Background
Cervical cancer is the fourth most common gynecological tumour and the second leading cause of cancer-related death in women worldwide, particularly in low- and middle-income countries [
1]. In 2020, an estimated 604 000 new cases of cervical cancer were diagnosed, and 342 000 deaths occurred worldwide due to this malignancy [
2]. The failure of cervical cancer therapy and poor outcomes are mostly due to the development of local invasion and distant metastasis [
3]. A large amount of evidence has demonstrated that epithelial-mesenchymal transition (EMT) plays a key role in the progression and metastasis of cervical cancer [
4]. Dysregulation of EMT-associated genes, such as N-cadherin, E-cadherin and Twist1, induces the dysregulation of EMT and contributes to the invasion and metastasis of cervical carcinoma [
4‐
6]. N-cadherin, as a marker of ongoing EMT, is widely recognized as a pivotal factor involved in cellular adhesion and tumour metastasis [
7]. Overexpression of N-cadherin is associated with high aggressiveness and motility of tumour cells by promoting EMT, which was observed in a range of tumours such as cervical cancer, melanoma and non-small cell lung cancer [
8‐
10]. On the other hand, histone acetylation is highlighted as one of the most important regulators of cancer EMT progression [
11]. However, the mechanisms whereby specific histone acetyltransferases regulate the progression of EMT in cervical cancer are poorly understood.
Histone acetylation impacts transcriptionally active euchromatin and is regulated by the coordination between histone acetyltransferases (HATs) and histone deacetylases (HDACs) [
11]. Histone acetylation has a key role in the dysregulation of EMT-associated genes and represents an essential mechanism of cancer progression and metastasis [
12‐
14]. Wang et al.reported that Tip60 histone acetyltransferase mediates the acetylation of SPZ1 and Twist1, promoting EMT progression in liver cancer [
15]. Hou et al.demonstrated that HDACs inhibit the acetylation and transcriptional activity of p65 and negatively regulate the EMT process in gastric cancer [
16]. Histone acetylation also plays an essential role in the development of cervical cancer. For example, the expression levels of histone H3 acetyl K9 and histone H3 trimethyl K4 are strongly correlated with the prognosis of cervical cancer patients [
17]. In addition, HAT GCN5 was reported to contribute to cell cycle proliferation in HPV-16 E7-expressing cells, indicative of its role in cervical cancer [
18]. However, to what extent histone acetylation plays a role in cervical cancer metastasis by regulating the EMT process remains to be explored.
In this study, we comprehensively analysed the expression patterns of histone acetylation genes in 128 cervical tissue specimens. We discovered that seven histone acetylation genes can potentially regulate the EMT pathway, including CSRP2BP, LPCAT1, NAT14, CREBBP, MSL3, ATF2 and GNPNAT1. Among these genes, CSRP2BP (also known as lysine (K) acetyltransferase 14, KAT14) was markedly overexpressed in cervical cancer tissues and cervical cancer cell lines and significantly associated with a poor prognosis and metastasis in cervical cancer patients. Overexpression of CSRP2BP significantly promoted cervical cancer cell proliferation, migration, invasion and resistance to cisplatin chemotherapy. We further identified that HAT CSRP2BP mediated EMT signalling and cervical cancer metastasis by interacting with SMAD4 to form a complex to activate N-cadherin transcription. Notably, CSRP2BP overexpression increased the acetylation level of H4 at the N-cadherin promoter. Our study suggests that HAT CSRP2BP is a key regulator of cervical cancer EMT and metastasis and may be a potential therapeutic target for cervical cancer.
Materials and methods
Gene expression profiles of cervical cancer
Gene expression profiles of cervical cancer were obtained from Gene Expression Omnibus (GEO) under the accession number GSE63514 [
19]. In total, transcriptomes of 128 frozen cervical samples spanning normalcy, cervical intraepithelial neoplasia (CINI-CINIII) lesions, and cervical cancer were analyzed in this study [
19]. Gene expression profiles were measured by Affymetrix U133 Plus 2.0 microarray platform. The processed data were downloaded for further analysis.
