Research ArticleExperimental Studies

Extracellular Acidity-mediated Expression of cPLA2γ Confers Resistance in Gastric Cancer Cells

SUNG-CHUL LIM, TAE-BUM LEE, BYUNG-SOO KANG and SONG IY HAN
Anticancer Research January 2021, 41 (1) 211-218; DOI: https://doi.org/10.21873/anticanres.14767

Abstract

Background/Aim: Extracellular acidity, a characteristic of solid tumors, has been proposed to be a critical factor for aggravating tumor malignancy and conferring resistance to therapeutics. Recently, acidity has been implicated in inflammatory responses, which are mediated through active lipid metabolites in various human tissues. In the present study, we investigated whether acidity can affect lipid-mediated signaling, and found that phospholipase A2 (PLA2) activity increased at acidic pH in SNU601 and AGS gastric carcinoma cell lines. Materials and Methods: To identify the PLA2 isoform that is responsible for the acidity-induced activity, we assessed mRNA levels of cPLA2 isotypes through real-time qPCR, and protein levels through immunoblot assay in cells cultured in acidic medium. Results: It was found that acidic pH conditions markedly elevated the PLA2γ expression. A gene interference study using specific siRNA of cPLA2γ suggested that expression of cPLA2γ in acidic culture conditions may be associated with protection of cancer cells in acidic environment, as shown by cell viability and clonogenic assays. In addition, expression of cPLA2γ appeared to confer cell resistance to anticancer drugs under acidic pH conditions. Conclusion: Acidity-induced cPLA2γ expression may exert protective effects by imparting resistance to the gastric cancer cells under acidic environment.

Key Words:

Gastric cancer (GC) is a frequently occurring malignancy and one of the major causes of cancer-related mortality worldwide (1). Although the development of surgical operation has brought quite successful results, there is still a large number of patients diagnosed with GC at advanced stages.

Recently, metabolic parameters of tumor tissues, such as extracellular acidity have been proposed to be critical in tumor malignancy and resistance to therapeutic agents (2, 3). Extracellular acidity is a characteristic feature of solid tumor as tumor cells undergo active aerobic and anaerobic glycolysis, resulting in accumulation of H+ and lactic acid (4). Such acidosis has been reported to confer an ineffective therapeutic environment leading to selection of more resistant and aggressive characteristics (5, 6). However, the mechanisms by which acidic pH microenvironment induces resistance in cancer cells are not well understood.

Various studies have shown that biologically active lipids, such as eicosanoids play an essential role in the control of various pathological processes associated with cancer. These lipid metabolites are synthesized through a complex enzymatic pathway, beginning with the release of arachidonic acid. Arachidonic acid generation is catalyzed by phospholipase A2 (PLA2) enzyme family through the hydrolysis of glycerophospholipids (7). So far, more than 30 different forms of PLA2 enzymes have been identified and classified into four main categories: secreted sPLA2s, cytosolic cPLA2s, calcium-independent iPLA2s, and platelet activating factor (PAF) acetyl hydrolase/oxidized lipid lipoprotein associated (Lp) PLA2s. Among the known isoforms, intracellular PLA2s in the group IV family (cPLA2s) are most studied and have been suggested to play a role in various physiological and pathological processes (8, 9). The group IV PLA2 family comprises of six members, including 4A, 4B, 4C, 4D, 4E, and 4F that are commonly referred to as cPLA2 α, β, γ, σ, ε, and ζ, respectively (10). The most extensively studied group IV PLA2 enzyme is cPLA2α, that plays crucial roles in the production of inflammatory lipid mediators with the help of COX and is overexpressed in multiple human cancers (11). Another member of group IV PLA2, cPLA2γ also modulates phospholipid remodeling in the cells (12), therefore, it may be linked to the COX pathway to produce prostanoids (7). However, cPLA2γ shows several structural and functional differences from cPLA2α indicating a distinct physiological role. cPLA2γ is constitutively associated with the membrane, and is calcium-independent unlike cPLA2α (13, 14). It is predominantly expressed in the cardiac and skeletal muscle in humans, and associated with mitochondria, ER and Golgi. Although the physiological significance or regulatory mechanism of cPLA2γ is not well studied, recent studies have shown that cPLA2γ plays roles in chemotaxis and invasion in breast cancer cells, and is involved in lipid droplet biogenesis and hepatitis C virus infection in hepatocytes. Previously, we demonstrated that acidic condition increased malignancy of GC cells (15). In the present study, we investigated whether PLA2 is related with cell viability under acidic environment that is unfavorable for survival.

