Secretory Pathway Calcium ATPase Research Articles

A Negative Feedback Loop in Ultraviolet A-Induced Senescence in Human Dermal Fibroblasts Formed by SPCA1 and MAPK.

Secretory pathway calcium ATPase 1 (SPCA1) is a calcium pump localized specifically to the Golgi. Its effects on UVA-induced senescence have never been examined. In our study, expression of SPCA1 was increased in UVA-irradiated human dermal fibroblasts (HDFs) by activating mitogen-activated protein kinase (MAPK) and its downstream transcription factor, c-jun. Dual-luciferase reporter and chromatin immunoprecipitation assays revealed that c-jun regulated SPCA1 by binding to its promoter. Furthermore, downregulating SPCA1 with siRNA transfection aggravated UVA-induced senescence due to an elevation of intracellular calcium concentrations and a subsequent increase in reactive oxygen species (ROS) and MAPK activity. In contrast, overexpression of SPCA1 reduced calcium overload, consequently lowering the ROS level and suppressing MAPK activation. This alleviated the cellular senescence caused by UVA irradiation. These results indicated that SPCA1 might exert a protective effect on UVA-induced senescence in HDFs via forming a negative feedback loop. Specifically, activation of MAPK/c-jun triggered by UVA transcriptionally upregulated SPCA1. In turn, the increased SPCA1 lowered the intracellular Ca2+ level, probably through pumping Ca2+ into the Golgi, leading to a reduction of ROS, eventually decreasing MAPK activity and diminishing UVA-induced senescence.

The slo-1 BK potassium channel interacts genetically with pmr-1 secretory pathway calcium ATPase during C. elegans embryonic cell migration.

The slo-1 BK potassium channel interacts genetically with pmr-1 secretory pathway calcium ATPase during C. elegans embryonic cell migration.

Abstract 5276: Secretory pathway calcium ATPase 2 (SPCA2) promotes cell survival and chemoresistance in receptor positive breast cancer cells

Abstract Introduction: Dysregulation of the Ca2+ toolkit has profound consequences for tumor growth and metastasis, raising hopes for novel avenues of therapeutic intervention. The Secretory Pathway Ca2+-ATPase Isoform 2 (SPCA2) has a dual function in sequestering Ca2+ and Mn2+ into secretory stores as well as eliciting their entry into cells by activating plasma membrane ion channels. We have previously showed that SPCA2 is implicated in breast cancer progression, microcalcifications, epithelial-mesenchymal transition, and metastasis. Methods and Results: High SPCA2 expression was associated with poor overall survival in receptor positive breast cancer patients (n=548, P =8.7e-0.6; KM Plotter). Depletion of SPCA2 (SPCA2 KD) in MCF-7 cells significantly reduced cell proliferation (P < 0.05). Analysis of the cell cycle (PI staining, Flow cytometry) revealed a significant increase (P < 0.05) in the number of cells in the G0/G1 phase, and significant increase in apoptosis (via TUNEL assay) (P < 0.05) in SPCA2 KD cells compared to control. Microarray analysis showed the p53 pathway is the most significantly upregulated pathway (P < 0.05) in SPCA2 KD cells compared to control. P53 knockout abrogated SPCA2 mediated cell cycle arrest and apoptosis. Depletion of SPCA2 increased reactive oxygen species (ROS, measured by DCFDA dye and MitoSox Red using flow cytometry) leading to DNA damage (confocal microscopy), and activation of ATM/ATR pathway (Immunoblotting, P < 0.05). As a consequence, SPCA2 KD cells showed specific hypersensitivity to DNA damaging agents used in breast cancer therapy (carboplatin, radiation, and doxorubicin) (determined by MTT assay) (P < 0.05). Thus SPCA2 is a novel molecular target in breast cancer therapy. Curcumin is currently being evaluated in clinical trials of breast cancer. We show that curcumin causes dose-dependence inhibition of SPCA2 expression (P < 0.05) in multiple receptor-positive cell lines, and that forced overexpression of SPCA2 decreased curcumin cytotoxicity. Interestingly, we did not observe these results with SPCA1, the housekeeping SPCA isoform, revealing isoform-specific function of Golgi calcium pumps in breast cancer subtypes. Conclusion: These novel findings point to a causal link between SPCA2, breast cancer progression, and chemoresistance to DNA damaging agents. Decrease of SPCA2 expression by curcumin may have therapeutic potential in treating receptor positive breast cancer. Citation Format: Monish Ram Makena, Donna Dang, Allatah Mekile, Phillip Buckhaults, Rajini Rao. Secretory pathway calcium ATPase 2 (SPCA2) promotes cell survival and chemoresistance in receptor positive breast cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5276.

