Alpha-2 Heremans Schmid Glycoprotein (AHSG) promotes the proliferation of bladder cancer cells by regulating the TGF-β signalling pathway.

Bladder cancer (BC) is one of the most common urinary tract malignancies and is the tenth most common cancer globally. Alpha-2 Heremans Schmid Glycoprotein (AHSG) is a multifunctional protein that plays different roles in the progression of multiple tumors. However, the role and mechanism of AHSG in the development and progression of BC are unknown. AHSG expression was assessed in BC cells and tissues using western blot and immunohistochemistry. Using plasmid and siRNA, overexpressed and knocked down AHSG in BC cells were constructed. A series of functional experiments, including CCK8, plate clone formation, and flow cytometry, were performed to evaluate cell proliferation and cycle. AHSG was expressed higher in BC cells and tissues than in normal bladder epithelial cells and non-tumor tissues. Functionally, the overexpression of AHSG significantly increased the proliferation of BC cells and promoted the cell cycle from G1 to the S phase, whereas the knockdown of AHSG gave the opposite result.Additionally, western blot results revealed that AHSG expression level was negatively correlated with the phosphorylation level of Smad2/3 protein, a key downstream molecule of the traditional TGF-β signaling pathway, suggesting that AHSG could antagonize the traditional TGF-β signaling pathway. Finally, the expression level of AHSG in the urine of BC patients was significantly higher than that of healthy subjects by ELISA, with specificity. Our study concluded that AHSG might be a novel marker of BC that promotes the proliferation of BC cells by regulating the TGF-β signaling pathway.

Highlights

AHSG promotes the proliferation of bladder cancer cells and regulates cell cycle.

AHSG antagonizes the TGF-β signaling pathway.

AHSG is expected to be a potential new target for bladder cancer diagnosis.

Introduction

Bladder cancer (BC) is a malignant tumor in the bladder mucosa and is the tenth most common cancer worldwide, with high morbidity and mortality and easy recurrence [1].Till 2018, about 1.6 million people worldwide have suffered from BC, including 550,000 new cases and 200,000 deaths [2]. The incidence was higher in North America (11.3/100,000) and Europe (11.9/100,000) and lower in Asia (3.6/100,000 in Asia) [3]. More than 50% of patients relapsed within 6–12 years after the first diagnosis [4-6]. In China, BC incidence is lower than the global average, ranking 85th globally, and in the number of cases, it ranks 2nd in the world [3]. Smoking, genetic predisposition, and occupational exposure to aromatic amines, polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, cyclophosphamide, pioglitazone, ionizing radiation, chlorination of drinking water, and subsequently trihalomethane levels are contributing factors to bladder cancer [7]. In addition, diet is also suspected to be a key factor; however, arsenic-contaminated food is a definitive dietary risk factor for BC [8-10]. The pathological type of BC, the urothelial carcinoma [11], is complicated and exhibits sex differences. Their incidence in men is approximately three to four times higher than in females [11,12] due to the activity of the sex steroid hormone, which plays a role in the occurrence of BC development. In vivo and in vitro experiments have proven that androgen and estrogen exhibit a biological role in bladder cancer [13]. Cystoscopy is considered the gold standard diagnostic method for BC; however, because of its invasive nature and high price, urine exanthematous cytology is used as an adjuvant detection method for BC. Furthermore, the detection sensitivity of urine exanthematous cytology for low-grade BC is considerably lower than that for high-grade BC [11,12]. Currently, total cystectomy or partial cystectomy is performed for the treatment of BC, based on its severity. Alternatively, neoadjuvant chemotherapy can be performed before surgical treatment [14]. Although diagnostic and therapeutic methods of BC have been developed, the increasing incidence and poor prognosis of BC indicate the need for understanding the underlying pathological mechanism of BC progression. Therefore, an in-depth study of the signaling pathways affecting the development of BC and its underlying mechanism will be necessary for its diagnosis and treatment.

