# Prp19 Facilitated p21-Dependent Senescence of Hepatocellular Carcinoma Cells

Authors: Jie Yin; Guang-Cong Zhang; Ying Fang; Xiang-Nan Yu; Tao-Tao Liu; Ling Dong; Xi-Zhong Shen
Journal: Journal of Oncology
 (2022)

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## Abstract

Introduction. Evidence suggests that the role of senescence in the development of cancer is context-dependent. An orthologue of human pre-mRNA processing factor 19 (Prp19) attenuates the senescence of human endothelial cells. Prp19 has been reported to be involved in the progression of hepatocellular carcinoma (HCC). This work aims to investigate the effect of Prp19 on the senescence of HCC. Materials and Methods. Senescence of L02 cells and HCC cells under different stimuli was detected through cell cycle analysis, SA-β-gal staining, and senescence associated secretory phenotype analysis. The relationship between Prp19 and senescence-related proteins was evaluated using real-time RT-PCR, western blot assay, and immunohistochemistry. Subcutaneous xenograft tumors in nude mice were used to evaluate the role of Prp19 on senescence in vivo. Data analysis was carried out using GraphPad Prism 6. Results. Prp19 facilitated the senescence of L02 cells and HCC cells under different stresses. Prp19 positively modulated p21 expression in the mRNA level. Downregulation of Prp19 promoted the growth of subcutaneous xenograft tumors generated by HCC cell lines. Conclusions. Prp19 may promote senescence of HCC cells via regulating p21 expression.


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## Body

## 1. Introduction

Primary liver cancer is the sixth most common cancer in the world and the fourth most common cause of cancer mortality [1]. Globally, hepatocellular carcinoma (HCC) is the dominant type of liver cancer, accounting for approximately 75% of the total [2]. Data from Japan demonstrated that for patients undergoing resection, tumor recurrence, including true recurrence due to dissemination and de novo tumors within the oncogenic liver, complicated 70% of cases at 5 years [3]. Although molecular therapy has shed light on the treatment of patients with advanced HCC, these drugs did not produce significant results [4]. Therefore, new targets are pursued in the treatment of HCC.Cellular senescence, a state of permanent cell cycle arrest, can be induced by multiple stimuli, such as telomere shortening, chromosomal disturbance, oxidative damage, and activation of oncogenes [5]. A large body of evidence has demonstrated a potent tumor suppressor role of senescence in HCC initiation [6–9]. The mechanisms of senescence in HCC are still elusive. Although senescent hepatocyte-secreted chemokines suppress the initiation of liver cancer, they can accelerate the growth of fully established HCC [10]. Therefore the role of senescence in development of HCC is context-dependent. Prosenescence therapy in conjunction with drugs that selectively eliminate senescent HCC cells could be an effective treatment of HCC [11].Senescence evasion factor, the human orthologue of Prp19, extends the life span of human endothelial cells by increasing resistance to stress [12]. Prp19 is a multifunctional protein involved in many cellular activities [13]. Previous studies have found that Prp19 participates in cell-cycle progression and chemotherapeutic resistance of HCC cells [14, 15]. Prp19 also facilitated invasion of HCC by promoting twist1-induced epithelial-mesenchymal transition [16]. Considering the important effect of senescence on the development of HCC, the role of Prp19 in senescence during the development of HCC is worth exploring in depth.In this study, we found a potential prosenescence role of Prp19 on HCC cells.β-Galactosidase (β-gal) staining and senescence associated secretory phenotype (SASP) analysis revealed that Prp19 facilitated senescence in L02 cells and HCC cells under different stresses. Prp19 positively modulated the expression of the senescence-related protein p21 at the transcriptional level. Inhibition of Prp19 promoted tumor growth of HCC cell lines in vivo.


## 2. Materials and Methods

### 2.1. Cell Lines

Immortalized normal hepatocyte L02 and liver cancer cell lines including Huh7, SMMC-7721, and SK-Hep1 were purchased from Cell Bank of Type Culture Collection of Chinese Academy of Sciences (Shanghai, China). HCC cell lines were cultured in Dulbecco’s modified Eagle’s medium with 10% fetal calf serum. L02 was cultured in RPMI 1640 with 20% fetal calf serum. The cells above were cultured in a humidified incubator at 37°C with 5% CO2.