Materials and Methods

Cell culture and acidic pH conditions. SNU-601 and AGS human GC cells were obtained from the Korean Cell Line Bank (Seoul, Republic of Korea). Cells were maintained in RPMI 1640 medium (Invitrogen, Carlsbad, CA, USA) supplemented with 10% (v/v) fetal bovine serum (FBS) and 1% Penicillin-Streptomycin at 37°C in an atmosphere containing 5% CO2. For experiments investigating the effect of acidic condition on GC cells, control medium was prepared by RPMI medium (pH 7.4) containing 1% FBS, and acidic pH medium was prepared by adding 5M HCl to the control medium to adjust to pH 6.4 or pH 6.0. Then, cells were incubated in pH 7.4 control medium or acidic pH-adjusted medium for 48 h or 72 h. Unless specified, chemicals were purchased from Calbiochem (San Diego, CA, USA).

Cell viability assays. The EZ-cytox viability assay was performed following the manufacturer’s protocol. Briefly, cells were plated in wells of a 24-well plate at a density of 5~8×104 cells/well, cultured for 24 h, and then incubated in the normal pH or acidic pH RPMI medium for 48 h. The EZ-cytox solution (Daeillab, Seoul, Republic of Korea) was added to the wells and incubated at 37°C in a CO2 incubator for 2 h. Subsequently, the plates were read using an enzyme-linked immunosorbent assay plate reader at 450 nm. The absorbance of the non-treated cells was set as 100% and cell survival was expressed as a percentage of this value.

Western blot analysis. Treated cells were lysed in whole-cell lysis buffer (50 mM Hepes, 150 mM NaCl, 1% Triton X-100, 5 mM EGTA, and protease inhibitor cocktail). Equal amounts of protein were electrophoretically separated using SDS-PAGE gel (10-12%) and transferred to a nitrocellulose membrane using the standard protocol. Antibodies were used to probe for c PLA2α (Cell signaling Technology, Danvers, MA, USA), JMJD7-cPLA2β (abcam, Cambridge, MA, USA), cPLA2γ (Novus Biologicals, Littleton, CO, USA), cPLA2σ (Novus Biologicals), cPLA2ζ (abcam), and α-tubulin (santa cruz Biotechnology, Santa Cruz, CA, USA). Signals were acquired using an Image Station 4000MM image analyzer (Kodak, Rochester, NY, USA).

Real-time reverse transcription-polymerase chain reaction. Real-time PCR was performed using the Light Cycler 2.0 (Roche, Basel, Switzerland). The reactions were prepared using the Fast Start DNA Master SYBR Green I Kit (Roche) according to the manufacturer’s protocol. The cDNA was amplified using gene-specific primers. Primers for PLA2G4C (P321848) were purchased from Bioneer. Primers for other genes were designed as follows: for β-actin, 5’-GACTATGACTTAGTTGCGTTA-3’ and 5’-GCCTTCATACATCTC AAGTTG-3’, for PLA2G4A, 5’-TGCATTTCTTAATGGGTGTCT-3’ and 5’-TCATCACTGTCCGAGCTATC-3’, for JMJD7-PLA2G4B, 5’-CAGGAGCTGAGTATTCGC-3’ and 5’-CCTCAGTCCTGCTTCT TT-3’ for PLA2G4D, 5’-CTTTGTGGACCTGTGGG-3’ and 5’-GTGTCTCCAGATTGTTCTCTT-3’ for PLA2G4F, 5’-CCTGTAC CAGGAGGAGA-3’ and 5’-CAACCTCATAGGGCGTG-3’. PCR was performed at 95°C for 10 min, followed by 45 cycles of 95°C for 15 s, 60°C for 5 s, and 72°C for 7 s. Data were analyzed using Light Cycler software version 4.0 (Roche). The 2ΔΔCt method was used for analysis of relative gene expression.

PLA2 activity assay. PLA2 activity was measured using cPLA2 activity assay kit according to the manufacturer’s protocol. Briefly, SNU601 cells were lysed following incubation in normal or acidic pH medium, and total PLA2 activity was measured by incubating the samples with a substrate, arachidonoyl thio-PC, for 1 h at room temperature in the assay buffer. The reactions were stopped by adding dithiobis nitrobenzoic acid (DTNB)/EGTA. The absorbances were measured at a wavelength of 405 nm. Activity was represented as a fold increase.