Collection of histone acetylation-related genes
The histone acetylation-related genes were obtained from gene ontology (GO) [
20]. The genes in GO term ‘ACETYLTRANSFERASE_ACTIVITY’ were downloaded from MSigDB database [
20]. In total, 88 genes were expressed in the transcriptomes of cervical cancers.
EMT scores
To calculate the EMT score for each sample, we first obtained the EMT-related genes from MSigDB [
21]. Next, we performed the single sample gene set enrichment analysis (ssGSEA) to calculate EMT enrichment score for each patient [
22].
Prioritization of genes in cervical cancer
To identify the histone acetylation-related genes that potentially correlated with EMT, we performed a two-step method to prioritize the genes. First, differential expression analysis was performed for patients with different states. Wilcoxon’s rank sum test was used to analyze the differences between the two states of patients in cervical cancer. Genes with a
p value ≤ 0.05 was considered as differentially expressed genes in cervical cancer. For all histone acetylation-related genes, we calculated the rank score R based on the combination of fold-change and
p-value:
$${R}_{i }=-log10\left({\mathrm{p}}_{i}\right)*log2\left({FC}_{i}\right)$$
where
\({\mathrm{p}}_{i}\) is
p-value for gene
i and
\({FC}_{i}\) is the fold-change comparison between cancer and normal samples.
Next, we identified the genes of which expressions were correlated with EMT scores in cervical cancer. Spearman correlation coefficients were calculated between the expressions of histone acetylation-related genes and EMT scores. Genes with a p value ≤ 0.05 and absolute spearman correlation coefficient (SCC) ≥ 0.3 were identified. Finally, genes with top ranked R scores and correlated with EMT scores were overlapped.
Gene set enrichment analysis
To identify the pathways potentially correlated with gene of interest, we first calculated the SCC between the expressions of candidate gene and all other genes. All protein coding genes were ranked based on the SCC and subjected to gene set enrichment analysis (GSEA) [
22]. The EMT pathway was used as the pathway for analysis.
Tissue specimens
A total of 208 paraffin-embedded human cervical cancer tissues were obtained from the Southern Medical University Nanfang Hospital, Hainan Provincial People's Hospital and the First Affiliated Hospital of Hainan Medical University between January 2010 and December 2016. Nineteen additional matched pairs of fresh cervical cancer tissue specimens (T) and adjacent noncancerous tissue (ANT) samples were obtained from the Department of Gynecology of Hainan Provincial People's Hospital from June to July 2019. All patients involved in this study were selected from the database and histologically confirmed as having cervical cancer, and none of these patients were treated with radiotherapy, immunotherapy or chemotherapy before surgery. For total protein isolation, 19 matched pairs of fresh cervical cancer tissue and ANT samples were obtained from patients immediately after surgery and snap-frozen at − 80 °C until use. The percentages of tumour purity in these tissues used for protein analyses were established by routine histopathological analyses [
23]. The study was approved by the Research Ethics Committee of the Southern Medical University Nanfang Hospital, Hainan Provincial People's Hospital and First Affiliated Hospital of Hainan Medical University IRB (HYLL-2020–060). Informed consent was obtained from each participant.
Immunohistochemistry (IHC)
IHC was performed on paraffin-embedded human cervical tissue, ANT and tumour xenograft sections as previously described [
23]. Primary antibodies, including anti-CSRP2BP (1:400; LS-B11653; LSBio), anti-N-cadherin (1:300; 13116S; Cell Signaling Technology), anti-E-cadherin (1:300; 3195; Cell Signaling Technology), and anti-Ki67 (1:400; sc-15402; Santa Cruz Biotechnology), were used to detect specific protein expression. The procedure which was performed without any primary antibody were used as a positive control. CSRP2BP staining was scored by two different pathologists who acted independently with regard to the evaluation of the intensity of staining and the proportion of positive staining. The staining index for CSRP2BP expression in cervical cancer was calculated by multiplying the two scores of the staining intensity and the proportion of positive cells. The median of all scores was used as a cut-off value for CSRP2BP. The optimal cut-off value was used as follows: a score of ≥ 6 was used to define tumours with high CSRP2BP expression, and a score of ≤ 4 indicated low CSRP2BP expression.
