A plazmamembrán típusú Ca2+ ATPáz 4b izoforma szerkezetbeli eltérései polarizált és nem-polarizált sejtekben = Distinct structural characteristics of the plasma membrane Ca2+ ATPase 4b forms in polarized and non-polarized cells

A Ca2+ jelátvitel egyik fontos eleme a plazmamembrán Ca2+ATPáz (PMCA), amely az extracelluláris térbe távolít el Ca2+ ionokat. A PMCA egyetlen polipeptidláncból álló integráns membránfehérje. C-terminális része a pumpa aktivitásának fő szabályozó régiója. A megfelelő Ca2+ jel kialakításához a PMCA aktivitásának közvetlen szabályozásán túl a PMCA lokalizációjának finom szabályozására is szükség van. Eredményeink azt bizonyítják, hogy a PMCA4b izoforma sejten belüli mozgását a C-terminálisán található összetett szabályozási rendszer befolyásolja: az intracelluláris kompartmentek felé irányító (savanyú régió, internalizációs/retenciós) és a fehérje plazmamembránba való kijutását elősegítő (PDZ-kötő szekvencia) motívumok. A PMCA4b C-terminálisán található PDZ-kötő szekvencia szerepe meghatározónak bizonyult a PMCA4b plazmamembránon belüli eloszlásának szempontjából is. Ehhez kötődve a PSD-95 PDZ-fehérje jellegzetes szigetszerű csoportokba rendezi a PMCA4b molekulákat a sejtfelszínen. Úgy találtuk, hogy speciálisan vérsejtekben és egyéb nem polarizált sejtekben a PMCA4b-nek lehasad egy rövid, C-terminális szakasza. A fehérje elsődleges szerkezetének megváltozásával átalakul a lokalizációt szabályozó rendszer összetétele. Ennek eredményeképpen polarizált és nem polarizált sejtekben a PMCA4b variáns sejten belüli mozgása, eloszlása a plazmamembránban és ezáltal részvétele a Ca2+ jelátvitelben nagy mértékben különbözhet egymástól. | Plasma membrane Ca2+ATPase (PMCA) plays a crucial role in cellular Ca2+ signaling. Its function is to remove excess Ca2+ from the cytosol to the extracellular space. PMCA is an integral membrane protein composed of a single polypeptide chain. It has a special carboxyl terminus that regulates the activity of the pump. In addition, the regulation of the localization of the pump is also crucial for proper Ca2+ signaling. Our results indicate that the intracellular trafficking of the PMCA4b isoform is determined by a complex regulatory mechanism. We found that the C-terminus contains motifs directing the pump to intracellular compartments (acidic cluster and retention/internalization signal) and to the plasma membrane (PDZ-binding sequence). Moreover, the C-terminal PDZ-binding sequence has a significant role in the distribution of the PMCA4b within the plasma membrane. Binding to this motif, a PDZ-domain protein (PSD-95) can arrange the PMCA4b molecules into clusters on the cell surface. We found that in various blood cells and other non-polarized cells a C-terminally truncated PMCA4b is expressed. This modification alters the regulatory system of the C-terminus on the localization of the pump. Therefore the trafficking and plasma membrane distribution of PMCA4b - that may influence the contribution of PMCA4b to Ca2+ signaling' might be considerably different in polarized and non-polarized cells

A plazmamembrán Ca2+ ATPáz 4b izoforma apoptotikus fragmentjét reprezentáló mutáns sejten belüli lokalizációja, stabilitása, hatásai a sejtek Ca2+ háztartására és szerepe az apoptózis folyamatban = Intracellular localization and stability of a mutant representing the apoptotic fragment of the plasma membrane Ca2+ ATPase 4b and its role in cellular Ca2+ homeostasis and apoptosis