The pancreas-specific form of secretory pathway calcium ATPase 2 regulates multiple pathways involved in calcium homeostasis

Acinar cell exocytosis requires spatiotemporal Ca2+ signals regulated through endoplasmic reticulum (ER) stores, Ca2+ATPases, and store-operated Ca2+ entry (SOCE). The secretory pathway Ca2+ATPase 2 (SPCA2) interacts with Orai1, which is involved in SOCE and store independent Ca2+ entry (SICE). However, in the pancreas, only a C-terminally truncated form of SPCA2 (termed SPAC2C) exists. The goal of this study was to determine if SPCA2C effects Ca2+ homeostasis in a similar fashion to the full-length SPCA2.Using epitope-tagged SPCA2C (SPCA2CFLAG) expressed in HEK293A cells and Fura2 imaging, cytosolic [Ca2+] was examined during SICE, SOCE and secretagogue-stimulated signaling. Exogenous SPCA2C expression increased resting cytosolic [Ca2+], Ca2+ release in response to carbachol, ER Ca2+ stores, and store-mediated and independent Ca2+ influx. Co-IP detected Orai1-SPCA2C interaction, which was altered by co-expression of STIM1. Importantly, SPCA2C's effects on store-mediated Ca2+ entry were independent of Orai1. These findings indicate SPCA2C influences Ca2+ homeostasis through multiple mechanisms, some of which are independent of Orai1, suggesting novel and possibly cell-specific Ca2+ regulation.

Secretory pathway calcium ATPase 1 (SPCA1) controls mouse neural tube closure by regulating cytoskeletal dynamics.

Neural tube closure relies on the apical constriction of neuroepithelial cells. Research in frog and fly embryos has found links between the levels of intracellular calcium, actomyosin dynamics and apical constriction. However, genetic evidence for a role of calcium in apical constriction during mammalian neurulation is still lacking. Secretory pathway calcium ATPase (SPCA1) regulates calcium homeostasis by pumping cytosolic calcium into the Golgi apparatus. Loss of function in Spca1 causes cranial exencephaly and spinal cord defects in mice, phenotypes previously ascribed to apoptosis. However, our characterization of a novel allele of Spca1 revealed that neurulation defects in Spca1 mutants are not due to cell death, but rather to a failure of neuroepithelial cells to apically constrict. We show that SPCA1 influences cell contractility by regulating myosin II localization. Furthermore, we found that loss of Spca1 disrupts actin dynamics and the localization of the actin remodeling protein cofilin 1. Taken together, our results provide evidence that SPCA1 promotes neurulation by regulating the cytoskeletal dynamics that promote apical constriction and identify cofilin 1 as a downstream effector of SPCA1 function.

Abstract 3301: Inhibition of the secretory pathway calcium ATPase 1 (SPCA1) in MDA-MB-231 breast cancer cells and the effect on protein expression

Abstract SPCA1 is a Ca2+ pump located on the membrane of the Golgi apparatus and is involved in controlling calcium levels within the Golgi. We have previously shown that SPCA1 is upregulated in some basal-like breast cancers. Given the role of the Golgi in protein trafficking and processing, we hypothesised that SPCA1 may be involved in regulating the expression of proteins important in cancer. To address this hypothesis we used 2D-DIGE to identify proteins that are altered when SPCA1 is silenced in MDA-MB-231 basal cancer cells. MDA-MB-231 cells were seeded into 6-well plates (75,000 cells/well) and treated with SPCA1 or non-targeting siRNA. Protein was isolated 72 h post siRNA treatment, and SPCA1 silencing was confirmed by immunoblotting. 2D-DIGE and MS/MS were used to identify proteins with differential expression with SPCA1 silencing. Heat shock protein 60 (HSP60) was identified as a protein potentially sensitive to SPCA1 silencing using 2D-DIGE. Immunoblotting and real time RT-PCR showed that SPCA1 silencing reduced HSP60 protein and mRNA expression by 81±2% and 60±7% (n=3, P<0.05), respectively. Given the role of HSP60 in cell death pathways, we also assessed the consequences of SPCA1 silencing on heat shock and staurosporine-induced cell death. SPCA1 silencing had no effect on heat shock-induced cell death but reduced the sensitivity of MDA-MB-231 breast cancer cells to staurosporine. Although further studies are required to fully characterize the functional consequences of HSP60 downregulation upon SPCA1 silencing, this work suggests that SPCA1 is a complex regulator of proteins important in cancer pathways. Citation Format: Jane M. Lee, Diana G. Ross, Gregory R. Monteith, Sarah J. Roberts-Thomson. Inhibition of the secretory pathway calcium ATPase 1 (SPCA1) in MDA-MB-231 breast cancer cells and the effect on protein expression. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3301. doi:10.1158/1538-7445.AM2014-3301

Cofilin recruits F-actin to SPCA1 and promotes Ca2+-mediated secretory cargo sorting.

