Hailey-Hailey disease is caused by mutations in ATP2C1 encoding a novel Ca(2+) pump

The Ca2+ pumps of the endoplasmic reticulum and Golgi apparatus

The various splice variants of the three SERCA- and the two SPCA-pump genes in higher vertebrates encode P-type ATPases of the P(2A) group found respectively in the membranes of the endoplasmic reticulum and the secretory pathway. Of these, SERCA2b and SPCA1a represent the housekeeping isoforms. The SERCA2b form is characterized by a luminal carboxy terminus imposing a higher affinity for cytosolic Ca(2+) compared to the other SERCAs. This is mediated by intramembrane and luminal interactions of this extension with the pump. Other known affinity modulators like phospholamban and sarcolipin decrease the affinity for Ca(2+). The number of proteins reported to interact with SERCA is rapidly growing. Here, we limit the discussion to those for which the interaction site with the ATPase is specified: HAX-1, calumenin, histidine-rich Ca(2+)-binding protein, and indirectly calreticulin, calnexin, and ERp57. The role of the phylogenetically older and structurally simpler SPCAs as transporters of Ca(2+), but also of Mn(2+), is also addressed.

Secretory pathway stress responses as possible mechanisms of disease involving Golgi Ca2+ pump dysfunction

In mammalian tissues, uptake of Ca(2+) and Mn(2+) by Golgi membranes is mediated by the secretory pathway Ca(2+) -ATPases, SPCA1 and SPCA2, encoded by the ATP2C1 and ATP2C2 genes. Loss of one copy of the ATP2C1 gene, which causes SPCA1 haploinsufficiency, leads to squamous cell tumors of keratinized epithelia in mice and to Hailey-Hailey disease, an acantholytic skin disease, in humans. Although the disease phenotypes resulting from SPCA1 haploinsufficiency in mice and humans are quite different, each species-specific phenotype is remarkably similar to those arising as a result of null mutations in one copy of the ATP2A2 gene, encoding SERCA2, the endoplasmic reticulum (ER) Ca(2+) pump. SERCA2 haploinsufficiency, like SPCA1 haploinsufficiency, causes squamous cell tumors in mice and Darier's disease, also an acantholytic skin disease, in humans. The phenotypic similarities between SPCA1 and SERCA2 haploinsufficiency in the two species, and the general functions of the two pumps in consecutive compartments of the secretory pathway, suggest that the underlying disease mechanisms are similar. In this review, we discuss evidence supporting the view that chronic Golgi stress and/or ER stress resulting from Ca(2+) pump haploinsufficiencies leads to activation of cellular stress responses in keratinocytes, with the predominance of proapoptotic pathways (although not necessarily apoptosis itself) leading to acantholytic skin disease in humans and the predominance of prosurvival pathways leading to tumors in mice.

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer's and Parkinson's disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.

Two patients with Hailey-Hailey disease, multiple primary melanomas, and other cancers

BACKGROUND

Hailey-Hailey Disease (HHD) is an autosomal dominant skin disorder that is characterized by erythematous and sometimes vesicular, weeping plaques of intertriginous regions. Squamous cell carcinoma and basal cell carcinoma arising in lesions of HHD have been described in the literature. To our knowledge, there are no reports of melanoma or noncutaneous malignant neoplasms associated with HHD.

OBSERVATIONS

We discuss the mechanisms of oncogenicity, including genetic, environmental, and iatrogenic factors, in 2 patients with HHD, multiple primary melanomas, and other cancers. Patient 1 had a mucoepidermoid carcinoma of the parotid gland. Patient 2 had a history of acute monoblastic leukemia and malignant peripheral nerve sheath tumor as well as radiologic evidence of an acoustic neurilemmoma.

CONCLUSIONS

The cause of the cancers in these 2 patients is likely multifactorial. We describe the patients to draw attention to the possible association between HHD and cancer. Additional research should be performed to determine whether patients with HHD have an increased incidence of cancer.

A case of Hailey-Hailey disease in an infant with a new ATP2C1 gene mutation

Familial benign chronic pemphigus or Hailey-Hailey disease (OMIM 169600) is an autosomal-dominant blistering disease. Here we present a rare case of familial benign chronic pemphigus in a Chinese infant. The 5-month-old proband, who showed diffusely distributed skin lesions, is the youngest patient of Hailey-Hailey disease ever reported. The detection of an ATP2C1 gene mutation in this infant confirmed the diagnosis. His mother carried the same mutation, but with no history of skin lesions.