Alpha-2 Heremans Schmid Glycoprotein (AHSG), also known as human fetoglobulin-A, has a molecular weight of about 63 kDa, exists in adult animals, including humans, and is mainly synthesized in liver parenchymal cells [15]. AHSG is considered a multifunctional protein [16], and its role in disease processes such as diabetes [17-19] and renal diseases [16-20], as well as its ability to inhibit ecotopic calcification [21], have been proven. In addition, AHSG also plays a role in the progression of various tumors. In tumor progression, there are two primary sources of AHSG: one is from the serum, and the other is from tumor cells. Moreover, AHSG plays different roles in different tumors. Previous studies have reported that AHSG can promote breast cancer progression [22] and tumorigenesis of lung cancer [23]. Conversely, in intestinal tumors, AHSG inhibits the progression of intestinal tumors [24]. However, the role of AHSG in the progression of BC is unclear. Therefore, based on the diversity of roles of AHSG in tumor progression and our findings that AHSG levels are elevated in the serum of bladder cancer patients, the purpose of the current study was to determine the level of AHSG secreted by bladder cancer cells and the effect of AHSG on the occurrence and development of bladder cancer and further explore the specific molecular mechanism of AHSG [25].

Studies have demonstrated that AHSG participates in the regulation of TGF-β signaling pathways. TGF-β signaling pathways include both conventional and non-conventional pathways. In the conventional pathway, TGF-β acts as a tumor suppressor to induce cell differentiation, senescence, and apoptosis via Smad protein-dependent signaling by inducing cell cycle arrest (in the G1 phase) and protein kinase inhibitors (p21 and p15) and by inhibiting proliferation drivers such as c-myc [26]. However, during neoplasm progression, cancerous cells often evade the inhibition of the TGF-β signaling pathway and fully exploit their tumorigenicity. In pancreatic, colon, stomach, and head and neck tumors, the TGF-β signaling pathway often fails to inhibit tumor growth through mutagenic inactivation of receptors and Smad proteins [27]. RAS are stimulated to promote cancer development [28].On the other hand, in the conventional TGF-β signaling pathway, AHSG has a homologous domain with TGF-β ǁ receptor. Hence, it can competitively bind to TGF-β ǁ receptor, block the formation of a dimer, inhibit the phosphorylation of the Smad2/3 protein [14], and antagonize signal transduction. AHSG inhibits the tumor suppressive effect of the TGF-β signaling pathway via the conventional pathway, thus playing a promoting role in tumor progression.

To study the role of AHSG in the development and progression of bladder cancer, we hypothesized that AHSG promotes the proliferation of bladder cancer cells by regulating the TGF-β signaling pathway. We examined the expression level of AHSG in bladder cancer tissues and investigated the effects of AHSG on the proliferation and cell cycle of bladder cancer cells. In addition, we explored the regulatory pathway of AHSG, hypothesizing that AHSG might be involved in the regulation of the TGF-β signaling pathway in the progression of bladder cancer. Therefore, we speculate that AHSG may become a new indicator and target for the clinical diagnosis and treatment of BC.

Materials and methods

Human tumor tissues

Thirty pairs of bladder carcinoma and paracancerous tissues were collected from the Pathology Department of The First Affiliated Hospital of Dalian Medical University from July 2020 to December 2020. All diagnoses of BC were confirmed by a professional pathologist. Tumor tissues were stored in formalin. All patients provided written informed consent. The present study was performed following the Declaration of Helsinki and was approved by the Ethics Committee of the First Affiliated Hospital of Dalian Medical University (Approval number:PJ-KS-KY-2022-170).