RNA interference (RNAi). For the RNAi experiment, siRNAs of PLA2G4C (Gene ID:5321) and a scrambled siRNA control were purchased from Bioneer (Daejeon, Republic of Korea). SNU601 cells were individually transfected with siRNA oligonucleotides using an Amaxa™ Transfection System (Basel, Switzerland) and grown for 48 h in the normal pH or acidic pH medium.

Clonogenic assays. Cells incubated in normal or acidic pH medium for 24 h were trypsinized, washed, and re-plated (2,000 cells/60 mm dish). After an incubation of 14 days in a 37°C/5% CO2 incubator, colonies were fixed and stained using crystal violet.

Caspase-3 activity assays. Caspase-3 activity assay was carried out using the caspase-3/CPP32 colorimetric assay kit (K-106-100, BioVision, Milpitas, CA, USA), according to the manufacturer’s protocol. Briefly, 200 μg of protein lysates in a 50-μl volume was mixed with a reaction buffer, mixed with DEVD-pNA substrate, incubated for 90 min, and the absorbance at 405 nm measured. A fold increase in the activity was determined by comparing the results of the treated samples with the level of the untreated control.

Statistical analysis. All numerical data are presented as mean±SE of three independent experiments. For statistical analysis, student’s t-test was used for simple comparisons, and one-way ANOVA with Tukey’s test was used for multiple comparison test. A p-value of 0.05 or less was considered statistically significant.

Results

Acidic culture conditions increased PLA2 activity in GC cells. In our previous study, we observed that the gastric cancer cells that were cultured in acidic conditions increased the expression of COX proteins (15). COX is involved in lipid metabolite-mediated signaling pathway. Lipid metabolites generated through the PLA2-mediated arachidonic acid/COX pathway play critical roles in tumor progression and malignancy, and extracellular acidity is implicated in various malignant properties of tumors. Therefore, we questioned whether extracellular acidity can also affect the upstream lipid-mediated signaling that is linked to COX pathway. Initially, we examined if acidic conditions can activate the PLA2 enzyme that generates arachidonic acid, an essential lipid mediator that serves as a substrate for COX enzyme and initiates important lipid-mediated signaling. To assess PLA2 activity, SNU601 and AGS gastric cancer cells were exposed to normal (pH 7.4) and acidic (pH 6.4 and pH 6.0) medium for 48 h and 72 h, respectively and the activity of PLA2 was determined. As shown in Figure 1, exposure to acidic pH showed increased PLA2 activities in both gastric carcinoma cells. Therefore, PLA2 enzymes appear to be activated or up-regulated under acidic pH conditions in these cells.

Figure 1.
Figure 1.

Acidic culture conditions increase PLA2 activity. SNU601 and AGS cells exposed to normal (pH 7.4) or acidic (pH 6.4 and pH 6.0) medium for 48 h or 72 h, were analyzed for PLA2 activity. *p<0.05, **p<0.01 vs. pH 7.4.

Acidic pH conditions induced PLA2γ expression. Since acidic pH conditions increased the PLA2 activity in GC cells, we explored whether the acidity influences the expression of cellular PLA2 enzymes. At first, we examined the mRNA expression levels of cPLA2 isotypes in SNU601 and AGS cells that were cultured at normal and acidic pH medium for 72 h by performing real-time PCR analysis. Although cPLA2α is known to be the most important member of cPLA2 for eicosanoid generation, the mRNA level of PLA2G4A gene coding cPLA2α was rarely altered under acidic conditions (Figure 2A and F). We also examined the expression of other cPLA2 isoforms under acidic culture conditions. The mRNA level of JMJD7-PLA2G4B read-through which was previously reported to be overexpressed in several human cancer tissues, was not increased in the present study (Figure 2B and G). PLA2G4D and PLA2G4F mRNA levels were not altered in acidic culture environment (Figure 2D, E, I and J). The level of PLA2G4E was not detected in these conditions. However, the PLA2G4C level increased remarkably with an increase in acidity (Figure 2C and H). Consistently, acidic pH culture increased the cPLA2γ protein level, however, the protein levels of other members were either not altered or undetected in immunoblotting (Figure 2K and L). This result indicates that acidic pH conditions increase the expression of cPLA2γ in both SNU601 and AGS GC cells.