### 2.2. shRNA Lentivirus Particles, siRNAs, Plasmids, and Reagents

Human Prp19 shRNA lentivirus particles and negative control shRNA lentivirus particles (61415-V, 108080, Santa Cruz) were used to transduce HCC lines following the manufacturer’s protocol. Stable HCC lines misexpressing Prp19 were selected with puromycin (Sigma-Aldrich, St. Louis, USA). siRNA targeting Prp19 and nonsense control siRNA were obtained from GenePharma (Shanghai, China), and the sequences are available in Supplementary Table1. siRNA transfection was carried out using Lipofectamine® 2000 transfection reagent (Invitrogen, CA, USA). Full-length human expression plasmids of human pcDNA3. 1-Prp19 and vector controls were described in our previous work [16]. The H-ras expression plasmid was purchased from Addgene (MA, USA). Plasmid transfection was performed with XtremeGENE HP DNA transfection reagent (Roche, Mannheim, Germany). Cisplatin was obtained from Sigma (Sigma-Aldrich, St. Louis, USA).


### 2.3. Cell Cycle Analysis

For flow cytometric analysis, cells were collected in phosphate buffered saline (PBS) and fixed in cold ethanol (70–80%) for at least 18 h. Fixed cells were washed three times in PBS and then were stained with propidium iodide (Becton Dickinson, San Jose, CA, USA) for 20 min at 4°C. Finally, cells were analyzed for cell cycle distribution using a BD FACSCalibur Flow Cytometer (Becton Dickinson, Franklin Lakes, NJ, USA). The experiments were independently repeated three times.


### 2.4. SA-β-Galactosidase Staining

1 × 105 cells were seeded into 12-well plate. Cells under corresponding treatments were rinsed with PBS, fixed with 4% formaldehyde in PBS, and then incubated with freshly prepared senescence-associated β-gal staining solution (Beyotime, Nantong, China) at 37°C overnight. β-gal positive cells were counted in randomly selected fields per 100 cells. Frozen xenograft tumors were evaluated for in vivo assay.


### 2.5. Real-Time RT-PCR, Western Blotting Assay, and Immunohistochemistry

The total RNA of HCC cells was extracted by TRIzol (Invitrogen, NY, USA). The synthesis of the first strand of cDNA was performed with the AMV RNA PCR kit (TaKaRa, Dalian, China) following the manufacturer’s protocol. Subsequent real-time PCR was performed using a SYBR Green Premix Ex Taq (TaKaRa, Dalian, China) on the ABI StepOne Plus system (Applied Biosystems, CA, USA). The primers used in real-time RT-PCR are listed in Supplementary Table2. Western blot assay was performed to analyze cell lysate extracts using ImageQuant LAS 4000mini (GEHealthcare, New Jersey, USA). The antibodies used are listed in Supplementary Table 3. Immunohistochemistry of paraffin-embedded sections was performed as reported elsewhere [17].


### 2.6. Animal Experiments

BALB/C nude mice (4 weeks old, male) were obtained from the Shanghai Institute of the Material Medicine of Chinese Academy of Science. Stable HCC cells misexpressing Prp19 were injected subcutaneously into the left armpit of nude mice (n = 5). The size of subcutaneous xenograft tumors was measured weekly after injection. Four weeks later, xenograft tumors were prepared for hematoxylin and eosin staining, immunohistochemistry analysis, and β-gal staining. Animal care and experimental protocols were approved by the Experimental Animal Care Commission of Shanghai Medical School of Fudan University (Shanghai, China) and are in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.


### 2.7. Statistical Analysis

GraphPad Prism 6 (La Jolla, CA, USA) was used for data analysis. Data were presented as the mean ± SEM of three independent studies. Student’st-test was used to compare differences between different groups. P value less than 0.05 was recognized as statistically significant. ∗p<0.05, ∗∗p<0.01, and ∗∗∗p<0.001.


## 2.1. Cell Lines

Immortalized normal hepatocyte L02 and liver cancer cell lines including Huh7, SMMC-7721, and SK-Hep1 were purchased from Cell Bank of Type Culture Collection of Chinese Academy of Sciences (Shanghai, China). HCC cell lines were cultured in Dulbecco’s modified Eagle’s medium with 10% fetal calf serum. L02 was cultured in RPMI 1640 with 20% fetal calf serum. The cells above were cultured in a humidified incubator at 37°C with 5% CO2.


