# KIF15 Promotes Proliferation and Growth of Hepatocellular Carcinoma

Authors: Yue-Feng Sun; Hong-Li Wu; Rui-Fang Shi; Lin Chen; Chao Meng
Journal: Analytical Cellular Pathology
 (2020)

---

## Abstract

Liver cancer is thought as the most common human malignancy worldwide, and hepatocellular carcinoma (HCC) accounts for nearly 90% liver cancer. Due to its poor early diagnosis and limited treatment, HCC has therefore become the most lethal malignant cancers in the world. Recently, molecular targeted therapies showed great promise in the treatment of HCC, and novel molecular therapeutic targets is urgently needed. KIF15 is a microtubule-dependent motor protein involved in multiple cell processes, such as cell division. Additionally, KIF15 has been reported to participate in the growth of various types of tumors; however, the relation between KIF15 and HCC is unclear. Herein, our study investigated the possible role of KIF15 on the progression of HCC and found that KIF15 has high expression in tumor samples from HCC patients. KIF15 could play a critical role in the regulation of cell proliferation of HCC, which was proved by in vitro and in vivo assays. In conclusion, this study confirmed that KIF15 could be a novel therapeutic target for the treatment of HCC.


---

## Body

## 1. Background

Liver cancer is one of the most common human malignancies in the world [1]. Hepatocellular carcinoma (HCC), accounting for nearly 90% of liver cancer, is the main form of liver cancer [2, 3]. Due to its poor early diagnosis and limited therapy methods, HCC is the most lethal malignant cancer worldwide [4]. Generally, the 5-year overall survival rate of HCC patients is still low [5, 6]. Even for HCC patients who undergo surgical therapy, the 5-year survival rate is less than 50% [7]. Chemotherapy and radiotherapy are the main treatments for HCC with multiple side effects [8, 9]. HCC has high metastasis and recurrence rates [10]. Therefore it is an urgent need to develop other potential treatments to combat this disease. Fortunately, molecular-targeted therapies show great promise in the treatment of HCC [11]. Several genes, such as CCNE1 and STAT3, were developed as therapeutic targets for HCC treatment [12, 13]. However, the effect of the therapy targets is limited and should therefore be explored further. In the future, developing novel molecular targets would have potential clinical value.Kinesin family contains more than forty members, which is involved in the transport of proteins and organelles in a microtubule-dependent manner [14]. Previous studies proved that KIFs were necessary for cell mitosis [15, 16]. KIF15, which is also known as Kinesin 12, is a microtubule-based and plus-end-directed motor protein involved in various cell processes, such as spindle assembly, plasma membrane trafficking, and cell division [17–19]. KIF15, together with KIF11, is reported to promote bipolar spindle formation [20]. KIF15 seems to be a good target for cancer as it plays a key role during cell mitosis. Actually, KIF15 has also been demonstrated to be involved in the growth of various types of tumors, such as pancreatic cancer, lung cancer, and breast cancer [21–23]. However, the possible functions of KIF15 in HCC tumorigenesis and the relationship with prognosis are unclear.In this study, we found that higher KIF15 expression was positively associated with the more number of tumor nodes and larger tumor size of HCC patients. Knockdown of KIF15 sufficiently blocked cell proliferation of HCC in vitro and in mice. Thus, KIF15 is acting as a potentially critical therapeutic target.


## 2. Materials and Methods

### 2.1. Antibodies, Primers, and Plasmids

A comprehensive score was made below: the score of staining intensity × (multiply) the score of stained cell percentage.The antibodies used in the study are as follows: Anti-KIF15 antibody (1 : 50 dilution for IHC and 1 : 100 dilution for WB, PA5-57305, Invitrogen), anti-β-actin antibody (1 : 2000 dilution for WB, mAb #3700, CST), anti-Ki67 antibody (1 : 1000 dilution for WB, 27309-1-AP, Proteintech), and anti-proliferating cell nuclear antigen (PCNA) antibody (1 : 50 dilution for IHC, and 1 : 500 dilution for WB, SAB2108448, Sigma-Aldrich).The sequences of KIF15 quantitative PCR primer are as follows: forward, 5′- AAGCAGGTAACATAAATCG-3′ and reverse, 5′- AATCCCGTAGTAAGAAGGT-3′. The quantitative PCR primer sequences of GAPDH are as follows: 5′-CGACCACTTTGTCAAGCTCA-3′ and 5′-GGTTGAGCACAGGGTACTTTATT-3′.Ready-to-package AAV shRNA clone of KIF15 was commercially purchased from Addgene. Additionally, the KIF15 shRNA sequences were as follows: sense, 5′- AACCAACCAAGTAATGAAGGTGA-3′.