Figure 2.
Figure 2.

Extracellular acidity increases mRNA and protein levels of cPLA2γ. SNU601 (A-E, K) and AGS (F-J, L) cells maintained in normal (pH 7.4) or acidic (pH 6.4 and pH 6.0) medium were analyzed for mRNA expression of PLA2G4A (A and F), JMJD7-PLA2G4B (B and G), PLA2G4C (C and H), PLA2G4D (D and I), and PLA2G4F (E and J) by real-time PCR, or protein expression by immunoblotting using antibodies against cPLA2α, JMJD7-cPLA2β, cPLA2γ, cPLA2σ, and cPLA2ζ (K and L). **p<0.01 vs. pH 7.4.

Increased level of cPLA2γ under acidic conditions is associated with cell viability. To understand the role of cPLA2γ overexpression in acidic culture conditions, we performed gene interference analysis. We transfected SNU601 cells using siRNA, specifically targeting the PLA2G4C gene. Thereafter, cell viability was assessed under normal and acidic pH conditions by performing EZ-cytox assay. Silencing of PLA2G4C had a minor effect on the viability of SNU601 cells under normal culture medium, however, it significantly decreased the survival rate of the cells upon exposure to acidic (pH 6.4 and pH 6.0) culture medium (Figure 3A-C). Moreover, silencing of PLA2G4C reduced colony forming ability under acidic conditions, and not under normal pH conditions (Figure 3D). The silencing efficiency of the PLA2G4C siRNAs was confirmed by the reduced cPLA2γ protein levels under acidic pH culture conditions (Figure 3E). Therefore, an increased expression of cPLA2γ may play a role in protecting SNU601 cells from the cytotoxic effect triggered by the acidic environment.

Figure 3.
Figure 3.

Silencing of cPLA2γ reduced cell viability and clonogenicity under acidic culture conditions. (A-C) SNU601 cells were transiently transfected with scrambled small interfering RNA (Cont RNAi) or PLA2G4C RNAi, and exposed to the normal (A) or acidic growth medium (B, C) for 48 h. Cells were harvested and mRNA expression of the genes encoding cPLA2γ was analyzed through real-time PCR, or subjected to immunoblot analysis to confirm the silencing effect of PLA2G4C RNAi (E). (D) SNU601 cells were transiently transfected with scrambled small interfering RNA (Cont RNAi) or PLA2G4C RNAi, and incubated in the indicated pH medium for 24 h. Subsequently, cells (2,000) were then re-plated on 60-mm dishes and cultured to detect colony formation. Colonies were stained and counted at 2 weeks post-incubation. *p<0.05, **p<0.01.

Elevated levels of cPLA2γ are involved in acidity-mediated resistance to anticancer drugs. Acidic microenvironment has been implicated in the resistance of cancers to chemotherapeutic treatments (5, 16). Since acidic pH increased the expression of cPLA2γ that was involved in cell viability under acidic culture conditions, we examined whether cPLA2γ induction is also related to acidity-mediated resistance to chemotherapeutics. To examine this, the cells with silenced PLA2G4C gene were exposed to the anticancer drug, doxorubicin under normal pH (pH 7.4) or acidic pH (pH 6.0) medium for 24 h or 48 h, and cytotoxicity was detected at each time point of incubation. As shown in our previous study (17), sensitivity of cells to doxorubicin was much lower in acidic pH conditions than in normal pH conditions (Figure 4A-C). However, the knockdown of PLA2G4C gene increased the sensitivity to doxorubicin in acidic culture medium as assessed by cytotoxicity assay (Figure 4A and B). In addition, silencing of PLA2G4C gene significantly elevated doxorubicin-induced caspase-3 activity under acidic pH conditions (Figure 4C). The silencing efficiency of the PLA2G4C siRNAs was visualized by reduced cPLA2γ protein levels under acidic pH culture conditions (Figure 4D). Thus, an increase in cPLA2γ expression appears to be involved in acidity-mediated resistance to anticancer drugs by reducing apoptosis of tumor cells.

Figure 4.
Figure 4.