## 2.2. shRNA Lentivirus Particles, siRNAs, Plasmids, and Reagents

Human Prp19 shRNA lentivirus particles and negative control shRNA lentivirus particles (61415-V, 108080, Santa Cruz) were used to transduce HCC lines following the manufacturer’s protocol. Stable HCC lines misexpressing Prp19 were selected with puromycin (Sigma-Aldrich, St. Louis, USA). siRNA targeting Prp19 and nonsense control siRNA were obtained from GenePharma (Shanghai, China), and the sequences are available in Supplementary Table1. siRNA transfection was carried out using Lipofectamine® 2000 transfection reagent (Invitrogen, CA, USA). Full-length human expression plasmids of human pcDNA3. 1-Prp19 and vector controls were described in our previous work [16]. The H-ras expression plasmid was purchased from Addgene (MA, USA). Plasmid transfection was performed with XtremeGENE HP DNA transfection reagent (Roche, Mannheim, Germany). Cisplatin was obtained from Sigma (Sigma-Aldrich, St. Louis, USA).


## 2.3. Cell Cycle Analysis

For flow cytometric analysis, cells were collected in phosphate buffered saline (PBS) and fixed in cold ethanol (70–80%) for at least 18 h. Fixed cells were washed three times in PBS and then were stained with propidium iodide (Becton Dickinson, San Jose, CA, USA) for 20 min at 4°C. Finally, cells were analyzed for cell cycle distribution using a BD FACSCalibur Flow Cytometer (Becton Dickinson, Franklin Lakes, NJ, USA). The experiments were independently repeated three times.


## 2.4. SA-β-Galactosidase Staining

1 × 105 cells were seeded into 12-well plate. Cells under corresponding treatments were rinsed with PBS, fixed with 4% formaldehyde in PBS, and then incubated with freshly prepared senescence-associated β-gal staining solution (Beyotime, Nantong, China) at 37°C overnight. β-gal positive cells were counted in randomly selected fields per 100 cells. Frozen xenograft tumors were evaluated for in vivo assay.


## 2.5. Real-Time RT-PCR, Western Blotting Assay, and Immunohistochemistry

The total RNA of HCC cells was extracted by TRIzol (Invitrogen, NY, USA). The synthesis of the first strand of cDNA was performed with the AMV RNA PCR kit (TaKaRa, Dalian, China) following the manufacturer’s protocol. Subsequent real-time PCR was performed using a SYBR Green Premix Ex Taq (TaKaRa, Dalian, China) on the ABI StepOne Plus system (Applied Biosystems, CA, USA). The primers used in real-time RT-PCR are listed in Supplementary Table2. Western blot assay was performed to analyze cell lysate extracts using ImageQuant LAS 4000mini (GEHealthcare, New Jersey, USA). The antibodies used are listed in Supplementary Table 3. Immunohistochemistry of paraffin-embedded sections was performed as reported elsewhere [17].


## 2.6. Animal Experiments

BALB/C nude mice (4 weeks old, male) were obtained from the Shanghai Institute of the Material Medicine of Chinese Academy of Science. Stable HCC cells misexpressing Prp19 were injected subcutaneously into the left armpit of nude mice (n = 5). The size of subcutaneous xenograft tumors was measured weekly after injection. Four weeks later, xenograft tumors were prepared for hematoxylin and eosin staining, immunohistochemistry analysis, and β-gal staining. Animal care and experimental protocols were approved by the Experimental Animal Care Commission of Shanghai Medical School of Fudan University (Shanghai, China) and are in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.


## 2.7. Statistical Analysis

GraphPad Prism 6 (La Jolla, CA, USA) was used for data analysis. Data were presented as the mean ± SEM of three independent studies. Student’st-test was used to compare differences between different groups. P value less than 0.05 was recognized as statistically significant. ∗p<0.05, ∗∗p<0.01, and ∗∗∗p<0.001.