Clinical samples

Urine samples used in the present study were collected in the First Affiliated Hospital of Dalian Medical University from July 2020 to January 2021. The present study was performed following the Declaration of Helsinki and was approved by the Ethics Committee of the First Affiliated Hospital of Dalian Medical University (Approval number: PJ-KS-KY-2022-170).All patients had signed informed consent, including 68 patients with BC, 47 with other urogenital system cancers involving prostate cancer, kidney cancer, renal pelvis tumor, adrenal tumors), 49 with urogenital system non-cancer diseases, including chronic glomerulonephritis, chronic kidney disease (CKD) 3–5 period, nephrotic syndrome and urinary tract stones), 68 patients with physical examination is a urine specimen. The patient’s age, gender, clinical diagnosis, operation and other information were queried in jiahe electronic medical record system of the First Affiliated Hospital of Dalian Medical University. The average age of the four groups was (68.25 ± 1.4) years, (63.21 ± 1.9) years, (63.53 ± 1.9) years, (67.47 ± 1.3) years, and the male proportion was 80.88%, 76.59%, 69.38%, 72.53%, respectively. There was no difference in age and sex among the four groups (all P > 0.05). Each sample was collected before the patients’ tumor resection surgery in the morning. The collected urine samples were centrifuged at 4°C and 1500 g for 15 min. The supernatant was taken and stored in a refrigerator at −80°C. The experiment was completed within 3 months.

Cell lines and cell culture

Human BC cell lines, T24 and 5637, and the human cystathionine epithelium perpetuated cellulite SV-40-immortalized human uroepithelial cell line (SV-HUC-1) were purchased from the American Culture Collection (ATCC, Manassas, VA, USA). According to Shuiqing Wu description [29], the cells were maintained in Roswell Park Memorial Institute Medium-1640 medium supplemented with 10% fetal bovine serum (FBS, Gibco, USA), 100 U/mL penicillin (Gibco, USA), and 100 µg/mL streptomycin (Gibco, USA) at 37°C in the presence of 5% CO2. The culture medium was renewed every 2–3 days.

Transient transfection

As H-L Cao describes [30], The AHSG overexpression sequence was inserted into the Pex-4 vector (GenePharma, Shanghai, China). T24 and 5637 transfected with the AHSG overexpression vector are described as the AHSG-Pex-4 group. Furthermore, T24 and 5637 transfected with the Pex-4 empty vector are defined as the Pex-4 group. The BC cell line with transient AHSG silencing was classified into 4 groups: control (cells transfected with the negative control); siAHSG-1 (cells transfected with AHSG-homo-169, sense: 5′-GAACUGCGAUGAUCCAGAATT-3′ and antisense: 5′-UUCUGGAUCAUCGCAGUUCTT-3′); siAHSG-2 (cells transfected with AHSG-homo-255, sense: 5′-CCUUGAACCAGAUUGAUGATT-3′ and antisense: 5′-UCAUCAAUCUGGUUCAAGGTT-3′); and siAHSG-3 (cells transfected with AHSG-homo-963, sense: 5′-CAGACUCCCAUGUGUUACUTT-3′ and antisense: 5′-AGUAACACAUGGGAGUCUGTT-3′) (GenePharma, Shanghai, China). Transfection was performed using a Lipofectamine 2000 Transfection kit (Invitrogen, USA). The ratio of siRNA/DNA was determined using Lipofectamine 2000, and the transfection process was performed according to the manufacturer’s protocol. Subsequent experiments were performed 48 h after cell transfection.

Cell proliferation assay

According to the manufacturer’s instructions, the alteration of cell proliferation rate was determined using Cell Counting Kit-8 (CCK8, Dojindo Laboratories, Kumamoto, Japan). As Caixiang Zhang describes [31], the cells were seeded into 96-well plates with a density of 4000 cells/well. After transfection, CCK8 solution was added into an FBS-free culture medium (1:9) and incubated at 37°C for 2 h. The absorbance at 450 nm (OD450 nm) was detected using a microplate reader, and data were recorded and analyzed.

Colony formation assay

Following Jie Han description [32], the cells were seeded into 6-well plates at a density of 2000 cells/well after AHSG siRNA or cDNA transfection. After culturing for 10 days, the surviving colonies were fixed with methanol at room temperature for 1 h, followed by crystal violet (Solarbio, Beijing, China) staining for 2 min. Images were acquired using an inverted microscope after washing with phosphate-buffered saline (PBS) three times, and data were recorded and analyzed.