Isolation and culture of primary cervical cancer cells
The surgical specimens were collected from patients with cervical cancer, cut into ~ 1 mm pieces and digested with 0.25% trypsin-250 followed by collagenase I. After then, digested tissues were pooled and washed in DMEM/F12 medium containing 10% FBS. After filtration with 200 mesh sieves, the cell suspensions were re-suspended with DMEM medium containing 10% FBS and seeded into culture flasks coated with polylysine. Medium was replenished every 24 h, and passage was performed when the cells reached 80% confluency.
Cell culture
The human cervical cancer cell lines Hela (HPV18 +), SiHa (HPV -) and C-33A (HPV16 +) were obtained from the Chinese Academy of Sciences Cell Bank (Shanghai China), and primary human cervical cancer cells (T1, T2, T3) were established based on previously reported methods [
24]. All cell lines were subjected to high glucose Dulbecco’s modified Eagle’s medium (DMEM, Gibco, CA, USA) supplemented with 10% foetal bovine serum (FBS, Gibco, CA, USA) and antibiotics (50 U/ml penicillin and 50 μg/ml streptomycin; both from Gibco, CA, USA) and maintained in 5% CO
2 and 37 °C atmosphere.
Plasmid construction and transfection
The coding sequence of the human CSRP2BP gene (NM_001392073, Origene, USA) was amplified and subcloned into the Xhol and BamHI sites of the pLVX-AcGFP-N1 lentiviral vector (PT3994-5, Clontech, USA) to generate the CSRP2BP expression plasmid. The Agel and EcoRI sites of the GV248-EGFP-puromycin lentiviral vector (GIDE77111, GENE, CN) were used to generate CSRP2BP shRNA constructs. The human CDH2 gene (NM_001308176, Origene, USA) was subcloned into the EcoRl and BamHl sites of the pSin-EF1α-puro lentiviral vector (SBI, USA). The coding sequence of the human H4 gene (NM_003548.2, Origene, USA) was subcloned into the EcoRl and BamHl sites of the pSin-EF1α-puro lentiviral vector (SBI, USA) to generate H4 expression plasmid. CSRP2BP mutants lacking the HAT domain (711–714 aa deleted), N-cadherin-Luc reporter mutants lacking the SEB2 and H4 mutants lacking the K5 site plasmids were generated using the KOD Plus Mutagenesis kit (Cade No. SMK-101, TOYOBO, Japan) according to the manufacturer’s instructions.
The vectors pMD2.G and psPAX2 were packaged in 293 T cells using calcium phosphate transfection. Then, transduced cells were selected for 7 days with puromycin (P7255-25MG, Sigma, USA). The surviving cells were amplified by monoclonal culture. Hela and C-33A stable cell lines expressing CSRP2BP and shCSRP2BP were established (Hela/C-33A-CSRP2BP, Hela/C-33A-Vector, Hela/C-33A-shCSRP2BP and Hela/C-33A-shcon). Protein and mRNA of transfected cells were taken for real time-PCR and Western blotting analyses. The primers used in this study are listed in supplemental Table S
1.
Western blotting
Western blotting was performed as described previously [
25] by using anti-CSRP2BP (LifeSpan BioSciences, USA), anti-H4, anti-acetylated H4 on lysine 5 (H415Kac), anti-acetylated H4 on lysine 12 (H412Kac) (Abcam, USA), and anti-N-cadherin (Cell Signaling Technology, MA) antibodies. Next, the membranes were incubated with secondary antibody for 1 h at RT, and then incubated with chemiluminescent substrate kit reagents (Millipore, USA); images were captured on a Tanon 4600SF instrument (Shanghai, China). The antibodies used in this study are listed in supplemental Table S
2.
RNA isolation and quantitative real-time PCR
Total RNA was extracted using TRIzol reagent (Invitrogen Life Technologies, USA) based on standard procedures. Complementary DNA (cDNA) was prepared with the Prime Script® RT reagent kit (Takara, Japan) according to the manufacturer’s instructions. The expression level of mRNA was quantified using a SYBR® Premix E2x Taq TM II kit (Takara, Japan). The relative expression level was determined by normalizing the expression level of each target to GAPDH, and the relative mRNA fold change was determined using the 2
(−∆∆Ct) method. Three independent experiments were performed with each carried out in triplicate. The primers used in this study are listed in supplemental Table S
3.
