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

Autosomal-dominant calcium ATPase disorders

Darier disease (DD) and Hailey-Hailey disease (HHD) are the only known autosomal-dominant Ca2+ ATPase disorders. Epidermal symptoms selectively occur in the affected individuals, the precise reason for which is still not fully understood. Here, we review the clinical, epidermal, and molecular features of the two genodermatoses. It is concluded that epidermal Ca2+ regulation disturbances and epigenetic factors may play an even more prominent role in the pathogenesis of DD and HHD than earlier appreciated.

Novel mutation in ATP2C1 gene in a Japanese patient with Hailey-Hailey disease

Hailey-Hailey disease (HHD) is an autosomal dominant disorder with recurrent eruption of vesicles and bullae involving predominantly the neck, groin and axillary regions. Histopathology shows suprabasal cleavage in epidermal cells. Recent studies have revealed that HHD is caused by mutations in the ATP2C1 gene encoding a novel Ca(2+) pump. We analyzed mutations of the ATP2C1 gene in 2 Japanese patients with HHD. The diagnosis of HHD was made based on the characteristic clinical features and histopathological evidence. All 27 exons and flanking intron boundaries were amplified by polymerase chain reaction and products analyzed by sequencing. As a result, we identified a novel missense mutation (A1087G) in exon 13 of the ATP2C1 gene in a patient. This mutation led the amino acid change from Thrto Ala in the phosphorylation protein domain. Another patient showed no mutation of the gene. These results demonstrate that a spectrum of ATP2C1 gene mutations is present in Japanese HHD patients.

Distribution of secretory pathway Ca2+ ATPase (SPCA1) in neuronal and glial cell cultures

1. Secretory pathway Ca(2+) ATPase type 1 (SPCA1) is a newly recognized Ca(2+)/Mn(2+)-transporting pump localized in membranes of the Golgi apparatus. 2. The expression level of SPCA1 in brain tissue is relatively high in comparison with other tissues. 3. With the aim to determine the expression of SPCA1 within the different types of neural cells, we investigated the distribution of SPCA1 in neuronal, astroglial, oligodendroglial, ependymal, and microglial cell cultures derived from rat brains. 4. Western Blot analysis with rabbit anti-SPCA1 antibodies revealed the presence of SPCA1 in homogenates derived from neuronal, astroglial, ependymal, and oligodendroglial, but not from microglial cells. 5. Cell cultures that gave rise to positive signal in the immunoblot analysis were also examined immunocytochemically. 6. Immunocytochemical double-labeling experiments with anti-SPCA1 serum in combination with antibodies against cell-type specific proteins showed a localization of the SPCA1signal within cells stained positively also for GFAP, alpha-tubulin or MBP. 7. These results definitely established the expression of SPCA1 in astroglial, ependymal, and oligodendroglial cells. 8. In addition, the evaluation of neuronal cultures for the presence of SPCA1 revealed an SPCA1-specific immunofluorescence signal in cells identified as neurons.

Consequences of depleted SERCA2-gated calcium stores in the skin

Sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2) pumps belong to the family of Ca2+-ATPases responsible for the maintenance of calcium in the endoplasmic reticulum. In epidermal keratinocytes, SERCA2-controlled calcium stores are involved in cell cycle exit and onset of terminal differentiation. Hence, their dysfunction was thought to provoke impaired keratinocyte cohesion and hampered terminal differentiation. Here, we assessed cultured keratinocytes and skin biopsies from a canine family with an inherited skin blistering disorder. Cells from lesional and phenotypically normal areas of one of these dogs revealed affected calcium homeostasis due to depleted SERCA2-gated stores. In phenotypically normal patient cells, this defect compromised upregulation of p21(WAF1) and delayed the exit from the cell cycle. Despite this abnormality it failed to impede the terminal differentiation process in the long term but instead coincided with enhanced apoptosis and appearance of chronic wounds, suggestive of secondary mutations. Collectively, these findings provide the first survey on phenotypic consequences of depleted SERCA-gated stores for epidermal homeostasis that explain how depleted SERCA2 calcium stores provoke focal lesions rather than generalized dermatoses, a phenotype highly reminiscent of the human genodermatosis Darier disease.

Dissection of the Functional Differences between Human Secretory Pathway Ca2+/Mn2+-ATPase (SPCA) 1 and 2 Isoenzymes by Steady-state and Transient Kinetic Analyses

Human secretory pathway Ca2+/Mn2+-ATPase (SPCA) 2 encoded by ATP2C2 is only expressed in a limited number of tissues, unlike the ubiquitously expressed SPCA1 pump (encoded by ATP2C1, the gene defective in Hailey-Hailey disease). It has not been determined whether there are significant functional differences between SPCA1 and SPCA2 pump enzymes. Therefore, steady-state and transient kinetic approaches were used to characterize the overall and partial reactions of the Ca2+ transport cycle mediated by the human SPCA2 enzyme upon heterologous expression in HEK-293 cells. The catalytic turnover rate of SPCA2 was found enhanced relative to SPCA1 pumps. SPCA2 displayed a very high apparent affinity for cytosolic Ca2+ (K0.5 = 0.025 microm) in activation of the phosphorylation activity but still 2.5-fold lower than that of SPCA1d. Our kinetic analysis traced both differences to the increased rate characterizing the E1 approximately PCa to E2-P transition of SPCA2. Moreover, the reduced rate of the E2 to E1 transition seems to contribute in determining the lower apparent Ca2+ affinity and the increased sensitivity to thapsigargin inhibition, relative to SPCA1d. SPCA2 also displayed a reduced apparent affinity for inorganic phosphate, which could be explained by the observed enhanced rate of the E2-P dephosphorylation. The insensitivity to modulation by pH and K+ concentration of the constitutively enhanced E2-P dephosphorylation of SPCA2 is similar to SPCA1d and possibly represents a novel SPCA-specific feature, which is not shared by sarco(endo)plasmic reticulum Ca2+-ATPases.