Organellar calcium buffers

Ca(2+) is an important intracellular messenger affecting many diverse processes. In eukaryotic cells, Ca(2+) storage is achieved within specific intracellular organelles, especially the endoplasmic/sarcoplasmic reticulum, in which Ca(2+) is buffered by specific proteins known as Ca(2+) buffers. Ca(2+) buffers are a diverse group of proteins, varying in their affinities and capacities for Ca(2+), but they typically also carry out other functions within the cell. The wide range of organelles containing Ca(2+) and the evidence supporting cross-talk between these organelles suggest the existence of a dynamic network of organellar Ca(2+) signaling, mediated by a variety of organellar Ca(2+) buffers.

Heterogeneous mutations of the ATP2C1 gene causing Hailey-Hailey disease in Hong Kong Chinese

BACKGROUND

Hailey-Hailey disease (HHD) is a rare autosomal dominant dermatosis. It causes suprabasilar acantholysis leading to vesicular and crusted erosions affecting the flexures. Mutation of ATP2C1 gene encoding the human secretory pathway Ca(2+) /Mn(2+) -ATPase (hSPCA1) was identified to be the cause of this entity.

OBJECTIVE

The aim of this study was to study the mutational profile of the ATP2C1 gene in Hong Kong Chinese patients with HHD.

METHODS

Patients with the clinical diagnosis of HHD proven by skin biopsy were included in this study. Mutation analysis was performed in 17 Hong Kong Chinese patients with HHD.

RESULTS

Ten mutations in the ATP2C1 gene were found. Six of these were novel mutations. The novel mutations included a donor splice site mutation (IVS22+1G>A); a missense mutation (c.1049A>T); two deletion mutations (c.185_188delAGTT and c.923_925delAAG); an acceptor splice site mutation (IVS21-1G>C) and an insertion mutation (c.2454dupT).

CONCLUSION

The six novel mutations provide additions to the HHD mutation database. No hot-spot mutation was found and high allelic heterogeneity was demonstrated in the Hong Kong Chinese patients.

A novel missense mutation of the ATP2C1 gene in a Chinese patient with Hailey-Hailey disease

Benign familial chronic pemphigus (Hailey-Hailey disease, HHD; MIM 169600) is a rare autosomal dominant hereditary disorder characterized by pruritic vesicles, painful erosions and scaly erythematous plaques at the sites of friction and flexures. Mutations in ATP2C1, which encoding the human secretory pathway Ca²(+)/Mn²(+)-ATPase protein 1 (hSPCA1), have been identified as the pathogenic gene of HHD. We found a novel, distinct, heterozygous mutation during study of a Chinese patient with HHD. We identified a C→T transition at nucleotide 1235 (p.Thr352IIe), in exon 13 of ATP2C1. This observation would be useful for genetic counseling and prenatal diagnosis for affected families and in expanding the repertoire of ATP2C1 mutations underlying HHD.

The Golgi apparatus: an organelle with multiple complex functions

Remarkable advances have been made during the last few decades in defining the organizational principles of the secretory pathway. The Golgi complex in particular has attracted special attention due to its central position in the pathway, as well as for its fascinating and complex structure. Analytical studies of this organelle have produced significant advances in our understanding of its function, although some aspects still seem to elude our comprehension. In more recent years a level of complexity surrounding this organelle has emerged with the discovery that the Golgi complex is involved in cellular processes other than the 'classical' trafficking and biosynthetic pathways. The resulting picture is that the Golgi complex can be considered as a cellular headquarters where cargo sorting/processing, basic metabolism, signalling and cell-fate decisional processes converge.

Identification of a gain-of-function mutation in a Golgi P-type ATPase that enhances Mn2+ efflux and protects against toxicity

P-type ATPases transport a wide array of ions, regulate diverse cellular processes, and are implicated in a number of human diseases. However, mechanisms that increase ion transport by these ubiquitous proteins are not known. SPCA1 is a P-type pump that transports Mn(2+) from the cytosol into the Golgi. We developed an intra-Golgi Mn(2+) sensor and used it to screen for mutations introduced in SPCA1, on the basis of its predicted structure, which could increase its Mn(2+) pumping activity. Remarkably, a point mutation (Q747A) predicted to increase the size of its ion permeation cavity enhanced the sensor response and a compensatory mutation restoring the cavity to its original size abolished this effect. In vivo and in vitro Mn(2+) transport assays confirmed the hyperactivity of SPCA1-Q747A. Furthermore, increasing Golgi Mn(2+) transport by expression of SPCA1-Q747A increased cell viability upon Mn(2+) exposure, supporting the therapeutic potential of increased Mn(2+) uptake by the Golgi in the management of Mn(2+)-induced neurotoxicity.

