Background
Gastric cancer (GC) is one of the most common malignant diseases globally, with a fifth-place incidence and fourth-place mortality in 2021 [
1]. The 5-year survival of GC remains below 25%, with lymph node metastasis occurring in over 10% of early-stage cases [
2]. The pathogenesis of GC is complex and remains incompletely elucidated. Key factors influencing GC development include
Helicobacter pylori (
H. pylori) infection, tumor microenvironment (TME), host polymorphisms, and gene expression disorders. Of these,
H. pylori infection is the strongest risk factor [
3]. In 2018,
H. pylori infection was estimated to be responsible for approximately 89% of new non-cardia GC cases and 20% of new cardia GC cases. [
4]. The gastric mucosa of over half the world's population is colonized by
H. pylori, which can cause chronic inflammation, ulcers, and even cancer if not completely eradicated [
5].
Several studies have demonstrated a correlation between GC and
H. pylori infection. For example,
H. pylori induces genetic and epigenetic alterations via chronic inflammation, leading to GC development [
6,
7].
H. pylori degrades tumor suppressor or activates oncogene to accelerate cell division and tumorigenic transformation and, ultimately, gastric carcinogenesis [
8,
9]. Additionally,
H. pylori disrupts cell tight junctions to induce epithelial-to-mesenchymal transition via downregulating adhesion molecules IQGAP1 and Afadin in gastric cells [
10,
11].
H. pylori also promotes cancer cell stemness by activating the NF-кB, ERK, JNK, and Hippo pathways [
12]. Despite all this, the molecular mechanism underlying
H. pylori's promotion of GC development remains incompletely understood. Consequently, researchers have recently focused on investigating the influence of
H. pylori on TME in the stomach.
TME consists of diverse cellular components, including normal fibroblasts, cancer-associated fibroblasts (CAFs), immune cells, endothelial cells, etc., soluble molecules like chemokines, enzymes, cytokines, etc., and extracellular matrix (ECM). Notably, the interaction between fibroblasts and cancer cells not only promotes tumor development but also triggers the activation of fibroblasts [
13]. The study by Krzysiek-Maczka and co-authors demonstrated that the infection with
H. pylori induced the activation of gastric fibroblasts, leading to the induction of epithelial-to-mesenchymal transition in gastric RGM-1 cells through the secretion of transforming growth factor [
14]. Furthermore, infection with
H. pylori elevated the expression of VCAM1 in CAFs to promote GC cell invasion via the JAK/STAT1 pathway [
15]. In our recent study [
16], we reported that the association among
H. pylori, normal fibroblasts, and GC cells induced the activation of fibroblast into CAFs and upregulation of Serpin family E member 1 (Serpin E1) by GC cells, thereby promoting gastric carcinogenesis. However, it remains unclear whether Serpin E1 is produced by fibroblasts or cancer cells in the inflammatory microenvironment induced by
H. pylori, and the underlying mechanism by which Serpin E1 promotes GC development remains elusive.
In physiological conditions, Serpin E1 (also called PAI-1) is found in plasma at low concentrations, ranging from 5 to 50 ng/mL, in its active conformation. Conversely, it is predominantly retained in platelets at significantly higher levels (about 300 ng/mL) in its latent conformation, exhibiting only 2–5% functional activity [
17]. Upon platelet activation, Serpin E1 was converted into active form and released into plasma to trigger the plasminogen/plasmin system through the inhibition of tissue- and urokinase-type plasminogen activators (uPA and tPA) [
18]. As a direct inhibitor of tPA and uPA, Serpin E1 prevents plasminogen activation and fibrin clot degradation, thereby contributing to thrombosis development in pathological conditions associated with cardiovascular disease [
19]. In addition, uPA-mediated plasminogen activation can induce pericellular proteolysis, tissue remodeling, and cell migration that favor tumor development [
17]. Therefore, it is plausible that Serpin E1 may exert anti-tumor effects. However, recent studies find that Serpin E1 is overexpressed in certain forms of tumor and exhibits a positive correlation with tumor progression [
20]. Growth factors, chemokines, and environmental stress, directly and indirectly, regulate Serpin E1 expression [
21]. It should be noted that most of these findings were primarily derived from investigations involving epithelial cancer cells.
