Human calumenin gene (CALU): cDNA isolation and chromosomal mapping to 7q32

CALU promotes lung adenocarcinoma progression by enhancing cell proliferation, migration and invasion

BACKGROUND

Lung cancer is the second most common cancer with the highest mortality in the world. Calumenin as a molecular chaperone that not only binds various proteins within the endoplasmic reticulum but also plays crucial roles in diverse processes associated with tumor development. However, the regulatory mechanism of calumenin in lung adenocarcinoma remains elusive. Here, we studied the impact of calumenin on lung adenocarcinoma and explored possible mechanisms.

METHODS

5-ethynyl-2'-deoxyuridine assay, colony formation, transwell and wound healing assays were performed to explore the effects of calumenin on the proliferation and migration of lung adenocarcinoma cells. To gain insights into the underlying mechanisms through which calumenin knockdown inhibits the migration and proliferation of lung adenocarcinoma, we performed Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Gene Set Enrichment Analysis and Ingenuity Pathway Analysis based on transcriptomics by comparing calumenin knockdown with normal A549 cells.

RESULTS

The mRNA and protein levels of calumenin in lung adenocarcinoma are highly expressed and they are related to an unfavorable prognosis in this disease. Calumenin enhances the proliferation and migration of A549 and H1299 cells. Gene Set Enrichment Analysis revealed that knockdown of calumenin in A549 cells significantly inhibited MYC and V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog signaling pathways while activating interferon signals, inflammatory signals, and p53 pathways. Ingenuity pathway analysis provided additional insights, indicating that the interferon and inflammatory pathways were prominently activated upon calumenin knockdown in A549 cells.

CONCLUSIONS

The anti-cancer mechanism of calumenin knockdown might be related to the inhibition of MYC and KRAS signals but the activation of interferon signals, inflammatory signals and p53 pathways.

Organellar Calcium Handling in the Cellular Reticular Network

Ca²⁺ is an important intracellular messenger affecting diverse cellular processes. In eukaryotic cells, Ca²⁺ is handled by a myriad of Ca²⁺-binding proteins found in organelles that are organized into the cellular reticular network (CRN). The network is comprised of the endoplasmic reticulum, Golgi apparatus, lysosomes, membranous components of the endocytic and exocytic pathways, peroxisomes, and the nuclear envelope. Membrane contact sites between the different components of the CRN enable the rapid movement of Ca²⁺, and communication of Ca²⁺ status, within the network. Ca²⁺-handling proteins that reside in the CRN facilitate Ca²⁺ sensing, buffering, and cellular signaling to coordinate the many processes that operate within the cell.

Novel Findings of Anti-Filarial Drug Target and Structure-Based Virtual Screening for Drug Discovery

Lymphatic filariasis and onchocerciasis caused by filarial nematodes are important diseases leading to considerable morbidity throughout tropical countries. Diethylcarbamazine (DEC), albendazole (ALB), and ivermectin (IVM) used in massive drug administration are not highly effective in killing the long-lived adult worms, and there is demand for the development of novel macrofilaricidal drugs affecting new molecular targets. A Ca2+ binding protein, calumenin, was identified as a novel and nematode-specific drug target for filariasis, due to its involvement in fertility and cuticle development in nematodes. As sterilizing and killing effects of the adult worms are considered to be ideal profiles of new drugs, calumenin could be an eligible drug target. Indeed, the Caenorhabditis elegans mutant model of calumenin exhibited enhanced drug acceptability to both microfilaricidal drugs (ALB and IVM) even at the adult stage, proving the roles of the nematode cuticle in efficient drug entry. Molecular modeling revealed that structural features of calumenin were only conserved among nematodes (C. elegans, Brugia malayi, and Onchocerca volvulus). Structural conservation and the specificity of nematode calumenins enabled the development of drugs with good target selectivity between parasites and human hosts. Structure-based virtual screening resulted in the discovery of itraconazole (ITC), an inhibitor of sterol biosynthesis, as a nematode calumenin-targeting ligand. The inhibitory potential of ITC was tested using a nematode mutant model of calumenin.

Changes in the in vitro activity of platinum drugs when administered in two aliquots

BACKGROUND

The management of ovarian cancer remains a challenge. Because of the lack of early symptoms, it is often diagnosed at a late stage when it is likely to have metastasized beyond ovaries. Currently, platinum based chemotherapy is the primary treatment for the disease. However acquired drug resistance remains an on-going problem. As cisplatin brings about apoptosis by intrinsic and extrinsic pathways, this study aimed to determine changes in activity of platinum drugs when administered in two aliquots as against a bolus and sought to determine association with changes in GSH, speciation of platinum drugs and changes in protein expression.