Calcium transport and signaling in the mammary gland: targets for breast cancer

The mammary gland is subjected to extensive calcium loads during lactation to support the requirements of milk calcium enrichment. Despite the indispensable nature of calcium homeostasis and signaling in regulating numerous biological functions, the mechanisms by which systemic calcium is transported into milk by the mammary gland are far from completely understood. Furthermore, the implications of calcium signaling in terms of regulating proliferation, differentiation and apoptosis in the breast are currently uncertain. Deregulation of calcium homeostasis and signaling is associated with mammary gland pathophysiology and as such, calcium transporters, channels and binding proteins represent potential drug targets for the treatment of breast cancer.

Novel mutations in the ATP2C1 gene in two patients with Hailey-Hailey disease

Benign familial chronic pemphigus (Hailey-Hailey disease, HHD) is a rare hereditary condition characterized by development of blisters at sites of friction and in the intertriginous areas. Mutations in the ATP2C1 gene, which encodes the human secretory pathway calcium ATPase 1 (hSPCA1), have been identified as possible causative mutations. Studying Hungarian patients with HHD, we found two novel, distinct, heterozygous mutations. In a 65-year-old man with a 41-year history of severe recurrent symptoms, a single nucleotide insertion, 1085insA, was detected. In a patient whose symptoms were induced by environmental contact allergens, we found a nonsense mutation, Q506X, in exon 17. Our study further illustrates the diversity of mutational events in the pathogenesis of HHD.

ATP2C1 Gene Mutation Analysis in Italian Patients with Hailey–Hailey Disease

Hailey-Hailey disease (HHD) is a rare autosomal dominant disorder characterized by recurrent skin lesions 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). In this report we describe the molecular studies performed in eight HHD cases from Italy that led us to identify six different mutations scattered through the ATP2C1 gene in seven of eight cases. Four of the detected mutations were novel. Our results confirm the high allelic heterogeneity of the ATP2C1 gene and support the notion that HHD is a genetically homogeneous disorder. Furthermore, we created a table summarizing all previously reported ATP2C1 mutations, adapting the nomenclature, if needed, according to the guidelines of the Human Genome Variation Society.

Keratinocytes cultured from patients with Hailey-Hailey disease and Darier disease display distinct patterns of calcium regulation

BACKGROUND

Hailey-Hailey disease (HHD) (OMIM 16960) and Darier disease (DD) (OMIM 124200) are dominantly inherited acantholytic skin diseases, respectively, caused by mutations in the genes encoding the Golgi secretory pathway Ca2+-ATPase (SPCA1, ATP2C1) and the sarco/endoplasmic reticulum Ca2+-ATPase type 2 (SERCA2, ATP2A2) genes.

OBJECTIVES

To investigate calcium regulation in keratinocytes cultured from patients with HHD and DD by measuring intracellular calcium resting levels and the cellular responses to ATP and thapsigargin.

METHODS

The study was carried out using keratinocyte cultures established from four patients with HHD and four with DD. Calcium concentrations were measured with fluorescence ratio imaging using fura-2 loading.

RESULTS

Control and HHD keratinocytes displayed approximately the same Ca2+ levels in resting phase, while DD keratinocytes showed elevated Ca2+ levels. Application of ATP caused less pronounced elevation of intracellular calcium concentration ([Ca2+]i) in both HHD and DD keratinocytes than in control cells. HHD keratinocytes did not lower their [Ca2+]i as efficiently as control keratinocytes after treatment with thapsigargin. In addition, DD keratinocytes were practically incapable of lowering their [Ca2+]i after treatment with thapsigargin.

CONCLUSIONS

The results demonstrate that the defects in SPCA1 and SERCA2 calcium ATPases result in distinct patterns of calcium metabolism. This is also supported by the different clinical features of the diseases.

Calcium and magnesium competitively influence the growth of a PMR1 deficientSaccharomyces cerevisiaestrain

PMR1, the Ca2+/Mn2+ ATPase of the secretory pathway in Saccharomyces cerevisiae was the first member of the secretory pathway Ca2+ ATPases (SPCA) to be characterized. In the past few years, pmr1Delta yeast have received more attention due to the recognition that the human homologue of this protein, hSPCA1 is defective in chronic benign pemphigus or Hailey-Hailey disease (HHD). Recent publications have described pmr1Delta S. cerevisiae as a useful model organism for studying the molecular pathology of HHD. Some observations indicated that the high Ca2+ sensitive phenotype of PMR1 defective yeast strains may be the most relevant in this respect. Here we show that the total cellular calcium response of a pmr1Delta S. cerevisiae upon extracellular Ca2+ challenge is decreased compared to the wild type strain similarly as observed in keratinocytes. Additionally, the novel magnesium sensitivity of PMR1 defective yeast is revealed, which appears to be a result of competition for uptake between Ca2+ and Mg2+ at the plasma membrane level. Our findings indicate that extracellular Ca2+ and Mg2+ competitively influence the intracellular Ca2+ homeostasis of S. cerevisiae. These observations may further our understanding of HHD.

Functional comparison between secretory pathway Ca2+/Mn2+-ATPase (SPCA) 1 and sarcoplasmic reticulum Ca2+-ATPase (SERCA) 1 isoforms by steady-state and transient kinetic analyses

Steady-state and transient kinetic studies were performed to functionally analyze the overall and partial reactions of the Ca(2+) transport cycle of the human secretory pathway Ca(2+)/Mn(2+)-ATPase 1 (SPCA1) isoforms: SPCA1a, SPCA1b, SPCA1c, and SPCA1d (encoded by ATP2C1, the gene defective in Hailey-Hailey disease) upon heterologous expression in mammalian cells. The expression levels of SPCA1 isoforms were 200-350-fold higher than in control cells except for SPCA1c, whose low expression level appears to be the effect of rapid degradation because of protein misfolding. Relative to SERCA1a, the active SPCA1a, SPCA1b, and SPCA1d enzymes displayed extremely high apparent affinities for cytosolic Ca(2+) in activation of the overall ATPase and phosphorylation activities. The maximal turnover rates of the ATPase activity for SPCA1 isoforms were 4.7-6.4-fold lower than that of SERCA1a (lowest for the shortest SPCA1a isoform). The kinetic analysis traced these differences to a decreased rate of the E(1) approximately P(Ca) to E(2)-P transition. The apparent affinity for inorganic phosphate was reduced in the SPCA1 enzymes. This could be accounted for by an enhanced rate of the E(2)-P hydrolysis, which showed constitutive activation, lacking the SERCA1a-specific dependence on pH and K(+).