Flow cytometry

Following Wenjie Luo description [33], The cells were collected, resuspended with pre-cooled PBS, centrifuged at room temperature for 5 minutes at 1500 g, and left to precipitate and break up the cells. The cell suspension was added to 1 mL of pre-cooled 70% ethanol and repeatedly mixed with maximum force to avoid clumping of cells. The mixture was then kept in a refrigerator at 4°C for more than 24 h. After fixation, the cells were centrifuged at 1000 g for 5 min, the supernatant was absorbed, and the cells were thoroughly washed with pre-cooled PBS. The cells were centrifuged to obtain cell precipitate. Subsequently, 0.5 ml of the prepared propidium iodide staining solution (Beyotime Biotechnology, Shanghai, China) was added, and the cells were gently blown so that the staining solution could fully contact the cells. An Eppendorf tube was wrapped in tin foil, warmed in a bath at 37°C for 30 min, and kept on Flow cytometer as soon as possible. Fluidized cytometry was used to detect the red fluorescence at the excitation wavelength of 488 nm and to detect dispersive light. DNA content and light emission were analyzed using suitable soft components.

Induction with human recombinant TGF-β

As per Pamela D. Thompson description [14], Human recombinant TGF-β powder (Beyotime Biotechnology, Shanghai, China) was dissolved in 100 ng/mL PBS solution containing albumin (2 mg/mL) (Beyotime Biotechnology, Shanghai, China). If the solution is used repeatedly for a long time, it must be packed according to the amount of each experiment and stored at −20°C. When the cells cultivated in 6-well plates grew to the required amount, 100 ng/mL human recombinant TGF-β solution was added to each well. It was then incubated for 30–60 min at 37°C and then used for subsequent experiments.

Western blotting

Following Hailong Hao description [34], Cell lysates were prepared in radioimmunoprecipitation lysis buffer containing protease inhibitor. The protein concentration was measured using a BCA kit (Beyotime Biotechnology, Beijing, China) and separated by 10% sodium dodecyl sulfate–polyacrylamide gel electrophoresis gel (Beyotime Biotechnology, Beijing, China). After transferring onto nitrocellulose membranes (Millipore, Billerica, MA, USA), 5% nonfat dry milk was used for blocking for 2 h at room temperature. Thereafter, the membranes were incubated at 4°C with the following primary antibodies: AHSG (1:1000, ABclonal), SMAD 2/SMAD 3 (1:1000, ABclonal), Phospho-Smad 2-S465/467+ Smad 3-S423/425 (1:1000, ABclonal), and GAPDH (1:2000, ABclonal). After washing with tris-buffered saline three times, the membranes were incubated with horseradish peroxidase-conjugated secondary antibody (1:5000, ABclonal) for 1 h. The protein bands were visualized using an ECL detection system and quantified using the Image J software (NIH, Bethesda, MD, USA).

Enzyme-linked immunosorbent assay (ELISA)

AHSG levels in the urine of BC patients were determined through ELISA (Elabscience, Wuhan, China) according to the manufacturer’s instructions. According to M Liu description [35], The samples (100 µL) were incubated at 37°C for 1.5 h. The liquid was poured out of the hole, and a biotinylated human AHSG antibody (100 µL) was added and then incubated at 37°C for 1 h. The plate was washed three times, and 100 µL of streptavidin-horseradish peroxidase conjugates were added and incubated for 1 h. The absorbance at 450 nm (OD450 nm) was detected and recorded after washing and staining. The AHSG levels in the urine were calculated using the standard curve obtained using excel.