The present study revealed that Serpin E1 was primarily expressed in CAFs, and its expression and secretion were enhanced upon infection with H. pylori, which further induced the expression of Serpin E1 in GC cells through their interaction. Serpin E1 derived from these cells and recombinant human Serpin E1 (recSerpin E1, 140–04, PeproTech, USA) activated chemotactic migration and p38 mitogen-activated protein kinase (MAPK) / vascular endothelial growth factor (VEGF) A-mediated angiogenesis of endothelial cells, thereby promoting GC cell proliferation and peritoneal dissemination. Here, our results uncover a novel mechanism underlying the development and progression of H. pylori-induced GC.
Materials and methods
H. pylori strain and cell lines
The East Asian strain
H. pylori GZ7 (
cagA +) was previously isolated from a Chinese patient with GC [
22]. The AGS human GC cell line (CRL-1739) and Hs738 human gastric fibroblast cell line (CRL-7869) were obtained from the American Type Culture Collection (ATCC, USA). Human GC cell line (MKN45) and the umbilical vein endothelial cells (HUVECs) were purchased from the Shanghai Cell Bank of the Chinese Academy of Sciences (Shanghai, China). Three primary CAFs and GC cells from the same patients with GC were previously isolated from resected GC tissues [
16]. All cells and strains were tested to eliminate the possibility of mycoplasma contamination. Informed consent was obtained from all patients, and the research was approved by Guizhou Medical University (No. 2017(43)).
H. pylori was cultured on Columbia blood agar plates supplemented with 10% sheep blood and 100 U/ml of H. pylori selective supplement (Oxoid, Basingstoke, UK) in a microaerobic environment with a temperature of 37 °C. All cells were grown in DMEM (D6429, Sigma, USA) supplemented 10% fetal bovine serum (FBS, #16000–044, Gibco, USA) and 1% penicillin–streptomycin (SV30010, Hyclone, USA).
Knockdown of Serpin E1
The siRNA targeting Serpin E1 (siSerpin E1) and control scrambled siRNA (siNC) were obtained from GenePharma Co., Ltd. (Shanghai, China). CAFs (2 × 105 cells) were grown in a 6-well plate and transfected with siSerpin E1 and siNC with Lipofectamine 2000 (#11668019, Invitrogen, Waltham, MA). Forty-eight hours later, the cells were harvested for western blotting and RT-qPCR analysis to determine Serpin E1expression. The sequence for siSerpin E1 (5′–3′) was as follows: GCUCAGACCAACAAGUUCATT; while that of siNC (5′–3′) was: UUCUUCGAACGUGUCACG UTT.
Construction of Serpin E1 lentivirus vector and generation of stable cell lines
Lentiviral vector expressing Serpin E1-enhanced green fluorescent protein (EGFP, non-fusion) and an EGFP-expressing control vector was constructed by JiKai Gene Company (Shanghai, China). Briefly, the human coding sequence (CDS) of Serpin E1(NM_000602) was obtained from the GenBank and synthesized with AgeI and NheI restriction enzyme sites at the two terminals. After restriction digestion with AgeI and NheI, the Serpin E1 CDS was ligated into the GV367 plasmid (Ubi-(AgeI)MCS(NheI)-SV40-EGFP-IRES-puromycin, Ji Kai), followed by transformation into E. coli DH5α. Subsequently, DH5α cells were cultured, and recombinant plasmid DNA was extracted for identification through sequencing. After successful construction of the recombinant GV367 lentiviral vector, GV367 and helper 1.0 and helper 2.0 (auxiliary packaging plasmids, obtained from JiKai Company) co-transfected into 293T cells using Lipofectamine TM 2000. Seventy-two hour later, the supernatant of the 293T cells was collected and purified by ultracentrifugation to obtain lentiviral particles carrying Serpin E1. Finally, viral titers were determined using a Luminescent assay.
Subsequently, CAFs and Hs738 cells (2 × 104) were infected with Serpin E1-EGFP lentivirus and an EGFP-expressing control lentivirus. After 12 h, the culture medium was replaced. Once an infection efficiency of over 90% was reached through microscopic observation of EGFP fluorescence, puromycin (3 μg/ml) was introduced for selection in the cultures. Following a two-week period, stable cell lines overexpressing Serpin E1 were established for subsequent detection of Serpin E1 expression.
