Calumenin Expression Research Articles

Astragalus injection mediates autophagy and myocardial remodeling in rats with ischemic cardiomyopathy through calumenin

To study the effects of astragalus injection on myocardial remodeling, calumenin and autophagy in rats with ischemic cardiomyopathy. Thirty-six male SD rats were divided into normal control group, ischemic cardiomyopathy group and astragalus injection group, 12 in each group. Electrocardiogram (ECG) and echocardiography were performed before operation in three groups. Rats in ischemic cardiomyopathy group and astragalus injection group underwent thoracotomy and ligation of coronary artery for 20 minutes, then thoracic cavity was closed after reperfusion. In the astragalus injection group,10 g/kg body weight of Astragalus injection was injected once a week, four times in total. Four weeks after operation, rats in three groups were executed by echocardiography and their hearts were collected for Hematoxylin-Eosin (HE) staining and Van Gieson (VG) staining to observe myocardial pathological changes. Calumenin, LC3-I, LC3-II expressions and LC3-I/LC3-II ratio were detected by Western blot. Compared with ischemic cardiomyopathy group, the echocardiography and myocardial pathology of rats in astragalus injection group changed obviously, and the expressions of calumenin, LC3-I, LC3-II and LC3-I/LC3-II ratio changed significantly (P＜0.01). Astragalus injection has apparent inhibitory effect on ventricular remodeling and autophagy of myocardial cells in rats with ischemic cardiomyopathy, which may be mediated by calumenin.

Expression and clinical significance of calumenin in brain gliomas

Objective To detect the expression of calumenin (CALU) in human brain glioma samples, to explore its effect on the patient′s outcome, and to analyze the related biological functions of the genes co-expressed with CALU. Methods A retrospective analysis was conducted on CALU sequencing expression and clinical data of 288 glioma patients with positive CALU expression in the mRNAseq_325 database of Chinese Glioma Genome Atlas (CGGA). We analyzed the effects of CALU expression levels on survival in different types of glioma patients. The multivariate Cox regression method was used to determine the relevant factors affecting the survival of glioma patients. Pearson correlation analysis was employed to screen the related genes co-expressed with CALU and their biological functions were explored using the online bioinformatic analysis tools. Results Among the 288 patients, the expression of CALU was 4.74±0.68, 5.49±1.12 and 6.17±0.94 in World Health Organization (WHO) grade Ⅱ, Ⅲ, and Ⅳ patients respectively, and 6.13±1.17 and 5.08±0.76 in isocitrate dehydrogenase l (IDH1) wild-type and IDH1 mutant gliomas respectively, and 5.79±0.07 and 4.71±0.07 in gliomas with 1p/19q non-codeletion and 1p/19q co-deletion. The comparative differences in the above indicators were statistically significant (all P 0.05). The median survival of CALU patients with high and low expression levels (144 cases in each) was 13.0(1-132)months and 82.5(2-149)months, respectively, which had statistically significant difference (P<0.01). In patients with WHO grade Ⅱ-Ⅳ gliomas, the high expression of CALU mainly reduced the survival time of grade Ⅲ and Ⅳ patients (both P<0.01). The multivariate Cox regression analysis showed that CALU expression was an independent factor influencing the survival of glioma patients (RR=2.193, 95%CI: 1.507-3.192, P<0.01). In the CGGA database, there were 325 genes that were positively correlated with CALU expression. The biological functions of those genes were mainly signal transduction, cell adhesion and cellular metabolism, and were mainly involved in endoplasmic reticulum protein processing, adhesion and cancer pathways. Conclusion CALU is significantly related to the malignancy of brain glioma and may serve as an independent prognostic factor in high grade glioma patients, which thus provides a potential therapeutic target in the future research. Key words: Glioma; Gene expression; Prognosis; Calumenin

Calumenin-1 Interacts with Climp63 to Cooperatively Determine the Luminal Width and Distribution of Endoplasmic Reticulum Sheets.

SummaryThe ER is composed of distinct structures like tubules, matrices, and sheets, all of which are important for its various functions. However, how these distinct ER structures, especially the perinuclear ER sheets, are formed remains unclear. We report here that the ER membrane protein Climp63 and the ER luminal protein calumenin-1 (Calu1) collaboratively maintain ER sheet morphology. We show that the luminal length of Climp63 is positively correlated with the luminal width of ER sheets. Moreover, the lumen-only mutant of Climp63 dominant-negatively narrows the lumen of ER sheets, demonstrating that Climp63 acts as an ER luminal bridge. We also reveal that Calu1 specifically interacts with Climp63 and antagonizes Climp63 in terms of both ER sheet distribution and luminal width. Together, our data provide insight into how the structure of ER sheets is maintained and regulated.