Genetic diagnosis of Hailey-Hailey disease in two Chinese families: novel mutations in the ATP2C1 gene

Hailey-Hailey disease (HHD; OMIM 169600), is an autosomal dominantly inherited disorder characterized by suprabasal cell separation of the epidermis. Mutations in ATP2C1, which encodes the human secretory pathway Ca(2+)/ Mn(2) +/- ATPase protein 1 (hSPCA1), have been identified as the pathogenic gene of HHD without evidence of genetic heterogeneity. In this study, the ATP2C1 gene was screened in two typical Chinese pedigrees with HHD, and two specific novel mutations of the ATP2CL gene were identified. Family 1 had a 16-base deletion mutation c.1068-1083del16 and family 2 had a substitution mutation c.1982T>G (p.Met661Arg). DNA sequencing of the three descendants of the probands revealed that they all had the normal genotype, indicating that there had been no transmission of the mutation.

Plasma membrane Ca2+-ATPases in the nervous system during development and ageing

Calcium signaling is used by neurons to control a variety of functions, including cellular differentiation, synaptic maturation, neurotransmitter release, intracellular signaling and cell death. This review focuses on one of the most important Ca²⁺ regulators in the cell, the plasma membrane Ca²⁺-ATPase (PMCA), which has a high affinity for Ca²⁺ and is widely expressed in brain. The ontogeny of PMCA isoforms, linked to specific requirements of Ca²⁺ during development of different brain areas, is addressed, as well as their function in the adult tissue. This is based on the high diversity of variants in the PMCA family in brain, which show particular kinetic differences possibly related to specific localizations and functions of the cell. Conversely, alterations in the activity of PMCAs could lead to changes in Ca²⁺ homeostasis and, consequently, to neural dysfunction. The involvement of PMCA isoforms in certain neuropathologies and in brain ageing is also discussed.

Monoallelic expression of Krt12 gene during corneal-type epithelium differentiation of limbal stem cells

PURPOSE

The purpose of this study was to characterize a Krt12-Cre knock-in mouse line for corneal epithelium-specific gene ablation and to analyze the allelic selection of the keratin 12 (Krt12) gene during corneal type-epithelium differentiation.

METHODS

Knock-in mice were generated by gene targeting. The authors examined the expression patterns of several reporter genes in the corneas of bitransgenic Krt12cre/+/ROSA(EGFP), Krt12Cre/+/ZEG, and Krt12Cre/+/ZAP mouse lines. Krt12 and cre recombinase (Cre) immunostaining was performed. Corneal epithelial cells from bitransgenic Krt12Cre/+/ROSA(EGFP) mice were examined by fluorescence-activated cell sorter.

RESULTS

Mosaic and spiral expression patterns of EGFP were observed in young and adult bitransgenic Krt12Cre/+/ZEG mice, respectively. Immunostaining revealed that Cre- cells were also Krt12 negative in the corneal epithelia of Krt12Cre/-/ZAP mice. Using FACS analysis, 60% to 70% of the corneal epithelial cells from Krt12Cre/+/ROSAEGFP mice were EGFP positive, whereas 20% to 30% were negative. RT-PCR revealed that EGFP+ cells express both Krt12Cre and Krt12+ alleles, whereas EGFP- cells express only Krt12+. In the Krt12Cre/- cornea, the number of epithelial cells expressing Cre is the same as that found in Krt12Cre/Cre, which can be explained by the fragility of corneal epithelial cells that did not produce Krt12 because the Krt12Cre allele was not transcribed.

CONCLUSIONS

These observations are consistent with the notion that clonal limbal stem cells randomly activate Krt12 alleles in the process of terminal differentiation. The authors suggest that this selection is advantageous for retaining epithelial cells expressing the Krt12+ allele and that it allows tolerance to structural mutations of Krt12.

Manganese-induced trafficking and turnover of the cis-Golgi glycoprotein GPP130

Manganese is an essential element that is also neurotoxic at elevated exposure. However, mechanisms regulating Mn homeostasis in mammalian cells are largely unknown. Because increases in cytosolic Mn induce rapid changes in the localization of proteins involved in regulating intracellular Mn concentrations in yeast, we were intrigued to discover that low concentrations of extracellular Mn induced rapid redistribution of the mammalian cis-Golgi glycoprotein Golgi phosphoprotein of 130 kDa (GPP130) to multivesicular bodies. GPP130 was subsequently degraded in lysosomes. The Mn-induced trafficking of GPP130 occurred from the Golgi via a Rab-7-dependent pathway and did not require its transit through the plasma membrane or early endosomes. Although the cytoplasmic domain of GPP130 was dispensable for its ability to respond to Mn, its lumenal stem domain was required and it had to be targeted to the cis-Golgi for the Mn response to occur. Remarkably, the stem domain was sufficient to confer Mn sensitivity to another cis-Golgi protein. Our results identify the stem domain of GPP130 as a novel Mn sensor in the Golgi lumen of mammalian cells.