### 2.2. Human Tissue Samples

The human hepatocellular carcinoma (HCC) tissue samples were obtained from patients in Tianjin Second People’s Hospital after liver biopsy from January 2013 to November 2018. To further assess the correlation between KIF15 expression and the progression of HCC, immunohistochemical (IHC) assays were performed. KIF15 expression level was manually divided into 4 groups according to the intensity of staining (0=negative; 1=low; 2=medium; 3=high). In addition, the proportion of stained cells (0 means 0% stained cells, 1 means 1–25% stained cells, 2 means 26–50% stained cells, and 3 means 51–100% stained cells). A comprehensive score (scoreofstainingintensity×scoreofstainedcellspercentage) <2 was considered as negative, 2–3 as low, and >4 as high. The sections of each patient were photographed within 5 visual fields, and 2 pathologists read the sections. The results were subsequently judged by double-blind method.


### 2.3. Cell Culture and Transfection

Both the Hep3B and SNU-475 human HCC cell lines were purchased from ATCC (Chicago, USA). Hep3B cells were maintained in EMEM culture medium and supplemented with 10% of fetal bovine serum (FBS). Additionally, SNU-475 cells were cultured in RPMI1640 (w/o Hepes) culture medium and supplemented with 20% FBS. Both of them were incubated at 37°C in a 5% CO2 incubator.The KIF15 shRNA plasmids were transfected into tumor cells using Invitrogen Lipofectamine® 2000 (Thermo Fisher Scientific, Inc.). The specific shRNA above to target KIF15 and scrambled sequence were used as negative control. Approximately 100,000 cells per well in 6-well plates based on the manufacturer’s protocol, then 3 groups were set, including sh-KIF15 group, which transfected with KIF15 shRNA plasmids; negative control group, which transfected with scrambled sequences; and mock group was without transfection (data not shown). Silence efficiency was measured by quantitative PCR and Western Blot assays after 48 hours transfection. These reduced cells were used to explore the relationship between KIF15 and cell proliferation. Then, the KIF15 stable depletion cells were screened and used for the in vitro and in vivo assays.


### 2.4. Quantitative-PCR Assay

Total RNA was extracted from Hep3B and SNU-475 HCC cells by Trizol reagent (Invitrogen). Then total RNA was reverse-transcribed using M-MLV reverse transcriptase (Promega). Quantitative PCR was conducted by SYBR mixture (Takara), and the relative expression levels of KIF15 was normalized to GAPDH.


### 2.5. Immunoblot Assay

Total proteins extracted from HCC cells or tissues were separated by SDS-PAGE assays, sequentially transferred onto PVDF membranes, followed by blocking with 5% fat-free dry milk in TBST buffer. Membranes were then incubated with primary antibodies for the detection of KIF15, Ki67, PCNA, andβ-actin at room temperature for two hours. After washing with TBST buffer, the membranes were incubated with HRP-conjugate secondary antibodies for 45 minutes. Signals were then visualized by an ECL kit.


### 2.6. Colony Formation Assay

Both Hep3B and SNU-475 cells were resuspended and seeded in 6-well plates with a density of 3000 cells/well and grown for 2 weeks. The colonies were then fixed with 4% paraformaldehyde (PFA) for 25 minutes and stained with 0.2% crystal violet for 20 minutes. Photographs were subsequently taken, and the difference of colony numbers between shControl and shKIF15 HCC cells were calculated and analyzed.