Manganese toxicity and Saccharomyces cerevisiae Mam3p, a member of the ACDP (ancient conserved domain protein) family

Manganese is an essential, but potentially toxic, trace metal in biological systems. Overexposure to manganese is known to cause neurological deficits in humans, but the pathways that lead to manganese toxicity are largely unknown. We have employed the bakers' yeast Saccharomyces cerevisiae as a model system to identify genes that contribute to manganese-related damage. In a genetic screen for yeast manganese-resistance mutants, we identified S. cerevisiae MAM3 as a gene which, when deleted, would increase cellular tolerance to toxic levels of manganese and also increased the cell's resistance towards cobalt and zinc. By sequence analysis, Mam3p shares strong similarity with the mammalian ACDP (ancient conserved domain protein) family of polypeptides. Mutations in human ACDP1 have been associated with urofacial (Ochoa) syndrome. However, the functions of eukaryotic ACDPs remain unknown. We show here that S. cerevisiae MAM3 encodes an integral membrane protein of the yeast vacuole whose expression levels directly correlate with the degree of manganese toxicity. Surprisingly, Mam3p contributes to manganese toxicity without any obvious changes in vacuolar accumulation of metals. Furthermore, through genetic epistasis studies, we demonstrate that MAM3 operates independently of the well-established manganese-trafficking pathways in yeast, involving the manganese transporters Pmr1p, Smf2p and Pho84p. This is the first report of a eukaryotic ACDP family protein involved in metal homoeostasis.

Transcriptional regulation of ATP2C1 gene by Sp1 and YY1 and reduced function of its promoter in Hailey-Hailey disease keratinocytes

Hailey-Hailey disease (HHD) is a blistering skin disease caused by malfunction of the Ca2+-dependent ATPase, ATP2C1. In this study, key regulatory regions necessary for the expression of the gene encoding human ATP2C1 were investigated. The transient reporter assay demonstrated that region +21/+57 was necessary for activation of the ATP2C1 promoter, and the electrophoretic mobility shift assay demonstrated that the region was recognized by the transcription factors, Sp1 and YY1. In accordance with this result, when Sp1 or YY1 was overexpressed in keratinocytes, an obvious increase in ATP2C1 promoter activity was observed, which was in contrast with the case where a mutant promoter lacking the binding sites for Sp1 and YY1 was used as the reporter. Ca2+-stimulation signal increased nuclear Sp1 proteins and ATP2C1 mRNA levels in normal keratinocytes. In contrast, both these increases were suppressed in keratinocytes from HHD patients. These results indicate that Sp1 and YY1 transactivate the human ATP2C1 promoter via cis-enhancing elements and that incomplete upregulation of ATP2C1 transcription contributes to the keratinocyte-specific pathogenesis of HHD. This is a report describing the regulation of the expression of ATP2C1.

The Secretory Pathway Ca2+/Mn2+-ATPase 2 Is a Golgi-localized Pump with High Affinity for Ca2+ Ions

Accumulation of Ca(2+) into the Golgi apparatus is mediated by sarco(endo)plasmic reticulum Ca(2+)-ATPases (SERCAs) and by secretory pathway Ca(2+)-ATPases (SPCAs). Mammals and birds express in addition to the housekeeping SPCA1 (human gene name ATP2C1, cytogenetic position 3q22.1) a homologous SPCA2 isoform (human gene name ATP2C2, cytogenetic position 16q24.1). We show here that both genes present an identical exon/intron layout. We confirmed that hSPCA2 has the ability to transport Ca(2+), demonstrated its Mn(2+)-transporting activity, showed its Ca(2+)- and Mn(2+)-dependent phosphoprotein intermediate formation, and documented the insensitivity of these functional activities to thapsigargin inhibition. The mRNA encoding hSPCA2 showed a limited tissue expression pattern mainly confined to the gastrointestinal and respiratory tract, prostate, thyroid, salivary, and mammary glands. Immunocytochemical localization in human colon sections presented a typical apical juxtanuclear Golgi-like staining. The expression in COS-1 cells allowed the direct demonstration of (45)Ca(2+) (K(0.5) = 0.27 microm) or (54)Mn(2+) transport into an A23187-releasable compartment.

Hailey-Hailey disease as an orthodisease of PMR1 deficiency in Saccharomyces cerevisiae

The term orthodisease has recently been introduced to define human disorders in which the pathogenic gene has orthologs in model organism genomes. Here, we describe Hailey-Hailey disease (HHD), a blistering skin disorder caused by haploinsufficiency of ATP2C1 as an orthodisease from a Saccharomyces cerevisiae perspective. ATP2C1 encodes the human secretory pathway Ca(2+)/Mn(2+) ATPase hSPCA1 and is orthologous to the PMR1 gene in S. cerevisiae. hSPCA1 fully complements PMR1 deficiency in yeast and pmr1DeltaS. cerevisiae has proved to be a valuable tool to screen ATP2C1 mutations and address potential pathogenic/pharmacologic mechanisms in HHD. Consequently, this human skin disorder is an ideal example of an orthodisease.

Calcium pump disorders of the skin

The causes of Darier disease (DD) and Hailey-Hailey disease (HHD) have eluded clinicians and scientists for more than 60 years. DD is characterized by loss of adhesion between suprabasal epidermal cells associated with abnormal keratinization, while loss of epidermal cell-to-cell adhesion is predominant in HHD. The genes for both conditions have recently been identified using candidate positional cloning approaches. The gene for DD (ATP2A2) encodes a calcium transport ATPase of the sarco (endo)plasmic reticulum (SERCA2) Verboomen et al. [1992: Biochem J 286(Pt 2):591-595], while the gene for HHD (ATP2C1) codes for a secretory pathway for calcium and manganese transport ATPase of the Golgi apparatus (SPCA1) Hu et al. [2000: Nat Genet 24:61-65]. These results have provided completely new insights into the role of calcium and/or manganese in maintaining skin integrity. Although the precise disease mechanisms remain to be understood, these discoveries open a new field in research for the understanding and the treatment of these distressing disorders.