Tight junctions in Hailey-Hailey and Darier's diseases

Hailey-Hailey disease (HHD) and Darier's disease (DD) are caused by mutations in Ca(2+)-ATPases with the end result of desmosomal disruption and suprabasal acantholysis. Tight junctions (TJ) are located in the granular cell layer in normal skin and contribute to the epidermal barrier. Aberrations in the epidermal differentiation, such as in psoriasis, have been shown to lead to changes in the expression of TJ components. Our aim was to elucidate the expression and dynamics of the TJ proteins during the disruption of desmosomes in HHD and DD lesions. Indirect immunofluorescence and avidin-biotin labeling for TJ, desmosomal and adherens junction proteins, and subsequent analyses with the confocal laser scanning microscope were carried out on 14 HHD and 14 DD skin samples. Transepidermal water loss (TEWL) was measured in normal and lesional epidermis of nine HHD and eight DD patients to evaluate the function of the epidermal barrier in HHD and DD skin. The localization of TJ proteins claudin-1, claudin-4, ZO-1, and occludin in perilesional HHD and DD epidermis was similar to that previously described in normal skin. In HHD lesions the tissue distribution of ZO-1 expanded to the acantholytic spinous cells. In agreement with previous findings, desmoplakin was localized intracellularly. In contrast claudin-1 and ZO-1 persisted in the cell-cell contact sites of acantholytic cells. TEWL was increased in the lesional skin. The current results suggest that TJ components follow different dynamics in acantholysis of HHD and DD compared to desmosomal and adherens junction proteins.

Calcium Pumps in Health and Disease

Ca2+-ATPases (pumps) are key actors in the regulation of Ca2+ in eukaryotic cells and are thus essential to the correct functioning of the cell machinery. They have high affinity for Ca2+ and can efficiently regulate it down to very low concentration levels. Two of the pumps have been known for decades (the SERCA and PMCA pumps); one (the SPCA pump) has only become known recently. Each pump is the product of a multigene family, the number of isoforms being further increased by alternative splicing of the primary transcripts. The three pumps share the basic features of the catalytic mechanism but differ in a number of properties related to tissue distribution, regulation, and role in the cellular homeostasis of Ca2+. The molecular understanding of the function of the pumps has received great impetus from the solution of the three-dimensional structure of one of them, the SERCA pump. These spectacular advances in the structure and molecular mechanism of the pumps have been accompanied by the emergence and rapid expansion of the topic of pump malfunction, which has paralleled the rapid expansion of knowledge in the topic of Ca2+-signaling dysfunction. Most of the pump defects described so far are genetic: when they are very severe, they produce gross and global disturbances of Ca2+ homeostasis that are incompatible with cell life. However, pump defects may also be of a type that produce subtler, often tissue-specific disturbances that affect individual components of the Ca2+-controlling and/or processing machinery. They do not bring cells to immediate death but seriously compromise their normal functioning.

A novel mutation in the ATP2C1 gene is associated with Hailey-Hailey disease in a Chinese family

BACKGROUND

A three-generation Chinese family with Hailey-Hailey disease (HHD) was identified and characterized. The proband developed HHD with severe recurrent blisters and crusted erosions involving the body folds. Skin biopsy studies showed epidermal hyperkeratosis and defects in cell-to-cell adhesion. Three other members in the family were also affected with HHD and had the same clinical manifestations. The purpose of this study was to identify the pathogenic gene or mutation in the family.

METHODS

All exons and exon-intron boundaries of ATP2C1 were polymerase chain reaction (PCR) amplified and sequenced with DNA samples from the proband. Restriction fragment length polymorphism (RFLP) analysis for the intron 23-exon 24 boundary of ATP2C1 was performed in all family members and in 100 normal control subjects.

RESULTS

A novel 2-bp deletion (c.2251delGT) was detected in exon 24 of the ATP2C1 gene. The mutation was present in the three other affected family members and in two asymptomatic young carriers, but not in the other normal family members or the 100 normal controls. The mutation resulted in a frameshift change and led to the formation of a premature termination codon (PTC) four amino acid residues downstream from the sixth transmembrane domain.

CONCLUSIONS

Our results indicate that the novel c.2251delGT (p.V751fs) mutation in the ATP2C1 gene is responsible for HHD in this Chinese family. This study expands the spectrum of ATP2C1 mutations associated with HHD.

Reevaluation of the normal epidermal calcium gradient, and analysis of calcium levels and ATP receptors in Hailey-Hailey and Darier epidermis

Electron probe microanalysis was used to analyze elemental content of human epidermis. The results revealed that the calcium content of the basal keratinocyte layer was higher than that of the lowest spinous cell layer in normal epidermis. This was surprising, as it is generally accepted that the calcium level increases with cellular differentiation from the proliferative basal layer to the stratum corneum. Hailey-Hailey disease (HHD) and Darier disease (DD) are caused by mutations in Ca(2+)-ATPases with the end result of desmosomal disruption and suprabasal acantholysis. The results demonstrated three major aberrations in HHD and DD lesions. First, in HHD and DD lesions the calcium content in the basal layer was lower than in the normal skin. Second, adenosine triphosphate (ATP) receptor P2Y2 was not localized to plasma membrane in acantholytic cells, whereas P2X7 appeared in the plasma membrane, potentially mediating apoptosis. Third, transition of keratin 14 to keratin 10 was abnormal as demonstrated by the presence of keratinocytes expressing both cytokeratins, which are usually exclusive in normal epidermis. Our results provide to our knowledge previously unreported elements for understanding how the disturbed calcium gradient is linked to the alterations in ATP receptors and keratin expression, leading to the clinical findings in HHD and DD.