METHODS

The efficacy of administering cisplatin, carboplatin and oxaliplatin in two aliquots with a time gap was investigated in ovarian A2780, A2780(cisR), A2780(ZD0473R) and SKOV-3 cell lines. The cellular accumulation of platinum, level of platinum - DNA binding and cellular glutathione level were determined, and proteomic studies were carried out to identify key proteins associated with platinum resistance in ovarian A2780(cisR) cancer cell line.

RESULTS

Much greater cell kill was observed with solutions left standing at room temperature than with freshly prepared solutions, indicating that the increase in activity on ageing was related to speciation of the drug in solution. Proteomic studies identified 72 proteins that were differentially expressed in A2780 and A2780(cisR) cell lines; 22 of them were restored back to normal levels as a result of synergistic treatments, indicating their relevance in enhanced drug action.

CONCLUSIONS

The proteins identified are relevant to several different cellular functions including invasion and metastasis, cell cycle regulation and proliferation, metabolic and biosynthesis processes, stress-related proteins and molecular chaperones, mRNA processing, cellular organization/cytoskeleton, cellular communication and signal transduction. This highlights the multifactorial nature of platinum resistance in which many different proteins with diverse functions play key roles. This means multiple strategies can be harnessed to overcome platinum resistance in ovarian cancer. The results of the studies can be significant both from fundamental and clinical view points.

A Novel Role of Cab45-G in Mediating Cell Migration in Cancer Cells

Ca²⁺-binding protein of 45 kDa (Cab45), a CREC family member, is reported to be associated with Ca²⁺-dependent secretory pathways and involved in multiple diseases including cancers. Cab45-G, a Cab45 isoform protein, plays an important role in protein sorting and secretion at Golgi complex. However, its role in cancer cell migration remains elusive. In this study, we demonstrate that Cab45-G exhibited an increased expression in cell lines with higher metastatic potential and promoted cell migration in multiple types of cancer cells. Overexpression of Cab45-G resulted in an altered expression of the molecular mediators of epithelial-mesenchymal transition (EMT), which is a critical step in the tumor metastasis. Quantitative real-time PCR showed that overexpression of Cab45-G increased the expression of matrix metalloproteinase-2 and -7 (MMP-2 and MMP-7). Conversely, knock-down of Cab45-G reduced the expression of the above MMPs. Moreover, forced expression of Cab45-G upregulated the level of phosphorylated ERK and modulated the secretion of extracellular proteins fibronectin and fibulin. Furthermore, in human cervical and esophageal cancer tissues, the expression of Cab45-G was found to be significantly correlated with that of MMP-2, further supporting the importance of Cab45-G on regulating cancer metastasis. Taken together, these results suggest that Cab45-G could regulate cancer cell migration through various molecular mechanisms, which may serve as a therapeutic target for the treatment of cancers.

Ca-Dependent Folding of Human Calumenin

Human calumenin (hCALU) is a six EF-hand protein belonging to the CREC family. As other members of the family, it is localized in the secretory pathway and regulates the activity of SERCA2a and of the ryanodine receptor in the endoplasmic reticulum (ER). We have studied the effects of Ca²⁺ binding to the protein and found it to attain a more compact structure upon ion binding. Circular Dichroism (CD) measurements suggest a major rearrangement of the protein secondary structure, which reversibly switches from disordered at low Ca²⁺ concentrations to predominantly alpha-helical when Ca²⁺ is added. SAXS experiments confirm the transition from an unfolded to a compact structure, which matches the structural prediction of a trilobal fold. Overall our experiments suggest that calumenin is a Ca²⁺ sensor, which folds into a compact structure, capable of interacting with its molecular partners, when Ca²⁺ concentration within the ER reaches the millimolar range.