## 3. Results

### 3.1. Prp19 Facilitates Senescence of L02 Cells

Our previous study suggested that Prp19 arrested the cell cycle of HCC cells at the G1 phase [14], we speculated that Prp19 may have an effect on senescence. Since the protein level of Prp19 in normal hepatocyte L02 was lower than that in HCC cells [16], Prp19 was overexpressed in L02 cells to evaluate the impact of Prp19 on the senescence of normal hepatocyte (Figure 1(a)). Upregulating Prp19 expression in L02 cells resulted in G1 arrest (Figure 1(a)), while more β-gal positive cells were observed in L02 cells overexpressing Prp19 compared with vector controls (Figure 1(b)). We also found that Prp19 promoted cisplatin-induced senescence of L02 cells (Figure 1(b)). Furthermore, overexpression of the H-ras oncogene in L02 cells led to senescence, while upregulation of Prp19 promoted H-ras-induced senescence in L02 cells (Figure 1(c)). Taken together, these results demonstrated that Prp19 facilitated the senescence of L02 cells with or without stimuli.Figure 1
Prp19 facilitates the senescence of L02 cells. (a) Cell cycle distribution of L02 cells transfected with myc-Prp19. (b) The effects of Prp19 on senescence of L02 cells were assessed using SA-β-galactosidase staining with or without incubation of 10 μM cisplatin for 24 h. (c) The effects of Prp19 on H-ras-induced senescence of L02 cells were assessed using SA-β-galactosidase. Null vector, NV. The data are shown as the mean ± SEM. Similar results were observed in three independent experiments. ∗p<0.05, ∗∗p<0.01, and ∗∗∗p<0.001. Black scale bar: 100 μm.
(a)(b)(c)


### 3.2. Inhibiting Prp19 Represses Senescence of HCC Cells

Prp19 expression was downregulated by siRNA silencing in Huh7 cells and SMMC-7721 cells (Figure2(a)). Inhibiting Prp19 significantly reduced percentages of Huh7 cells and SMMC-7721 cells in G1 phase (Figure 2(b)). Downregulation of Prp19 in HCC cells decreased the percentages of β-gal positive cells compared with nonsense controls (Figure 2(c)). As indicated in Figure 2(d), silencing Prp19 expression in HCC cells also obviously inhibited cisplatin-induced senescence. Compared to controls, CXCL-1 mRNA was significantly decreased in Huh7 cells following knockdown of Prp19, while CXCL-1, IL-6, and IL-8 mRNAs were significantly reduced in SMMC-7721 cells after knockdown of Prp19 (Figure 2(e)). Taken together, Prp19 knockdown in HCC cells inhibited senescence and also attenuated cisplatin-induced senescence.Figure 2
Inhibiting Prp19 represses senescence of HCC cells. (a) Prp19 expression was decreased by siRNA silencing in HCC cells. (b) Cell cycle distribution of HCC cells with Prp19 knockdown. (c) The effects of Prp19 on HCC cells senescence were assessed using SA-β-galactosidase. (d) The effects of Prp19 on HCC cells senescence were assessed using SA-β-galactosidase staining with or without incubation of 10 μM cisplatin for 24 h. (e) Relative IL6, IL1a, IL1b, IL8, and CXCL1 transcript levels in human HCC cell lines were determined by qRT-PCR. The levels of mRNA were normalized to ACTIN and presented relative to the control cells. Negative control, NC. The data are shown as the mean ± SEM. Similar results were observed in three independent experiments. ∗p<0.05 and ∗∗p<0.01. Black scale bar: 100 μm.
(a)(b)(c)(d)(e)


### 3.3. Prp19 Modulates p21 Expression in L02 Cells and HCC Cells

Western blot assay showed that p21 rather than p53 or p16 was increased in L02 cells overexpressing Prp19 (Figure3(a)). Prp19 knockdown in HCC cells showed a robust reduction in p21 protein expression, while silencing Prp19 did not affect p53 or p16 protein expression, two other important senescence modulators (Figure 3(b)). Considering the vital role of Prp19 in pre-mRNA processing, we assessed p21 mRNA levels in HCC cells with Prp19 downregulation. Real-time RT-PCR analysis showed that silencing Prp19 significantly decreased p21 mRNA levels in HCC cells compared with controls (Figure 3(c)). These findings suggested that Prp19 may participate in the senescence of HCC cells by regulating the expression of p21 mRNA.Figure 3
Prp19 modulates p21 expression in L02 cells and HCC cells. (a) Western blot assay of p16, p21, and p53 expression in L02 cells overexpressing Prp19. (b) Western blot assay of p16, p21, and p53 expression in HCC cells with Prp19 knockdown. (c) Relative levels of Prp19 and p21 transcripts in human HCC cell lines were determined by qRT-PCR. Levels of mRNA were normalized to ACTIN and presented relative to the control cells. Negative control, NC. The data are shown as the mean ± SEM.∗∗∗p<0.001.
(a)(b)(c)