Expression of cPLA2γ is associated with acidity-mediated drug resistance. SNU601 cells were transiently transfected with scrambled small interfering RNA (Cont RNAi) or PLA2G4C RNAi, and exposed to the normal (pH 7.4) (A) or acidic (pH 6.0) (B) medium containing 0.5 μM or 1 μM doxorubicin for the indicated time points. Then cell viability was assessed through the EZ-cytox assay. (C) SNU601 cells transiently transfected with scrambled small interfering RNA (Cont RNAi) or PLA2G4C RNAi were incubated in the normal or acidic medium with or without 1 μM doxorubicin for 48 h, and cells were harvested and subjected to caspase-3 activity assay. (D) SNU601 cells transiently transfected with scrambled small interfering RNA (Cont RNAi) or PLA2G4C RNAi were incubated in the acidic (pH 6.0) medium for 48 h and subjected to immunoblot analysis to confirm the silencing effect. *p<0.05.

Discussion

Extracellular acidity confers a harsh tumor environment that inhibits the progression of cell cycle and stimulates apoptotic signaling. Among heterogeneous tumor cell populations, certain cells can adapt to this harsh environment through up-regulation of the defense system. Thereby, the cells that withstand this crisis will continue to proliferate to fill the space created by dead cells. Therefore, the acidic microenvironment is implicated in the selection of more resistant and malignant traits of the tumor. Consistent with this, we previously observed that gastric cancer cells exposed to acidic pH culture conditions were more invasive and resistant to chemotherapeutic drugs compared to cells that were cultured in normal pH (15, 17).

Resistance of cancer cell is related to multiple factors and among them, cellular defense system may be one of the important therapeutic targets. Herein, we identified a specific defense modulator stimulated in acidic environment. It is notable that the acidic microenvironment is implicated in the activation of inflammatory responses in various cell types, including immune cells, fibroblasts, and endothelial cells (18-20). Moreover, chronic inflammation is closely associated with tumor progression.

Lipid metabolism-associated pathways have been shown to play a crucial role in induction of cancer progression under metabolic stress (21). In addition, we previously observed that acidic culture environment increased the expression of COX proteins, which are activated by PLA2-mediated arachidonic acid signaling. Therefore, we questioned whether extracellular acidity can also affect the upstream lipid-mediated signaling, such as PLA2 pathway. Indeed, critical role cPLA2 is implicated in pulmonary tumor metastasis (22).

In the present study, we explored the possible effects of acidic pH on the activation of upstream lipid signaling mediator; PLA2 activity was found to increase in response to acidity. Moreover, investigation of the levels of the cytosolic PLA2 isoform showed a significant increase in cPLA2γ in response to acidic culture conditions.

When we examined the role of cPLA2γ using the gene silencing analysis, it seemed to play protective roles under acidic pH environment as indicated by decrease in cell viability and clonogenicity. Furthermore, elevation of cPLA2γ was linked to drug sensitivity under acidic pH conditions, and consequently, the cellular response to doxorubicin was increased in PLA2γ-silenced cells. However, knockdown of cPLA2γ had no effect on viability and drug-responses in the cells at normal pH. This might be attributed to the fact that the cells had low expression of cPLA2γ at normal pH conditions. cPLA2γ was shown to possess similar catalytic activity as cPLA2α because the catalytic domain is conserved in both enzymes (9). Hence, cPLA2γ may contribute to the biosynthesis of lipid metabolites through arachidonic acid generation, thereby participating in various malignant phenotypes of cancer. This is in agreement with our results that showed that acidity-mediated cPLA2γ expression contributes to malignant phenotypes, such as increase in cell survival and resistance to stressful stimuli. Moreover, the enzymatic analyses of cPLA2γ by various studies have shown that it possesses lysophospholipase and transacylation activities in addition to phospholipase A2 activity (23, 24). Therefore, cPLA2γ may be able to contribute to lipid signaling through lysophospholipase and transacylation activities. The exact role of cPLA2γ is still not understood, however, a positive association with cancer has been suggested in recent studies. Suppression of cPLA2γ through gene silencing-induced apoptosis of rat mammary tumor cells by NFkB/lipocalin 2 pathway (25), and SNP of cPLA2γ was linked to a worse prognosis in patients with CRC (26).