Molecular and clinical characterization in Japanese and Korean patients with Hailey-Hailey disease: six new mutations in the ATP2C1 gene

BACKGROUND

The autosomal dominant disorder Hailey-Hailey disease (HHD) results from mutations in the ATP2C1 gene, which encodes the human secretory pathway Ca2+/Mn2+ -ATPase protein 1. To date, over 90 pathological mutations scattered throughout ATP2C1 have been described with no indication of mutational hotspots or clustering of mutations. No paradigm for genotype-phenotype correlation has emerged.

OBJECTIVES

To determine the pathogenic ATP2C1 abnormality in additional patients with HHD in order to provide further contributions to the understanding of the molecular basis of this disorder and to add the data to the known mutation database.

METHODS

In this study, we investigated eight unrelated Japanese and Korean patients with HHD. We performed direct nucleotide sequencing of the ATP2C1 gene in all patients and RT-PCR analysis, using RNA extracted from a skin biopsy, in a patient with the mildest clinical features.

RESULTS

We identified seven different heterozygous mutations in seven of the eight investigated patients, including three new single nucleotide deletion/duplication mutations: c.520delC; c.681dupA; c.956delC, three new donor splice site mutations: c.360+1G>C; c.899+1G>T; c.1570+2T>C, as well as a previously described nonsense mutation: p.Arg153X. RT-PCR analysis in the mildest affected patient with a heterozygous c.360+1G>C mutation, demonstrated expression of a short in-frame mutant transcript with exon 5 skipping, which may account for the mild phenotype.

CONCLUSIONS

The results expand the known mutation spectrum in HHD and show the importance of RNA analysis for understanding the genotype-phenotype correlations more precisely.

Activity and localization of the secretory pathway Ca2+-ATPase isoform 1 (SPCA1) in different areas of the mouse brain during postnatal development

Ca2+ and Mn2+ play an important role in many events in the nervous system, ranging from neural morphogenesis to neurodegeneration. As part of the homeostatic control of these ions, the Secretory Pathway Ca2+-ATPase isoform 1 (SPCA1) mediates the accumulation of Ca2+ or Mn2+ with high affinity into Golgi reservoirs. This SPCA1 represents a relatively recently characterized P-type pump that is highly expressed in nervous tissue, but information on its involvement in neural maturation is currently lacking. In this study, we have analyzed the expression and distribution of the SPCA1 pump in mouse brain during postnatal development. RT-PCR and Western blot assays showed that SPCA1 is particularly highly expressed at nearly constant levels during this entire period of development in cortex, hippocampus, and cerebellum. In spite of the apparently unchanged expression levels, functional assays showed that SPCA-associated Ca2+-ATPase activity increased with the stage of development in these areas. Immunohistochemical studies pointed to SPCA1 localization in Golgi stacks of the soma and the initial part of primary dendritic trunk in main cortical, hippocampal and cerebellar neurons from the earliest postnatal stages. This suggests a potential role in intracellular signaling and in Golgi secretory processes involved in dendritic growth and in functional maturation of the mouse nervous system.

Genetic diagnosis in a Chinese Hailey-Hailey disease pedigree with novel ATP2C1 gene mutation

Hailey-Hailey disease (HHD) is an autosomal dominant skin disorder characterized by recurrent eruption of vesicles and bullae at the sites of friction and in the intertriginous areas. Mutations in the ATP2C1 gene encoding the human secretory pathway calcium ATPase 1 (hSPCA1) have been identified as the causative mutations in HHD. In this study, we used direct sequencing and restriction endonuclease digestion to analyze mutations of the ATP2C1 gene in a Chinese three-generation pedigree. A heterozygous T-to-C transition at nucleotide 1004 in exon 12 of ATP2C1 gene was detected. After summarizing the reported cases with ATP2C1 mutation, we concluded that the T1004C transition resulted in a novel missense mutation of leucine condon (CTG) to proline (CCG) at amino acid residue 335(L335P) in hSPCA1. Here, a genetic diagnosis was made for the proband's daughter before the clinical presentation. The study realized the molecular diagnosis in the HHD pedigree. Our findings should be useful for genetic counseling and prenatal diagnosis for the affected family and in demonstrating the critical role of the ATP2C1 gene in the pathogenesis of HHD further.

