Background
Cervical cancer is the fourth common cause of death in women worldwide [
1]. Nearly 530,000 women with cervical cancer were diagnosed and 26,6000 women died from cervical cancer worldwide in 2012 [
2]. Generally, human papillomavirus infection (HPV) causes more than 90% of cases [
3]. However, most people with HPV infection do not develop cervical cancer. HPV 16 and 18 are the main cause for cervical cancer globally, while HPV 31 and 45 are the second causes for another patient [
4]. At present, pelvic surgery is the main treatment for early cervical cancer in the world [
5]. Additionally, chemotherapy can be used to treat cervical cancer. Chemotherapy has become a common method in the adjuvant therapy of women with early cervical cancer, especially those patients with advanced or recurrent cancer [
6]. However, a wide variety of chemotherapy drugs for the treatment of cervical cancer have many side effects such as neurotoxicity, which lead to the limitations of its application and function [
7]. Therefore, it is a primary concern to develop a novel drug with minimal side effects for preventing and treating the cervical cancer.
Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) is a hydroxycinnamic acid and an abundant phenolic phytochemical in vegetables and fruits, which has antioxidant and antitumor activities [
8]. FA has been identified in Chinese medicine herbs such as
Angelica sinensis,
Cimicifuga heracleifolia and
Ligusticum chuangxiong [
9,
10]. In the previous studies, FA is an effective antioxidant agent that protects DNA from oxidative damage and prevents lipid peroxidation through reducing oxidative stress [
11]. In many tumor cell lines such as human osteosarcoma, human glioblastoma (U87MG), and prostate cancer, FA can induce cytotoxicity [
12‐
14]. Due to the inhibition of cyclooxygenase-2, FA is considered to be an anti-proliferative agent [
15]. In addition, FA has radioprotective function on human lymphocytes in previous studies, and FA may induce cell apoptosis in cancer [
16]. Besides, studies also found that FA inhibits the cell activities and enhanced oxidative DNA damage in HeLa and ME-180 human cervical cancer cells [
17]. However, the current research on the inhibitory effect and mechanism of FA in human cervical cancer cells is unclear.
Therefore, this study aimed to explore the effect of FA on Hela and Caski human cervical cancer cells as well as its molecular mechanism. In thist study, we study the changes of FA on genes and proteins expression, cell proliferation, invasion, cycle and apoptosis in Hela and Caski human cervical cancer cell.
Materials and methods
Chemicals
FA was purchased from Meilunbio (Dalian Meilun Biotechnology Co., LTD. Liaoning, China). Antibodies for P53, P21, Cyclin D1, Cyclin E, Beclin-1, LC3-II, Atg12-Atg5 and β-actin used for Western blot analysis were purchased from Wanleibio (Shenyang, Liaoning, China). Super moloney-murine leukemia virus (M-MLV) reverse transcriptase for fluorescence quantification was purchased from BioTeke (Beijing, China) and RNA simple Total RNA Kit was purchased from TIANGEN (Beijing, China).
Cell culture
Hela and Caski cells were purchased from Shanghai Cell Bank of Chinese Academy of Sciences. Hela cells were incubated in DMEM medium with 40% fetal bovine serum (FBS), and Caski cells were incubated in RPMI-1640 medium containing 10% FBS. These cells were seed in 96-well plate and placed in an incubator at 37 °C and 5% CO2.
Cell proliferation assay
MTT assay was used to assay the cell proliferation using various concentrations of FA (0.5, 1.0, 1.5, 2.0 mM). The cells who were treated without FA were the control group. Each experiment was performed in triplicate. After cultured for 48 h, MTT at a concentration of 0.2 mg/ml was added to the plates for 4 to 6 h. Then, cell viability was measured using an MTT mixture according to manufacturer’s instruction. Formazan formation was quantified spectrophotometrically at 490 nm (reference wavelength 630 nm) using a microplate reader. As follows: viability % = (OD value of experimental group/OD value of control group) × 100%.
Real-time PCR
Total RNA was extracted from the control and FA-treated cells using the Total RNA Extraction Kit following the manufacturer’s instructions. cDNA was synthesized using 1 µL M-MLV reverse transcriptase. Subsequently, Atg5, Beclin-1, and MMP-9 expression levels were detected with real-time PCR quantification based on SYBR Green PCR Master Mix (Solarbio, Beijing, China), and melting curves were acquired after amplification. β-actin was set as a reference gene. The primer sequence is shown in Table
1.