### 3.4. Prp19 Knockdown PromotesIn Vivo Tumor Growth of HCC Cells

Senescence is an important barrier against cell proliferation. A previous study showed that Prp19 had no significant impact on HCC cell proliferationin vitro [16]. To investigate the role of Prp19 on tumor growth in vivo, we generated two stable HCC cell lines misexpressing Prp19 and then established subcutaneous xenograft models of HCC. Compared to the NTC groups, Prp19 expression was attenuated in the shPrp19 groups (Figure 4(a)). In this model, tumor volume was measured weekly. The mean tumor volume and weight in the NTC groups were significantly decreased compared to the shPrp19 groups (Figures 4(b) and 4(c)). In the shPrp19 groups, the expression of Prp19 and p21 was decreased in xenograft tumor tissues compared to the NTC groups (Figures 4(d) and 4(e)). Unlike the NTC group, there were fewer senescent areas in the xenograft tissues of the shPrp19 group (Figures 4(d) and 4(f)). Abovementioned data suggested that Prp19 knockdown inhibited HCC cell senescence and promoted tumor growth of HCC cells in vivo.Figure 4
Prp19 knockdown promotes tumor growth of HCCin vivo. (a) Prp19 protein expression of stable HCC cell lines misexpressing Prp19. (b) Images of the subcutaneous xenograft tumors generated by HCC cells misexpressing Prp19 in nude mice. The weights of the xenograft tumors are summarized in the lower panel. (c) Comparison of tumor size at the indicated time after implantation (n = 5). (d) Representative images of HE, IHC staining of Prp19 and p21, and SA-β-galactosidase staining in xenograft tumors (original magnification 200x). (e) Prp19 and p21 protein expression in xenograft tumors. (f) Statistically analysis of SA-β-galactosidase positive cells in xenograft tumors. Values are mean ± SEM, ∗p<0.05and ∗∗p<0.01. Black scale bar: 100 μm.
(a)(b)(c)(d)(e)(f)


## 3.1. Prp19 Facilitates Senescence of L02 Cells

Our previous study suggested that Prp19 arrested the cell cycle of HCC cells at the G1 phase [14], we speculated that Prp19 may have an effect on senescence. Since the protein level of Prp19 in normal hepatocyte L02 was lower than that in HCC cells [16], Prp19 was overexpressed in L02 cells to evaluate the impact of Prp19 on the senescence of normal hepatocyte (Figure 1(a)). Upregulating Prp19 expression in L02 cells resulted in G1 arrest (Figure 1(a)), while more β-gal positive cells were observed in L02 cells overexpressing Prp19 compared with vector controls (Figure 1(b)). We also found that Prp19 promoted cisplatin-induced senescence of L02 cells (Figure 1(b)). Furthermore, overexpression of the H-ras oncogene in L02 cells led to senescence, while upregulation of Prp19 promoted H-ras-induced senescence in L02 cells (Figure 1(c)). Taken together, these results demonstrated that Prp19 facilitated the senescence of L02 cells with or without stimuli.Figure 1
Prp19 facilitates the senescence of L02 cells. (a) Cell cycle distribution of L02 cells transfected with myc-Prp19. (b) The effects of Prp19 on senescence of L02 cells were assessed using SA-β-galactosidase staining with or without incubation of 10 μM cisplatin for 24 h. (c) The effects of Prp19 on H-ras-induced senescence of L02 cells were assessed using SA-β-galactosidase. Null vector, NV. The data are shown as the mean ± SEM. Similar results were observed in three independent experiments. ∗p<0.05, ∗∗p<0.01, and ∗∗∗p<0.001. Black scale bar: 100 μm.
(a)(b)(c)