A jelen kutatási periódus alatt egy fontos Ca2+ transzport fehérje, a plazma membrán Ca2+ ATPáz (PMCA4b) struktúra/funkció változásait tanulmányoztuk az apoptózis valamint a nekrózis folyamatai alatt. Eredményeink azt bizonyítják, hogy a PMCA4b fehérjét - függetlenül az apoptózist kiváltó októl - a kaszpáz-3 proteáz hasítja és egy 120 kDa molekulatömegű fragment képződik. A fehérje közben elveszíti C-terminális regulátor régióját, és -szuper aktívvá - válik. A "szuper aktív" PMCA fragmentnek megfelelő mutáns a plazmamembránban lokalizálódik és képes a citoszólikus Ca2+ szint szabályozására. Ezzel szemben oxidatív stresszt kiváltó szerek hatására a PMCA jelentős mértékű internalizációja és a citoszólikus Ca2+ szint hosszan tartó megemelkedése figyelhető meg. A C-terminális régió meghatározónak bizonyult a PMCA4b plazmamembránban történő eloszlásának szempontjából is. Kimutattuk, hogy a PSD-95 állványfehérje a PMCA C-terminálisán található PDZ-kötő motívumon keresztül elősegíti a PMCA kijutását a plazmamembránba, és itt a képződő fehérje-komplex szigetszerű csoportokba rendeződik. Vizsgálataink elősegíthetik a Ca2+ homeosztázis felborulására visszavezethető egyes malignus elváltozások illetve degeneratív betegségek közötti összefüggések jobb megismerését. | During the present research period we studied structural and functional changes of an essential Ca2+ extrusion protein, the plasma membrane Ca2+ pump (PMCA), during apoptosis and necrosis. We followed truncation of PMCA4b during apoptosis induced by mitochondrial or receptor-mediated pathways and found that a similar fragment of 120 kDa was formed and remained intact for several hours after treatment. We constructed a C-terminally truncated mutant that corresponded to this 120 kDa fragment and showed that it was fully and constitutively active, and targeted properly to the plasma membrane. In contrast, arsenate or excitotoxic concentration of glutamate induced PMCA internalization and consequently, resulted in an impaired Ca2+ clearance from the cytoplasm. We also showed that interaction with the postsynaptic?density-95 (PSD-95) scaffolding protein increased the plasma membrane expression of PMCA4b and redistributed the pump into clusters. The clustering of PMCA4b was fully dependent on the presence of its C-terminus. We suggest that loss of function internalization of PMCAs and/or disruption of specific Ca2+ signaling microdomains may contribute to the Ca2+ dysregulation that accompanies a number of degenerative diseases

Plasma membrane Ca2+-ATPases can shape the pattern of Ca2+ transients induced by store-operated Ca2+ entry

Calcium (Ca2+) is a critical cofactor and signaling mediator in cells, and the concentration of cytosolic Ca2+ is regulated by multiple proteins, including the plasma membrane Ca2+-ATPases (adenosine triphosphatases) (PMCAs), which use ATP to transport Ca2+ out of cells. PMCA isoforms exhibit different kinetic and regulatory properties; thus, the presence and relative abundance of individual isoforms may help shape Ca2+ transients and cellular responses. We studied the effects of three PMCA isoforms (PMCA4a, PMCA4b, and PMCA2b) on Ca2+ transients elicited by conditions that trigger store-operated Ca2+ entry (SOCE) and that blocked Ca2+ uptake into the endoplasmic reticulum in HeLa cells, human embryonic kidney (HEK) 293 cells, or primary endothelial cell isolated from human umbilical cord veins (HUVECs). The slowly activating PMCA4b isoform produced long-lasting Ca2+ oscillations in response to SOCE. The fast-activating isoforms PMCA2b and PMCA4a produced different effects. PMCA2b resulted in rapid and highly PMCA abundance-sensitive clearance of SOCE-mediated Ca2+ transients, whereas PMCA4a reduced cytosolic Ca2+, resulting in the establishment of a higher than baseline cytosolic Ca2+ concentration. Mathematical modeling showed that slow activation was critical to the sustained oscillation induced by the "slow" PMCA4b pump. The modeling and experimental results indicated that the distinct properties of PMCA isoforms differentially regulate the pattern of SOCE-mediated Ca2+ transients, which would thus affect the activation of downstream signaling pathways

Histone deacetylase inhibitor- and PMA-induced upregulation of PMCA4b enhances Ca2+ clearance from MCF-7 breast cancer cells

The expression of the plasma membrane Ca2+ ATPase (PMCA) isoforms is altered in several types of cancer cells suggesting that they are involved in cancer progression. In this study we induced differentiation of MCF-7 breast cancer cells by histone deacetylase inhibitors (HDACis) such as short chain fatty acids (SCFAs) or suberoylanilide hydroxamic acid (SAHA), and by phorbol 12-myristate 13-acetate (PMA) and found strong upregulation of PMCA4b protein expression in response to these treatments. Furthermore, combination of HDACis with PMA augmented cell differentiation and further enhanced PMCA4b expression both at mRNA and protein levels. Immunocytochemical analysis revealed that the upregulated protein was located mostly in the plasma membrane. To examine the functional consequences of elevated PMCA4b expression, the characteristics of intracellular Ca2+ signals were investigated before and after differentiation inducing treatments, and also in cells overexpressing PMCA4b. The increased PMCA4b expression – either by treatment or overexpression – led to enhanced Ca2+ clearance from the stimulated cells. We found pronounced PMCA4 protein expression in normal breast tissue samples highlighting the importance of this pump for the maintenance of mammary epithelial Ca2+ homeostasis. These results suggest that modulation of Ca2+ signaling by enhanced PMCA4b expression may contribute to normal development of breast epithelium and may be lost in cancer