Table 1
Primer sequences of the genes used in this study
MMP-9 | F: 5′-AGTCCACCCTTGTGCTCTTC-3′ |
R: 5′-GCCACCCGAGTGTAACCAT-3′ |
Atg5 | F: 5′-GTATCATCCCACAGCCAAC-3′ |
R: 5′-GCAAAGTAAGACCAGCCC-3′ |
Beclin-1 | F: 5′-AACCAGATGCGTTATGCC-3′ |
R: 5′-CGTAAGGAACAAGTCGGTAT-3′ |
β-actin | F: 5′-CTTAGTTGCGTTACACCCTTTCTTG-3′ |
R: 5′-CTGTCACCTTCACCGTTCCAGTTT-3′ |
Western blotting
Protein expression levels of P53, P21, Cyclin D1, Cyclin E, Beclin-1, LC3-II, and Atg12–Atg5 were determined by Western blotting. β-actin is a reference protein. The protocol was performed according to the previous study [
18]. The primary antibodies (1:1000 dilution) were purchased from Meilunbio, then the sheep anti-rabbit secondary antibodies (1:5000) were used. The OD values of bands were visualized using Gel-Pro-Analyzer software.
Transwell invasion assay
The Transwell compartments (Corning, USA) were placed into a 24-well plate and pre-coated with 50 μL diluted Matrigel. At first, Hela or Caski cells were cultured in the upper chamber including DMEM or RPMI-1640 medium with free FBS, followed by treatment with various concentrations of FA (0, 1.0, 2.0, 4.0 mM). Subsequently, DMEM or RPMI-1640 medium supplemented with FBS was added to the lower chamber, and cells were performed to migrate for 48 h at 37 °C. The cells in the lower chamber were stained with crystal violet and then were counted under a microscope.
Cell cycle and apoptosis
The Hela and Caski cells were treated with various concentrations of FA (0, 1.0, 2.0, 4.0 mM). After 48 h, cells were collected and washed twice with cold PBS. Then cells were incubated in a 1 mL of mixed solution including 20 mg/mL of propidium iodide (PI) and 10 U/mL of RNaseA (KGA214, KeyGen, Nanjing, China) for 30 min at room temperature. Cell cycle was assayed through the ModFit software after fluorescence-activated cell sorting (FACS). For apoptosis analysis, the Annexin V-FITC/PI apoptosis detection kit (KeyGEN Bio TECH, Nanjing, China) was used following the manufacturer’s instruction.
Statistical analysis
All data were presented as mean ± standard deviation. The differences between two groups were detected using the two sample independent T test. The one-way ANOVA was applied for comparison among three or more groups following LSD method. The linear regression method was used to evaluate the dose–effect relationship (R2). For all the analysis, P < 0.05 was considered significant difference. SPSS 19.0 (SPSS Inc., NY, USA) was used in the present study.
Discussion
Our study showed that FA had a significant inhibitation effect on Hela and Caski human cervical cancer cells in a concentration-dependent manner. In addition, FA inhibited cell invasion through reducing MMP-9 mRNA expression. FA induced cell apoptosis and G0/G1 phase arrest in Hela and Caski cells through inducing the cell cycle-related proteins expression such as p53 and p21, and reduced Cyclin D1 and Cyclin E levels. Moreover, FA decreased the autophagy-related proteins such as LC3-II, Beclin1 and Atg12-Atg5 in a dose-dependent manner.
Cell cycle is closely related to tumorigenesis. Many tumor-inhibitory factors are involved in cell cycle, such as P53 and its downstream regulators [
19]. P21 and P53 genes as the stimulated markers, are involved in cell cycle and apoptosis [
20]. P21 is a controller of the G1 and S phases of the cell cycle progression, and thus the overexpression of P21 occurs to repair cell cycle arrest in injured cells [
21]. Additionally, P53 protein is a transcription factor that plays an important role in cell growth, DNA repair and cell apoptosis [
22]. If P53 gene is downexpressed, the risk of tumorigenesis will increase due to the increased number of impaired DNA [
22]. The loss-of-function mutation in the P53 gene contributes to the development of the tumor, and CD44 expression is usually inhibited by the binding of P53 and CD44 promoters. Therefore, an increased expression of CD44 was detected in the mutant P53 tumor cells [
23]. One of the cell surface markers associated with cancer stem cells (CSCs) in several types of tumors [
24,
25]. Another metabolic heterogeneity leads to the inability to produce the same therapeutic effect on whole cancer cells, and cancer stem cells have shown to cause With several biological properties of conventional anti-tumor therapeutics, metabolic programming is crucial for CSCs to maintain unlimited self-renewal potential and over-adaptation to rapid changes in the tumor microenvironment [
26‐
28], due to the presence of CSCs leading to intratumoral Heterogeneity is the main reason why we cannot induce the same therapeutic effect in whole cancer cells [
29]. CSCs are likely to contribute to the formation of minimal residual disease (MRD) [
30,
31], and MRD is expected to be at potential recurrence and distant Transfer plays an important role [
32]. Similarly, P53 and P21 proteins levels were increased in FA groups. Moreover, downexpression of the cell cycle-related proteins such as cyclinD1 and cyclin E and the inhibition of G1/S can lead to cell cycle arrest [
33]. In this study, the levels of cyclin D1 and cyclin E1 proteins were decreased and the levels of P53 and P21 proteins were up-regulated in FA-treated Hela and Caski cells, indicating that FA induced the G1/S cell cycle arrest.