Cell proliferation examination
For the cell growth curve, 1 × 104 cells were seeded to 6-well plates and cultured for 6 days. The cells were counted every day to draw the cell growth curve. The 5-ethynyl-2’-deoxyuridine (EdU) assay was performed with the Cell-Light EdU Apollo 567 kit (RiboBio, China) according to the manufacturer’s instructions. All images were photographed with a fluorescence microscope (Olympus, DP72). EdU quantification was performed as the ratio of the number of red fluorescence cells, i.e., EdU + , to the total number of DAPI + cells in a given field. At least six randomly selected fields from each sample were scored. All experiments were independently performed three times, totally 18 fields to analyze. For colony formation, cells were harvested and seeded into 6-well plates with amount of 1 × 103 cells/well. On day 10, the cell colonies were stained with Giemsa stain for 15 min after fixation with 4% paraformaldehyde (Biosharp, China) for 30 min. Colonies with > 50 cells were counted. Three independent experiments were performed.
Wound healing assay
Wound healing assays were established by using Ibidi Culture Insert chambers (Ibidi, Germany) following the manufacturer’s protocol. Briefly, a total of 45 × 10
4 cells were added to each well of the chamber. After 24 h, wound closure was monitored, and images were captured at different time points using an Olympus microscope (Olympus). Data were analyzed by using previously published methods [
25].
Transwell migration assays
Cell invasion assays were performed using 12-well tissue culture plate inserts (8.0 μm pores, BIOFIL, China) precoated with Matrigel (BD Biosciences). First, cells were suspended in 200 μL of serum-free medium and plated in the upper chambers, whereas 600 μL of medium supplemented with 10% FBS was placed in the lower chambers. After 24 h of incubation, the cells on the lower surface of the membrane filter were fixed and stained and then counted with an inverted microscope (Olympus, IX71).
Immunofluorescence
Cells grown on cover slides were fixed with methanol and acetone (1:1) for 20 min at -20 °C, permeabilized with 0.5% Triton X-100 for 20 min, blocked with 5% BSA (Beyotime, China) in phosphate buffered saline (PBS) containing 0.1% Tween-20 for 1 h, and then incubated with a primary antibody at 4 °C overnight. Subsequently, the slides were incubated with Alexa Flour® 488 IgG anti-mouse (Abcam, US) or Alexa Flour® 594 IgG anti-rabbit (Abcam, US) at room temperature for 1 h. DAPI was used to stain the nuclei for 5 min. Fluorescence images were taken using the confocal microscopy (Olympus Fluoview FV3000).
Flow cytometry and chemoresistance model in vitro
Flow cytometry was performed using a BD FACS Aria II cell sorter (Becton Dickinson, San Jose, CA) to analyse the cell cycle through propidium iodide (Sigma, China) staining. Briefly, cells were plated in 6-well plates (1 × 105 cells/well) and cultured until they reached 90% confluency. Through flow cytometry, the annexin V + /PI cells were analysed after the indicated cells were treated with cisplatin (20 μg/ml, 40 μg/ml, 80 μg/ml) for a 24 h culture. Modfit LT 3.1 trial cell cycle analysis software or FlowJo software was used to analyse the cell cycle.
Coimmunoprecipitation (Co-IP) assay
Plasmids expressing flag-HA-tagged SMAD3 and flag-HA-tagged SMAD4 were cotransfected into Hela cells with HA-tagged CSRP2BP by using Lipo2000™ Transfection Reagent (Invitrogen, CA, USA) according to the manufacturer’s instructions. Hela cells were lysed with RAPI (Biosharp, China) lysis buffer containing 1 × PMSF (Cell Signaling Technology, MA, USA) and 1 × protease inhibitor cocktail (Cell Signaling Technology, MA, USA). The supernatant was collected after centrifugation, and then incubated with the anti-flag antibody at 4 °C for 2 h. The antigen–antibody complex was precipitated with protein A/G (Invitrogen, CA, USA), and Western blotting was performed to examine the target proteins.