### 2.7. MTT Assay

Hep3B and SNU-475 cells were seeded into 96-well plates with a density of 1000 cells/well and maintained for 48 hours. Cells were then treated with 5 mg/ml MTT for 3 hours and washed with PBS twice. Subsequently, the stained cells with MTT were extracted by 200-μL DMSO, and the posttreated MTT solution which has turned its colour from yellow to blue was measured at 570 nm.


### 2.8. Tumor Growth In Vivo

The nude BalB/c mice (6-8 weeks, 20-24 g) were bought from Beijing Vital River Laboratory Animal Technology Co., Ltd. (Beijing, China). To measure the volume of tumors in vivo,2×106 Hep3B HCC cells were stably infected with control or KIF15 shRNA lentivirus and then injected subcutaneously into the right flank of female nude mice. After nearly 2 weeks, tumors (50 mm 3) were established, and the tumor volume was measured per week and calculated in length×width2/2. The difference of tumor volume between shKIF15 and shControl groups was analyzed.


### 2.9. Statistics

Data in this study were analyzed using SPSS 22.0 software. For the immunohistochemistry (IHC) assays, correlations between KIF15 expression and the clinical pathological characteristics were assessed byχ2 tests. In addition, the associations of prognosis, tumor progression, and KIF15 expression were evaluated through the Kaplan-Meier (KM) method and log-rank tests. Data are shown as the mean±standarddeviation (SD) in vitro and in vivo experiments. Student’s t-test was used for statistical comparisons. Additionally, a value of P<0.05 was set to be statistically significant.


## 2.1. Antibodies, Primers, and Plasmids

A comprehensive score was made below: the score of staining intensity × (multiply) the score of stained cell percentage.The antibodies used in the study are as follows: Anti-KIF15 antibody (1 : 50 dilution for IHC and 1 : 100 dilution for WB, PA5-57305, Invitrogen), anti-β-actin antibody (1 : 2000 dilution for WB, mAb #3700, CST), anti-Ki67 antibody (1 : 1000 dilution for WB, 27309-1-AP, Proteintech), and anti-proliferating cell nuclear antigen (PCNA) antibody (1 : 50 dilution for IHC, and 1 : 500 dilution for WB, SAB2108448, Sigma-Aldrich).The sequences of KIF15 quantitative PCR primer are as follows: forward, 5′- AAGCAGGTAACATAAATCG-3′ and reverse, 5′- AATCCCGTAGTAAGAAGGT-3′. The quantitative PCR primer sequences of GAPDH are as follows: 5′-CGACCACTTTGTCAAGCTCA-3′ and 5′-GGTTGAGCACAGGGTACTTTATT-3′.Ready-to-package AAV shRNA clone of KIF15 was commercially purchased from Addgene. Additionally, the KIF15 shRNA sequences were as follows: sense, 5′- AACCAACCAAGTAATGAAGGTGA-3′.


## 2.2. Human Tissue Samples

The human hepatocellular carcinoma (HCC) tissue samples were obtained from patients in Tianjin Second People’s Hospital after liver biopsy from January 2013 to November 2018. To further assess the correlation between KIF15 expression and the progression of HCC, immunohistochemical (IHC) assays were performed. KIF15 expression level was manually divided into 4 groups according to the intensity of staining (0=negative; 1=low; 2=medium; 3=high). In addition, the proportion of stained cells (0 means 0% stained cells, 1 means 1–25% stained cells, 2 means 26–50% stained cells, and 3 means 51–100% stained cells). A comprehensive score (scoreofstainingintensity×scoreofstainedcellspercentage) <2 was considered as negative, 2–3 as low, and >4 as high. The sections of each patient were photographed within 5 visual fields, and 2 pathologists read the sections. The results were subsequently judged by double-blind method.