Nevertheless, cPLA2γ has a distinct regulatory mechanism from cPLA2α because of several differences in structure, distribution, and regulation. cPLA2α is ubiquitously expressed in mammalian tissues, however, the human cPLA2γ mRNA is predominantly found in cardiac and skeletal muscle, and to a lesser extent in brain (14). In addition, lack of the regulatory phosphorylation sites and C2 domain are the structural features of cPLA2γ that are important for association to the membrane and critical for activity of cPLA2α. Another obvious difference in regulatory mechanism is that cPLA2γ is calcium-independent, while other members of cytosolic PLA2s are all calcium-dependent. The calcium independence of this enzyme appears to be an important feature to be used in acidic environments because extracellular acidity increases large fluxes in calcium concentrations (27). Conclusively, based on the findings of the present study, we suggest that cPLA2γ could be an important therapeutic target for resistant cancer cells under acidic environment. Moreover, further study of the mechanism of cPLA2γ expression and activation may provide an effective strategy to overcome extracellular acidity-mediated cancer resistance.

Acknowledgements

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1D1A1 A01060533 and NRF-2018R1D1A1B07046430). We would like to thank Dr. Mi-Rae Lee and Dr. Hyoin Hwang for their excellent technical assistance.

Footnotes

  • ↵* These Authors contributed equally to this study.

  • Authors’ Contributions

    Conceptualization, SIH, TBL and BSK; methodology and writing, SCL and SIH; review and editing, all Authors.

  • Conflicts of Interest

    The Authors declare no conflicts of interest.

  • Received November 13, 2020.
  • Revision received December 1, 2020.
  • Accepted December 2, 2020.