Western blotting
The western blotting procedure was conducted according to standard protocols. Cells were lysed for 10 min with RIPA lysis solution (89,901, ThermoFisher, USA) supplemented with 1% protease inhibitors (#11873580001, Roche, USA). Subsequently, the lysates were subjected to electrophoresis in 12% SDS-PAGE gels after boiling at 100 °C for 10 min. The proteins were transferred to a PVDF membrane (Millipore, USA). The membranes were then pretreated with nonfat milk and subsequently incubated with primary and secondary antibodies. Protein bands were detected using ECL luminescent solution (Millipore), followed by quantification using Image J software. The detailed information regarding the antibodies utilized can be found in Additional file
1: Table S1.
Immunohistochemistry (IHC)
Subcutaneous xenograft tumors and intraperitoneal tumors were excised from nude mice that were killed by an overdose of anesthesia. The tumors were fixed in 10% formalin, followed by paraffin embedding and sectioning into 5-μm thick slices. Deparaffinization of the slices was performed using xylene, followed by rehydration with a series of increasing ethanol concentrations. Antigen retrieval was achieved through high-pressure treatment in 0.01 M citrate buffer (pH 6.0), while endogenous peroxidases were inhibited using 3% H
2O
2. After that, the slices were incubated at 4 ℃ overnight with primary antibodies, including Ki67, Serpin E1, CD31, and VEGFA, followed by a 2-h incubation with HRP-conjugated secondary antibodies at room temperature. The signals were then visualized with a DAB kit (ab64238, Abcam, UK), The DAB-visualized slices were counterstained in hematoxylin, acid alcohol, and deionized water in sequential order. Subsequently, the slices underwent dehydrated in graded ethanol and cleared with xylene. Microscopic image was captured. Staining was quantified with Image J analysis software, and IHC score was determined by multiplying the percentage score with the intensity score. Details of antibodies used for immunohistochemistry are provided in Additional file
1: Table S1.
Immunofluorescence
Cells, including H. pylori-infected CAFs, HUVECs co-cultured indirectly with Hs738 overexpressing Serpin E1, and recSerpin E1-treated HUVECs, were grown in 24-well plates on a cover slide for 72 h and fixed using 4% paraformaldehyde. Following permeabilization with 0.3% Triton X-100 and blocking with 5% BSA (#15260037, ThermoFisher), anti-Serpin E1 and anti-VEGFA antibodies were added to the slide overnight at 4 °C. This cover slide was then treated using a secondary antibody conjugated to fluorochrome for 2 h, and cell nucleus was stained by DAPI. Following images were taken, the integrated immunofluorescence (IF) intensity was quantified using Image J software.
For polychromatic immunofluorescent staining, tumor tissues from nude mice were fixed in 4% paraformaldehyde, embedded in paraffin, and sectioned into slices with a thickness of 5 cm. Then, the slices were stained with a four-color multiplex fluorescence immunohistochemical staining kit (abs50012, Absin) following the manufacturer's instructions. After dewaxing, clearing, and rehydrating steps, microwave-assisted antigen retrieval was performed using a sodium citrate buffer, followed by blocking of endogenous peroxidase activity with 0.3% H
2O
2 and washing with TBST containing 5% goat serum. Next, the slices were incubated with primary antibodies and subsequently treated with HRP-labeled secondary antibodies (goat anti-rabbit/mouse). The slices were developed using the fluorescent dye provided in the kit. Subsequently, the slices underwent another round of antigen retrieval step followed by incubation with another primary antibody until complete antigen staining was achieved. Finally, nuclear visualization was achieved by counterstaining the slices with DAPI. Confocal images were acquired using a confocal microscope, and relative fluorescence intensity was quantified utilizing Image J software. The details of antibodies used can be found in Additional file
1: Table S1.
Human cytokine array
After infecting CAFs with
H. pylori for 6 h at an MOI of 50, the free and dead
H. pylori were thoroughly washed with PBS. The cultures were continued for another 7 days. The supernatants from CAFs with or without
H. pylori infection were collected to determine cytokine levels using a Proteome Profiler Human Cytokine Array Kit (ARY005B, R&D Systems, USA), comprising 36 cytokines, following the manufacturer’s protocol. Briefly, the arrays spotted on nitrocellulose membranes were blocked at room temperature for 1 h with blocking buffer. Concurrently, the cell supernatants and a cocktail of biotinylated detection antibody were mixed and incubated for 1 h at room temperature, followed by overnight incubation at 4 °C with the membrane. Subsequently, the membranes were incubated with HRP-conjugated streptavidin at room temperature for 30 min, followed by exposure to ECL substrate (Promega, USA). Blots were visualized by chemiluminescence utilizing ECL. A comprehensive list of human cytokines included in this array refer to our previous publication [
16].