Measuring Calumenin Impact on ER-Calcium Depletion Using Transient Calumenin Overexpression and Silencing.

Calumenin is a secretory pathway protein regulating different endoplasmic reticulum (ER) proteins such as the sarco-endoplasmic reticulum calcium ATPase (SERCA) pumps. Combined with its diverse cellular distribution, its calcium-binding ability, and its interaction with proteins involved in calcium signaling, it is easy to speculate on future description of important roles of calumenin in calcium homeostasis in many cell types, as it was initially observed in muscle cells. In this chapter, we describe basic techniques to modulate calumenin expression and detect its impact on ER calcium content using classic transfection and Western blot techniques, as well as ER calcium measurement using microplate reader.

Effect of creatine phosphate sodium on miRNA378, miRNA378* and calumenin mRNA in adriamycin-injured cardiomyocytes

To investigate the effect of creatine phosphate sodium (sodium phosphocreatine) on miRNA378, miRNA378* and calumenin mRNA in adriamycin-injured suckling mouse myocardium. The suckling mouse myocardium of primary culture were randomly divided into control group, adriamycin group and treatment group. To identify the suckling mouse myocardium, Smooth muscle actin-α (α-SMA) was monitored by immunohistochemical method. Cardiac function was evaluated by transthoracic echocardiography. The mRNA change of miRNA378, miRNA378* and calumenin mRNA were detected by quantitative real-time PCR. The expression of calumenin and GRP78 were identified by western blot. Mitochondrial damage and vacuolization were found in adriamycin-induced suckling mouse myocardium compared with control group, while creatine phosphate sodium could reduce this phenomenon. Compared with the control group, the mRNA of miRNA378, miRNA378* and calumenin in adriamycin group was reduced, while creatine phosphate sodium could increase this phenomenon. The expression of calumenin and GRP78 were decreased after adriamycin treatment in suckling mouse myocardiums, creatine phosphate sodium increased the expression of calumenin and GRP78. The results of this experiment might be closely related to the effects of that creatine phosphate sodium reduced the pathological mechanism of suckling mouse myocardium with myocarditis caused by adriamycin.

The correlation research on miRNA378* and calumenin,endoplasmic reticulum stress,apoptosis in suckling mouse myocardial cells infected with coxsackie virus B3

To investigate the effects of silencing miRNA378* on apoptosis, endoplasmic reticulum stress and calumenin of cardiomyocyte with coxsackie virus B3 (CVB3) infection. Primary cultured suckling mouse myocardium were divided into control group (normal cell), coxsackie virus infection group (normal cell and coxsackie virus B3), miRNA378* control group (normal cell +coxsackie virus B3+miRNA378* empty plasmid), miRNA378* silencing plasmid group(normal cells + coxsackie virus B3 + miRNA378* silencing plasmid). Four groups of cells were transfected, infected and treated in CO2 incubator at 37℃. The α-SMA protein, cell apoptosis rate, calumenin, glucose regulated protein 78 (GRP78), activation transcription factor 6(ATF6) and transcription factors c/ebp homologue protein (CHOP) in endoplasmic reticulum were analyzed. By detecting α-SMA protein, the isolated suckling mouse ventricular myocardium were confirmed. TUNEL detection of different groups of ventricular cell apoptosis found that coxsackie virus group of ventricular myocytes apoptosis was significant. Compared with the coxsackie virus infection group of myocardial cells, miRNA378* silencing plasmid expression of cardiomyocyte apoptosis cells significantly reduced(P<0.01). The expressions of GRP78, ATF6 and CHOP were increased compared with those infected by Coxsackie virus infection (P<0.01), while the expressions of calumenin were decreased (P<0.01). CVB3 infected myocardial cells effected miRNA378* expression. It can trigger endoplasmic reticulum stress and activates signaling pathway factor and increase myocardial cell apoptosis.>.