Severe Impairment of Quality of Life in Hailey‐Hailey Disease

Hailey-Hailey disease (a skin fragility disorder) runs a chronic course and may cause important disability. However, little has been formally investigated concerning the quality of life (QoL) of patients affected by this disorder. We studied the impact of Hailey-Hailey disease on the QoL of 22 consecutive patients seen at our dermatological clinic. Patients were examined by a dermatologist, and they were asked to complete two self-administered questionnaires: the Skindex-29, in order to determine their QoL, and the 12-item General Health Questionnaire, to evaluate psychological distress. Completed questionnaires were returned by 20 patients. Even in patients with few body sites involved, median overall QoL scores were much higher than those observed in other skin conditions in all three domains investigated by the Skindex-29 (i.e. symptoms, emotions and social functioning). This was true also for the levels of psychological distress. QoL impairment was substantial irrespective of the number of body sites involved. Our findings document a great impact of Hailey-Hailey disease on patients' QoL. Therefore, a more aggressive therapeutic approach may be warranted in all patients, including those with few lesions.

A Novel Isoform of the Secretory Pathway Ca2+,Mn2+-ATPase, hSPCA2, Has Unusual Properties and Is Expressed in the Brain

Unlike lower eukaryotes, mammalian genomes have a second gene, ATP2C2, encoding a putative member of the family of secretory pathway Ca2+,Mn(2+)-ATPases, SPCA2. Human SPCA2 shares 64% amino acid identity with the protein defective in Hailey Hailey disease, hSPCA1. We show that human SPCA2 (hSPCA2) has a more limited tissue distribution than hSPCA1, with prominent protein expression in brain and testis. In primary neuronal cells, endogenous SPCA2 has a highly punctate distribution that overlaps with vesicles derived from the trans-Golgi network and is thus different from the compact perinuclear distribution of hSPCA1 seen in keratinocytes and nonpolarized cells. Heterologous expression in a yeast strain lacking endogenous Ca2+ pumps reveals further functional differences from hSPCA1. Although the Mn(2+)-specific phenotype of hSPCA2 is similar to that of hSPCA1, Ca2+ ions are transported with much poorer affinity, resulting in only weak complementation of Ca(2+)-specific yeast phenotypes. These observations suggest that SPCA2 may have a more specialized role in mammalian cells, possibly in cellular detoxification of Mn2+ ions, similar to that in yeast. We point to the close links between manganese neurotoxicity and Parkinsonism that would predict an important physiological role for SPCA2 in the brain.

The effect of extracellular calcium concentration on calcium-mediated cell signaling in NF1 tumor suppressor-deficient keratinocytes

Capacitative calcium entry and calcium wave propagation were studied in keratinocytes from healthy volunteers and patients with type 1 neurofibromatosis (NF1) in calcium-depleted and in low calcium culture medium. In previous studies, we found evidence that mutations of the NF1 tumor suppressor gene can lead to altered calcium-mediated cell signaling in keratinocytes cultured in the presence of a high extracellular calcium concentration. The present study demonstrated that the differences between normal and NF1 keratinocytes were dependent on extracellular calcium concentration. Specifically, when keratinocytes were exposed to thapsigargin under calcium-depleted culture conditions the subsequent increase in free intracellular calcium concentration was moderate in NF1 keratinocytes compared to controls. The finding indicates lowered endoplasmic calcium stores in NF1 which may also in part explain the reduced activation signal for capacitative calcium influx and the wound-induced intracellular Ca2+ transient observed in NF1 keratinocytes maintained in culture medium containing 0.05 mM calcium. The differences between control and NF1 keratinocytes were most pronounced when the cells were cultured in the presence of a high (1.8 mM) calcium concentration. Since elevated extracellular calcium levels induce keratinocytes to form cellular contacts and lead to terminal differentiation, markedly aberrant responses of NF1 keratinocytes in the presence of a high calcium concentration may help to explain previous findings on impaired formation of cellular junctions and differentiation in NF1 deficient cells.

Deficiency of ATP2C1, a Golgi ion pump, induces secretory pathway defects in endoplasmic reticulum (ER)-associated degradation and sensitivity to ER stress

Relatively few clues have been uncovered to elucidate the cell biological role(s) of mammalian ATP2C1 encoding an inwardly directed secretory pathway Ca2+/Mn2+ pump that is ubiquitously expressed. Deficiency of ATP2C1 results in a human disease (Hailey-Hailey), which primarily affects keratinocytes. ATP2C1-encoded protein is detected in the Golgi complex in a calcium-dependent manner. A small interfering RNA causes knockdown of ATP2C1 expression, resulting in defects in both post-translational processing of wild-type thyroglobulin (a secretory glycoprotein) as well as endoplasmic reticulum-associated protein degradation of mutant thyroglobulin, whereas degradation of a nonglycosylated misfolded secretory protein substrate appears unaffected. Knockdown of ATP2C1 is not associated with elevated steady state levels of ER chaperone proteins, nor does it block cellular activation of either the PERK, ATF6, or Ire1/XBP1 portions of the ER stress response. However, deficiency of ATP2C1 renders cells hypersensitive to ER stress. These data point to the important contributions of the Golgi-localized ATP2C1 protein in homeostatic maintenance throughout the secretory pathway.

Allelic loss underlies type 2 segmental Hailey-Hailey disease, providing molecular confirmation of a novel genetic concept

Hailey-Hailey disease (HHD) is an autosomal dominant trait characterized by erythematous and oozing skin lesions preponderantly involving the body folds. In the present unusual case, however, unilateral segmental areas along the lines of Blaschko showing a rather severe involvement were superimposed on the ordinary symmetrical phenotype. Based on this observation and similar forms of mosaicism as reported in other autosomal dominant skin disorders, we postulated that in such cases, 2 different types of segmental involvement can be distinguished. Accordingly, the linear lesions as noted in the present case would exemplify type 2 segmental HHD. In the heterozygous embryo, loss of heterozygosity occurring at an early developmental stage would have given rise to pronounced linear lesions reflecting homozygosity or hemizygosity for the mutation. By analyzing DNA and RNA derived from blood and skin samples as well as keratinocytes of the index patient with various molecular techniques including RT-PCR, real-time PCR, and microsatellite analysis, we found a consistent loss of the paternal wild-type allele in more severely affected segmental skin regions, confirming this hypothesis for the first time, to our knowledge, at the molecular and cellular level.