Immunohistochemistry analysis

As per Sandip Pravin Patel description [36], the tissue sections were deparaffinised in xylol and rehydrated with decreasing ethanol concentrations, followed by antigen retrieved in citrate buffer (pH: 6.0) (Beyotime Biotechnology, Beijing, China). Endogenous peroxidases were removed using 0.3% H2O2(Beyotime Biotechnology, Beijing, China), and nonspecific binding sites were blocked using a complete serum. Thereafter, the sections were incubated with a primary antibody (AHSG: 1:100, Proteintech, Wuhan, China) at 37°C for 1 h. The sections were treated with a second antibody (HRP Goat Anti-Mouse IgG:1:5000, ABclonal, Shaghai, China) after washing with PBS. The sections were visualized with diaminobenzidine and counterstained with hematoxylin. An ordinary light microscope was used to detect the presence of brown or tan particles in the nucleus and cytoplasm as a positive result, which was independently double-blind scored by two senior physicians in the Department of Pathology. The score of positive cells was given as follows: no positive cells, 0 points; positive cells >25% and <50%, 2 points; positive cells >50% and <75%, 3 points; positive cells >75%, 4 points. The color strength score was given as follows: 0 for no color; 1 for light yellow; 2 for brown; 3 for tan. The total score for staining determination was calculated as follows: score of positive cells × score of staining intensity.

Statistical analysis

All data from three independent experiments are expressed as the mean ± standard error of the mean. Statistical analysis by SPSS17.0 (SPSS Inc., Chicago, IL, USA), and charts using GraphPad Prism 6.0 (https://www.graphpad.com/). Student’s t-test was used to compare the differences between the two sets of data and one-way analysis of variance (ANOVA) was used to analyze the comparisons of continuous variables between multiple groups. P < 0.05(*) was considered statistically significant, P < 0.01(**), P < 0.001 (***), and P < 0.0001 (****) indicate that the experimental results had statistically significant differences.

Results

In the current study, we investigated the effect of AHSG on the proliferation and cell cycle of bladder cancer cells. First, we detected and analyzed the expression of AHSG in bladder cancer cells and tissues. Subsequently, AHSG was overexpressed and knocked down in bladder cancer cell lines T24 and 5637, and then cell proliferation and cell cycle changes were measured. Furthermore, the effect of AHSG on the phosphorylation level of Smad2/3 protein, a key molecule downstream of the traditional TGF-β signaling pathway, was detected. Finally, the expression of AHSG in the urine of patients with bladder cancer was measured. The present study demonstrated that AHSG promotes the proliferation of bladder cancer cells by regulating the TGF-β signaling pathway, thus promoting bladder cancer progression, suggesting that AHSG may be a potential target for clinical diagnosis and treatment of bladder cancer.

AHSG levels in BC cells and tissues

AHSG levels in human normal bladder epithelial cell lines SV-HUC-1 and BC cell lines T24 and 5637 were detected by western blotting. The results are shown in Figure 1a. AHSG level was markedly higher in the T24 and 5637 cell lines than in the SV-HUC-1 cell line. AHSG level in 24 pairs of BC tissues and paracancerous tissues was detected by immunohistochemistry. The results are shown in Figure 1(b) (1–5). AHSG was less expressed in the normal bladder epithelium of the paracancerous tissues, with a staining intensity score of 3.000 ± 0.7323, whereas it was highly expressed in the BC tissues, with a staining intensity score of 6.000 ± 0.7397, which was significantly higher than that of the adjacent tissues.

Figure 1.

Levels of Alpha-2 Heremans Schmid Glycoprotein (AHSG) in bladder cancer (BC) cells and tissues.

Transfection efficiency of overexpression/knockdown of AHSG in the T24 and 5637 cells

The T24 and 5637 cells were transfected with the AHSG-Pex-4 vector, which was overexpressed using plasmid technology. The three AHSG siRNAs were named siAHSG-1, siAHSG-2, and siAHSG-3, and the three siAHSGs and negative control were transfected into the T24 and 5637 cells. The transfection efficiency of the two methods was detected by western blotting. As shown in Figure 2, AHSG-Pex-4 overexpression increased AHSG expression in the T24 and 5637 cells, whereas all three siAHSGs significantly reduced AHSG expression. siAHSG-1 exhibited the best transfection efficiency. Therefore, subsequent experiments were performed using siAHSG-1.