The effect of astragalus injection on the expression of endoplasmic reticulum stress chaperonin GRP78 and GRP94 mRNA in adriamycin-injured cardiomyocytes with calumenin silencing by shRNA

To investigate the effect of astragalus injection on the endoplasmic reticulum stress in adriamycin(ADR)-injured cardiomyocytes with calumenin silencing by shRNA. Firstly, the stable lentiviral calumenin shRNAvector was constructed. Secondly, in vitro cultured neonatal rat cardiac myocytes were randomly divided into control group、normal group (3 mg/L ADR), lentivirus infection group (lentivirus infection+3 mg/L ADR), Astragalus group 1 (3 mg/L ADR+Astragalus), Astragalus group 2 (lentivirus infection+3 mg/L ADR+Astragalus). The mRNA epression level of calumenin expression and reticulum stress chaperone in GRP78, GRP94 of each group was monitored by real-time PCR. ①Compared with that of the control group, the calumenin mRNA expression in the normal group was reduced(P<0.05), yet its mRNA level in lentivirus the infection group and the Astragalus group 2 was further reduced(P<0.01). Compared with that of the normal group, the mRNA contents of calumenin in the Astragalus group 1 was increased(P<0.05). The expression of calumenin in Astragalus group 2 was increased comparing with lentivirus infection group (P<0.01). ②Compared with that in the control group, the expression of reticulum stress chaperone in GRP78, GRP 94 in lentivirus infection group and normal group was significantly increased (P<0.01); Compared with that in the normal group, the expression of reticulum stress chaperone in GRP78, GRP94 in Astragalus group 1 was reduced(P<0.01); Compared with that in the lentivirus infection group, the expression of reticulum stress chaperone in GRP78, GRP94 in the Astragalus group 2 was obviously decreased(P<0.01). ①Calumenin can alleviate endoplasmic reticulum stress induced by ADR-injured myocardial cells. ②Astragalus injection can restrain the endoplasmic reticulum stress induced by adriamycin, which may be achieved by the calumenin protein.

Protective effect of miR378* on doxorubicin‐induced cardiomyocyte injury via calumenin

Doxorubicin (Dox) is a highly effective antitumor antibiotic, however myocardial toxicity severely limits its use clinically. The pathogenesis of doxorubicin‐induced cardiomyopathy is unclear. In Dox cardiomyopathy mice, there is a decline in cardiac function, a change in myocardial pathology and a reduction in miR378* expression. Expression changes in calumenin, an endoplasmic reticulum stress (ERS) chaperone protein and pathway factor, as well as apoptosis, were observed in cardiomyocytes after doxorubicin‐induced injury. However, miR378* increased calumenin expression, eased ERS, and reduced cardiomyocyte apoptosis, while, silencing miR378* reduced calumenin expression, aggravated ERS, and increased cardiomyocyte apoptosis. The above results indicate that miR378* alleviates ERS and inhibits the activation of the ERS‐mediated apoptosis signaling pathway in cardiomyocytes via regulating calumenin expression, thereby reducing cardiomyocyte apoptosis after doxorubicin‐induced injury. Increasing miR378* expression may be a new way to improve cardiac function and quality of life in patients with Dox cardiomyopathy.

Ibutilide treatment protects against ER stress induced apoptosis by regulating calumenin expression in tunicamycin treated cardiomyocytes.

BackgroundIbutilide, a class III antiarrhythmic agent has been shown to be cardioprotective in treating atrial fibrillation, promoting cardioconversion and recently this agent has been shown to protect against ER stress induced apoptosis in cardiomyocytes. In this study we begin to identify the mechanism by which ibutilide exerts its cardioprotection in tunicamycin treated cardiomyocytes. We examined ER stress markers including calumenin; a calcium binding ER chaperone protein that has recently been linked to ER stress in cardiomyocytes, in our treated cells.MethodsTo assess the effect of ibutilide we used the well characterized in vitro model of ER stress induced apoptosis in rat neonatal cardiomyocytes (RNC). RNC were treated with tunicamycin and the degree of ER stress was assessed by quantifying mRNA and protein levels of GRP78, GRP94 and calumenin, and examined the extent of apoptosis by assessing the protein levels of caspase-3/9/12, CHOP, ATF6, p-PERK, spliced XBP-1, the ratio of Bax/Bcl-2 and the percentage of deoxynucleotidyl-transferase- mediated dUTP nick end labeling (TUNEL) positive cells.ResultsWe demonstrate ibutilide attenuated the up-regulation of ER stress markers GRP78 and GRP94 and rescued the decline in calumenin mRNA and protein levels in tunicamycin treated cardiomyocytes. The up-regulation of apoptotic markers caspase-3, CHOP, ATF6, p-PERK, spliced XBP-1, the ratio of Bax/Bcl-2 and the percentage of TUNEL positive cells were also attenuated after ibutilide treatment while the protein levels of Caspase-9 and Caspase-12 were unaffected.ConclusionsThis study suggests another cardioprotective effect of the antiarrhythmic agent ibutilide whereby pretreatment leads to the attenuation of ER stress induced apoptosis by regulating calumenin expression. This study provides further evidence for the role of calumenin in the cardiomyocyte ER stress response.