Plasmids expressing flag-HA-tagged H4 and flag-HA-tagged H4K5 mutants were respectively transfected into Hela-CSRP2BP cells using Lipo2000™ Transfection Reagent (Invitrogen, CA, USA) according to the manufacturer’s instructions. After 48 h, the supernatant was collected and incubated with the anti-flag antibody at 4 °C overnight. The antigen–antibody complex was precipitated with protein A/G (Invitrogen, CA, USA), and Western Blot was followed to examine the expression of H4Ac.
siRNA transfection
siRNA duplexes against N-cadherin and SMAD4 were transfected into Hela-CSRP2BP, Hela-Vector cells by using Lipofectamine™ RNA iMAX Transfection Reagent (Invitrogen, CA, USA) according to the manufacturer’s instructions. The siRNA duplex sense sequences were as follows: si–N-cadherin: 5’-CCAGUGACUCUUAAGAGAA-3’, si-SMAD4: 5’-CCACCAAGUAAUCGUGCAU-3’.
Luciferase reporter assays
The region of the CDH2 promoter (~ 2 kb) was amplified using the primers and subcloned into the PLG3-basic luciferase reporter plasmid to synthesize the pGL-3-N-cadherin promoter plasmid. The coding sequences of the human CSRP2BP gene (NM_001392073, Origene, USA) and SMAD4 gene (NM_000018.10, Origene, USA) were amplified and subcloned into the Xhol and BamHI sites of the PCGN vector (PT3994-5, Clontech, USA). Luciferase activity was measured as described previously [
26].
Xenograft models
BALB/c-nu mice (n = 20, 5–6 weeks of age, Gem Pharmatech. Co. LTD) were kept in aseptic conditions under constant temperature and humidity. The mice were randomly divided into four groups, and each mouse received a groin subcutaneous injection of a 100 μL suspension of 1 × 106 cells. Tumour growth was detected with callipers every 2 days, and tumour volume was calculated using the following formula: Volume = (length × width2)/2. Magnetic resonance imaging (MRI) was used to evaluate the tumours in the mice. To further evaluate the metastatic potential of CSRP2BP, mice (n = 5) were transplanted with 1 × 106 cells suspended in 100 μL PBS by tail intravenous injection. Six weeks after transplantation, all mice were sacrificed, and the tumours were harvested and imaged by a chemiluminescent imaging system (Sacecreation).
Chromatin immunoprecipitation (ChIP)
Cells were fixed with 37% formaldehyde for 10 min, treated with 0.125 M glycine for 5 min and centrifuged at 3000 × g at 4 °C for 5 min to collect the crude nuclear fraction. The nuclear pellet was incubated with 1% SDS lysis buffer and sonicated to shear genomic DNA into 100 ~ 400 bp fragments. Genomic DNA fragments were transferred to slide-A-Lyzer™ G2 (Invitrogen Life Technologies, CA, USA) at 4 °C for 4 h. Immune complexes were precipitated with protein A/G beads (Invitrogen Life Technologies, USA), and soluble chromatin complexes were immunoprecipitated with human IgG antibody (Proteintech), H4ac antibody (Active Motif) or CSRP2BP antibody (Life Span Biotechnology) in ChIP dilution buffer overnight at 4 °C. The beads were sequentially washed with a low salt buffer, a high salt buffer, LiCl wash buffer, and TE buffer. The immunoprecipitated chromatin complexes were eluted in ChIP direct elution buffer at 65 °C for 30 min and incubated at 65 °C overnight to cross-link the chromatin complexes. DNAs were isolated using a QIAGEN DNA kit (28,106, Germany). The extracted DNA was analysed by real-time PCR. Primers to detect N-cadherin promoter occupancy were listed in Supplemental Table S
4.
RNA-seq
Total RNA from cells for RNA sequencing was isolated using TRIzol reagent (Invitrogen Life Technologies, USA) based on standard procedures. RNA quality was evaluated with an Agilent 2100 bioanalyzer and a NanoDrop 2000. Libraries were constructed using the standard Illumina library construction process. Each library was sequenced on an Illumina NovaSeq 6000 in 150 PE mode by Beijing Berry Genomics Co., Ltd. (Beijing, China).