## 2.3. Cell Culture and Transfection

Both the Hep3B and SNU-475 human HCC cell lines were purchased from ATCC (Chicago, USA). Hep3B cells were maintained in EMEM culture medium and supplemented with 10% of fetal bovine serum (FBS). Additionally, SNU-475 cells were cultured in RPMI1640 (w/o Hepes) culture medium and supplemented with 20% FBS. Both of them were incubated at 37°C in a 5% CO2 incubator.The KIF15 shRNA plasmids were transfected into tumor cells using Invitrogen Lipofectamine® 2000 (Thermo Fisher Scientific, Inc.). The specific shRNA above to target KIF15 and scrambled sequence were used as negative control. Approximately 100,000 cells per well in 6-well plates based on the manufacturer’s protocol, then 3 groups were set, including sh-KIF15 group, which transfected with KIF15 shRNA plasmids; negative control group, which transfected with scrambled sequences; and mock group was without transfection (data not shown). Silence efficiency was measured by quantitative PCR and Western Blot assays after 48 hours transfection. These reduced cells were used to explore the relationship between KIF15 and cell proliferation. Then, the KIF15 stable depletion cells were screened and used for the in vitro and in vivo assays.


## 2.4. Quantitative-PCR Assay

Total RNA was extracted from Hep3B and SNU-475 HCC cells by Trizol reagent (Invitrogen). Then total RNA was reverse-transcribed using M-MLV reverse transcriptase (Promega). Quantitative PCR was conducted by SYBR mixture (Takara), and the relative expression levels of KIF15 was normalized to GAPDH.


## 2.5. Immunoblot Assay

Total proteins extracted from HCC cells or tissues were separated by SDS-PAGE assays, sequentially transferred onto PVDF membranes, followed by blocking with 5% fat-free dry milk in TBST buffer. Membranes were then incubated with primary antibodies for the detection of KIF15, Ki67, PCNA, andβ-actin at room temperature for two hours. After washing with TBST buffer, the membranes were incubated with HRP-conjugate secondary antibodies for 45 minutes. Signals were then visualized by an ECL kit.


## 2.6. Colony Formation Assay

Both Hep3B and SNU-475 cells were resuspended and seeded in 6-well plates with a density of 3000 cells/well and grown for 2 weeks. The colonies were then fixed with 4% paraformaldehyde (PFA) for 25 minutes and stained with 0.2% crystal violet for 20 minutes. Photographs were subsequently taken, and the difference of colony numbers between shControl and shKIF15 HCC cells were calculated and analyzed.


## 2.7. MTT Assay

Hep3B and SNU-475 cells were seeded into 96-well plates with a density of 1000 cells/well and maintained for 48 hours. Cells were then treated with 5 mg/ml MTT for 3 hours and washed with PBS twice. Subsequently, the stained cells with MTT were extracted by 200-μL DMSO, and the posttreated MTT solution which has turned its colour from yellow to blue was measured at 570 nm.


## 2.8. Tumor Growth In Vivo

The nude BalB/c mice (6-8 weeks, 20-24 g) were bought from Beijing Vital River Laboratory Animal Technology Co., Ltd. (Beijing, China). To measure the volume of tumors in vivo,2×106 Hep3B HCC cells were stably infected with control or KIF15 shRNA lentivirus and then injected subcutaneously into the right flank of female nude mice. After nearly 2 weeks, tumors (50 mm 3) were established, and the tumor volume was measured per week and calculated in length×width2/2. The difference of tumor volume between shKIF15 and shControl groups was analyzed.


## 2.9. Statistics

Data in this study were analyzed using SPSS 22.0 software. For the immunohistochemistry (IHC) assays, correlations between KIF15 expression and the clinical pathological characteristics were assessed byχ2 tests. In addition, the associations of prognosis, tumor progression, and KIF15 expression were evaluated through the Kaplan-Meier (KM) method and log-rank tests. Data are shown as the mean±standarddeviation (SD) in vitro and in vivo experiments. Student’s t-test was used for statistical comparisons. Additionally, a value of P<0.05 was set to be statistically significant.