The actin filament severing protein cofilin-1 (CFL-1) is required for actin and P-type ATPase secretory pathway calcium ATPase (SPCA)-dependent sorting of secretory proteins at the trans-Golgi network (TGN). How these proteins interact and activate the pump to facilitate cargo sorting, however, is not known. We used purified proteins to assess interaction of the cytoplasmic domains of SPCA1 with actin and CFL-1. A 132-amino acid portion of the SPCA1 phosphorylation domain (P-domain) interacted with actin in a CFL-1-dependent manner. This domain, coupled to nickel nitrilotriacetic acid (Ni-NTA) agarose beads, specifically recruited F-actin in the presence of CFL-1 and, when expressed in HeLa cells, inhibited Ca(2+) entry into the TGN and secretory cargo sorting. Mutagenesis of four amino acids in SPCA1 that represent the CFL-1 binding site also affected Ca(2+) import into the TGN and secretory cargo sorting. Altogether, our findings reveal the mechanism of CFL-1-dependent recruitment of actin to SPCA1 and the significance of this interaction for Ca(2+) influx and secretory cargo sorting.

Secretory cargo sorting at the trans-Golgi network.

Sorting of proteins for secretion from cells is crucial for normal physiology and the regulation of key cellular events. Although the sorting of lysosomal hydrolases at the trans-Golgi network (TGN) for delivery to pre-lysosomes is well characterized, the corresponding mechanism by which secreted proteins are sorted for plasma-membrane delivery remains poorly understood. Recent discoveries have revealed a novel sorting mechanism that requires the linkage between the cytoplasmic actin cytoskeleton to the membrane-anchored Ca(2+) ATPase, SPCA1 (secretory pathway calcium ATPase 1), and the luminal 45 kDa Ca(2+)-binding protein, Cab45, for successful sorting of a subset of proteins at the TGN. We review progress in understanding these processes.

The Secretory Pathway Calcium ATPase PMR-1/SPCA1 Has Essential Roles in Cell Migration during Caenorhabditis elegans Embryonic Development

Maintaining levels of calcium in the cytosol is important for many cellular events, including cell migration, where localized regions of high calcium are required to regulate cytoskeletal dynamics, contractility, and adhesion. Studies show inositol-trisphosphate receptors (IP3R) and ryanodine receptors (RyR), which release calcium into the cytosol, are important regulators of cell migration. Similarly, proteins that return calcium to secretory stores are likely to be important for cell migration. The secretory protein calcium ATPase (SPCA) is a Golgi-localized protein that transports calcium from the cytosol into secretory stores. SPCA has established roles in protein processing, metal homeostasis, and inositol-trisphosphate signaling. Defects in the human SPCA1/ATP2C1 gene cause Hailey-Hailey disease (MIM# 169600), a genodermatosis characterized by cutaneous blisters and fissures as well as keratinocyte cell adhesion defects. We have determined that PMR-1, the Caenorhabditis elegans ortholog of SPCA1, plays an essential role in embryogenesis. Pmr-1 strains isolated from genetic screens show terminal phenotypes, such as ventral and anterior enclosure failures, body morphogenesis defects, and an unattached pharynx, which are caused by earlier defects during gastrulation. In Pmr-1 embryos, migration rates are significantly reduced for cells moving along the embryo surface, such as ventral neuroblasts, C-derived, and anterior-most blastomeres. Gene interaction experiments show changing the activity of itr-1/IP3R and unc-68/RyR modulates levels of embryonic lethality in Pmr-1 strains, indicating pmr-1 acts with these calcium channels to regulate cell migration. This analysis reveals novel genes involved in C. elegans cell migration, as well as a new role in cell migration for the highly conserved SPCA gene family.

New insights into store-independent Ca2+ entry: secretory pathway calcium ATPase 2 in normal physiology and cancer

Recent studies in secretory pathway calcium ATPases (SPCA) revealed novel functions of SPCA2 in interacting with store-operated Ca2+ channel Orai1 and inducing Ca2+ influx at the cell surface. Importantly, SPCA2-mediated Ca2+ signaling is uncoupled from its conventional role of Ca2+-ATPase and independent of store-operated Ca2+ signaling pathway. SPCA2-induced store-independent Ca2+ entry (SICE) plays essential roles in many important physiological processes, while unbalanced SICE leads to enhanced cell proliferation and tumorigenesis. Finally, we have summarized the clinical implication of SICE in oral cancer prognosis and treatment. Inhibition of SICE may be a new target for the development of cancer therapeutics.