Cell Counting Kit-8 (CCK-8) assay
GC cells (0.5 × 104) treated with recSerpin E1 (1 and 10 ng/ml) were grown in 96-well plates. After culturing for different time points, 10μl CCK-8 (CK04, Dojindo, Japan) were added to each well. The absorbance at 450 nm was measured after a two-hours incubation at 37 °C.
CAFs (4.5 × 103) were mixed with AGS cells (5 × 102) at a 9:1 ratio and seeded in 12-well plates. Alternatively, GC cells treated with recSerpin E1 were plated in 6-well plates. Following a 15-day incubation at 37 °C, cell colonies were stained with 0.5% crystal violet solution and counted. In the co-culture system, only cancer cells have the capacity to form colonies, whereas CAFs exhibited loose growth. Consequently, the colony number represents the proliferative ability of cancer cells.
Transwell assay
In 24-well plates, Serpin E1 knockdown CAFs (1 × 105), Serpin E1 overexpression CAFs (1 × 104), and recSerpin E1 (1ng/ml) were added to the lower chamber of Transwell inserts. GC cells (0.5–1 × 104) were seeded to the upper chamber with or without Matrigel (#356234, Corning, NY, USA). After 48 h of co-culture for invasion assays and 24 h for migration assays or treatment with recSerpin E1 for 72 h, the migrated and invaded cells on the lower surface of the membrane were fixed by 4% paraformaldehyde solution, stained by 0.1% crystal violet, and counted from five randomly selected fields.
In vivo tumorigenesis assay
The animal research protocol was approved by Guizhou Medical University's animal ethics committee (No: 1702155). Primary GC cells (1 × 106) and CAFs or Hs738 cells (4 × 106) stably expressing Serpin E1-EGFP (non-fusion) or EGFP (Control) were mixed at a ratio of 1:4 in 250 μl of PBS and subsequently subcutaneously and peritoneally injected into male nude mice (4-week-old, n = 3 or 5 per group) obtained from Chongqing Tengxin Biotechnology (China). Subcutaneous tumor growth was assessed by monitoring tumor volume (V = 1/2 × length × width2) every two days. On the 24th or 28th day after cell injection, all mice were killed with an excessive dosage of anesthesia using 1% pentobarbital sodium at a dosage of 100 mg/kg (intraperitoneal injection), and both subcutaneous tumors and peritoneal tumor nodules were collected for HE, IHC, and immunofluorescence staining.
Chemotaxis assay
In a 6-well plate, CAFs or Hs738 cells were incubated with H. pylori for 6 h at 50 MOI. Subsequently, the medium was exchanged for fresh medium to eliminate any free or dead bacteria. Matrigel was diluted in a ratio of 1:8 with DMEM and loaded onto an 8 μm pore size membrane in the upper chamber of Transwell inserts, which were placed within a 24-well plate. Following Matrigel polymerization, HUVECs (1 × 104) were seeded on top of the Matrigel, and fibroblasts, either infected or uninfected with H. pylori, their respective conditioned medium (diluted by half using fresh medium), and recSerpin E1 (1 ng/ml) were added into the lower chambers. After incubation for 48–72 h, the Transwell inserts were removed and fixed. The migrated HUVECs were stained with 0.1% crystal violet and counted.
Matrigel was diluted 1:4 with DMEM and incubated at 37 °C for 2 h in a 12-well plate or the Transwell lower chamber within a 24-well plate. After polymerization of the Matrigel, HUVECs suspended in DMEM (10% FBS) were seeded on top of the Matrigel in each plate. Subsequently, recSerpin E1 (1 ng/ml) and an anti-Serpin E1 antibody (2 μg/ml) were added into each well with a time interval of 6 h in the 12-well plate. Alternatively, Serpin E1-overexpressed CAFs (1 × 105) were grown in the upper chamber with a membrane of 0.4-μm pore size (preventing cellular migration through the membrane) in a 24-well plate. After incubation for 24 or 72 h, the formation of tubular structures by HUVECs in tissue culture plates or the lower Transwell chambers was observed and documented using an inverted microscope. The mean length and branch point of tubes from three independent wells were quantified using Image J software.