The Ca2+/Mn2+ pumps in the Golgi apparatus

Recent evidence highlights the functional importance of the Golgi apparatus as an agonist-sensitive intracellular Ca(2+) store. Besides Ca(2+)-release channels and Ca(2+)-binding proteins, the Golgi complex contains Ca(2+)-uptake mechanisms consisting of the well-known sarco/endoplasmic reticulum Ca(2+)-transport ATPases (SERCA) and the much less characterized secretory-pathway Ca(2+)-transport ATPases (SPCA). SPCA supplies the Golgi compartments and, possibly, the more distal compartments of the secretory pathway with both Ca(2+) and Mn(2+) and, therefore, plays an important role in the cytosolic and intra-Golgi Ca(2+) and Mn(2+) homeostasis. Mutations in the human gene encoding the SPCA1 pump (ATP2C1) resulting in Hailey-Hailey disease, an autosomal dominant skin disorder, are discussed.

Calcium release from the Golgi apparatus and the endoplasmic reticulum in HeLa cells stably expressing targeted aequorin to these compartments

Extracellular agonists mobilize Ca2+ from SERCA-comprising intracellular Ca2+ stores located in both the Golgi apparatus and the endoplasmic reticulum. Ca2+ release from both these compartments was studied in HeLa cells stably expressing the luminescent Ca2+ indicator aequorin specifically targeted to these compartments. Changes in lumenal [Ca2+] as detected by the aequorin measurements were correlated with parallel changes in total Ca2+ content of the stores. The latencies and initial rates of Ca2+ release from the Golgi apparatus and the endoplasmic reticulum were quite similar. However, maximal Ca2+ release measured with Golgi-targeted aequorin terminated faster than that from the endoplasmic reticulum. The rate and extent of Ca2+ depletion from both compartments correlated well with the peak amplitude of the cytosolic [Ca2+] rise. Time-course experiments further revealed that the peak of the cytosolic Ca2+ response occurred before the lumenal [Ca2+] reached its lowest level. We conclude that both the Golgi apparatus and the endoplasmic reticulum contribute to the rise in cytosolic [Ca2+] upon agonist stimulation, but the kinetics of the Ca2+ release are different.

SPCA1 pumps and Hailey-Hailey disease

Both the endoplasmic reticulum and the Golgi apparatus are agonist-sensitive intracellular Ca2+ stores. The Golgi apparatus has Ca2+-release channels and a Ca2+-uptake mechanism consisting of sarco(endo)plasmic-reticulum Ca2+-ATPases (SERCA) and secretory-pathway Ca2+-ATPases (SPCA). SPCA1 has been shown to transport both Ca2+ and Mn2+ in the Golgi lumen and therefore plays an important role in the cytosolic and intra-Golgi Ca2+ and Mn2+ homeostasis. Human genetic studies have provided new information on the physiological role of SPCA1. Loss of one functional copy of the SPCA1 (ATP2C1) gene causes Hailey-Hailey disease, a skin disorder arising in the adult age with recurrent vesicles and erosions in the flexural areas. Here, we review recent experimental evidence showing that the Golgi apparatus plays a much more important role in intracellular ion homeostasis than previously anticipated.

Phenotypes of SERCA and PMCA knockout mice

P-type Ca2+-ATPases of the sarco(endo)plasmic reticulum (SERCAs) and plasma membrane (PMCAs) are responsible for maintaining the Ca2+ gradients across cellular membranes that are required for regulation of Ca2+-mediated signaling and other biological processes. Gene-targeting studies of SERCA isoforms 1, 2, and 3 and PMCA isoforms 1, 2, and 4 have confirmed some of the general functions proposed for these pumps, such as a major role in excitation-contraction coupling for SERCA1 and SERCA2 and housekeeping functions for PMCA1 and SERCA2, but have also revealed some unexpected phenotypes. These include squamous cell cancer and plasticity in the regulation of Ca2+-mediated exocytosis in SERCA2 heterozygous mutant mice, modulation of Ca2+ signaling in SERCA3-deficient mice, deafness and balance disorders in PMCA2 null mice, and male infertility in PMCA4 null mice. These unique phenotypes provide new information about the cellular functions of these pumps, the requirement of their activities for higher order physiological processes, and the pathophysiological consequences of pump dysfunction.

Darier’s disease: from dyskeratosis to endoplasmic reticulum calcium ATPase deficiency

The skin is the body's largest organ and has an essential barrier protective function against physical, chemical, and pathogen aggressions and prevents fluid loss. The outer layer of the skin, known as the epidermis, plays a key role in this protection, through a tightly regulated differentiation programme from basal keratinocytes to the stratum corneum at the skin surface. During this process, keratinocytes from the base of the epidermis undergo major morphological and functional changes during their migration through the spinous and granular layers, to become terminally differentiated corneocytes which will be shed from the skin's surface. The role of extracellular Ca2+ in cell-to-cell adhesion and in epidermal differentiation was known to be important, but the identification of the sarco/endoplasmic reticulum Ca2+ transport ATPase (ATP2A2) as the defective gene in a rare genetic skin disease known as Darier's disease, came as a surprise and shed light on the key role of Ca2+ signaling in the homeostasis of the epidermis.

The expression, activity and localisation of the secretory pathway Ca2+ -ATPase (SPCA1) in different mammalian tissues

The distribution of the secretory pathway Ca2+ -ATPase (SPCA1) was investigated at both the mRNA and protein level in a variety of tissues. The mRNA and the protein for SPCA1 were relatively abundant in rat brain, testis and testicular derived cells (myoid cells, germ cells, primary Sertoli cells and TM4 cells; a mouse Sertoli cell line) and epididymal fat pads. Lower levels were found in aorta (rat and porcine), heart, liver, lung and kidney. SPCA activities from a number of tissues were measured and shown to be particularly high in brain, aorta, heart, fat pads and testis. As the proportion of SPCA activity compared to total Ca2+ ATPase activity in brain, aorta, fat pads and testis were relatively high, this suggests that SPCA1 plays a major role in Ca2+ storage within these tissues. The subcellular localisation of SPCA1 was shown to be predominantly around the Golgi in both human aortic smooth muscle cells and TM4 cells.

