelming output of high-throughput microarray experiments, we propose a methodology to facilitate interpretation of biological data in the context of existing knowledge. Through the probabilistic integration of explicit and implicit data sources a functional interaction network can be constructed. Each edge connecting two proteins is weighted by a confidence value capturing the strength and reliability of support for that interaction given the combined data sources. The resulting network is examined in conjunction with expression data to identify groups of genes with significant temporal or tissue specific patterns. In contrast to unstructured gene lists, these networks often represent coherent functional groupings.

Results

By linking from shared functional categorizations to primary biological resources we apply this method to craniofacial microarray data, generating biologically testable hypotheses and identifying candidate genes for craniofacial development.

Conclusion

The novel methodology presented here illustrates how the effective integration of pre-existing biological knowledge and high-throughput experimental data drives biological discovery and hypothesis generation.

Force-Induced Prolyl Cis−Trans Isomerization in Elastin-like Polypeptides

Elastin-like polypeptides (ELPs) are stimulus-responsive polymers that contain repeats of five amino acids, Val-Pro-Gly-Xaa-Gly (VPGXG), where Xaa is a guest residue that can be any amino acid with the exception of proline. While studying the conformational mechanics of ELPs over a range of solvent conditions by single-molecule force spectroscopy, we noticed that some force-extension curves showed temperature-independent, extensional transitions that could not be fitted with a freely jointed chain or worm-like chain model. Here we show that the observed molecular elongation results from the force-induced peptidyl-prolyl cis-trans isomerization in prolines, which are repeated every fifth residue in the main chain of ELPs. Control experiments with poly(L-proline) demonstrate the similarity of the conformational transition between poly(L-proline) and ELPs. In contrast, the force-extension behavior of poly(L-lysine) showed no deviation in the relevant force range. Force-extension curves in hysteresis experiments showed an elongational difference between extension and relaxation pathways that suggests that the cis conformational state of the prolines could be exhausted on the time scale of the experiment. We present further computational evidence for this mechanism by Monte Carlo simulation of the force-extension behavior using an elastically coupled, two-state model. We believe ours is the first demonstration of force-induced prolyl cis-trans isomerization in proline-containing polypeptides. Our results suggest that single-molecule force spectroscopy could provide an alternate means to assay this important conformational transition in polypeptides.

Loss of secretory pathway FK506-binding proteins results in cold-sensitive lethality and associate extracellular matrix defects in the nematode Caenorhabditis elegans

The FK506-binding proteins (FKBs) represent ubiquitous enzymes that catalyze the rate-limiting peptidyl prolyl cis-trans isomerization step in protein folding. The nematode Caenorhabditis elegans has eight FKBs, three of which (FKB-3, -4, and -5) have dual peptidyl prolyl cis-trans isomerase (PPIase) domains, signal peptides and ER retention signals. PPIase activity has been detected for recombinant FKB-3. Both FKB-3 and -5 are expressed in the exoskeleton-synthesizing hypodermis with transcript peaks that correspond to the molting and collagen synthesis cycles. FKB-4 is expressed at a low level throughout development. No phenotypes were observed in deletion mutants in each of the secretory pathway FKBs. Combined triple and fkb-4, -5 double deletion mutants were however found to arrest at 12 degrees C, but developed normally at 15-25 degrees C. This cold-sensitive larval lethal effect was not maternally derived, occurred during embryogenesis, and could be rescued following the transgenic introduction of a wild type copy of either fkb-4 or fkb-5. The temperature-sensitive defects also affected molting, cuticle collagen expression, hypodermal seam cell morphology, and the structural integrity of the cuticular extracellular matrix. This study establishes that the secretory pathway FK506-binding PPIase enzymes are essential for normal nematode development, collagen biogenesis, and the formation of an intact exoskeleton under adverse physiological conditions.

The human FK506-binding proteins: characterization of human FKBP19

Analysis of the human repertoire of the FK506-binding protein (FKBP) family of peptidyl-prolyl cis/trans isomerases has identified an expansion of genes that code for human FKBPs in the secretory pathway. There are distinct differences in tissue distribution and expression levels of each variant. In this article we describe the characterization of human FKBP19 (Entrez Gene ID: FKBP11), an FK506-binding protein predominantly expressed in vertebrate secretory tissues. The FKBP19 sequence comprises a cleavable N-terminal signal sequence followed by a putative peptidyl-prolyl cis/trans isomerase domain with homology to FKBP12. This domain binds FK506 weakly in vitro. FKBP19 mRNA is abundant in human pancreas and other secretory tissues and high levels of FKBP19 protein are detected in the acinar cells of mouse pancreas.

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.

Versatility of the endoplasmic reticulum protein folding factory

The endoplasmic reticulum (ER) is dedicated to import, folding and assembly of all proteins that travel along or reside in the secretory pathway of eukaryotic cells. Folding in the ER is special. For instance, newly synthesized proteins are N-glycosylated and by default form disulfide bonds in the ER, but not elsewhere in the cell. In this review, we discuss which features distinguish the ER as an efficient folding factory, how the ER monitors its output and how it disposes of folding failures.

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.

Human Nischarin/imidazoline receptor antisera-selected protein is targeted to the endosomes by a combined action of a PX domain and a coiled-coil region

Around 50 mammalian and 15 yeast proteins are known to contain the phox (PX) domain, the majority (about 30) of which is classified as sorting nexins (SNXs). The PX domain, a hallmark of these proteins, is a conserved stretch of about 120 amino acids and is recently shown to mediate phosphoinositide binding. A few PX domain proteins (including some SNXs) have been shown to participate in diverse cellular processes such as protein sorting, signal transduction, and vesicle fusion. In this report, we present our results supporting a role of human IRAS to act as a SNX. The mouse homologue, previously identified as Nischarin, has been shown to interact with the alpha(5) subunit of integrin and inhibit cell migration (Alahari, S. K., Lee J. W., and Juliano R. L. (2000) J. Cell Biol. 51, 1141-1154). Its human homologue (imidazoline receptor antisera-selected (IRAS)), on the other hand, contains an NH(2)-terminal extension and is a larger protein of 1504 amino acids consisting of an NH(2)-terminal PX domain, 5 putative leucine-rich repeats, a predicted coiled-coil domain, and a long COOH-terminal region. We show that it has the ability to homo-oligomerize via its coiled-coil region. The PX domain of IRAS is essential for association with phosphatidylinositol 3-phosphate-enriched endosomal membranes. However, the PX domain of IRAS alone is insufficient for its localization to endosomes, unless the coiled-coil domain was included or it is artificially dimerized by glutathione S-transferase. Interaction of human IRAS with alpha(5) integrin is not affected by the NH(2)-terminal extension, and overexpression of IRAS could cause a redistribution of surface alpha(5) integrin to intracellular endosomal structures.