References

  1. ↵
    1. Bray F,
    2. Ferlay J,
    3. Soerjomataram I,
    4. Siegel RL,
    5. Torre LA and
    6. Jemal A
    : Global cancer statistics 2018: Globocan estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin 68(6): 394-424, 2018. PMID: 30207593. DOI: 10.3322/caac.21492
    OpenUrlCrossRefPubMed
  2. ↵
    1. Justus CR,
    2. Dong L and
    3. Yang LV
    : Acidic tumor microenvironment and ph-sensing g protein-coupled receptors. Front Physiol 4: 354, 2013. PMID: 24367336. DOI: 10.3389/fphys.2013.00354
    OpenUrlCrossRefPubMed
  3. ↵
    1. Brisson L,
    2. Reshkin SJ,
    3. Gore J and
    4. Roger S
    : Ph regulators in invadosomal functioning: Proton delivery for matrix tasting. Eur J Cell Biol 91(11-12): 847-860, 2012. PMID: 22673002. DOI: 10.1016/j.ejcb.2012.04.004
    OpenUrlCrossRefPubMed
  4. ↵
    1. Tannock IF and
    2. Rotin D
    : Acid ph in tumors and its potential for therapeutic exploitation. Cancer Res 49(16): 4373-4384, 1989. PMID: 2545340.
    OpenUrlAbstract/FREE Full Text
  5. ↵
    1. Taylor S,
    2. Spugnini EP,
    3. Assaraf YG,
    4. Azzarito T,
    5. Rauch C and
    6. Fais S
    : Microenvironment acidity as a major determinant of tumor chemoresistance: Proton pump inhibitors (ppis) as a novel therapeutic approach. Drug Resist Updat 23: 69-78, 2015. PMID: 26341193. DOI: 10.1016/j.drup.2015.08.004
    OpenUrlCrossRefPubMed
  6. ↵
    1. Raghunand N and
    2. Gillies RJ
    : Ph and drug resistance in tumors. Drug Resist Updat 3(1): 39-47, 2000. PMID: 11498364. DOI: 10.1054/drup.2000.0119
    OpenUrlCrossRefPubMed
  7. ↵
    1. Funk CD
    : Prostaglandins and leukotrienes: Advances in eicosanoid biology. Science 294(5548): 1871-1875, 2001. PMID: 11729303. DOI: 10.1126/science.294.5548.1871
    OpenUrlAbstract/FREE Full Text
  8. ↵
    1. Burke JE and
    2. Dennis EA
    : Phospholipase a2 structure/function, mechanism, and signaling. J Lipid Res 50 Suppl: S237-242, 2009. PMID: 19011112. DOI: 10.1194/jlr.R800033-JLR200
    OpenUrlCrossRef
  9. ↵
    1. Murakami M,
    2. Masuda S and
    3. Kudo I
    : Arachidonate release and prostaglandin production by group ivc phospholipase a2 (cytosolic phospholipase a2gamma). Biochem J 372(Pt 3): 695-702, 2003. PMID: 12611587. DOI: 10.1042/BJ20030061
    OpenUrlCrossRefPubMed
  10. ↵
    1. Ohto T,
    2. Uozumi N,
    3. Hirabayashi T and
    4. Shimizu T
    : Identification of novel cytosolic phospholipase a(2)s, murine cpla(2){delta}, {epsilon}, and {zeta}, which form a gene cluster with cpla(2){beta}. J Biol Chem 280(26): 24576-24583, 2005. PMID: 15866882. DOI: 10.1074/jbc.M413711200
    OpenUrlAbstract/FREE Full Text
  11. ↵
    1. Tosato G,
    2. Segarra M and
    3. Salvucci O
    : Cytosolic phospholipase a2{alpha} and cancer: A role in tumor angiogenesis. J Natl Cancer Inst 102(18): 1377-1379, 2010. PMID: 20729476. DOI: 10.1093/jnci/djq324
    OpenUrlCrossRefPubMed
  12. ↵
    1. Stewart A,
    2. Ghosh M,
    3. Spencer DM and
    4. Leslie CC
    : Enzymatic properties of human cytosolic phospholipase a(2)gamma. J Biol Chem 277(33): 29526-29536, 2002. PMID: 12039969. DOI: 10.1074/jbc.M204856200
    OpenUrlAbstract/FREE Full Text
  13. ↵
    1. Pickard RT,
    2. Strifler BA,
    3. Kramer RM and
    4. Sharp JD
    : Molecular cloning of two new human paralogs of 85-kda cytosolic phospholipase a2. J Biol Chem 274(13): 8823-8831, 1999. PMID: 10085124. DOI: 10.1074/jbc.274.13.8823
    OpenUrlAbstract/FREE Full Text
  14. ↵
    1. Underwood KW,
    2. Song C,
    3. Kriz RW,
    4. Chang XJ,
    5. Knopf JL and
    6. Lin LL
    : A novel calcium-independent phospholipase a2, cpla2-gamma, that is prenylated and contains homology to cpla2. J Biol Chem 273(34): 21926-21932, 1998. PMID: 9705332. DOI: 10.1074/jbc.273.34.21926
    OpenUrlAbstract/FREE Full Text
  15. ↵
    1. Lim SC,
    2. Hwang H and
    3. Han SI
    : Ellagic acid inhibits extracellular acidity-induced invasiveness and expression of cox1, cox2, snail, twist 1, and c-myc in gastric carcinoma cells. Nutrients 11(12), 2019. PMID: 31835645. DOI: 10.3390/nu11123023
    OpenUrlCrossRef
  16. ↵
    1. Thews O,
    2. Gassner B,
    3. Kelleher DK,
    4. Schwerdt G and
    5. Gekle M
    : Impact of hypoxic and acidic extracellular conditions on cytotoxicity of chemotherapeutic drugs. Adv Exp Med Biol 599: 155-161, 2007. PMID: 17727260. DOI: 10.1007/978-0-387-71764-7_21