Functional expression of heterologous proteins in yeast: insights into Ca2+signaling and Ca2+-transporting ATPases

The baker's yeast Saccharomyces cerevisiae is a well-developed, versatile, and widely used model organism. It offers a compact and fully sequenced genome, tractable genetics, simple and inexpensive culturing conditions, and, importantly, a conservation of basic cellular machinery and signal transducing pathways with higher eukaryotes. In this review, we describe recent technical advances in the heterologous expression of proteins in yeast and illustrate their application to the study of the Ca2+homeostasis machinery, with particular emphasis on Ca2+-transporting ATPases. Putative Ca2+-ATPases in the newly sequenced genomes of organisms such as parasites, plants, and vertebrates have been investigated by functional complementation of an engineered yeast strain lacking endogenous Ca2+pumps. High-throughput screens of mutant phenotypes to identify side chains critical for ion transport and selectivity have facilitated structure-function analysis, and genomewide approaches may be used to dissect cellular pathways involved in Ca2+transport and trafficking. The utility of the yeast system is demonstrated by rapid advances in the study of the emerging family of Golgi/secretory pathway Ca2+,Mn2+-ATPases (SPCA). Functional expression of human SPCA1 in yeast has provided insight into the physiology, novel biochemical characteristics, and subcellular localization of this pump. Haploinsufficiency of SPCA1 leads to Hailey-Hailey disease (HDD), a debilitating blistering disorder of the skin. Missense mutations, identified in patients with HHD, may be conveniently assessed in yeast for loss-of-function phenotypes associated with the disease.

Hailey–Hailey Disease: Identification of Novel Mutations in ATP2C1 and Effect of Missense Mutation A528P on Protein Expression Levels

ATP2C1, encoding the human secretory pathway Ca(2+)-ATPase (hSPCA1), was recently identified as the defective gene in Hailey-Hailey disease (HHD), an autosomal dominant skin disorder characterized by abnormal keratinocyte adhesion in the suprabasal layers of the epidermis. In this study, we used denaturing high-performance liquid chromatography to screen all 28 exons and flanking intron boundaries of ATP2C1 for mutations in 9 HHD patients. Nine different mutations were identified. Five of these mutations, including one nonsense, one deletion, two splice-site, and one missense mutation, have not been previously reported. Recently, functional analysis of a series of site-specific mutants, designed to mimic missense mutations found in ATP2C1, uncovered specific defects in Ca(2+) and/or Mn(2+) transport and protein expression in mutant hSPCA1 polypeptides. In order to investigate the molecular and physiological basis of HHD in the patient carrying missense mutation A528P, located in the putative nucleotide binding domain of the molecule, site-directed mutagenesis was employed to introduce this mutation into the wild-type ATP2C1 (hSPCA1) sequence. Functional analyses of HHD-mutant A528P demonstrated a low level of protein expression, despite normal levels of mRNA and correct targeting to the Golgi, suggesting instability or abnormal folding of the mutated hSPCA1 polypeptides. Analogous to conclusions drawn from our previous studies, these results further support the theory of haploinsufficiency as a prevalent mechanism for the dominant inheritance of HHD, by suggesting that the level of hSPCA1 in epidermal cells is critical.

Calcium pumps and keratinocytes: lessons from Darier's disease and Hailey-Hailey disease

Darier's disease and Hailey-Hailey disease are autosomal dominantly inherited skin disorders in which desmosomal adhesion between keratinocytes is abnormal. ATP2A2 and ATP2C1 have been identified as the causative genes for Darier's disease and Hailey-Hailey disease, respectively. ATP2A2 encodes the sarco(endo)plasmic reticulum Ca(2+)-ATPase isoform 2 (SERCA2) pump, while ATP2C1 encodes a secretory pathway Ca(2+)/Mn(2+)-ATPase (SPCA1) found in the Golgi apparatus. We review recent work into the function of these pumps in human keratinocytes and discuss how mutations in these genes might cause these diseases by altering the formation or stability of desmosomes.

Role for plasma membrane-related Ca2+-ATPase-1 (ATP2C1) in pancreatic beta-cell Ca2+ homeostasis revealed by RNA silencing

Changes in intracellular Ca(2+) concentration play a key role in the regulation of insulin secretion by glucose and other secretagogues. Here, we explore the importance of the secretory pathway Ca(2+)-ATPase, plasma membrane-related Ca(2+)-ATPase-1 (PMR1; human orthologue ATP2C1) in intracellular Ca(2+) homeostasis in pancreatic islet beta-cells. Endogenous PMR1 mRNA and protein were detected in both isolated rat islets and beta-cell-derived lines (MIN6 and INS1). Subcellular fractionation of the cell lines revealed PMR1 immunoreactivity in both microsomal and dense-core secretory vesicle-enriched fractions. Correspondingly, depletion of cellular PMR1 with small interfering RNAs inhibited Ca(2+) uptake into the endoplasmic reticulum and secretory vesicles by approximately 20%, as assessed using organelle-targeted aequorins in permeabilized INS1 cells. In intact cells, PMR1 depletion markedly enhanced flux though L-type Ca(2+) channels and augmented glucose-stimulated, but not basal, insulin secretion. Whereas average cytosolic [Ca(2+)] increases in response to 30.0 mmol/l glucose were unaffected by PMR1 depletion, [Ca(2+)] oscillation shape, duration, and decay rate in response to glucose plus tetraethylammonium were modified in PMR1-depleted single cells, imaged using fluo-3-acetoxymethylester. PMR1 thus plays an important role, which is at least partially nonoverlapping with that of sarco(endo-)plasmic reticulum Ca(2+)-ATPases, in the control of beta-cell Ca(2+) homeostasis and insulin secretion.