Genome-wide association study of primary tooth eruption identifies pleiotropic loci associated with height and craniofacial distances

Twin and family studies indicate that the timing of primary tooth eruption is highly heritable, with estimates typically exceeding 80%. To identify variants involved in primary tooth eruption, we performed a population-based genome-wide association study of 'age at first tooth' and 'number of teeth' using 5998 and 6609 individuals, respectively, from the Avon Longitudinal Study of Parents and Children (ALSPAC) and 5403 individuals from the 1966 Northern Finland Birth Cohort (NFBC1966). We tested 2 446 724 SNPs imputed in both studies. Analyses were controlled for the effect of gestational age, sex and age of measurement. Results from the two studies were combined using fixed effects inverse variance meta-analysis. We identified a total of 15 independent loci, with 10 loci reaching genome-wide significance (P < 5 × 10(-8)) for 'age at first tooth' and 11 loci for 'number of teeth'. Together, these associations explain 6.06% of the variation in 'age of first tooth' and 4.76% of the variation in 'number of teeth'. The identified loci included eight previously unidentified loci, some containing genes known to play a role in tooth and other developmental pathways, including an SNP in the protein-coding region of BMP4 (rs17563, P = 9.080 × 10(-17)). Three of these loci, containing the genes HMGA2, AJUBA and ADK, also showed evidence of association with craniofacial distances, particularly those indexing facial width. Our results suggest that the genome-wide association approach is a powerful strategy for detecting variants involved in tooth eruption, and potentially craniofacial growth and more generally organ development.

Does CALU SNP rs1043550 contribute variability to therapeutic warfarin dosing requirements?

OBJECTIVES

Calumenin, a molecular chaperone, exerts a regulatory effect on the vitamin K-dependent γ-carboxylation redox cycle that inhibits transfer of the reduced vitamin K from VKORC1, the pharmacological target of warfarin, to the γ-carboxylase. Because of its polymorphic structure and central role in the warfarin metabolic pathway, a contributory role for calumenin to warfarin dose variability has been posited. The current study sought to validate modulation of therapeutic dosing requirements by a single nucleotide polymorphisms (SNP) occurring in the calumenin gene (CALU) reported in previous studies. The CALU SNP was further modeled to detect interaction with SNPs occurring in VKORC1, CYP2C9, and CYP4F2 genes and characterize any additional contribution to variability in therapeutic warfarin dose requirement.

SETTING

The study was undertaken in an established, well-characterized cohort of subjects treated with warfarin in the Anticoagulation Clinic of Marshfield Clinic in Marshfield, Wisconsin.

METHODS

Subjects (N=491) previously genotyped for SNPS known to contribute variability to therapeutic warfarin dose requirement were genotyped for CALU SNP rs1043550, using TaqMan assays. Contribution of CALU SNP rs1043550 was modeled relative to other genotypic and phenotypic characteristics including gender, diagnosis, age, body surface area, underlying indication for warfarin, comorbidities, and pharmacological exposures. Interaction between SNPs impacting on warfarin dose requirements and calumenin SNPs was also modeled.

RESULTS

Small differences in warfarin dosing requirements detected among individuals encoding the mutant G allele in the calumenin SNP were not statistically or clinically significant relative to therapeutic warfarin dose requirement and did not independently contribute significantly to the warfarin dosing model. Interaction between calumenin and VKORC1 SNPs contributed only minor additional variability to that ascribed to the wild type VKORC1 genotype.

CONCLUSIONS

The impact of the CALU SNP on warfarin dose variability was minor and did not contribute significantly to therapeutic warfarin dose requirement in our study cohort. While no contribution was noted for the SNP examined in the present study, further examination of interaction between genetic elements contributing major impact on therapeutic warfarin dose requirements and genes exhibiting a lesser contribution is warranted.

Optimal dosing of warfarin and other coumarin anticoagulants: the role of genetic polymorphisms

Coumarin anticoagulants, which include warfarin, acenocoumarol and phenprocoumon, are among the most widely prescribed drugs worldwide. There is now a large body of published data showing that genotype for certain common polymorphisms in the genes encoding the target vitamin K epoxide reductase (G-1639A/C1173T) and the main metabolizing enzyme CYP2C9 (CYP2C9*2 and *3 alleles) are important determinants of the individual coumarin anticoagulant dose requirement. Additional less common polymorphisms in these genes together with polymorphisms in other genes relevant to blood coagulation such as the cytochrome P450 CYP4F2, gamma-glutamyl carboxylase, calumenin and cytochrome P450 oxidoreductase may also be significant predictors of dose, especially in ethnic groups such as Africans where there have been fewer genetic studies compared with European populations. Using relevant genotypes to calculate starting dose may improve safety during the initiation period. Various algorithms for dose calculation, which also take patient age and other characteristics into consideration, have been developed for all three widely used coumarin anticoagulants and are now being tested in ongoing large randomised clinical trials. One recently completed study has provided encouraging results suggesting that calculation of warfarin dose on the basis of individual patient genotype leads to few adverse events and a higher proportion of time within the therapeutic coagulation rate window, but these findings still need confirmation.