    OpenUrlCrossRefPubMed
  17. ↵
    1. Hong R and
    2. Han SI
    : Extracellular acidity enhances tumor necrosis factor-related apoptosis-inducing ligand (trail)-mediated apoptosis via dr5 in gastric cancer cells. Korean J Physiol Pharmacol 22(5): 513-523, 2018. PMID: 30181698. DOI: 10.4196/kjpp.2018.22.5.513
    OpenUrlCrossRefPubMed
  18. ↵
    1. Riemann A,
    2. Ihling A,
    3. Thomas J,
    4. Schneider B,
    5. Thews O and
    6. Gekle M
    : Acidic environment activates inflammatory programs in fibroblasts via a camp-mapk pathway. Biochim Biophys Acta 1853(2): 299-307, 2015. PMID: 25461841. DOI: 10.1016/j.bbamcr.2014.11.022
    OpenUrlCrossRef
    1. Dong L,
    2. Li Z,
    3. Leffler NR,
    4. Asch AS,
    5. Chi JT and
    6. Yang LV
    : Acidosis activation of the proton-sensing gpr4 receptor stimulates vascular endothelial cell inflammatory responses revealed by transcriptome analysis. PLoS One 8(4): e61991, 2013. PMID: 23613998. DOI: 10.1371/journal.pone.0061991
    OpenUrlCrossRefPubMed
  20. ↵
    1. Etulain J,
    2. Negrotto S,
    3. Carestia A,
    4. Pozner RG,
    5. Romaniuk MA,
    6. D’Atri LP,
    7. Klement GL and
    8. Schattner M
    : Acidosis downregulates platelet haemostatic functions and promotes neutrophil proinflammatory responses mediated by platelets. Thromb Haemost 107(1): 99-110, 2012. PMID: 22159527. DOI: 10.1160/TH11-06-0443
    OpenUrlCrossRefPubMed
  21. ↵
    1. Neagu M,
    2. Constantin C,
    3. Popescu ID,
    4. Zipeto D,
    5. Tzanakakis G,
    6. Nikitovic D,
    7. Fenga C,
    8. Stratakis CA,
    9. Spandidos DA and
    10. Tsatsakis AM
    : Inflammation and metabolism in cancer cell-mitochondria key player. Front Oncol 9: 348, 2019. PMID: 31139559. DOI: 10.3389/fonc.2019.00348
    OpenUrlCrossRefPubMed
  22. ↵
    1. Jeong WC,
    2. Kim KJ,
    3. Ju HW,
    4. Back HK,
    5. Kim HK,
    6. Im SY and
    7. Lee HK
    : Cytoplasmic phospholipase a2 metabolites play a critical role in pulmonary tumor metastasis in mice. Anticancer Res 30(9): 3421-3427, 2010. PMID: 20944117.
    OpenUrlAbstract/FREE Full Text
  23. ↵
    1. Yamashita A,
    2. Tanaka K,
    3. Kamata R,
    4. Kumazawa T,
    5. Suzuki N,
    6. Koga H,
    7. Waku K and
    8. Sugiura T
    : Subcellular localization and lysophospholipase/transacylation activities of human group ivc phospholipase a2 (cpla2gamma). Biochim Biophys Acta 1791(10): 1011-1022, 2009. PMID: 19501189. DOI: 10.1016/j.bbalip.2009.05.008
    OpenUrlCrossRefPubMed
  24. ↵
    1. Asai K,
    2. Hirabayashi T,
    3. Houjou T,
    4. Uozumi N,
    5. Taguchi R and
    6. Shimizu T
    : Human group ivc phospholipase a2 (cpla2gamma). Roles in the membrane remodeling and activation induced by oxidative stress. J Biol Chem 278(10): 8809-8814, 2003. PMID: 12502717. DOI: 10.1074/jbc.M212117200
    OpenUrlAbstract/FREE Full Text
  25. ↵
    1. Nanashima N,
    2. Yamada T,
    3. Shimizu T and
    4. Tsuchida S
    : Deletion of phospholipase a2 group ivc induces apoptosis in rat mammary tumour cells by the nuclear factor-kappab/lipocalin 2 pathway. Biochem J 469(2): 315-324, 2015. PMID: 26013918. DOI: 10.1042/BJ20150064
    OpenUrlAbstract/FREE Full Text
  26. ↵
    1. Olsen RS,
    2. Andersson RE,
    3. Zar N,
    4. Lofgren S,
    5. Wagsater D,
    6. Matussek A and
    7. Dimberg J
    : Prognostic significance of pla2g4c gene polymorphism in patients with stage ii colorectal cancer. Acta Oncol 55(4): 474-479, 2016. PMID: 26364726. DOI: 10.3109/0284186X.2015.1073350
    OpenUrlCrossRefPubMed
  27. ↵
    1. Noguchi F,
    2. Inui S,
    3. Fedele C,
    4. Shackleton M and
    5. Itami S
    : Calcium-dependent enhancement by extracellular acidity of the cytotoxicity of mitochondrial inhibitors against melanoma. Mol Cancer Ther 16(5): 936-947, 2017. PMID: 28223427. DOI: 10.1158/1535-7163.MCT-15-0235
    OpenUrlAbstract/FREE Full Text
Back to top

In this issue

Print
Download PDF
Article Alerts
Email Article
Citation Tools
Reprints and Permissions
Extracellular Acidity-mediated Expression of cPLA2γ Confers Resistance in Gastric Cancer Cells
SUNG-CHUL LIM, TAE-BUM LEE, BYUNG-SOO KANG, SONG IY HAN
Anticancer Research Jan 2021, 41 (1) 211-218; DOI: 10.21873/anticanres.14767
Twitter logo Facebook logo Mendeley logo

Jump to section

Keywords