Figure 2.

Transfection efficiency of overexpressed/knockdown Alpha-2 Heremans Schmid Glycoprotein (AHSG) in T24 and 5637 detected by western blotting.

Effect of AHSG expression on the proliferation and cell cycle of the T24 and 5637 cells

CCK8 and clone formation assays were performed to detect changes in the proliferation ability of the T24 and 5637 cells after AHSG overexpression/knockdown. The proliferation and clone formation abilities of the T24 and 5637 cells were significantly increased after AHSG overexpression (Figure 3(a-b)), whereas they were decreased considerably after AHSG knockdown (Figure 3(c-d)). To further explore the effect of AHSG expression on the cell cycle of BC cells, flow cytometry was used for the detection of changes in the cell cycle of the T24 and 5637 cells after AHSG overexpression/knockdown, and we discovered that AHSG overexpression promoted the cell cycle from the G1 phase to the S phase in the T24 and 5637 cells (Figure 3(e-f)). On the contrary, AHSG knockdown arrested the cell cycle of the T24 and 5637 cells in the G1 phase (Figure 3 (g-h)).

Effects of overexpression/knockdown of Alpha-2 Heremans Schmid Glycoprotein (AHSG) on the proliferation and cell cycle of T24 and 5637.

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AHSG expression was negatively correlated with the phosphorylation level of Smad2/3 protein, a key molecule downstream of the traditional TGF-β signaling pathway

After AHSG overexpression/knockdown in the T24 and 5637 cells, the cells were induced by human recombinant TGF-β for 30–60 min. Western blotting was performed to detect the effect of AHSG expression on the phosphorylation level of Smad2/3 protein. The results revealed that the phosphorylation level of Smad2/3 protein (p-Smad2/3/total Smad2/3) was significantly decreased after AHSG overexpression (Figure 4(a-b)), whereas it was significantly increased after AHSG knockdown (Figure 4(c-d)). These results indicated that AHSG expression was negatively correlated with the phosphorylation level of Smad2/3 protein.

Figure 4.

The effect of overexpression/knockdown of Alpha-2 Heremans Schmid Glycoprotein (AHSG) in T24 and 5637 on the phosphorylation level of Smad2/3 protein, a key molecule downstream of the TGF-β conventional pathway.

AHSG levels in the urine of patients with BC

Urine samples of 68 patients with BC, 47 patients with other cancers of the genitourinary system, 49 patients with non-tumor diseases of the genitourinary system, and 68 healthy subjects were analyzed by ELISA. The results are shown in Figure 5(a). AHSG levels in the urine samples of patients with BC [(6420 ± 475.1) ng/mL] were significantly higher than those of the healthy subjects [(527.3 ± 40.94) ng/mL] (P < 0.0001), and they were higher than those of patients with other genitourinary cancers [(3755 ± 417.2) ng/mL] as well as genitourinary non-tumor diseases [(4880 ± 330.0) ng/mL] (P < 0.05). Figure 5(b) shows the receiver operating characteristic curve analysis of the 64 patients with BC and the 64 healthy subjects, and the area under curve value is 0.9548 (95% confidence interval: 0.9188 to 0.9908, P < 0.0001).

Figure 5.

The levels of Alpha-2 Heremans Schmid Glycoprotein (AHSG) in the urine of bladder cancer (BC) patients.

Discussion

At present, factors leading to BC and the underlying specific pathogenesis are yet unclear. The incidence rate and recurrence rate of BC are high, and the early stage is challenging to diagnose. In more than 90% of patients with BC, incipient symptoms are painless, intermittent, and flesh eye whole hematuria. However, the grade, malignancy, size, extent, and several tumors are not necessarily in direct proportion to the amount of blood and the length of hematuria duration. Sometimes, when flesh eye hematuria occurs, tumors may have been already developed to the late stage [37]. Therefore, based on a high malignancy degree, rapid disease progression, and a low pre-survival rate of BC, finding a new marker for the early detection and diagnosis of BC is vital for the bedside treatment of the disease and improvement in it.