Actin reorganization is abnormal and cellular ATP is decreased in Hailey-Hailey keratinocytes

Actin reorganization and the formation of adherens junctions are necessary for normal cell-to-cell adhesion in keratinocytes. Hailey-Hailey disease (HHD) is blistering skin disease, resulting from mutations in the Ca2+ ATPase ATP2C1, which controls Ca2+ concentrations in the cytoplasm and Golgi of human keratinocytes. Because actin reorganization is among the first responses to raised cytoplasmic Ca2+, we examined Ca2+-induced actin reorganization in normal and HHD keratinocytes. Even though HHD keratinocytes display raised baseline cytoplasmic Ca2+, we found that actin reorganization in response to Ca2+ was impaired in HHD keratinocytes. Defects in actin reorganization were linked to a marked decrease in cellular ATP in HHD keratinocytes, which persists, in vivo, in HHD epidermis. Defective actin reorganization was reproduced in normal keratinocytes in which the intracellular ATP concentration had been lowered pharmacologically. ATP concentrations in undifferentiated keratinocytes markedly declined after extracellular Ca2+ was increased, but then recovered to a new baseline that was approximately 150% of the previous baseline. In contrast, ATP concentrations in HHD keratinocytes did not change in response to increased extracellular Ca2+. This report provides new insights into how the ATP2C1-controlled ATP metabolism mediates Ca2+-induced cell-to-cell adhesion in normal keratinocytes. In addition, these findings implicate inadequate ATP stores as an additional cause in the pathogenesis of HHD and suggest novel therapeutic options.

Human Keratinocyte ATP2C1 Localizes to the Golgi and Controls Golgi Ca2+ Stores

Hailey-Hailey disease (MIM16960) is a blistering skin disease caused by mutations in the Ca2+ ATPase ATP2C1. We found that the abnormal Ca2+ signaling seen in Hailey-Hailey disease keratinocytes correlates with decreased protein levels of ATP2C1. Human ATP2C1 protein approximated 115 kDa in size. The ATP2C1 is localized to the Golgi apparatus in human keratinocytes, similar to its localization in yeast and Caenorhabditis elegans. To test whether the ATP2C1 controls Golgi Ca2+ stores, we measured intraorganelle Ca2+ concentrations using specifically targeted aequorins. Whereas normal keratinocytes display Golgi Ca2+ levels comparable to other epithelial cells, Hailey-Hailey disease keratinocyte Golgi Ca2+ refill is slower, and the maximum Ca2+ concentration reached is significantly lower. These findings were replicated in vivo, because clinically normal Hailey-Hailey disease epidermis contained lower Ca2+ stores and displayed an abnormal Ca2+ gradient. In this report we localize the ATP2C1, demonstrate its physiologic relevance in mammalian cells, and measure intraorganelle Golgi Ca2+ in keratinocytes.

Packing interactions between transmembrane helices alter ion selectivity of the yeast Golgi Ca2+/Mn2+-ATPase PMR1

PMR1 is the yeast secretory pathway pump responsible for high affinity transport of Mn2+ and Ca2+ into the Golgi, where these ions are sequestered and effectively removed from the cytoplasm. Phenotypic growth assays allow for convenient screening of side chains important for Ca2+ and Mn2+ transport. Earlier we demonstrated that mutant Q783A at the cytoplasmic interface of M6 could transport Ca2+, but not Mn2+. Scanning mutagenesis of side chains proximal to residue Gln-783 in membrane helices M2, M4, M5, and M6 revealed additional residues near the cytoplasmic interface, notably Leu-341 (M5), Phe-738 (M5), and Leu-785 (M6) that are sensitive to substitution. Importantly, we obtained evidence for a packing interaction between Val-335 in M4 and Gln-783 in M6 that is critical for Mn2+ transport. Thus, mutant V335G mimics the Mn2+ transport defect of Q783A and mutant V335I can effectively suppress the Mn2+-defective phenotype of Q783A. These changes in ion selectivity were confirmed by cation-dependent ATP hydrolysis using purified enzyme. Other substitutions at these sites are tolerated individually, but not in combination. Exchange of side chains at 335 and 783 also results in ion selectivity defects, suggesting that the packing interaction may be conformation-sensitive. Homology models of M4, M5, and M6 of PMR1 have been generated, based on the structures of the sarcoplasmic reticulum Ca2+-ATPase. The models are supported by data from mutagenesis and reveal that Gln-783 and Val-335 show conformation-sensitive packing at the cytoplasmic interface. We suggest that this region may constitute a gate for access of Mn2+ ions.

Four novel mutations in ATP2C1 found in Chinese patients with Hailey-Hailey disease

BACKGROUND

Familial benign chronic pemphigus or Hailey-Hailey disease (HHD; OMIM 169600) is an autosomal dominant blistering disease. Pathogenic mutations in ATP2C1 encoding a novel Ca2+ pump have recently been identified.

OBJECTIVES

To identify mutations in ATP2C1 in Chinese patients with HHD.

METHODS

Eleven unrelated Chinese patients with HHD were subjected to mutation detection in ATP2C1. Eight of them had a family history of HHD. The 27 coding exons and their flanking sequences were amplified and sequenced.

RESULTS

Five of the 11 patients were identified to have heterozygous mutations including three nonsense mutations and two splicing mutations in ATP2C1.

CONCLUSIONS

Four novel mutations, nonsense mutations S887X and W795X and splicing mutations 118-1 g-->a and 1890+1del(gtgag)ins53, were found in this series of Chinese patients with HHD.