Statistical analyses
All statistical analyses were performed using the SPSS software package (version 19.0, SPSS, Inc.) and Prism 5.0 software (GraphPad, La Jolla, CA, USA). Data are presented as the mean ± standard deviation (SD) of at least three independent experiments. The independent sample t test was used for comparing data of groups to identify significant differences. The Kaplan‒Meier method was used for progression-free survival (PFS) and overall survival (OS) analysis, and significance was determined by the log-rank test. Multivariate logistic regression was performed to identify the independent risk factors related to the prognosis of cervical cancer. The relationships between CSRP2BP expression level and clinicopathological features were tested by the χ2 test or Fisher’s exact test. The differences were considered statistically significant at P < 0.05.
Discussion
The metastasis of cervical cancer is closely correlated with a poor prognosis and low 5-year survival rates in cervical cancer patients [
40]. Therefore, there is an urgent need to unravel the precise mechanisms underpinning the metastasis of cervical cancer. EMT is an important process during metastasis, and histone acetylation is one of the most important regulators of cervical cancer metastasis. In the present study, we analysed cervical tissue gene expression data and identified the histone acetylation-related genes that potentially correlated with EMT. We found that the histone acetyltransferase CSRP2BP was highly expressed in cervical cancer and positively correlated with EMT scores. In addition, CSRP2BP exhibited increased expression with CINIII and invasive cancer, indicative of the association of increased CSRP2BP expression with the development of cervical lesion. Mechanistically, we found that 1) CSRP2BP promoted cervical cancer EMT and metastasis by upregulating N-cadherin, and 2) CSRP2BP increased N-cadherin expression by acetylating H4K5 and H4K12 in the promotor region of N-cadherin through cooperation with Smad4 (F
ig.
7I). These results provided strong evidence that CSRP2BP was an important histone acetyltransferase and oncogenic factor in EMT and metastasis of cervical cancer.
Acetylation is one of the posttranscriptional modifications (PTMs) influencing various aspects of protein biology [
41]. Histone acetylation and deacetylation is mediated by HATs and HDACs, and its balance is required for normal function of a variety of cells and tissues. Indeed, accumulating evidence has shown that aberrant histone acetylation contributes to pathogenesis of many diseases, such as cancer, chronic inflammation and diabetes [
42,
43]. HATs catalyse acetylation associated with gene transcription, and a growing number of studies have highlighted the role of HAT dysfunction in the initiation and development of various cancers, such as breast and liver cancers [
44]. However, the precise mechanisms underlying how HATs regulate the progression and metastasis of cervical cancer are still elusive. The histone acetyltransferase CSRP2BP is a co-activator for CRP2, and our previous study revealed that CSRP2BP was a driver of smooth muscle gene expression [
26]. However, the role of CSRP2BP in the metastasis of cervical cancer is poorly understood. In the present study, we found that 1) the CSRP2BP expression was significantly increased in clinical cervical cancer tissues and cell lines, 2) CSRP2BP overexpression promoted tumour growth and metastasis in both vitro and vivo, 3) CSRP2BP knockdown significantly inhibited tumour growth and metastasis, and 4) clinically, elevated expression of CSRP2BP was significantly correlated with decreased overall survival rates. These findings support the premise that CSRP2BP is an oncogenic factor and potentially a biomarker for the long-term survival of cervical cancer patients.
It is important to note that a significant association between the CSRP2BP expression and the clinicopathological characteristics of cervical cancer patients was observed, including FIGO stage and HPV16/18 infection. More importantly, overexpression of CSRP2BP induced but knockdown of CSRP2BP suppressed E6/E7 expression. Thus, it was highly likely that CSRP2BP participated in the process of HPV infection and the development of the cervical lesion, although the underlying mechanisms need further investigation. On the other hand, CSRP2BP overexpression was associated with poor OS in 138 patients with stage I, but not with OS in 70 patients with stage II. Gene expression analysis showed that the expression of CSRP2BP was higher in cervical cancer and CINIII compared with normal tissues. These findings suggested that CSRP2BP may play a vital role in the carcinogenesis and progression of cervical cancer. Further studies on the potential role of CSRP2BP in cervical basement membrane discontinuity (breaks or absence) would be of great interest.