SLC24A5 encodes a trans-Golgi network protein with potassium-dependent sodium-calcium exchange activity that regulates human epidermal melanogenesis

A non-synonymous single nucleotide polymorphism in the human SLC24A5 gene is associated with natural human skin color variation. Multiple sequence alignments predict that this gene encodes a member of the potassium-dependent sodium-calcium exchanger family denoted NCKX5. In cultured human epidermal melanocytes we show using affinity-purified antisera that native human NCKX5 runs as a triplet of approximately 43 kDa on SDS-PAGE and is partially localized to the trans-Golgi network. Removal of the NCKX5 protein through small interfering RNA-mediated knockdown disrupts melanogenesis in human and murine melanocytes, causing a significant reduction in melanin pigment production. Using a heterologous expression system, we confirm for the first time that NCKX5 possesses the predicted exchanger activity. Site-directed mutagenesis of NCKX5 and NCKX2 in this system reveals that the non-synonymous single nucleotide polymorphism in SLC24A5 alters a residue that is important for NCKX5 and NCKX2 activity. We suggest that NCKX5 directly regulates human epidermal melanogenesis and natural skin color through its intracellular potassium-dependent exchanger activity.

Eight novel mutations of ATP2C1 identified in 17 Chinese families with Hailey-Hailey disease

BACKGROUND

Hailey-Hailey disease (HHD) is a rare autosomal dominantly inherited dermatosis, characterized by persistent blisters and erosions of the skin. It was recently discovered that HHD was caused by mutations in the ATP2C1 gene, a Ca2+ pump located in the Golgi apparatus.

OBSERVATION

In this study, we sequenced the ATP2C1 gene from blood samples of 31 patients in 17 unrelated Chinese families and 120 healthy individuals. Eight novel mutations were identified in 9 families, including 3 insertion/deletions (nt 1464-1487/1462-1485 del, 1523 del AT, 2375 del TTGT), 3 splicing-site mutations [360(-2)a-->g, 1415(-2)a-->c, 2243(+2)t-->c], and 2 missense mutations (P307L, D648Y).

CONCLUSION

Eight mutations were found in 8 unrelated families and 1 sporadic case, and these new findings have further improved our understanding of the role of ATP2C1 in HHD.

Functional and immunocytochemical evidence for the expression and localization of the secretory pathway Ca2+-ATPase isoform 1 (SPCA1) in cerebellum relative to other Ca2+ pumps

Membrane fractions of pig cerebellum show Ca2+-ATPase activity and Ca2+ transport due to the presence of the secretory pathway Ca2+-ATPase (SPCA). The SPCA1 isoform shows a wide distribution in the neurons of pig cerebellum, where it is found in the Golgi complex of the soma of Purkinje, stellate, basket and granule cells, and also in more distal components of the secretory pathway associated with a synaptic localization such as in cerebellar glomeruli. The SPCA1 may be involved in loading the Golgi complex and the secretory vesicles of these specific neuronal cell types with Ca2+ and also Mn2+. This study of the cellular and subcellular localization of SPCA1 pumps relative to the sarco(endo) plasmic reticulum Ca2+-ATPase and plasma membrane Ca2+-ATPase pumps hints to a possible specific role of SPCA1 in controlling the luminal secretory pathway Ca2+ (or Mn2+) levels as well as the local cytosolic Ca2+ levels. In addition, it helps to specify the zones that are most vulnerable to Ca2+ and/or Mn2+ dyshomeostasis, a condition that is held responsible of an increasing number of neurological disorders.

Involucrin Expression Is Decreased in Hailey–Hailey Keratinocytes Owing to Increased Involucrin mRNA Degradation

Hailey-Hailey disease (HHD) (MIM 16960) is an autosomal-dominant blistering skin disease caused by a mutation in the Ca2+-ATPase ATP2C1 (protein SPCA1), responsible for controlling Ca2+ concentrations in the cytoplasm and Golgi in human keratinocytes. Cytosolic Ca2+ concentrations, in turn, play a major role in the regulation of keratinocyte differentiation. To study how ATP2C1 function impacts keratinocyte differentiation, we assessed involucrin expression in HHD keratinocytes. Involucrin is a protein that makes up the cornified envelope of keratinocytes and is expressed in response to increased intracellular Ca2+ concentrations. Even though HHD keratinocytes suffer from abnormally high cytosolic Ca2+, we found that these cells expressed lower involucrin protein levels at both low and high extracellular Ca2+ concentrations when compared with normal control keratinocytes. Decreased involucrin protein levels were caused by lower involucrin mRNA levels in HHD keratinocytes. Decreased involucrin mRNA, in turn, was caused by increased rates of involucrin mRNA degradation. Ca2+-sensitive involucrin AP-1 promotor activity was increased, both in HHD keratinocytes and in an small interfering RNA (siRNA) experimental model, suggesting compensatory promoter upregulation in the face of increased mRNA degradation. This report provides new insights into differentiation defects in HHD and its relationship to Ca2+ signaling.