## 3. Results

### 3.1. KIF15 Is Highly Expressed in Human HCC Samples and Correlated with the Progression of HCC

To explore the potential role of KIF15 in the development of HCC, immunohistochemical analysis of surgery samples from 74 HCC patients was performed, and the expression levels of KIF15 was then detected. Obviously, the staining results showed that KIF15 was mainly localized in the cytoplasm and highly expressed in the HCC tissue (Figure1(a)). Tumor samples are then divided into two groups according to the staining level of KIF15, including high and low-expression groups (Figure 1(a)). As a comparison, KIF15 showed significant low expression in the adjacent tissues (Figure 1(b)), suggesting that KIF15 might play a role in the development of HCC.Figure 1
KIF15 expression was associated with poor prognosis of patients who underwent HCC. (a) Immunohistochemical staining of KIF15 protein in human HCC tissues (×100 and ×200 magnification, respectively). (b) Immunohistochemical staining of KIF15 in the corresponding adjacent tissues (×100 and ×200 magnification, respectively).
(a)
(b)Clinicopathological characteristic analysis showed the difference between low- and high-expression KIF15 groups. Interestingly, the expression level of KIF15 in the HCC tissues was significantly correlated with the number of tumor nodes and tumor size, suggesting a possible link between KIF15 expression and HCC progression (Table1). However, there were no obvious significant difference between high and low KIF15 groups at patient age, gender, tumor grade, lymph node metastasis, and AFP level (Table 1). All these data revealed that KIF15 expression was positively associated with the number of tumor nodes and tumor size of HCC patients.Table 1
Relationships of KIF15 and clinicopathological characteristics in 74 patients with hepatocellular carcinoma.
Feature
Alln=74
KIF15 expression
χ2
P
Low
High
n=38
n=36
Age (year)
0.464
0.496
<55
40
22
18
≥55
34
16
18
Gender
0.452
0.501
Male
42
23
19
Female
32
15
17
Number of tumor nodes
9.759
0.002∗
Single
30
22
8
Multiple ≥2
44
16
28
Tumor grade
2.805
0.094
Low
32
20
12
High
42
18
24
Tumor size
7.952
0.005∗
≥5 cm
50
20
30
<5 cm
24
18
6
Lymph node metastasis
0.260
0.610
No
43
21
22
Yes
31
17
14
AFP (ng/mL)
1.891
0.169
<50
22
14
8
≥50
52
24
28


### 3.2. Knockdown of KIF15 Blocked Proliferation of HCC Cells

Excessive cell proliferation could lead to the development of tumors. We next examined whether the effect of KIF15 on HCC was due to the promotion of cell proliferation. The expression of KIF15 was inhibited by KIF15-targeted shRNA in two types of HCC cell lines: Hep3B and SNU-475, respectively, and the silence efficiency was detected by quantitative PCR and immunoblot assays, respectively. Results showed that KIF15-shRNA treated Hep3B, and SNU-475 cells obviously decreased the expression of KIF15 in both mRNA and protein levels (Figures2(a) and 2(b)).Figure 2
KIF15 expression was effectively inhibited in both Hep3B and SNU-475 human HCC cells caused by its shRNA plasmids. (a) Quantitative PCR assays revealed the dramatically reduced expression level of KIF15 caused by its shRNA in Hep3B and SNU-475 cells, respectively. (b) Immunoblot assays confirmed the efficiently silencing of KIF15 caused by the transfection of its shRNA plasmids in Hep3B and SNU-475 cells. Results are presented asmean±SD, ∗P<0.05.
(a)
(b)We further explore the effects of KIF15 on cell proliferation of HCC through colony formation and MTT assays. Results indicated that the colony formation capacity was significantly restrained by KIF15 repression, consistent with the obviously decreased cell numbers (Figure3(a)). Additionally, MTT assays showed that KIF15 depletion resulted in a significant decreased OD value at 570 nm in both Hep3B and SNU-475 cells (Figure 3(b)). We also examined the expression levels of Ki67 and PCNA, two proliferative biomarkers, respectively. A significantly dropped expression of ki67 and PCNA in KIF15 shRNA-transfected group was found, suggesting a decline in proliferative capacity (Figures 3(c) and 3(d)).Figure 3
KIF15 promotes HCC cell proliferation in vitro. (a) Hep3B and SNU-475 cells transfected with control or KIF15 shRNA, and the proliferation capacity was quantified by colony formation assays. (b) The results of MTT assays showed the inhibition of cell proliferation caused by KIF15 depletion. (c) Immunoblot assays showed Ki67 expression level in control or KIF15 knockdown Hep3B and SNU-475 cells. (d) The results of immunoblot assays revealed the expression level of PCNA in control or KIF15 ablation HCC cells. Results are presented asmean±SD, ∗P<0.05.
(a)
(b)
(c)
(d)