Effects of caspase inhibitor z-VAD-fmk on the expressions of calumenin, caspase-3, GRP78 and GRP94 in adriamycin-injured cardiomyocytes

To study the effects of Caspase broad spectrum inhibitor Z-VAD-FMK on the expressions of calumenin,caspase-3, GRP78 and GRP94 in adriamycin-injured cardiomyocytes and to discuss whether there is a regulation relationship between calumenin and endo-plasmic reticulum stress and myocardial apoptosis. The primary cultured suckling mouse myocardium were randomly divided into control group (cardiomyocyte), adriamycin group (3 mg/L adriamycin + cardiomyocyte) and z-VAD-fm group (3 mg/L adriamycin + 0.1 μmol/L Z-VAD-fmk + cardiomyocyte), each group of cardiomyocytes were cultured in CO2 incubator at 37℃ for 24 h (n=3). The expres-sion ofα -SMA protein in ventricular myocytes was detected by immunohistochemical method. The expressions of calumenin, GRP78, GRP94 and Caspase-3 in the myocardial cells were detected by Western blot. Compared with the control group, the expression of calumenin in adriamycin induced myocardial cells was significantly decreased (P < 0.01), while the expressions of GRP78, GRP94 and Caspase-3 ex-pression were increased (P < 0.01). Compared with adriamycin group, the expression of calumenin in z-VAD-fm group was increased (P < 0.01), while the expressions of GRP78, GRP94 and caspase-3 were decreased (P < 0.01). The caspase inhibitor z-VAD-fmk inhibited the expression of caspase and increased the expression of calumenin in adriamycin induced myocardial cells, and thus alleviated the endoplasmic reticulum stress.

Calumenin contributes to ER-Ca2+ homeostasis in bronchial epithelial cells expressing WT and F508del mutated CFTR and to F508del-CFTR retention

Cystic Fibrosis (CF) is the most frequent fatal genetic disease in Caucasian populations. Mutations in the chloride channel CF Transmembrane Conductance Regulator (CFTR) gene are responsible for functional defects of the protein and multiple associated dysregulations. The most common mutation in patients with CF, F508del-CFTR, causes defective CFTR protein folding. Thus minimal levels of the receptor are expressed at the cell surface as the mutated CFTR is retained in the endoplasmic reticulum (ER) where it correlates with defective calcium (Ca2+) homeostasis. In this study, we discovered that the Ca2+ binding protein Calumenin (CALU) is a key regulator in the maintenance of ER-Ca2+ calcium homeostasis in both wild type and F508del-CFTR expressing cells. Calumenin modulates SERCA pump activity without drastically affecting ER-Ca2+ concentration. In addition, reducing Calumenin expression in CF cells results in a partial restoration of CFTR activity, highlighting a potential function of Calumenin in CFTR maturation. These findings demonstrate a pivotal role for Calumenin in CF cells, providing insights into how modulation of Calumenin expression or activity may be used as a potential therapeutic tool to correct defects in F508del-CFTR.

The relationship between miRNA378, calumenin and endoplasmic reticulum stress in suckling mouse myocardium with myocarditis caused by adriamycin

To investigate the relationship between miRNA378, calumenin and endoplasmic reticulum stress in suckling mouse myocardium with myocarditis caused by adriamycin. The suckling mouse myocardium of primary culture were randomly divided into control group, adriamycin group, lentivirus infection miRNA378 over expression control group, lentivirus infection miRNA378 over expression group, lentivirus infection miRNA378 silence control group and lentivirus infection miRNA378 silence group. Firstly to identify the suckling mouse myocardium, α-SMA was monitored by immunohistochemical method, and secondly the ventricular myocytes were transfered by lentivirus plasmids. Then the expression change of miRNA378, calumenin and glucose regulated protein 78(GRP78) mRNA were detected by Quantitative Real-time PCR. Compared with the adriamycin infection group, the expression of calumenin mRNA in lentivirus infection miRNA378 over expression group was increased(P<0.01), while the expression of GRP78 mRNA was reduced(P<0.01); Compared with the adriamycin infection group, the expressions of calumenin and GRP78 mRNA in lentivirus infection miRNA378 silence group did not change insignificantly. Adriamycin injection may cause expression of calumenin in suckling mouse myocardium with myocarditis reduced, which may lead to the endoplasmic reticulum stress. This effect is related with miRNA378.