Loss of the Atp2c1 secretory pathway Ca(2+)-ATPase (SPCA1) in mice causes Golgi stress, apoptosis, and midgestational death in homozygous embryos and squamous cell tumors in adult heterozygotes

Loss of one copy of the human ATP2C1 gene, encoding SPCA1 (secretory pathway Ca(2+)-ATPase isoform 1), causes Hailey-Hailey disease, a skin disorder. We performed targeted mutagenesis of the Atp2c1 gene in mice to analyze the functions of this Golgi membrane Ca(2+) pump. Breeding of heterozygous mutants yielded a normal Mendelian ratio among embryos on gestation day 9.5; however, null mutant (Spca1(-/-)) embryos exhibited growth retardation and did not survive beyond gestation day 10.5. Spca1(-/-) embryos had an open rostral neural tube, but hematopoiesis and cardiovascular development were ostensibly normal. Golgi membranes of Spca1(-/-) embryos were dilated, had fewer stacked leaflets, and were expanded in amount, consistent with increased Golgi biogenesis. The number of Golgi-associated vesicles was also increased, and rough endoplasmic reticulum had fewer ribosomes. Coated pits, junctional complexes, desmosomes, and basement membranes appeared normal in mutant embryos, indicating that processing and trafficking of proteins in the secretory pathway was not massively impaired. However, apoptosis was increased, possibly the result of secretory pathway stress, and a large increase in cytoplasmic lipid was observed in mutant embryos, consistent with impaired handling of lipid by the Golgi. Adult heterozygous mice appeared normal and exhibited no evidence of Hailey-Hailey disease; however, aged heterozygotes had an increased incidence of squamous cell tumors of keratinized epithelial cells of the skin and esophagus. These data show that loss of the Golgi Ca(2+) pump causes Golgi stress, expansion of the Golgi, increased apoptosis, and embryonic lethality and demonstrates that SPCA1 haploinsufficiency causes a genetic predisposition to cancer.

Two novel mutations of the ATP2C1 gene in Chinese patients with Hailey-Hailey disease

Hailey-Hailey disease (HHD; OMIM 169600) is an autosomal dominant blistering disease. Pathogenic mutations in ATP2C1 encoding the human secretory pathway Ca(2+)/Mn(2+)-ATPase protein 1 (hSPCA1) have been identified since 2000. The aim of this study was to report a Chinese pedigree and a sporadic case of HHD and to explore the genetic mutations. The Chinese pedigree and the sporadic case of typical HHD were subjected to mutation detection of ATP2C1. The 27 coding exons and their flanking sequences were amplified and sequenced. The heterozygous C to T transition at nucleotide 2753 in exon 26 and G to T transition at nucleotide 2090 in exon 21 of the ATP2C1 gene were identified in a pedigree and a sporadic case of HHD, respectively. The C2753T transition resulted in a novel nonsense mutation of glutamine codon (CAG) to a stop codon (TAG) at amino acid residue 865 (Q865X) and the G2090T transition resulted in a novel missense mutation of glycine condon (GGA) to Valine (GUA) at amino acid residue 645 (G645V) in hSPCA1. This study should be useful for genetic counseling and prenatal diagnosis for affected families and in expanding the repertoire of ATP2C1 mutations underlying HHD.

Calcium in the Golgi apparatus

The secretory-pathway Ca2+-ATPases (SPCAs) represent a recently recognized family of phosphorylation-type ATPases that supply the lumen of the Golgi apparatus with Ca2+ and Mn2+ needed for the normal functioning of this structure. Mutations of the human SPCA1 gene (ATP2C1) cause Hailey-Hailey disease, an autosomal dominant skin disorder in which keratinocytes in the suprabasal layer of the epidermis detach. We will first review the physiology of the SPCAs and then discuss how mutated SPCA1 proteins can lead to an epidermal disorder.

Mutations in the ATP2C1 gene in Chinese patients with Hailey-Hailey disease

Hailey-Hailey disease (HHD; MIM 16960) is a rare autosomal dominant hereditary disorder characterized by recurrent eruption of vesicles and bullae, predominantly involving the body folds. It is caused by heterozygous mutations in the ATP2C1 gene, encoding the human secretory pathway Ca2+/Mn2+-ATPase protein 1 (hSPCA1). When we studied Chinese patients with HHD, we found two different heterozygous mutations, Q506X and G353V, the former previously reported in a Hungarian patient, and the latter being a novel mutation. In a 38-year-old patient from a four-generation pedigree with a 3-year history of severe recurrent blisters, we identified a C-->T transition at nucleotide 1696, c(1696C-->T), in exon 17 of ATP2C1, resulting in a nonsenes mutation, Gln506X, which resulted in a premature termination codon. In the second patient, who represented a occurrence of sporadic Hailey-Hailey disease, a G-->T transversion of nucleotide, c(G1238T), in exon 13 of ATP2C1 was detected, which resulted in a Gly353-->Val amino acid substitution (G353V). Our molecular findings further demonstrate that the mutational events in the human ATP2C1 gene encoding the hSPCA1 pump play an important role in the pathogenesis of HHD.