The intracellular transport and secretion of calumenin-1/2 in living cells

Calumenin isoforms 1 and 2 (calu-1/2), encoded by the CALU gene, belong to the CREC protein family. Calu-1/2 proteins are secreted into the extracellular space, but the secretory process and regulatory mechanism are largely unknown. Here, using a time-lapse imaging system, we visualized the intracellular transport and secretory process of calu-1/2-EGFP after their translocation into the ER lumen. Interestingly, we observed that an abundance of calu-1/2-EGFP accumulated in cellular processes before being released into the extracellular space, while only part of calu-1/2-EGFP proteins were secreted directly after attaching to the cell periphery. Moreover, we found the secretion of calu-1/2-EGFP required microtubule integrity, and that calu-1/2-EGFP-containing vesicles were transported by the motor proteins Kif5b and cytoplasmic dynein. Finally, we determined the export signal of calu-1/2-EGFP (amino acid positions 20–46) and provided evidence that the asparagine at site 131 was indispensable for calu-1/2-EGFP stabilization. Taken together, we provide a detailed picture of the intracellular transport of calu-1/2-EGFP, which facilitates our understanding of the secretory mechanism of calu-1/2.

The rapidly expanding CREC protein family: members, localization, function, and role in disease

Although many aspects of the physiological and pathophysiological mechanisms remain unknown, recent advances in our knowledge suggest that the CREC proteins are promising disease biomarkers or targets for therapeutic intervention in a variety of diseases. The CREC family of low affinity, Ca2+-binding, multiple EF-hand proteins are encoded by five genes, RCN1, RCN2, RCN3, SDF4, and CALU, resulting in reticulocalbin, ER Ca2+-binding protein of 55 kDa (ERC-55), reticulocalbin-3, Ca2+-binding protein of 45 kDa (Cab45), and calumenin. Alternative splicing increases the number of gene products. The proteins are localized in the cytosol, in various parts of the secretory pathway, secreted to the extracellular space or localized on the cell surface. The emerging functions appear to be highly diverse. The proteins interact with several different ligands. Rather well-described functions are attached to calumenin with the inhibition of several proteins in the endoplasmic or sarcoplasmic reticulum membrane, the vitamin K(1) 2,3-epoxide reductase, the gamma-carboxylase, the ryanodine receptor, and the Ca2+-transporting ATPase. Other functions concern participation in the secretory process, chaperone activity, signal transduction as well as participation in a large variety of disease processes.

Proteomic profiling of fibroblasts reveals a modulating effect of extracellular calumenin on the organization of the actin cytoskeleton

CREC proteins constitute a family of EF-hand calcium binding proteins localized to the secretory pathway. Calumenin is the only member known to be secreted. Recently, it was shown that thrombin-activated thrombocytes liberate calumenin, which also is found in atherosclerotic lesions but not in normal vasculature. To study the possible effects of calumenin extracellularly, we used proteomic profiling of fibroblasts cultured in absence and in presence of calumenin. Using 2-DE and MS/MS, we show that normal fibroblasts contain several 28-29-kDa N-terminal and a 16-kDa C-terminal fragment of beta- or gamma-actin. Extracellularly added calumenin decreases the levels of both the N-terminal and C-terminal actin fragments, and, in addition, decreases the expression level of septin 2, which interacts with the actin cytoskeleton and is involved in cytokinesis. Labeling of S-phase fibroblasts with bromo-2'deoxy-uridine indicates that calumenin added to the medium also modulates the cell cycle. Our study thus indicates that calumenin may have an autocrine or a paracrine effect on the cells in its vicinity, and, therefore, may be involved in the pathophysiology of thrombosis or in wound healing.

Calumenin, a multiple EF-hands Ca2+-binding protein, interacts with ryanodine receptor-1 in rabbit skeletal sarcoplasmic reticulum