### 3.3. KIF15 Depletion Inhibits HCC Proliferation in Mice

To explore the relationship between KIF15 and HCC in mice, Hep3B cells were infected with shKIF15 lentivirus to stably restrain the expression of KIF15. Cells infected with control or KIF15 shRNA plasmids were then injected subcutaneously into nude mice. After 2 weeks following injection, tumors began to develop, and tumor volume was measured each week. The volume of KIF15 depletion group tumors were markedly smaller than control (Figure4(a)). We also detected KIF15 expression in tumor tissues of mice by immunohistochemistry assays. Expectably, data showed that the KIF15 expression levels in KIF15 knockdown group was markedly decreased compared with control (Figure 4(b)).Figure 4
KIF15 facilitated HCC growth in mice. (a) Hep3B cells infected with control or KIF15 shRNA lentivirus were subcutaneously implanted into nude mice. After 2 weeks, tumors were isolated, and volume was examined every 3 days (n=4 in each group). Tumor growth curve was calculated and analyzed according to the average volume of 4 tumors in each group. (b) IHC assays indicated the expression level of KIF15 in control or KIF15 depletion tumor tissues isolated from mice. (c) IHC assays revealed the expression level of Ki67 in control or KIF15 depletion tumor tissues taken from mice. Results are presented as mean±SD, ∗P<0.05.
(a)
(b)
(c)In previous assays, we found that the depletion of KIF15 would lead to the downregulation of Ki67 and PCNA. In order to confirm in vivo, we detected the expression levels of Ki67 in tumor tissues and found that the knockdown of KIF15 would significantly suppress the expression of Ki67 (Figure4(c)). Collectively, these results demonstrated that KIF15 could play a vital role in the proliferation of HCC.


## 3.1. KIF15 Is Highly Expressed in Human HCC Samples and Correlated with the Progression of HCC

To explore the potential role of KIF15 in the development of HCC, immunohistochemical analysis of surgery samples from 74 HCC patients was performed, and the expression levels of KIF15 was then detected. Obviously, the staining results showed that KIF15 was mainly localized in the cytoplasm and highly expressed in the HCC tissue (Figure1(a)). Tumor samples are then divided into two groups according to the staining level of KIF15, including high and low-expression groups (Figure 1(a)). As a comparison, KIF15 showed significant low expression in the adjacent tissues (Figure 1(b)), suggesting that KIF15 might play a role in the development of HCC.Figure 1
KIF15 expression was associated with poor prognosis of patients who underwent HCC. (a) Immunohistochemical staining of KIF15 protein in human HCC tissues (×100 and ×200 magnification, respectively). (b) Immunohistochemical staining of KIF15 in the corresponding adjacent tissues (×100 and ×200 magnification, respectively).
(a)
(b)Clinicopathological characteristic analysis showed the difference between low- and high-expression KIF15 groups. Interestingly, the expression level of KIF15 in the HCC tissues was significantly correlated with the number of tumor nodes and tumor size, suggesting a possible link between KIF15 expression and HCC progression (Table1). However, there were no obvious significant difference between high and low KIF15 groups at patient age, gender, tumor grade, lymph node metastasis, and AFP level (Table 1). All these data revealed that KIF15 expression was positively associated with the number of tumor nodes and tumor size of HCC patients.Table 1
Relationships of KIF15 and clinicopathological characteristics in 74 patients with hepatocellular carcinoma.
Feature
Alln=74
KIF15 expression
χ2
P
Low
High
n=38
n=36
Age (year)
0.464
0.496
<55
40
22
18
≥55
34
16
18
Gender
0.452
0.501
Male
42
23
19
Female
32
15
17
Number of tumor nodes
9.759
0.002∗
Single
30
22
8
Multiple ≥2
44
16
28
Tumor grade
2.805
0.094
Low
32
20
12
High
42
18
24
Tumor size
7.952
0.005∗
≥5 cm
50
20
30
<5 cm
24
18
6
Lymph node metastasis
0.260
0.610
No
43
21
22
Yes
31
17
14
AFP (ng/mL)
1.891
0.169
<50
22
14
8
≥50
52
24
28