SERCA pumps and human diseases

Sarco(endo)plasmic reticulum (SER) Ca2+ ATPases represent a highly conserved family of Ca2+ pumps which actively transport Ca2+ from the cytosol to the SER against a large concentration gradient. In humans, 3 genes (ATP2A1-3) generate multiple isoforms (SERCAla,b, SERCA2a-c, SECA3a-f) by developmental or tissue-specific alternative splicing. These pumps differ by their regulatory and kinetic properties, allowing for optimized function in the tissue where they are expressed. They play a central role in calcium signalling through regenerating SER Ca2+ stores, maintaining appropriate Ca2+ levels in this organelle and shaping cytosolic and nuclear Ca2+ variations which govern cell response. Defects in ATP2A1 encoding SERCA1 cause recessive Brody myopathy, mutations in ATP2A2 coding for SERCA2 underlie a dominant skin disease, Darier disease and its clinical variants. SERCA2a expression is reduced in heart failure in human and in mice models. Gene-targeting studies in mouse confirmed the expected function of these isoforms in some cases, but also resulted in unexpected phenotypes: SERCA1 null mutants die from respiratory failure, SERCA2 heterozygous mutant mice develop skin cancer with age and SERCA3 null mice display no diabetes. These unique phenotypes have provided invaluable information on the role of these pumps in specific tissues and species, and have improved our understanding of Ca2+ regulated processes in muscles, the heart and the skin in human and in mice. Although the understanding of the pathogenesis of these diseases is still incomplete, these recent advances hold the promise of improved knowledge on the disease processes and the identification of new targets for therapeutic interventions.

Diseases involving the Golgi calcium pump

Secretory-pathway Ca2(+)-transport ATPases (SPCA) provide the Golgi apparatus with Ca2+ and Mn2+ needed for the normal functioning of this organelle. Loss of one functional copy of the human SPCA1 gene (ATP2C1) causes Hailey-Hailey disease, a rare skin disorder characterized by recurrent blisters and erosions in the flexural areas. Here, we will review the properties and functional role of the SPCAs. The relationship between Hailey-Hailey disease and its defective gene (ATP2C1) will be adressed as well.

Calcium gradients and the Golgi

Changes in intracellular free calcium regulate many intracellular processes. With respect to the secretory pathway and the Golgi apparatus, changes in calcium concentration occurring either in the adjacent cytosol or within the lumen of the Golgi act to regulate Golgi function. Conversely, the Golgi sequesters calcium to shape cytosolic calcium signals as well as initiate them by releasing calcium via inositol-1,4,5-triphosphate (IP(3)) receptors, located on Golgi membranes. Local calcium transients juxtaposed to the Golgi (arising from release by the Golgi or other organelles) can activate calcium dependent signalling molecules located on or around the Golgi. This review focuses on the reciprocal relationship between the cell biology of the Golgi apparatus and intracellular calcium homeostasis.

Identification and characterization of calcium and manganese transporting ATPase (PMR1) gene of Pichia pastoris

A gene homologous to Saccharomyces cerevisiae PMR1 has been cloned in the methylotrophic yeast Pichia pastoris. The entire P. pastoris PMR1 gene (PpPMR1) codes a protein of 924 amino acids. Sequence analysis of the PpPMR1 cDNA and the genomic DNA revealed that there is no intron in the coding region. The putative gene product contains all of the conserved regions observed in P-type ATPases and exhibits 66.2%, 60.3% and 50.6% identity to Pichia angusta (Hansenula polymorpha), Saccharomyces cerevisiae PMR1 and human ATP2C1 gene products, respectively. A pmr1 null mutant strain of P. pastoris exhibited growth defects in media with the addition of EGTA, but with supplementation of Ca2+ to a calcium-deficient media reversed the growth defects of the mutant strain. Manganese reversed the growth defects of the mutant strain; however, the cell growth was not as profound as the Ca2+ -supplemented media. The results demonstrated that the P. pastoris gene encodes the functional homologue of the S. cerevisiae PMR1 gene product, a P-type Ca2+/Mn2+ -ATPase. The DNA sequence of the P. pastoris PMR1 gene has been submitted to GenBank under Accession No. DQ239958.