Multifaceted plasma membrane Ca2+ pumps: From structure to intracellular Ca2+ handling and cancer

Plasma membrane Ca2+ ATPases (PMCAs) are intimately involved in the control of intracellular Ca2+ concentration. They reduce Ca2+ in the cytosol not only by direct ejection, but also by controlling the formation of inositol-1,4,5-trisphosphate and decreasing Ca2+ release from the endoplasmic reticulum Ca2+ pool. In mammals four genes (PMCA1-4) are expressed, and alternative RNA splicing generates more than twenty variants. The variants differ in their regulatory characteristics. They localize into highly specialized membrane compartments and respond to the incoming Ca2+ with distinct temporal resolution. The expression pattern of variants depends on cell type; a change in this pattern can result in perturbed Ca2+ homeostasis and thus altered cell function. Indeed, PMCAs undergo remarkable changes in their expression pattern during tumorigenesis that might significantly contribute to the unbalanced Ca2+ homeostasis of cancer cells

The plasma membrane Ca2+ pump PMCA4b inhibits the migratory and metastatic activity of BRAF mutant melanoma cells

Oncogenic mutations of BRAF lead to constitutive ERK activity that supports melanoma cell growth and survival. While Ca2+ signaling is a well-known regulator of tumor progression, the crosstalk between Ca2+ signaling and the Ras-BRAF-MEK-ERK pathway is much less explored. Here we show that in BRAF mutant melanoma cells the abundance of the plasma membrane Ca2+ ATPase isoform 4b (PMCA4b, ATP2B4) is low at baseline but markedly elevated by treatment with the mutant BRAF specific inhibitor vemurafenib. In line with these findings gene expression microarray data also shows decreased PMCA4b expression in cutaneous melanoma when compared to benign nevi. The MEK inhibitor selumetinib-similarly to that of the BRAF-specific inhibitor-also increases PMCA4b levels in both BRAF and NRAS mutant melanoma cells suggesting that the MAPK pathway is involved in the regulation of PMCA4b expression. The increased abundance of PMCA4b in the plasma membrane enhances [Ca2+ ]i clearance from cells after Ca2+ entry. Moreover we show that both vemurafenib treatment and PMCA4b overexpression induce marked inhibition of migration of BRAF mutant melanoma cells. Importantly, reduced migration of PMCA4b expressing BRAF mutant cells is associated with a marked decrease in their metastatic potential in vivo. Taken together, our data reveal an important crosstalk between Ca2+ signaling and the MAPK pathway through the regulation of PMCA4b expression and suggest that PMCA4b is a previously unrecognized metastasis suppressor

Expression of calcium pumps is differentially regulated by histone deacetylase inhibitors and estrogen receptor alpha in breast cancer cells

Background: Remodeling of Ca2+ signaling is an important step in cancer progression, and altered expression of members of the Ca2+ signaling toolkit including the plasma membrane Ca2+ ATPases (PMCA proteins encoded by ATP2B genes) is common in tumors. Methods: In this study PMCAs were examined in breast cancer datasets and in a variety of breast cancer cell lines representing different subtypes. We investigated how estrogen receptor alpha (ER-α) and histone deacetylase (HDAC) inhibitors regulate the expression of these pumps. Results: Three distinct datasets displayed significantly lower ATP2B4 mRNA expression in invasive breast cancer tissue samples compared to normal breast tissue, whereas the expression of ATP2B1 and ATP2B2 was not altered. Studying the protein expression profiles of Ca2+ pumps in a variety of breast cancer cell lines revealed low PMCA4b expression in the ER-α positive cells, and its marked upregulation upon HDAC inhibitor treatments. PMCA4b expression was also positively regulated by the ER-α pathway in MCF-7 cells that led to enhanced Ca2+ extrusion capacity in response to 17β-estradiol (E2) treatment. E2-induced PMCA4b expression was further augmented by HDAC inhibitors. Surprisingly, E2 did not affect the expression of PMCA4b in other ER-α positive cells ZR-75-1, T-47D and BT-474. These findings were in good accordance with ChIP-seq data analysis that revealed an ER-α binding site in the ATP2B4 gene in MCF-7 cells but not in other ER-α positive tumor cells. In the triple negative cells PMCA4b expression was relatively high, and the effect of HDAC inhibitor treatment was less pronounced as compared to that of the ER-α positive cells. Although, the expression of PMCA4b was relatively high in the triple negative cells, a fraction of the protein was found in intracellular compartments that could interfere with the cellular function of the protein. Conclusions: Our results suggest that the expression of Ca2+ pumps is highly regulated in breast cancer cells in a subtype specific manner. Our results suggest that hormonal imbalances, epigenetic modifications and impaired protein trafficking could interfere with the expression and cellular function of PMCA4b in the course of breast cancer progression. © 2018 The Author(s)