Calumenin has a role in the alleviation of ER stress in neonatal rat cardiomyocytes

Disturbance of endoplasmic reticulum (ER) homeostasis causes ER stress (ERS), and triggers the unfolded protein response (UPR) that consequently reduces accumulation of unfolded proteins by increasing the quantity of ER chaperones. Calumenin, a Ca2+-binding protein with multiple EF hand motifs, which is located in the ER/SR, is highly expressed during the early developmental stage of the heart, similar to other ER-resident chaperones. The aim of this study was to investigate the functional role of calumenin during ERS in the heart. Like other chaperones (e.g., GRP94 and GRP78), calumenin expression was highly upregulated during ERS induced by 10μg/ml tunicamycin, but attenuated in the presence of 500μM PBA, the chemical chaperone in neonatal rat ventricular cardiomyocytes (NRVCs). Upon 7.5-fold overexpression of calumenin using a recombinant adenovirus system, the expression levels of ERS markers (GRP78, p-PERK, and p-elF2α) and ER-initiated apoptosis markers (CHOP and p-JNK) were reduced, whereas the survival protein BCL-2 was upregulated during ERS compared to the control. Evaluation of cell viability by TUNEL assay showed that apoptosis was also significantly reduced by calumenin overexpression in ERS-induced cells. Taken together, our results suggest that calumenin plays an essential role in the alleviation of ERS in neonatal rat cardiomyocytes.

Spatio-temporal expression analysis of the calcium-binding protein calumenin in the rodent brain

Calumenin is a Ca2+-binding protein that belongs to the CREC superfamily. It contains six EF-hand domains that exhibit a low affinity for Ca2+ as well as an endoplasmic reticulum retention signal. Calumenin exhibits a broad and relatively high expression in various brain regions during development as demonstrated by in situ hybridization. Signal intensity of calumenin is highest during the early development and then declines over time to reach a relatively low expression in adult animals. Immunohistochemistry indicates that at the P0 stage, calumenin expression is most abundant in migrating neurons in the zones around the lateral ventricle. In the brain of adult animals, it is expressed in various glial and neuronal cell types, including immature neurons in subgranular zone of hippocampal dentate gyrus. At the subcellular level, calumenin is identified in punctuate and diffuse distribution mostly in somatic regions where it co-localizes with endoplasmic reticulum (ER) and partially Golgi apparatus. Upon subcellular fractionation, calumenin is enriched in fractions containing membranes and is only weakly present in soluble fractions. This study points to a possible important role of calumenin in migration and differentiation of neurons, and/or in Ca2+ signaling between glial cells and neurons.

Characterization of calumenin in mouse heart

Calumenin is a multiple EF-hand Ca2+-binding protein located in the endo/sarcoplasmic reticulum of mammalian hearts. Calumenin belongs to the CREC family of Ca2+-binding proteins having multiple EF-hands. Ca2+ homeostasis in the sarcoplasmic reticulum (SR) of mammalian hearts is maintained by RyR2, SERCA2 and other associated SR resident proteins. Evidence suggests that calumenin interacts with RyR2 and SERCA2, and therefore changes in the expression of calumenin could alter Ca2+ cycling in mouse heart. In this review, current knowledge of the biochemical and functional roles of calumenin in mouse heart is described.

Evaluation of the effect of new vitamin D3 derivatives, BGP-013 and BGP-015, administration on human carcinomas

