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Effect and Mechanism of lncRNA CERS6-AS1 on the Biological Behavior of Prostate Cancer Cell

Objective To investigate the effect of long noncoding RNA (lncRNA) CERS6 antisense RNA1 (CERS6-AS1) on the biological behavior of prostate cancer cells DU145 and its mechanism. Methods RT-PCR was used to detect the relative level of CERS6-AS1 and miR-16-5p in prostate cancer tissues, adjacent tissues, prostate cancer cells DU145, and human normal prostate epithelial cells RWPE-1. DU145 cells were divided into control group, si-CERS6-AS1 group, si-NC group, miR-16-5p mimic group, miR-NC group, and si-CERS6-AS1+miR-16-5p inhibitor group. And CCK-8 method and colony formation test was applied to detect cell proliferation ability, flow cytometry was selected to calculate cell apoptosis, and scratch healing test was employed to assess cell migration ability. Western blot was determined to detect high mobility protein A2 (HMGA2) expression. RT-PCR and dual-luciferase reporter experiments were used to analyze the targeting relationship among CERS6-AS1, miR-16-5p, and HMGA2. Results Compared with the adjacent tissues, the relative level of CERS6-AS1 in prostate cancer tissue was increased (P < 0.05), and the relative level of miR-16-5p was decreased (P < 0.05). Compared with RWPE-1 cells, the relative level of CERS6-AS1 in DU145 cells was increased (P < 0.05), and the relative level of miR-16-5p was decreased (P < 0.05). Compared with the control group and the si-NC group, the HMGA2 protein expression, the colony formation number, and the scratch healing rate of DU145 cells in the si-CERS6-AS1 group and the miR-16-5p mimic group were reduced (P < 0.05), and the relative level of miR-16-5p and the proliferation inhibition rate and apoptosis were increased (P < 0.05). miR-16-5p is specifically bound to CERS6-AS1 and HMGA2, respectively. Compared with the si-CERS6-AS1 group, the HMGA2 protein expression, the colony formation number, and the scratch healing rate of DU145 cells in the si-CERS6-AS1+miR-16-5p inhibitor group were increased (P < 0.05), and the cell proliferation inhibition rate and apoptosis rate were reduced (P < 0.05). Conclusion Silencing CERS6-AS1 can inhibit the proliferation and migration of prostate cancer cell DU145 and induce cell apoptosis, the mechanism is related to the regulation of the miR-16-5p/HMGA2 axis.


Introduction
Prostate cancer is the second most common cancer among men in the world. In 2021, there were about 1.3 million new cases of prostate cancer and about 359000 deaths [1]. Androgen deprivation therapy through surgery or drugs is the standard first-line treatment for patients with metastatic prostate cancer, but most patients will develop castration resistant prostate cancer within 2~3 years, and their survival status is still very poor [1]. Therefore, further exploring the regulatory mechanism of prostate cancer progression is of great significance to develop new treatment strategies.
Long chain noncoding RNA (lncRNA) is a class of RNA molecules with transcripts longer than 200 NT, which can regulate gene expression at different levels. It has been found that lncRNA can interact with microRNA (miRNA), participate in regulating the expression of target mRNA, and play an important role in tumorigenesis and metastasis [2,3]. There is evidence that the upregulated expression of CERS6 antisense RNA1 (CERS6-AS1) can predict the poor prognosis in patients with liver cancer [4].
Overexpression of CERS6-AS1 in breast cancer can promote the proliferation of breast cancer cells and inhibit cell apoptosis [5]. However, the role of CERS6-AS1 in prostate cancer has not been reported. miR-16-5p is a tumor suppressor. Studies have found that miR-16-5p can induce the decline of prostate cancer cell viability and G0/G1 cycle arrest and improve its radiosensitivity by targeting cyclin D1/E1 [6]. Sequence analysis found that miR-16-5p is a potential target of CERS6-AS1, so this study speculated that CERS6-AS1 may target miR-16-5p to play a role in prostate cancer. Therefore, the purpose of this study is to analyze the expression of CERS6-AS1 and miR-16-5p in prostate cancer tissues and to explore the mechanism of CERS6-AS1 targeting miR-16-5p on the biological behavior of prostate cancer cells.

Materials and Methods
2.1. Materials 2.1.1. Tissue Source. The prostate cancer tissues and adjacent tissues of patients with primary prostate cancer who underwent surgical resection in our hospital from January 2018 to October 2019 were collected. The average age was 62:0 ± 9:5 years. Inclusion criteria were as follows: primary prostate cancer diagnosed by histology; it was agreed to collect tumor tissues and paired adjacent tissues for research. Exclusion criteria were as follows: patients with other malignant tumors. This study was approved by the ethics committee of our hospital and conforms to the principles of the declaration of Helsinki. Written informed consent was obtained from each participant.