In a previous study, we collected the sera of patients with BC and healthy subjects, performed matrix-assisted laser desorption/ionization-time of flight mass spectrometry to screen and identify the differentially expressed AHSG, and verified its increased expression in the sera of patients with BC by ELISA [25]. AHSG is a glycoprotein synthesized by the liver with a molecular weight of 63 kDa. It is a multifunctional protein that can participate in calcium homeostasis and regulate bone development [38]. Moreover, AHSG can inhibit the phosphorylation of insulin receptors and receptor substrates, leading to insulin resistance, increasing the risk of type II diabetes mellitus [17-19] and can cause kidney damage [16-20]. In addition, AHSG affects the disease course of diverse tumors. Studies have illustrated that in tumor progression, two types of AHSG occur, one is serum AHSG and another is secreted by tumor cells themselves, and in different tumors, two types of AHSG exhibit a different trend of increase or decrease, as well as the promotion and inhibition of tumor progression, is also different [39]. Studies on serum levels of AHSG revealed that serum concentrations of AHSG in patients with gastric cancer were significantly higher than those in healthy controls [40].In contrast, serum concentrations of AHSG are significantly reduced in some hematological malignancies [41,42]. Cellular level studies on tumors have demonstrated that AHSG promotes the tumorigenesis of breast cancer [22] and lung cancer [23]. Conversely, in intestinal tumors, AHSG inhibits the progression of intestinal tumors [42]. However, the role of AHSG in the development and progression of BC has not been reported. In previous studies, we observed that AHSG was elevated in the serum of patients with bladder cancer and speculated that AHSG might be involved in the occurrence and development of BC [25]. However, in the current study, we discovered for the first time that AHSG could promote the proliferation and influence the cell cycle of bladder cancer cells.

AHSG might be involved in the regulation of the TGF-β signaling pathway [22]. TGF-β, also known as transgenic growth factor-β, is a relatively large superfamily of cellular factors, including TGF-βs (TGF-β1, β2, and β3), excitins, inhibitins, anti-mullierian hormone, bone-forming proteins, growth differentiation factors, gelatine-derived neurotrophic factors [43]. TGF-β signaling pathways play a role in regulating ganglionic cell viability functions, such as cell growth, differentiation, apoptosis, locomotion, invasion, extracellular substrate production, angiogenesis, and vaccination response [44]. Two pathways in the TGF-β signaling pathway exist during cancer progression, the traditional pathway and the non-traditional pathway, which is also known as the uncommonly known TGF-β ‘bidirectional action.’ In the traditional pathway, TGF-β plays a role in the inhibition of tumorigenesis by inducing or stimulating the activation of periodic opalabinase inhibitors (p16INK4A, p15INK4B, p21CIP1, and p27Kip1) in the G1 phase and weakened c-myc and DNA-bound protein inhibitory agents (inhibitor of DNA binding (ID)-1 and ID-2) to inhibit cell proliferation and induce cell senescence and apoptosis via Smad protein-dependent signaling pathways [43]. However, with tumor progression, the components of the TGF-β signaling pathway, including receptors and Smad proteins, are mutated and deactivated, which cannot cause changes in c-myc, ID-1, and ID-2, and its growth inhibition is ineffective [45]. Various non-Smad-dependent signaling pathways, including extracellular signal-regulated kinase, mitogen-activated protein kinase, phosphoinositide 3-kinases, Akt pathways, are activated and induce epithelial-mesenchymal transition (EMT), which plays a role in promoting tumor progression [45]. To conclude, the role of the TGF-β signaling pathway in cancer progression is very complex, and the current study only focused on the anti-tumor effect of the TGF-β signaling pathway. Studies have revealed that AHSG has a domain homologous to TGF-β II receptor, which blocks the binding of TGF-β to its receptor and inhibits the phosphorylation of Smad2/3 protein, thereby antagonizing signal transduction and impeding the tumor suppressive effect of the TGF-β signaling pathway via traditional pathways, thus promoting tumor progression [22].In this study, we observed a significant negative correlation between AHSG expression and Smad2/3 protein phosphorylation level in BC cells, suggesting that AHSG antagonized the traditional TGF-β signaling pathway, impeding its tumor suppressive role, thus promoting BC progression.