The effect of MMP-9 on tumorigenesis and target therapy is well known [
34], which degrades collagen and increases the bioavailability of vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-β) [
35]. Activation of MMP-9 led to the cell migration, and the upregulated MMP-9 are associated with invasion, metastasis and poor prognosis in different types of cancers such as colon, ovarian and prostate cancer [
36‐
38]. Metastasis is an important step in the progression of tumors, revealing the metastasis of malignant cells from the original site to distant organs and tissues. Epithelial-mesenchymal transition (EMT) is an important process in cancer cell metastasis and cell invasion, in which epithelial cells enhance resistance to apoptosis, enhance migration and invasiveness [
25]. MMP-9 is also closely related to the metastasis of malignant tumors, so we studied the changes of MMP-9 in cervical cancer HeLa cells and Caski cells under the action of FA. In this study, the expression of MMP-9 was decreased in FA groups. Besides, FA inhibited the cell invasion. Therefore, FA inhibited the cell invasion in Hela and Caski cervical cancer cells through reducing the expression of MMP-9.
Autophagy is a double-edged sword for cancer. Studies on drug relocation have shown that “conventional” agents used to treat diseases other than cancer can have antitumor therapeutic effects through activation or suppression of autophagy, and some against autophagy. The latest advances in novel treatment strategies to treat or prevent malignancy [
39]. There are studies that have found that ferulic acid has been used in patients with diseases other than malignant tumors. Autophagy can protect cells by inhibiting apoptosis or necrosis, and also promote cell death in coordination with apoptosis. Additionally, autophagy can also induce apoptosis [
40]. As a specific marker of autophagosome formation, LC3 exist in the form of LC3-I and LC3-II when autophagy was inactivated or activated [
41]. In addition, Beclin-1 is the first mammalian autophagy gene, which may drive the formation of autophagosome by binding to VPS34 [
42]. Beclin-1 is an important modifier of autophagy and is closely related to tumorigenesis. Autophagy often involved in biological process such as tumor progression and chemoresistance through constituting a stress adaptation that avoids cell death [
43]. It has been reported that LC3-II and Beclin-1 are prognostic factors of various human cancers. The downexpression of Beclin-1 is ovarian epithelial cancer associated with prognosis in ovarian cancer [
44], and the expression of LC3-II is associated with a good prognosis of hepatocellular carcinoma [
45]. Moreover, tumor suppressor P53 can also be induced autophagy death in cancer cells [
46]. Among them, two ubiquitin-like conjugate systems were required during the formation of autophagosome, such as the Atg12 and LC3-II systems. The LC3-II is downstream of the Atg12 system, the Atg12 coupled to Agt5 to form an irreversible Atg12-Atg5 complex [
47]. Therefore, this study showed that FA inhibited autophagy through reducing the levels of LC3-II, Beclin-1 and Atg12-Atg5 proteins.
In summary, FA has a significant inhibitory effect on human Hela and Caski cervical cancer cells. FA can also significantly inhibit cell proliferation and invasion. It might be acted as an anti-cancer drug through inhibiting the autophagy and inducing cell cycle arrest in human cervical carcinoma cells. This research provides a theoretical basis for the treatment of human cervical cancer using FA. However, the molecular mechanism is not yet enough comprehensive, and further study is needed.
Authors’ contributions
JG: data management, data analysis,manuscript writing. YW, YZ: data analysis, project development. YK, QL: manuscript editing. HY, LG: data collection. WG, SY: manuscript writing. All authors read and approved the final manuscript.