## 3.2. Knockdown of KIF15 Blocked Proliferation of HCC Cells

Excessive cell proliferation could lead to the development of tumors. We next examined whether the effect of KIF15 on HCC was due to the promotion of cell proliferation. The expression of KIF15 was inhibited by KIF15-targeted shRNA in two types of HCC cell lines: Hep3B and SNU-475, respectively, and the silence efficiency was detected by quantitative PCR and immunoblot assays, respectively. Results showed that KIF15-shRNA treated Hep3B, and SNU-475 cells obviously decreased the expression of KIF15 in both mRNA and protein levels (Figures2(a) and 2(b)).Figure 2
KIF15 expression was effectively inhibited in both Hep3B and SNU-475 human HCC cells caused by its shRNA plasmids. (a) Quantitative PCR assays revealed the dramatically reduced expression level of KIF15 caused by its shRNA in Hep3B and SNU-475 cells, respectively. (b) Immunoblot assays confirmed the efficiently silencing of KIF15 caused by the transfection of its shRNA plasmids in Hep3B and SNU-475 cells. Results are presented asmean±SD, ∗P<0.05.
(a)
(b)We further explore the effects of KIF15 on cell proliferation of HCC through colony formation and MTT assays. Results indicated that the colony formation capacity was significantly restrained by KIF15 repression, consistent with the obviously decreased cell numbers (Figure3(a)). Additionally, MTT assays showed that KIF15 depletion resulted in a significant decreased OD value at 570 nm in both Hep3B and SNU-475 cells (Figure 3(b)). We also examined the expression levels of Ki67 and PCNA, two proliferative biomarkers, respectively. A significantly dropped expression of ki67 and PCNA in KIF15 shRNA-transfected group was found, suggesting a decline in proliferative capacity (Figures 3(c) and 3(d)).Figure 3
KIF15 promotes HCC cell proliferation in vitro. (a) Hep3B and SNU-475 cells transfected with control or KIF15 shRNA, and the proliferation capacity was quantified by colony formation assays. (b) The results of MTT assays showed the inhibition of cell proliferation caused by KIF15 depletion. (c) Immunoblot assays showed Ki67 expression level in control or KIF15 knockdown Hep3B and SNU-475 cells. (d) The results of immunoblot assays revealed the expression level of PCNA in control or KIF15 ablation HCC cells. Results are presented asmean±SD, ∗P<0.05.
(a)
(b)
(c)
(d)


## 3.3. KIF15 Depletion Inhibits HCC Proliferation in Mice

To explore the relationship between KIF15 and HCC in mice, Hep3B cells were infected with shKIF15 lentivirus to stably restrain the expression of KIF15. Cells infected with control or KIF15 shRNA plasmids were then injected subcutaneously into nude mice. After 2 weeks following injection, tumors began to develop, and tumor volume was measured each week. The volume of KIF15 depletion group tumors were markedly smaller than control (Figure4(a)). We also detected KIF15 expression in tumor tissues of mice by immunohistochemistry assays. Expectably, data showed that the KIF15 expression levels in KIF15 knockdown group was markedly decreased compared with control (Figure 4(b)).Figure 4
KIF15 facilitated HCC growth in mice. (a) Hep3B cells infected with control or KIF15 shRNA lentivirus were subcutaneously implanted into nude mice. After 2 weeks, tumors were isolated, and volume was examined every 3 days (n=4 in each group). Tumor growth curve was calculated and analyzed according to the average volume of 4 tumors in each group. (b) IHC assays indicated the expression level of KIF15 in control or KIF15 depletion tumor tissues isolated from mice. (c) IHC assays revealed the expression level of Ki67 in control or KIF15 depletion tumor tissues taken from mice. Results are presented as mean±SD, ∗P<0.05.
(a)
(b)
(c)In previous assays, we found that the depletion of KIF15 would lead to the downregulation of Ki67 and PCNA. In order to confirm in vivo, we detected the expression levels of Ki67 in tumor tissues and found that the knockdown of KIF15 would significantly suppress the expression of Ki67 (Figure4(c)). Collectively, these results demonstrated that KIF15 could play a vital role in the proliferation of HCC.