## 3.2. Inhibiting Prp19 Represses Senescence of HCC Cells

Prp19 expression was downregulated by siRNA silencing in Huh7 cells and SMMC-7721 cells (Figure2(a)). Inhibiting Prp19 significantly reduced percentages of Huh7 cells and SMMC-7721 cells in G1 phase (Figure 2(b)). Downregulation of Prp19 in HCC cells decreased the percentages of β-gal positive cells compared with nonsense controls (Figure 2(c)). As indicated in Figure 2(d), silencing Prp19 expression in HCC cells also obviously inhibited cisplatin-induced senescence. Compared to controls, CXCL-1 mRNA was significantly decreased in Huh7 cells following knockdown of Prp19, while CXCL-1, IL-6, and IL-8 mRNAs were significantly reduced in SMMC-7721 cells after knockdown of Prp19 (Figure 2(e)). Taken together, Prp19 knockdown in HCC cells inhibited senescence and also attenuated cisplatin-induced senescence.Figure 2
Inhibiting Prp19 represses senescence of HCC cells. (a) Prp19 expression was decreased by siRNA silencing in HCC cells. (b) Cell cycle distribution of HCC cells with Prp19 knockdown. (c) The effects of Prp19 on HCC cells senescence were assessed using SA-β-galactosidase. (d) The effects of Prp19 on HCC cells senescence were assessed using SA-β-galactosidase staining with or without incubation of 10 μM cisplatin for 24 h. (e) Relative IL6, IL1a, IL1b, IL8, and CXCL1 transcript levels in human HCC cell lines were determined by qRT-PCR. The levels of mRNA were normalized to ACTIN and presented relative to the control cells. Negative control, NC. The data are shown as the mean ± SEM. Similar results were observed in three independent experiments. ∗p<0.05 and ∗∗p<0.01. Black scale bar: 100 μm.
(a)(b)(c)(d)(e)


## 3.3. Prp19 Modulates p21 Expression in L02 Cells and HCC Cells

Western blot assay showed that p21 rather than p53 or p16 was increased in L02 cells overexpressing Prp19 (Figure3(a)). Prp19 knockdown in HCC cells showed a robust reduction in p21 protein expression, while silencing Prp19 did not affect p53 or p16 protein expression, two other important senescence modulators (Figure 3(b)). Considering the vital role of Prp19 in pre-mRNA processing, we assessed p21 mRNA levels in HCC cells with Prp19 downregulation. Real-time RT-PCR analysis showed that silencing Prp19 significantly decreased p21 mRNA levels in HCC cells compared with controls (Figure 3(c)). These findings suggested that Prp19 may participate in the senescence of HCC cells by regulating the expression of p21 mRNA.Figure 3
Prp19 modulates p21 expression in L02 cells and HCC cells. (a) Western blot assay of p16, p21, and p53 expression in L02 cells overexpressing Prp19. (b) Western blot assay of p16, p21, and p53 expression in HCC cells with Prp19 knockdown. (c) Relative levels of Prp19 and p21 transcripts in human HCC cell lines were determined by qRT-PCR. Levels of mRNA were normalized to ACTIN and presented relative to the control cells. Negative control, NC. The data are shown as the mean ± SEM.∗∗∗p<0.001.
(a)(b)(c)


## 3.4. Prp19 Knockdown PromotesIn Vivo Tumor Growth of HCC Cells

Senescence is an important barrier against cell proliferation. A previous study showed that Prp19 had no significant impact on HCC cell proliferationin vitro [16]. To investigate the role of Prp19 on tumor growth in vivo, we generated two stable HCC cell lines misexpressing Prp19 and then established subcutaneous xenograft models of HCC. Compared to the NTC groups, Prp19 expression was attenuated in the shPrp19 groups (Figure 4(a)). In this model, tumor volume was measured weekly. The mean tumor volume and weight in the NTC groups were significantly decreased compared to the shPrp19 groups (Figures 4(b) and 4(c)). In the shPrp19 groups, the expression of Prp19 and p21 was decreased in xenograft tumor tissues compared to the NTC groups (Figures 4(d) and 4(e)). Unlike the NTC group, there were fewer senescent areas in the xenograft tissues of the shPrp19 group (Figures 4(d) and 4(f)). Abovementioned data suggested that Prp19 knockdown inhibited HCC cell senescence and promoted tumor growth of HCC cells in vivo.Figure 4
Prp19 knockdown promotes tumor growth of HCCin vivo. (a) Prp19 protein expression of stable HCC cell lines misexpressing Prp19. (b) Images of the subcutaneous xenograft tumors generated by HCC cells misexpressing Prp19 in nude mice. The weights of the xenograft tumors are summarized in the lower panel. (c) Comparison of tumor size at the indicated time after implantation (n = 5). (d) Representative images of HE, IHC staining of Prp19 and p21, and SA-β-galactosidase staining in xenograft tumors (original magnification 200x). (e) Prp19 and p21 protein expression in xenograft tumors. (f) Statistically analysis of SA-β-galactosidase positive cells in xenograft tumors. Values are mean ± SEM, ∗p<0.05and ∗∗p<0.01. Black scale bar: 100 μm.
(a)(b)(c)(d)(e)(f)