The early clinical manifestation of bladder cancer is simple, and the differential diagnosis is difficult. At present, the gold standard for diagnosing BC is cystoscopy and urine exanthematous cytology. The sensitivity of cystoscopy is 73%, but the specificity is only 37%, and it is invasive [46]. Although exfoliation cytology is more convenient and less expensive than cystoscopy, it has low sensitivity in diagnosing low-grade BC and is prone to misdiagnosis [46]. Therefore, finding a convenient, fast, and noninvasive detection method that can assist the two types of examinations for improving the sensitivity and specificity of BC diagnosis is particularly important. In recent years, proteomic detection methods based on biological body fluids such as urine and serum have attracted the interest of researchers, which provides a new idea for exploring BC-specific proteins and the diagnosis and prognosis of BC [47]. Compared with blood, urine is the filtrate of blood and is easy to obtain, which can also relieve patients’ pain. Furthermore, urine proteins are rich and stable. As 70% of these proteins come from the urinary system, and the bladder is a vital organ to store urine, proteins that can represent bladder status were generated in bladder tumor progression and were excreted in the urine, which is expected to act as biomarkers for the diagnosis and to monitor the occurrence and development of BC. In the present study, we indicated that AHSG levels in the urine of patients with BC were significantly higher than those of the healthy subjects. In addition, AHSG can be differentiated from patients with diseases exhibiting hematuria symptoms, such as renal cancer and, prostate cancer, glomerulonephritis, urinary calculi. These results suggested that AHSG may be a potential indicator and target in the clinical diagnosis of BC. Besides, urine samples are easy to obtain and detect, which is expected to alleviate the pain of patients and realize the early diagnosis of bladder cancer.

To summarize, our study demonstrated that AHSG promotes the proliferation of bladder cancer cells by regulating the TGF-β signaling pathway, thereby promoting bladder cancer progression, suggesting that AHSG may be a potential target for clinical diagnosis and treatment of bladder cancer.

However, this subject also has some limitations, providing us with further research direction. Firstly, we found that AHSG can promote the proliferation of bladder cancer cells by regulating the cell cycle, but we did not clarify which Cyclin it acts on. Therefore, subsequent studies can further explore the effects of AHSG on cyclin-related proteins such as Cyclin D1, CDK2 and P27 [48]. Secondly, we only studied the effects of AHSG on the proliferation ability and cell cycle of BC cells, but the effects of AHSG on migration, invasion, and EMT were not studied. Therefore, further studies are needed to study the AHSG effect on migration, invasion, and EMT. Thirdly, the current study is limited to the study of traditional pathways via which AHSG regulates the TGF-β signaling pathway, whereas the exploration of the specific molecular mechanism via which AHSG regulates the non-traditional pathway can be used as the direction of future research, providing a new idea for further exploration BC pathogenesis. Fourthly, due to the limited number of patients recruited, we did not find any association between urinary AHSG levels and BC stage and grade. Therefore, more patients at different stages of BC development should be recruited in future studies to explore the association between urinary AHSG levels and BC development dynamics.Fifthly, this study is limited to in vitro experiments, so in vivo experiments, such as animal experiments, can be added in subsequent studies to enhance the clinical significance of this research.

Conclusion

Our results suggest that AHSG antagonizes the TGF-β signaling pathway by inhibiting the phosphorylation of Smad2/3 protein, promotes the proliferation of bladder cancer cells and regulates the cell cycle, thereby promoting the progression of bladder cancer. This means AHSG is expected to be a potential new indicator and target for clinical diagnosis of bladder cancer. However, in vivo experiments are needed to confirm this conclusion.

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