## 4. Discussion

Hepatocellular carcinoma (HCC) is known as a major contributor to the worldwide cancer burden [1, 2, 11]. Given the limited methods to combat this disease, understanding the molecular mechanism of HCC progression and screening effective therapeutic targets will be critical to identify HCC treatments in the future [11]. To date, several drugs that target different therapeutic targets have shown great promise; however, the clinical outcomes of these drugs have been largely suboptimal [11–13]. In this study, we found a new therapeutic target for the treatment of HCC, KIF15, which is closely related to the number of tumor nodes and tumor size and directly involved in the proliferation regulation of HCC cells. The underlying molecular mechanisms need further study.In addition to KIF15 of this study, a variety of KIFs are reported to be involved in tumor progression. In previous studies, KIF1B, KIF3B, and KIF14 promoted growth of hepatocellular carcinoma and was correlated with the prognosis of hepatocellular carcinoma patients [24–26]. KIF3B was involved in the migration of seminoma cancer cells [27]. Similarly, KIF1B depletion blocks cell invasion of glioma [28]. In breast cancer, KIFC1 was overexpressed [29]. Also, KIF2A promotes cell proliferation and invasion and is associated with prognosis of breast cancer patients [30]. KIF15, together with other KIFs, might act as potential therapeutic targets in multiple types of tumors.Actually, except HCC, KIF15 also affects the growth and development of several other tumors. KIF15 ablation inhibits endocrine therapy-resistant breast cancer [23]. Additionally, KIF15 is high-expressed in lung cancer and involved in cancer development by regulating the cell cycle [22]. KIF15 also promotes the proliferation of pancreatic cancer via MEK–ERK pathway [21]. Interestingly, we found that in HCC, KIF15 also promotes the growth of HCC by promoting cell proliferation, possibly also through the MEK/ERK signaling pathway. MEK–ERK is involved in the regulation of cell proliferation, and its deregulation could result in tumorigenesis [21, 31, 32]. The MEK–ERK pathway is also reported to regulate diverse cellular processes such as survival, motility, and differentiation of cells [33]. The next step is to test whether KIF15 can promote HCC through the MEK/ERK pathway.As mitotic Kinesin motors, KIF15 and KIF11 seem to have several similar functions during bipolar spindle formation, they work through distinct mechanisms [18]. Overexpression of KIF15 promotes cell division, and based design of KIF15 inhibitors might become novel therapeutic agents for cancer and may be a viable strategy for overcoming chemotherapeutic resistance [34, 35]. Since we found that KIF15 promoted HCC proliferation, KIF15 therefore became a good therapeutic target for HCC because of their role during mitosis. And a new study reported that KIF15 downregulation delayed tumor initiation, growth, and metastasis in vitro and in vivo [36]. Based on the previous data and our results combination, drug therapy targeting both KIF15 could be considered as lead therapies in further drug development for HCC.


## 5. Conclusions

Collectively, our results demonstrated that KIF15 was highly expressed in human HCC tissues. We also found the link between KIF15 expression level and clinical features of HCC patients: the expression level of KIF15 in the HCC tissues was significantly correlated with the number of tumor nodes and tumor size. Furthermore, KIF15 facilitated HCC cell proliferation in vitro and in mice. Therefore, we have a preliminary mechanism study of KIF15 in HCC development and provide a novel therapeutic target for the treatment of HCC.



---

*Source: 6403012-2020-04-03.xml*