## 4. Discussion

Senescence is an important cellular response to various stimuli such as oncogene activation as well as exposure to DNA damage. Prp19 was reported to reduce DNA damage-induced senescence in mouse skin and increase the resistance to stress in human endothelial cells [12, 18]. Mouse embryonic fibroblast cell lines with reduced Prp19 levels displayed a decreased proliferative potential in vitro [19]. The abovementioned studies implied that Prp19 may modulate senescence. Aging is a major risk factor for the progression of liver disease to HCC [20]. Cirrhosis is characterized by replicative senescence due to short telomeres and no expression of telomerase in mature hepatocytes [21]. This study found that Prp19 promoted L02 cells senescence under different stimuli, including DNA damage exposure and oncogene activation. Taking into account the gradual elevation of Prp19 expression from normal liver to HCC in a previous study [16], this finding indicated the underlying role of Prp19 in senescence during the development of liver cirrhosis.Prp19 expression is abundant in many human cancers, including HCC [16, 22, 23]. It was reported that Prp19 repressed cell proliferation and tumor growth via upregulating the protein expression of p21 [23]. We also identified the role of Prp19 in the progression of the cell cycle in HCC [14]. Recently, mechanisms behind senescence and drug-induced senescence have been partially unveiled in HCC [9, 20, 24]. This work indicated that Prp19 downregulation inhibited senescence as well as cisplatin-induced senescence in HCC cells. Although no significant impact of Prp19 on the proliferation of HCC cells was observed in vitro, we found that repression of Prp19 in HCC cells facilitated tumor growth in vivo. It was demonstrated that the secretion of the interleukins IL-6, IL-8, and CXCL-1 increased oncogene-induced growth arrest caused by Ras and Braf [25, 26]. In this study, Prp19 down-regulation resulted in the decreased mRNA expression of SASP factors such as CXCL-1, IL-6, and IL-8 in HCC cells, which may account for the proliferation of tumor with Prp19 deficiency. A recent study reported that while senescent hepatocyte-secreted chemokines suppressed liver cancer initiation, they may accelerate the growth of fully established HCC [10]. Since the pro or antitumorigenic effect of senescence depends on the context, the promoting role of Prp19 on the progression of HCC may be partly owing to its impact on senescence.It is well recognized that the p53-p21 and the p16-RB pathways are critical for senescence [27]. Among these important regulators of senescence, we found Prp19 positively modulated p21 expression rather than p53 or p16 expression in L02 cells and HCC cells. Prp19 silencing was reported to comprise p21 mRNA splicing [28]. Here, we found that inhibiting Prp19 expression decreased the p21 mRNA level in HCC cells. This study did not observe the modulation of Prp19 in p53 expression, and the molecular mechanism underlying Prp19-induced alteration of p21 needs further study in the future.In summary, this work first revealed the positive role of Prp19 on senescence in L02 cells and HCC cells under different stimuli. Furthermore, we found that Prp19 robustly modulated p21 expression in HCC cells. Repression of Prp19 resulted in a reduction of senescence and acceleration of tumor growthin vivo. It was reported that inhibition of Prp19 made HCC cells less resistant to chemotherapeutic agents [15]. Compromised senescence in HCC cells with Prp19 deficiency may drive cell cycle progression, resulting in increased chemotherapeutic sensitivity, rendering Prp19 a potential target in HCC management.



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*Source: 5705896-2022-03-21.xml*