Calumenin is a multiple EF-hand Ca2+-binding protein located in endo/sarcoplasmic reticulum of mammalian tissues. In the present study, we cloned two rabbit calumenin isoforms (rabbit calumenin-1 and -2, GenBank Accession Nos. SY225335 and AY225336, respectively) by RT-PCR. Both isoforms contain a 19 aa N-terminal signal sequence, 6 EF-hand domains, and a C-terminal ER/SR retrieval signal, HDEF. Both calumenin isoforms exist in rabbit cardiac and skeletal muscles, but calumenin-2 is the main isoform in skeletal muscle. Presence of calumenin in rabbit sarcoplasmic reticulum (SR) was identified by Western blot analysis. GST-pull down and co-immunoprecipitation experiments showed that ryanodine receptor 1 (RyR1) interacted with calumenin-2 in millimolar Ca2+ concentration range. Experiments of gradual EF-hand deletions suggest that the second EF-hand domain is essential for calumenin binding to RyR1. Adenovirus-mediated overexpression of calumenin-2 in C2C12 myotubes led to increased caffeine-induced Ca2+ release, but decreased depolarization-induced Ca2+ release. Taken together, we propose that calumenin-2 in the SR lumen can directly regulate the RyR1 activity in Ca2+-dependent manner.

Characterization of isoforms and genomic organization of mouse calumenin

Calumenin is a multiple EF-hand protein located in endo/sarcoplasmic reticulum of mammalian heart and other tissues [J. Biol. Chem. 272 (1997) 18232; Genomics 49 (1998) 331; Biochim. Biophys. Acta 1386 (1998) 121]. In the present study, a new isoform of mouse calumenin (mouse calumenin 2) was cloned by RT-PCR and genomic DNA PCR. The deduced amino acid sequence of mouse calumenin 2 is 315 aa long with the calculated MW of 37,064 and pI of 4.26. It has 92% aa sequence identity to previously identified mouse calumenin [J. Biol. Chem. 272 (1997) 18232] (mouse calumenin 1). The difference in the aa sequence was restricted to the first two EF-hand regions (residues 74-138). Northern blot analysis shows that mouse calumenin 2 is highly expressed in heart, lung, testis and unpregnant uterus. The expression of mouse calumenin 2 appears to decrease when fetal development is progressed. Genomic DNA PCR, sequencing and data mining of mouse genome database were utilized to examine the exon-intron boundaries of mouse calumenin genes. Both mouse calumenin 1 and 2 genes encompass six exons, and five of them (Exon1, 3, 4, 5 and 6) are identical. However, mouse calumenin 1 contains Exon2-1, whereas mouse calumenin 2 contains a neighboring Exon2-2. The calumenin genes are localized on mouse chromosome 6 having conserved synteny with human chromosome 7q32. For comparison, the genomic organization of human calumenin was also examined using the published human genome database (UCSC Genome Bioinformatics at ). Like mouse calumenin genes, two human calumenin genes also consist of five identical exons (Exon1, 3, 4, 5 and 6) and a different Exon2. The present study suggests that the genomic organization of calumenin genes is well conserved between human and mouse.

Comparative genome mapping in the sequence-based era: early experience with human chromosome 7

The success of the ongoing Human Genome Project has resulted in accelerated plans for completing the human genome sequence and the earlier-than-anticipated initiation of efforts to sequence the mouse genome. As a complement to these efforts, we are utilizing the available human sequence to refine human-mouse comparative maps and to assemble sequence-ready mouse physical maps. Here we describe how the first glimpses of genomic sequence from human chromosome 7 are directly facilitating these activities. Specifically, we are actively enhancing the available human-mouse comparative map by analyzing human chromosome 7 sequence for the presence of orthologs of mapped mouse genes. Such orthologs can then be precisely positioned relative to mapped human STSs and other genes. The chromosome 7 sequence generated to date has allowed us to more than double the number of genes that can be placed on the comparative map. The latter effort reveals that human chromosome 7 is represented by at least 20 orthologous segments of DNA in the mouse genome. A second component of our program involves systematically analyzing the evolving human chromosome 7 sequence for the presence of matching mouse genes and expressed-sequence tags (ESTs). Mouse-specific hybridization probes are designed from such sequences and used to screen a mouse bacterial artificial chromosome (BAC) library, with the resulting data used to assemble BAC contigs based on probe-content data. Nascent contigs are then expanded using probes derived from newly generated BAC-end sequences. This approach produces BAC-based sequence-ready maps that are known to contain a gene(s) and are homologous to segments of the human genome for which sequence is already available. Our ongoing efforts have thus far resulted in the isolation and mapping of >3,800 mouse BACs, which have been assembled into >100 contigs. These contigs include >250 genes and represent approximately 40% of the mouse genome that is homologous to human chromosome 7. Together, these approaches illustrate how the availability of genomic sequence directly facilitates studies in comparative genomics and genome evolution.