Enzyme-linked immunosorbent assay (ELISA)
CAFs were grown in 6-well plates and infected with H. pylori for 6 h. Free-floating bacteria were eliminated by washing with PBS. After 3 days, the culture supernatant was collected to determine Serpin E1 levels using a human Serpin E1 ELISA kit (EK1136, MultiSciences, China). Alternately, HUVECs were co-cultured with Serpin E1-overexpressed or control Hs738 cells in both direct and indirect co-culture systems, where CAFs were grown in the upper chambers of Transwell insert and HUVECs in the lower chambers. After 48 h, the culture supernatants were collected to determine VEGFA levels using a human VEGFA ELISA kits (EK183, MultiSciences).
Statistical analysis
The analyses of the data were performed by the SPSS 16.0 software. Image J software was employed to analyze the images from tube formation and IHC experiments. GraphPad Prism 5 was used for graph generation. An unpaired two-tailed Student’s t-test was utilized to compare the two groups, while two-way and one-way analysis of variance were employed to compare multiple groups. Each experiment underwent a minimum of three repetitions. All images shown were representative images from three independent tests or samples. Data is represented as mean ± standard deviation, with statistically significant defined as p < 0.05.
Discussion
The infection with
H. pylori stimulates the production and secretion of chemokines and cytokines by epithelial cells into the ECM, thereby contributing to tumor initiation and progression. However, Serpin E1 has received limited attention in this context. Microarray and RNA sequencing data analysis from GC tissues revealed that Serpin E1 was overexpressed in cancer tissues compared to peri-cancer tissues, and its overexpression was related to poorer patient survival [
27]. Suh et al. [
28] reported that Serpin E1 was upregulated over twofold in GC patients with advanced stages and lymph node metastases. Previous studies primarily focused on Serpin E1 expression in cancer cells [
29]. However, the present study demonstrates that Serpin E1 expression is predominantly found in CAFs rather than cancer cells in GC tissues from the same patients, and
H. pylori infection specifically promotes the expression of Serpin E1 in CAFs.
The expression of Serpin E1 in
H. pylori-infected CAFs was found to be independent of other chemokines and cytokines, despite the known regulation of Serpin E1 transcription by transforming growth factor-beta 1 (TGF-b1), interleukin (IL)-6, and tumor necrosis factor (TNF)-α, in renal and adipose tissues [
30,
31]. Our study, using a human cytokine array consisting of 36 chemokines and cytokines such as IL-6, TNF, IL-8, and others, revealed that only Serpin E1, MIF, IL-8, and CXCL1 were detected in the supernatant of
H. pylori-infected CAFs. Notably, among these factors examined, Serpin E1 exhibited the highest abundance, suggesting a directly stimulation of its production by CAFs upon
H. pylori infection. This finding is partially supported by Keates et al. [
32], who reported that soluble factors from media separated from bacteria using a 0.1-μm filter did not affect the release of Serpin E1 by AGS cells.
Our study, including previous research [
16], confirms that the interaction between fibroblasts and GC cells induces the expression of Serpin E1 in cancer cells. Importantly, the overexpression of Serpin E1 in fibroblasts has the strongest induction effects despite its low expression in GC cells in vitro. Furthermore, the overexpression of Serpin E1 in both fibroblast and GC cell enhance cancer cell proliferation, invasion, and migration in vitro, as well as subcutaneous tumor growth and/or intraperitoneal dissemination in nude mice. Conversely, knocking down Serpin E1 in fibroblasts exhibits the opposite effect in vitro. Similar results are also obtained when treating GC cells with recSerpin E1. Collectively, our findings reveal that
H. pylori infection promotes Serpin E1 expression in fibroblasts, which then interact with GC cells to induce its expression in cancer cells, thereby jointly contributing to GC development and progression. However, the underlying mechanism remains unclear.