Cab45 is required for Ca2+-dependent secretory cargo sorting at the trans-Golgi network

Ca(2+) import into the lumen of the trans-Golgi network (TGN) by the secretory pathway calcium ATPase1 (SPCA1) is required for the sorting of secretory cargo. How is Ca(2+) retained in the lumen of the Golgi, and what is its role in cargo sorting? We show here that a soluble, lumenal Golgi resident protein, Cab45, is required for SPCA1-dependent Ca(2+) import into the TGN; it binds secretory cargo in a Ca(2+)-dependent reaction and is required for its sorting at the TGN.

Cofilin-mediated sorting and export of specific cargo from the Golgi apparatus in yeast

The mechanism of cargo sorting at the trans-Golgi network (TGN) for secretion is poorly understood. We previously reported the involvement of the actin-severing protein cofilin and the Ca(2+) ATPase secretory pathway calcium ATPase 1 (SPCA1) in the sorting of soluble secretory cargo at the TGN in mammalian cells. Now we report that cofilin in yeast is required for export of selective secretory cargo at the late Golgi membranes. In cofilin mutant (cof1-8) cells, the cell wall protein Bgl2 was secreted at a reduced rate and retained in a late Golgi compartment, whereas the plasma membrane H(+) ATPase Pma1, which is transported in the same class of carriers, reached the cell surface. In addition, sorting of carboxypeptidase Y (CPY) to the vacuole was delayed, and CPY was secreted from cof1-8 cells. Loss of the yeast orthologue of SPCA1 (Pmr1) exhibited similar sorting defects and displayed synthetic sickness with cof1-8. In addition, overexpression of PMR1 restored Bgl2 secretion in cof1-8 cells. These findings highlight the conserved role of cofilin and SPCA1/Pmr1 in sorting of the soluble secretory proteins at the TGN/late Golgi membranes in eukaryotes.

Golgi Calcium Pump Secretory Pathway Calcium ATPase 1 (SPCA1) Is a Key Regulator of Insulin-like Growth Factor Receptor (IGF1R) Processing in the Basal-like Breast Cancer Cell Line MDA-MB-231

Calcium signaling is a key regulator of pathways important in tumor progression, such as proliferation and apoptosis. Most studies assessing altered calcium homeostasis in cancer cells have focused on alterations mediated through changes in cytoplasmic free calcium levels. Here, we show that basal-like breast cancers are characterized by an alteration in the secretory pathway calcium ATPase 1 (SPCA1), a calcium pump localized to the Golgi. Inhibition of SPCA1 in MDA-MB-231 cells produced pronounced changes in cell proliferation and morphology in three-dimensional culture, without alterations in sensitivity to endoplasmic reticulum stress induction or changes in global calcium signaling. Instead, the effects of SPCA1 inhibition in MDA-MB-231 cells reside in altered regulation of calcium-dependent enzymes located in the secretory pathway, such as proprotein convertases. Inhibition of SPCA1 produced a pronounced alteration in the processing of insulin-like growth factor receptor (IGF1R), with significantly reduced levels of functional IGF1Rβ and accumulation of the inactive trans-Golgi network pro-IGF1R form. These studies identify for the first time a calcium transporter associated with the basal-like breast cancer subtype. The pronounced effects of SPCA1 inhibition on the processing of IGF1R in MDA-MB-231 cells independent of alterations in global calcium signaling also demonstrate that some calcium transporters can regulate the processing of proteins important in tumor progression without major alterations in cytosolic calcium signaling. Inhibitors of SPCA1 may offer an alternative strategy to direct inhibitors of IGF1R and attenuate the processing of other proprotein convertase substrates important in basal breast cancers.

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.

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.

Calcium Secretion into Milk

Ionized calcium ([Ca(2+)]) is present in milk at concentrations around 3 mM, a concentration that drives the formation of complexes with citrate, phosphate, and casein, thereby generating compounds that carry the major portion of calcium in milk. In humans and cows, where it has been studied, changes in milk calcium appear to be regulated by the amount of citrate and casein in milk rather than changes in [Ca(2+)]. Most or all of the calcium in milk is likely derived through exocytosis of secretory vesicles derived from the Golgi compartment where a calcium ATPase mediates transport from the cytoplasm. The identity of the transporters is not yet certain but gene expression for the plasma membrane calcium ATPase, PMCA2bw, and the secretory pathway calcium ATPase, SPCA, is highly upregulated during lactation. Currently nothing appears to be known about the mechanisms that mediate transport of calcium across the basolateral membrane of the alveolar cell.