Disturbance of endoplasmic reticulum (ER) homeostasis causes ER stress (ERS), and triggers the unfolded protein response (UPR) that consequently reduces accumulation of unfolded proteins by increasing the quantity of ER chaperones. Calumenin, a Ca2+-binding protein with multiple EF hand motifs, which is located in the ER/SR, is highly expressed during the early developmental stage of the heart, similar to other ER-resident chaperones. The aim of this study was to investigate the functional role of calumenin during ERS in the heart. Like other chaperones (e.g., GRP94 and GRP78), calumenin expression was highly upregulated during ERS induced by 10 μg/ml tunicamycin, but attenuated in the presence of 500 μM PBA, the chemical chaperone in neonatal rat ventricular cardiomyocytes (NRVCs). Upon 7.5-fold overexpression of calumenin using a recombinant adenovirus system, the expression levels of ERS markers (GRP78, p-PERK, and p-elF2α) and ER-initiated apoptosis markers (CHOP and p-JNK) were reduced, whereas the survival protein BCL-2 was upregulated during ERS compared to the control. Evaluation of cell viability by TUNEL assay showed that apoptosis was also significantly reduced by calumenin overexpression in ERS-induced cells. Taken together, our results suggest that calumenin plays an essential role in the alleviation of ERS in neonatal rat cardiomyocytes.

Characterization of bromadiolone resistance in a danish strain of Norway rats, rattus norvegicus, by hepatic gene expression profiling of genes involved in vitamin k‐dependent γ‐carboxylation

The present study characterizes the anticoagulant resistance mechanism in a Danish bromadiolone-resistant strain of Norway rats (Rattus norvegicus), with a Y139C VKORC1 mutation. We compared liver expression of the VKORC1 gene, which encodes a protein of the vitamin K 2,3-epoxide reductase complex, the NQO1 gene, which encodes a NAD(P)H quinone dehydrogenase and the Calumenin gene between bromadiolone-resistant and anticoagulant-susceptible rats upon saline and bromadiolone administration. Additionally, we established the effect of bromadiolone on the gene expression in the resistant and susceptible phenotype. Bromadiolone had no effect on VKORC1 and NQO1 expression in resistant rats, but induced significantly Calumenin expression in the susceptible rats. Calumenin expression was similar between the resistant and the susceptible rats upon saline administration but twofold lower in resistant rats after bromadiolone treatment. These results indicate that Danish bromadiolone resistance does not involve an overexpression of calumenin. Independent of the treatment, we observed a low VKORC1 expression in resistant rats, which in conjugation with the Y139C polymorphism most likely explains the low VKOR activity and the enhanced need for vitamin K observed in Danish resistant rats. Furthermore the bromadiolone resistance was found to be associated with a low expression of the NQO1 gene.

P.1.b.011 The differences of electroencephalogram coherence between schizophrenia and bipolar disorder

Calumenin is a Ca2+-binding protein that belongs to the CREC superfamily. It contains six EF-hand domains that exhibit a low affinity for Ca2+ as well as an endoplasmic reticulum retention signal. Calumenin exhibits a broad and relatively high expression in various brain regions during development as demonstrated by in situ hybridization. Signal intensity of calumenin is highest during the early development and then declines over time to reach a relatively low expression in adult animals. Immunohistochemistry indicates that at the P0 stage, calumenin expression is most abundant in migrating neurons in the zones around the lateral ventricle. In the brain of adult animals, it is expressed in various glial and neuronal cell types, including immature neurons in subgranular zone of hippocampal dentate gyrus. At the subcellular level, calumenin is identified in punctuate and diffuse distribution mostly in somatic regions where it co-localizes with endoplasmic reticulum (ER) and partially Golgi apparatus. Upon subcellular fractionation, calumenin is enriched in fractions containing membranes and is only weakly present in soluble fractions. This study points to a possible important role of calumenin in migration and differentiation of neurons, and/or in Ca2+ signaling between glial cells and neurons.

Calumenin, a Ca2+-binding protein retained in the endoplasmic reticulum with a novel carboxyl-terminal sequence, HDEF.

We have identified and characterized a cDNA encoding a novel Ca2+-binding protein named calumenin from mouse heart by the signal sequence trap method. The deduced amino acid sequence (315 residues) of calumenin contains an amino-terminal signal sequence and six Ca2+-binding (EF-hand) motifs and shows homology with reticulocalbin, Erc-55, and Cab45. These proteins seem to form a new subset of the EF-hand protein family expressed in the lumen of the endoplasmic reticulum (ER) and Golgi apparatus. Purified calumenin had Ca2+-binding ability. The carboxyl-terminal tetrapeptide His-Asp-Glu-Phe was shown to be responsible for retention of calumenin in ER by the retention assay, immunostaining with a confocal laser microscope, and the deglycosylation assay. This is the first report indicating that the Phe residue is included in the ER retention signal. Calumenin is expressed most strongly in heart of adult and 18.5-day embryos. The calumenin gene (Calu) was mapped at the proximal portion of mouse chromosome 7.