Serpin E1 has three distinct conformational states that are determined by the state of its reactive center loop (RCL) state: a metastable active form with an intact RCL exposed at the molecule surface, capable of binding to and inhibiting uPA/tPA activity; a stable latent form with an internalized and intact RCL within the protein core; and a cleaved form with a disrupted RCL [
33]. Based on its structure characteristics, Serpin E1 interacts with uPA/tPA, vitronectin, and lipoprotein receptor through distinct domains [
20]. The interaction between Serpin E1 and vitronectin stabilizes the active conformation of Serpin E1 by slowing the conversion of active to latent form, thereby modulating vitronectin and plasmin activity for ECM remodeling and promotion of angiogenesis in vivo [
34]. However, in vitro experiments lacking ECM have shown that
H. pylori infection, fibroblast- or GC cell-derived Serpin E1, and recSerpin E1 exert chemotactic and pro-proliferative effects on HUVECs, as well as stimulating tube formation of HUVECs in the present study. The findings suggest the involvement of alternative mechanism in Serpin E1-induced angiogenesis.
VEGFA serves as a key regulator of tumor angiogenesis, exerting precise control over the migration, proliferation, and vascular permeability of vascular endothelial cells. In malignancies, it is synthesized by diverse types of cells such as tumor and stromal cells like endothelial cells [
35]. Hypoxia-inducible factor 1α and inflammatory cytokines like TNFα and interleukins have been demonstrated to induce VEGFA transcription [
36]. Here, we found that Serpin E1, a new inflammatory cytokine secreted by fibroblasts and GC cells upon
H. pylori infection, enhanced VEGFA expression and secretion, as well as tube information in HUVECs. This result was further supported by treating HUVECs with recSerpin E1. Moreover, blocking Serpin E1 using an anti-Serpin E1 antibody effectively suppressed recSerpin E1-mediated increases in VEGFA expression and tube formation in HUVECs. Furthermore, tumorigenicity assays on nude mice revealed that fibroblast-derived Serpin E1 promoted angiogenesis and/or VEGFA expression in subcutaneous and peritoneal tumors. Our previous study also unveiled an increased angiogenesis formation in the subcutaneous tumor of nude mice injected with GC cells overexpressing Serpin E1 [
16]. Interestingly, Serpin E1 also stimulates VEGFA expression in CAFs in vitro, suggesting that both HUVECs and CAFs may serve as the primary sources of VEGFA within the gastric tumor microenvironment infected by
H. pylori. MAPKs constitute a vast family of serine/threonine kinases, with ERK, p38, and JNK-mediated pathways playing a pivotal role. Upon receiving stimuli such as reactive oxygen species induced by
H. pylori infection, it initiates a phosphorylation cascade of MAPKs, resulting in multiple cellular responses encompassing cell proliferation, apoptosis, invasion, metastasis, autophagy, et al. These responses are linked to the malignant behavers of tumor cells [
37]. The activation of the p38 MAPK pathway induced by
H. pylori infection in MKN45 cells has been shown to upregulate VEGFA expression through the use of its specific inhibitor SB203580 [
38]. In liver cancer HepG2 cells, Panahi et al. [
39] revealed that high glucose-induced inflammatory responses led to Serpin E1 upregulation, accompanied by activation of three crucial MAPK pathways. Therefore, we co-treat HUVECs with recSerpin E1 and (E)-osmundacetone (a universal inhibitor of MAPK phosphorylation), resulting in a significant reduction only in p38 MAPK phosphorylation levels accompanied by downregulation of VEGFA. This finding suggests that Serpin E1 facilitates VEGFA expression by activating the p38 MAPK signaling pathway in HUVECs. Therefore, Serpin E1 derived from fibroblasts and subsequently cancer cells stimulates VEGFA expression through the p38 MAPK pathway in HUVECs, thereby contributing to GC development and progression.
Additionally, we observed that Serpin E1 at a concentration of 10 ng/mL, below the normal plasma levels of 5–50 ng/ml, exhibited inhibitory rather than promotional effects on the in vitro growth of GC cells. Conversely, Fang's study used 10 ng/mL recSerpin E1 (obtained from the same company) to stimulate colony formation and migration of breast cancer SKBR-3 cells but did not provide information regarding seeded cell density [
40]. The underlying reason for this discrepancy remained unclear. We speculated that the use of 96-well plates in our experiment and a relatively low cell density (0.5 × 10
4) seeded in the culture plates may result in cytotoxicity and subsequent growth inhibition at a concentration of 10 ng/ml recSerpin E1. Furthermore, the specific type of GC cells used in our study might also contribute to the observed cytotoxicity at this concentration.
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