Method
2.2.1. Cell Culture. DU145 cells and RWPE-1 cells were cultured in DMEM medium containing 10% fetal bovine serum and in 37°C incubator containing 5% CO 2 . When the cell density was 80%, the cells were digested with 0.25% trypsin and subcultured in the ratio of 1 : 3.

Cell Transfection and Grouping.
A 24-well plate was taken, and 500 μL medium containing 1 × 105 DU145 cells was added to each well, and transfection was carried out when the density was 40%. Use 50 μL serum free medium diluted with 20 pmol RNA and recorded as solution A. Use 50 μL serum free medium dilution 2 μL liposome Lipofectamine 2000, recorded as liquid B. Gently mix liquid A and liquid B and let them stand for 5 min. Suck liquid B and add it to liquid A, flick it and mix it evenly, and place at room temperature for 15 min. During transfection, the 24well plate medium was replaced with serum-free medium with 400 μL per well. A/B complex was slowly added into the medium, shaken well, and incubated for 6 h. After serum-free medium was removed, the medium was changed to normal medium for further culture. Cells were collected and transfected for 48 h, RNA was extracted according to "1.2.2," and the relative levels of CERS6-AS1 or miR-16-5P were detected by RT-PCR to detect the transfection effect. DU145 cells were divided into si-CERS6-AS1 group, si-NC group, miR-16-5P mimic group, miR-NC group, and si-CERS6-AS1+miR-16-5p inhibitor group according to different transfection vector or oligonucleotide experiments. Normal DU145 cells were recorded as the control group.

The Proliferation of DU145 Cells Was
Detected by CCK-8 Experiment. DU145 cells in each group were inoculated into 96-well plates at a density of 1 × 103 cells/well for 48 h after transfection, and 3 replicates were set. After cell adhesion, add 10 μL CCK-8 solution to each well and continue to culture for 2 h. The absorbance (A) at 450 nm was measured by spectrophotometer. The experiment was repeated three times.

Colony Formation Assay Was
Used to Detect the Clonogenic Ability of DU145 Cells. DU145 cells in each group were inoculated into 6-well plates at a density of 1 × 103 cells per well after transfection of 48 h. The plates were slowly rotated to evenly disperse the cells, and the cells were placed in an incubator for incubation for 12-14 days, set in 3 2 Applied Bionics and Biomechanics repetitions. Change the medium every three days. When cell colonies were seen, the culture was terminated, and the colonies were fixed with methanol for 20 min and stained with 0.1% crystal violet for 20 min. The number of colonies with more than 50 cells was counted under an optical microscope. The experiment was repeated three times.

Apoptosis of DU145 Cells Was Detected by Flow
Cytometry. DU145 cells transfected for 48 h in each group were digested with 0.25% trypsin, and 1 × 105 cells were suspended in 500 μL 1× binding buffer. Annexin V-FITC (5 μL) and PI (5 μL) were successively added to each group for fine staining. After 20 min of dark incubation, apoptosis rate of DU145 cells in each group was analyzed by flow cytometry.    3 Applied Bionics and Biomechanics incubated on ice for 30 min and centrifuged at 12000 r/min at 4°C for 15 min to collect supernatant. Protein concentration was determined by BCA kit. 30 μg cell protein was isolated by SDS-Page (100 V and 100 min), wetted (300 mA and 20 min) onto NC membrane, sealed with 5% skim milk at room temperature for 2 h, and then added with primary antibody of HMGA2 and GAPDH (diluted at 1 : 500 by volume ratio) for 12 h at 4°C and secondary antibody (diluted at 1 : 1000 by volume ratio) for 2 h at room temperature. The protein bands were colored with chemiluminescence kit. Image J software measured the gray values of HMGA2 and GAPDH strips, and the HMGA2 expression level was expressed by the ratio of HMGA2 and GAPDH strips.

Statistical
Methods. SPSS 21.0 software was used for statistical analysis, and the data were expressed as mean ± standard deviation (x ± s). Independent sample t-test was used for the comparison between the two groups, and oneway ANOVA and SNK-q test were used for the comparison between the multiple groups. P < 0:05 was regarded as statistically significant.

Effects of Overexpression of miR-16-5p on Proliferation,
Apoptosis, and Migration of DU145. Compared with the control group and miR-NC group, the relative level of miR-16-5p and proliferation inhibition rate and apoptosis rate of DU145 cells in miR-16-5p mic group were significantly increased (P < 0:05), and the expression of HMGA2 protein and colony formation number and scratch healing rate were significantly decreased (P < 0:05), see Figure 4 and Table 2.

Control
Annexin V-FITC

Applied Bionics and Biomechanics
3.6. Inhibition of miR-16-5p Can Reverse the Effects of CERS6-AS1 on Proliferation, Apoptosis, and Migration of DU145 Cells. Compared with the control group, the relative level of miR-16-5p and proliferation inhibition rate and apoptosis rate of DU145 cells in si-CERS6-AS1 group were significantly increased (P < 0:05), and the expression of HMGA2 protein and colony formation number and scratch healing rate were significantly decreased (P < 0:05). Compared with si-CERS6-AS1 group, the relative level of miR-16-5p and proliferation inhibition rate and apoptosis rate of cells in the si-CERS6-AS1+miR-16-5p inhibitor group decreased significantly (P < 0:05), and the expression of HMGA2 protein and the number of colony formation and scratch healing rate increased significantly (P < 0:05), see Figure 6 and Table 4.