Intracellular calcium pool emptying induces DNA synthesis in HaCaT keratinocytes

Calcium signaling provides a central control mechanism for growth, differentiation and apoptosis of epidermal keratinocytes. Moreover, calcium signaling is important for carcinogenesis in view of the observations suggesting that emptying of intracellular stores in keratinocytes [e.g. by a selective blocker of calcium pump in the endoplasmic reticulum (ER), thapsigargin] facilitates skin cancer development. In this work, we analyzed whether calcium content in the intracellular stores is linked to HaCaT keratinocyte growth and apoptosis control. Treatment with thapsigargin caused calcium release from the intracellular pool and permanent pool depletion (up to 24 h) could be achieved using a high dose (1 micro M) of this inhibitor. HaCaT cells cultured in these conditions exhibited an increased rate of DNA synthesis, assessed by the BrdU incorporation assay. Moreover, a weak stimulation of involucrin (terminal differentiation marker) was observed. Studies where intracellular free calcium (Cai2+) was chelated with BAPTA [1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid] revealed that abrogation of thapsigargin-induced Cai2+elevation did not counteract its effects on DNA synthesis, but blocked thapsigargin-induced involucrin expression. Apoptosis was readily achieved by extracellular calcium chelation using EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid], but was not observed after thapsigargin or BAPTA alone or in combination. In conclusion, depletion of intracellular calcium stores causes stimulation of keratinocyte proliferation independently of the elevation of Cai2+.

Similar Ca(2+)-signaling properties in keratinocytes and in COS-1 cells overexpressing the secretory-pathway Ca(2+)-ATPase SPCA1

Mutations in the ubiquitously expressed secretory-pathway Ca(2+)-ATPase (SPCA1) Ca(2+) pump result in Hailey-Hailey disease, which almost exclusively affects the epidermal part of the skin. We have studied Ca(2+) signaling in human keratinocytes by measuring the free Ca(2+) concentration in the cytoplasm and in the lumen of both the Golgi apparatus and the endoplasmic reticulum. These signals were compared with those recorded in SPCA1-overexpressing and control COS-1 cells. Both the sarco(endo)plasmic-reticulum Ca(2+)-ATPase (SERCA) and SPCA1 can mediate Ca(2+) uptake into the Golgi stacks. Our results indicate that keratinocytes mainly used the SPCA1 Ca(2+) pump to load the Golgi complex with Ca(2+) whereas the SERCA Ca(2+) pump was mainly used in control COS-1 cells. Cytosolic Ca(2+) signals in keratinocytes induced by extracellular ATP or capacitative Ca(2+) entry were characterized by an unusually long latency reflecting extra Ca(2+) buffering by an SPCA1-containing Ca(2+) store, similarly as in SPCA1-overexpressing COS-1 cells. Removal of extracellular Ca(2+) elicited spontaneous cytosolic Ca(2+) transients in keratinocytes, similarly as in SPCA1-overexpressing COS-1 cells. With respect to Ca(2+) signaling keratinocytes and SPCA1-overexpressing COS-1 cells therefore behaved similarly but differed from control COS-1 cells. The relatively large contribution of the SPCA1 pumps for loading the Golgi stores with Ca(2+) in keratinocytes may, at least partially, explain why mutations in the SPCA1 gene preferentially affect the skin in Hailey-Hailey patients.

Effect of Hailey-Hailey Disease mutations on the function of a new variant of human secretory pathway Ca2+/Mn2+-ATPase (hSPCA1)

ATP2C1, encoding the human secretory pathway Ca2+/Mn2+ ATPase (hSPCA1), was recently identified as the defective gene in Hailey-Hailey Disease (HHD), an autosomal dominant skin disorder characterized by persistent blisters and erosions. To investigate the underlying cause of HHD, we have analyzed the changes in expression level and function of hSPCA1 caused by mutations found in HHD patients. Mutations were introduced into hSPCA1d, a novel splice variant expressed in keratinocytes, described here for the first time. Encoded by the full-length of optional exons 27 and 28, hSPCA1d was longer than previously identified splice variants. The protein competitively transported Ca2+ and Mn2+ with equally high affinity into the Golgi of COS-1 cells. Ca2+- and Mn2+-dependent phosphoenzyme intermediate formation in forward (ATP-fuelled) and reverse (Pi-fuelled) directions was also demonstrated. HHD mutant proteins L341P, C344Y, C411R, T570I, and G789R showed low levels of expression, despite normal levels of mRNA and correct targeting to the Golgi, suggesting instability or abnormal folding of the mutated hSPCA1 polypeptides. P201L had little effect on the enzymatic cycle, whereas I580V caused a block in the E1 approximately P --> E2-P conformational transition. D742Y and G309C were devoid of Ca2+- and Mn2+-dependent phosphoenzyme formation from ATP. The capacity to phosphorylate from Pi was retained in these mutants but with a loss of sensitivity to both Ca2+ and Mn2+ in D742Y and a preferential loss of sensitivity to Mn2+ in G309C. These results highlight the crucial role played by Asp-742 in the architecture of the hSPCA1 ion-binding site and reveal a role for Gly-309 in Mn2+ transport selectivity.

Darier's disease: epidemiology, pathophysiology, and management

Darier's disease is a rare cutaneous disease with an autosomal dominant mode of inheritance. Greasy papules and plaques arise on the seborrheic areas and in the flexures and almost all patients have nail abnormalities. Acantholysis and dyskeratosis are the typical histological findings. The underlying defect is a result of mutations in the ATP2A2 gene on chromosome 12q23-24 that encodes for a sarco/endoplasmic reticulum calcium ATPase (SERCA 2). Acantholysis is thought to result from desmosome breakdown. Darier's disease is an example of a dominantly inherited disease caused by haplo-insufficiency. Oral retinoids are the most effective treatment but their adverse effects are troublesome. Topical retinoids, topical corticosteroids, surgery, and laser surgery have their advocates but evidence for efficacy is sparse.

When calcium goes wrong: genetic alterations of a ubiquitous signaling route

In all eukaryotic cells, the cytosolic concentration of calcium ions ([Ca2+]c) is tightly controlled by complex interactions among transporters, pumps, channels and binding proteins. Finely tuned changes in [Ca2+]c modulate a variety of intracellular functions, and disruption of Ca2+ handling leads to cell death. Here we review the human genetic diseases associated with perturbations in the Ca2+ signaling machinery. Despite the importance of Ca2+ in physiology and pathology, the number of known genetic diseases that can be attributed to defects in proteins directly involved in Ca2+ homeostasis is limited to few examples, which will be discussed. This paucity in contrast with the wide molecular repertoire may depend on the extreme severity of the phenotype (leading to death in utero) or, conversely, on functional compensation due to redundancy. In the latter case, it stands to reason that other genetic defects in calcium signaling have yet to be identified owing to their subtle phenotype.