We further observed that the CSRP2BP overexpression decreased the sensitivity of cervical cancer cells to cisplatin in a dose-dependent manner, suggesting the involvement of CSRP2BP in the chemotherapy resistance of cervical cancer. Based on the above findings, we speculated that CSRP2BP might serve as a novel biomarker and a potential therapeutic target for cervical cancer treatment.
EMT is a vital process contributing to cervical cancer progression, invasion and metastasis and characterized by the loss of epithelial markers, such as E-cadherin, and the gain of mesenchymal markers, such as N-cadherin and vimentin [
45]. The activation of EMT, especially through the upregulation of N-cadherin, have been shown to make a great contribution to cancer metastasis, and interestingly, HATs play a vital regulatory role in EMT [
46]. However, whether CSRP2BP participates in the regulation of the EMT process in cervical cancer is still unknown. Here, we revealed that N-cadherin expression was significantly increased in CSRP2BP-overexpressing Hela cells as analysed by RNA-seq. KEGG analysis also showed that EMT-related signalling was activated in CSRP2BP-overexpressing cells. Moreover, depletion of N-cadherin compromised the effects of overexpressed CSRP2BP on Hela cells. Thus, CSRP2BP overexpression increased N-cadherin expression in both vitro and vivo and promoted cervical cancer metastasis at least in part through upregulating N-cadherin. Moreover, the RNA-seq results revealed many other genes associated with cell adhesion were also significantly changed in CSRP2BP-overexpressing Hela cells. Future studies should be directed to probe the potential roles of these genes individually and collectively in cervical cancer progression and metastasis.
Our previous study showed that CSRP2BP strongly acetylated H3 and H4 [
26]. However, whether CSRP2BP-induced acetylation of H3 and/or H4 is implicated in its upregulation of N-cadherin expression and promotion of cervical cancer carcinogenesis is still unknown. In the present study, we found that CSRP2BP overexpression significantly increased acetylation of H4 lysine 5 and 12 by binding to the SEB2 region of the promotor of N-cadherin. Furthermore, the CSRP2BP HAT domain mutant (711–714 aa deleted), which exhibited reduced HAT ability, was incapable of increasing N-cadherin expression with SMAD4, as seen for wild-type CSRP2BP, suggesting that CSRP2BP promoted N-cadherin transcription primarily by acetylating histones. A previous study demonstrated that HPV oncoprotein E7, which plays a central role in cervical carcinogenesis, promoted E7-expressing cell proliferation through acetylating H3K9 in the promoter of E2F1 mediated by the HAT GCN5, suggesting that H3 acetylation also contributes to cervical carcinogenesis [
18]. Intriguingly, we found that CSRP2BP did not affect the acetylation level of H3 in cervical cancer cells. Thus, we speculated that 1) acetylation of H3 and H4 by different HATs may have differential physiological/pathological roles, and 2) acetylation of H3 and/or H4 by CSRP2BP is context dependent. Hence, investigating the regulatory networks underlying H3 and H4 acetylation by CSRP2BP in a variety of cell types and disease models is of great interest.
SMAD4 is one of the essential transcriptional regulators of EMT-associated genes including N-cadherin and also plays an essential role in the progression of cervical cancer [
47‐
49]. Given the regulation of N-cadherin expression by CSRP2BP in cervical cancer, we hypothesized that CSRP2BP mediates the N-cadherin expression through SMAD4. Indeed, we found that CSRP2BP interacted with SMAD4 and that SMAD4 was a key transcription factor in CSRP2BP-mediated N-cadherin transcription. Previous findings showed that CSRP2BP mediates target gene expression through some transcription factors such as SRF [
26]. Based on these findings, we reckoned that different transcription factors are important components for CSRP2BP-mediated functional networks, which are presumably context-dependent. Whether the CSRP2BP/SMAD4 complex coordinates with other factors to control specific H4 acetylation and EMT-associated gene expression in cervical cancer progression and metastasis awaits further investigation.
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