The CREC family, a novel family of multiple EF-hand, low-affinity Ca(2+)-binding proteins localised to the secretory pathway of mammalian cells

The CREC family consists of a number of recently discovered multiple (up to seven) EF-hand proteins that localise to the secretory pathway of mammalian cells. At present, the family includes reticulocalbin, ERC-55/TCBP-49/E6BP, Cab45, calumenin and crocalbin/CBP-50. Similar proteins are found in quite diverse invertebrate organisms such as DCB-45 and SCF in Drosophila melanogaster, SCF in Bombyx mori, CCB-39 in Caenorhabditis elegans and Pfs40/PfERC in Plasmodium falciparum. The Ca(2+) affinity is rather low with dissociation constants around 10(-4)-10(-3) M. The proteins may participate in Ca(2+)-regulated activities. Recent evidence has been obtained that some CREC family members are involved in pathological activities such as malignant cell transformation, mediation of the toxic effects of snake venom toxins and putative participation in amyloid formation.

Calumenin interacts with serum amyloid P component

We recently reported the identification of human calumenin, a novel Ca(2+) binding, transformation-sensitive and secreted protein [Vorum et al. (1998) Biochim. Biophys. Acta 1386, 121-131; Vorum et al. (1999) Exp. Cell Res. 248, 473-481] belonging to the family of multiple EF-hand proteins of the secretory pathway that include reticulocalbin, ERC-55, Cab45 and crocalbin. In order to further investigate the extracellular functions of calumenin we immobilized the recombinant protein to a column. After application of a placental tissue extract we were able to elute one protein that interacts with calumenin in the presence of Ca(2+). Amino acid sequencing identified this protein as serum amyloid P component (SAP). Furthermore, we verified and characterized the calumenin-SAP interaction by the surface plasmon resonance technique. The findings indicate that calumenin may participate in the immunological defense system and could be involved in the pathological process of amyloidosis that leads to formation of amyloid deposits seen in different types of tissues.

Human calumenin localizes to the secretory pathway and is secreted to the medium

Calumenin belongs to a family of multiple EF-hand proteins that include reticulocalbin, ERC-55, and Cab45. Reticulocalbin and ERC-55 localize to the ER due to a C-terminal HDEL retrieval signal. Cab45 contains a HEEF C-terminal sequence and is localized to the Golgi apparatus. The murine homologue of calumenin is reported to be present in the ER due to a C-terminal HDEF retrieval signal. The human homologue differs from the murine at 7 amino acid positions but the HDEF signal is conserved. However, in the cultured human cell lines, HaCaT keratinocytes, normal and transformed MRC-5 fibroblasts, as well as in transfected COS-1 cells, human calumenin could be demonstrated in the ER as well as in the Golgi complex. Especially in MRC-5 cells, a certain heterogeneity was observed, with some of the cells having calumenin localized solely to the ER while in other cells calumenin could be demonstrated in the ER as well as in the Golgi complex. Immunoelectron microscopy of placental syncytiotrophoblast cells showed that a substantial fraction of calumenin is localized in close association with the ER membrane. In addition, the protein may be recovered from the medium of cultured cells in an endoglycosidase H-resistant form, suggesting that the glycosylated protein has been further modified in the Golgi apparatus and secreted to the medium.

Cloning of two new human helicase genes of the RecQ family: biological significance of multiple species in higher eukaryotes

Two new human DNA helicase genes, RecQ4 and RecQ5, that belong to the RecQ helicase family were cloned and characterized. The addition of these genes increases the total to five helicase genes in the human RecQ family, which includes helicases involved in Bloom and Werner syndromes, the genetic diseases manifesting the distinctive but overlapping clinical phenotypes of immunodeficiency, premature aging, and an enhanced risk of cancer. The RecQ4 helicase is as large as the Bloom (BLM) and Werner (WRN) helicases, and its gene expression profile is organ-specific, resembling that of BLM helicase. In contrast, the RecQ5 helicase has a low molecular weight, similar to the human progenitor RecQ1 helicase, and is expressed in all the organs examined. All five human helicase genes are expressed in cultured K562 leukemia and fibroblast cells. Synchronized K562 cell cultures showed that the genes RecQ4 and BLM, and RecQ1 and WRN, seem to be upregulated at the G1/S and G2/M phases, respectively, of the cell cycle. The biological significance of multiple species of human RecQ helicases, which are apparently nonessential for life but may be related to distinct diseases, is discussed in light of the fact that unicellular organisms, like Escherichia coli and yeast, contain only one species of helicase of this particular family.

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.