Discussion
lncRNA can affect the proliferation, apoptosis, metastasis, and invasion of prostate cancer cells, providing a potential target for inhibiting the occurrence and metastasis of prostate cancer [7]. This study analyzed the difference in CERS6-AS1 expression levels between prostate cancer, adjacent tissues, and normal prostate epithelial cells. The results showed that CERS6-AS1 was significantly upregulated in prostate cancer and prostate cell DU145. Relevant studies have shown that patients with pancreatic ductal carcinoma with high expression of CERS6-AS1 have a short overall survival time. Knockout of CERS6-AS1 can weaken the proliferation, migration, and invasion of pancreatic ductal carcinoma cells, induce apoptosis, and inhibit tumor growth in vivo [8]. The high expression of CERS6-AS1 in breast cancer can promote the proliferation of cancer cells and inhibit the apoptosis [9]. In this study, si-CERS6-AS1 was transfected for functional analysis. It was found that after silencing CERS6-AS1, the proliferation, clone formation, and migration of DU145 cells were inhibited, but the apoptosis rate increased, which was consistent with the anticancer effect of knockdown CERS6-AS1 reported by Yun et al. These findings suggest that CERS6-AS1 plays an oncogene role in prostate cancer, and silencing CERS6-AS1 may be a potential treatment strategy for prostate cancer.
Many studies have shown that lncRNA can eliminate the inhibitory effect of miRNA on its target genes by binding with miRNA, so as to play a regulatory role in the progression of prostate cancer. For example, lncRNA MEG3 can affect the proliferation, metastasis, and apoptosis rate of prostate cancer cells. This regulation depends on the regulation of miR-9-5p and its target gene QKI-5 [10]. lncRNA LOXL1-AS1 mediates the resistance of prostate cancer cells to adriamycin by upregulating EGFR expression by targeting miR-let-7a-5p [11]. Previous studies have shown that CERS6-AS1 can bind to miR-15a-5p and miR-125a-5p and function in pancreatic ductal carcinoma and breast cancer [9,10]. miR-16-5p is a tumor suppressor. Studies have pointed out that upregulating the expression of miR-16-5p can inhibit the proliferation and metastasis of liver cancer cells [12]. miR-16-5p inhibits the survival of prostate cancer cells by targeting protein kinase 3 (AKT3), regulates cell cycle distribution, and induces apoptosis [13]. In addition, miR-16-5p also mediates the inhibitory effect of knockdown Linc0021 on the biological behavior of nonsmall cell lung cancer [14]. This study found that the expression of miR-16-5p was downregulated in prostate cancer tissues and DU145 cells and confirmed that miR-16-5p was negatively regulated by CERS6-AS1. The verification of the function of miR-16-5p showed that overexpression of miR-16-5p significantly inhibited the proliferation, clone formation, and migration of DU145 cells and promoted apoptosis, which was consistent with the anticancer effect of silencing CERS6-AS1.
Further exploration found that HMGA2 was a potential target of miR-16-5p. Studies have shown that HMGA2 expression is upregulated in prostate cancer, which is related to lymph node metastasis and Gleason grade. Downregulation of HMGA2 can inhibit proliferation, invasion, and migration and increase the rate of apoptosis [15,16]. This study confirmed that miR-16-5p targeted negative regulation of HMGA2 expression, and silencing CERS6-AS1     Note: Compared with control group, * P < 0:05; compared with si-CERS6-AS1 group, # P < 0:05. 7 Applied Bionics and Biomechanics significantly inhibited HMGA2 expression by upregulating miR-16-5p, suggesting that CERS6-AS1/miR-16-5p/HMGA2 axis may exist in prostate cancer. The response experiment showed that inhibiting the expression of miR-16-5p significantly reversed the effects of silencing CERS6-AS1 on the proliferation, apoptosis, migration, and HMGA2 expression of DU145 cells, which further indicated that the carcinogenic effect of CERS6-AS1 in prostate cancer was achieved at least in part by regulating the miR-16-5p/HMGA2 axis.
In conclusion, the expression of CERS6-AS1 is upregulated in prostate cancer, and silencing CERS6-AS1 can inhibit the proliferation and migration of DU145 cells and promote cell apoptosis. The mechanism is related to the upregulation of miR-16-5p/HMGA2 axis. These findings suggest that CERS6-AS1/miR-16-5p/HMGA2 axis may be a potential target for treatment of ovarian cancer before treatment.

Data Availability
The data used to support this study are available from the corresponding author upon request.

Conflicts of Interest
The authors declare that they have no conflicts of interest.