Knockdown of KRAB domain-associated protein 1 suppresses the proliferation, migration and invasion of thyroid cancer cells by regulating P68/DEAD box protein 5.

KRAB domain-associated protein 1 (KAP-1) has been reported to be an oncogene in diverse tumors. KAP-1 was found to have abundant existence in malignant thyroid tissues, but its role in thyroid cancer hasn't been elucidated clearly. This study was carried out to explore the role of KAP-1 in thyroid cancer, and to clarify its molecular mechanism. The expressions of KAP-1 and P68/DEAD box protein 5 (DDX5) were assessed under the help of qRT-PCR and western blot. Then, we downregulated KAP-1 or upregulated DDX5 by cell transfection in TPC-1 cells. A series of cellular experiments on proliferation, apoptosis, migration and invasion were conducted with CCK-8, EdU, TUNEL, wound-healing and Transwell assays. Besides, the relationship between KAP-1 and DDX5 was verified by co-immunoprecipitation (Co-IP). The results showed that both of KAP-1 and DDX5 were upregulated in thyroid cancer cells. Loss-of-function experiments revealed that KAP-1 knockdown imparted suppressive effects on cell proliferation, migration and invasion, but promoted cell apoptosis. Additionally, KAP-1 was demonstrated to interact with DDX5 and positively regulate DDX5 expression. The following rescued experiments exhibited that the inhibitory effects of KAP-1 knockdown on cellular activities of thyroid cancer and Wnt/β-catenin signaling were also partly reversed by DDX5 overexpression. Moreover, activation of Wnt/β-catenin signaling retarded the anti-tumor activity of KAP-1 knockdown. In conclusion, the data in this study disclosed that KAP-1 silence helped to repress the cell proliferation, migration and invasion by degrading DDK5, so as to hinder the development of thyroid cancer.

Highlights

KAP-1 knockdown suppressed cell proliferation, migration and invasion in TPC-1 cells;

KAP-1 knockdown represses the progression of thyroid cancer partly through regulating DDX5;

Wnt/β-catenin signaling is critical for the regulation of KAP-1/DDX5 axis in thyroid cancer.

Introduction

Thyroid cancer featuring an increasing rate of incidence is the most frequent endocrine malignant tumor. There are about 550,00 people suffering from thyroid cancer globally [1]. As soci-economy quickly advances, thyroid cancer has higher incidence rate and seriously threatens public health and welfare. Currently, the standard therapy for most patients with thyroid cancer is surgical resection, and adjuvant therapies including thyrotropin (TSH) suppression and radioiodine therapy (RAI) are usually applied for patients with high-risk features; however, the prognosis of recurrent thyroid cancer is far from satisfaction [2,3]. Therefore, understanding the molecular mechanism of thyroid cancer is particularly important.

KRAB domain-associated protein 1 (KAP-1) is a universal co-repressor for KRAB domain-containing zinc-finger proteins (KRAB-ZFPs) which initiate epigenic silencing for endogenous retroviruses in early stages of development [4,5]. It has been proved that KAP-1 is involved in the regulation of diverse malignant tumor progression. For instance, KAP-1 overexpression brought about peritoneal dissemination and poor prognosis of gastric cancer patients and KAP-1 provided a survival advantage to gastric cancer cells [6]. KAP-1 overexpression was also proved broadly existed in hepatocellular carcinoma cell lines and was positively correlated with late tumor stage and poor prognosis of clinical patients [7]. At present, the research concerning on the association between KAP-1 and thyroid cancer is little. Only a previous study reported a higher frequency of KAP-1 in malignant thyroid tissues, and a higher expression of KAP-1 in larger tumors (>4 cm) and in relapse patients, suggesting that KAP-1 might have an important role in thyroid malignancy [8], therefore, its further regulatory role in thyroid cancer is necessary to be discovered.

Being an ATP-dependent RNA helicase, P68/DEAD box protein 5 (DDX5) participates in multiple cellular processes, such as cell proliferation and organ development [9]. In addition, DDX5 plays important regulatory roles in various solid tumors, thus participating in the advancement of multiple tumors. Previous studies have suggested an oncogenic role for DDX5 in malignant tumors. DDX5 was found to be abnormally abundant in breast cancer, colon cancer, prostate cancer, et al., and DDX5 overexpression promoted tumorigenesis [10-13]. In particular, DDX5 was found to be highly expressed in tumor tissue of patients suffering from thyroid cancer [14], but the exact role that it acts in thyroid cancer still needs further elucidation. Coincidentally, by searching BioGRID Database Statistics, it was found that KAP-1 could interact with DDX5. Thus, their interactions and precise roles in thyroid cancer are deserved to be explored.

This study was designed with the purpose of determining the roles of KAP-1 and DDX5 in thyroid cancer cells, as well as investigating the detailed molecular mechanism. These data may shed new insights into the improvement of thyroid cancer.

Material and methods

Cell culture

BeNa Culture Collection (Beijing, China) was the provider of normal thyroid epithelial Nthy-ori 3–1 cells and human thyroid carcinoma cell lines (TPC-1, IHH-4, and B-CPAP). RPMI-1640 medium supplemented with 10% fetal bovine serum (FBS; Life Technologies Corp., USA), 100 U/ml penicillin and 100 μg/ml streptomycin (Gibco, Carlsbad, CA, USA) was applied to culture Nthy-ori 3–1 cells. The thyroid carcinoma cell lines were cultured in Dulbecco’s Modified Eagle Medium (DMEM) which contained 10% FBS and 1% penicillin/streptomycin mixture. The incubation of all cells was operated with 5% CO2 at 37°C.

Cell transfection

Two types of short hairpin RNA targeting KAP-1 (shRNA-KAP-1-1 and shRNA-KAP-1-2) and their negative control (shRNA-NC) were constructed by GenePharma Co. Ltd. The full length of DDX5 open reading frame was amplified and ligated into pcDNA3.1 to achieve DDX5 overexpression (Ov-DDX5). The empty pcDNA3.1 vector acted as a negative control (Ov-NC). TPC-1 cells were plated into 6-well plates until the confluence has reached 60–80%. The transfection of plasmids to TPC-1 cells was performed with the favor of Lipofectamine 3000 reagent (Life Technologies).

Cell counting kit-8 (CCK-8) assay

TPC-1 cells that inoculated in 96-well plates (5 × 103 cells/well) were incubated in 5% CO2 at 37°C for 24 h, 48 h, and 72 h, respectively. Afterward, each well as given 10 μl of CCK-8 solution (Dojindo Molecular Technologies, Gaithersburg, MD) and the cells were further incubated for 2 h. Finally, the absorbance at 450 nm was assessed under the help of a microplate reader (BioTek, Vermont, USA) [15].

Wound-healing assay

The migration ability was determined in application of wound-healing assay. In brief, cells were inoculated in 6-well plates until 100% confluence has reached. A sterile pipette tip was utilized to create a wound and the cell medium was refreshed with serum-free DMEM. The plates kept incubation for 24 h. The wound image at 0 h and 24 h was captured under an inverted microscope [15].

Transwell assay

In order to figure out the effects of KAP-1 silence on the invasive capability of cells, transwell assay was applied. In brief, 200 μl of cell suspension (1 × 105 cells) was added to the upper chamber of a 24-well transwell chamber (Corning, NY, USA) pre-coated with Matrigel (BD Biosciences, San Jose, CA, USA). 500 μl of DMEM containing 10% FBS was put into the lower chamber. The cells were wiped out from the upper chamber, and the invaded cells got fixed with 4% paraformaldehyde and stained with 0.05% crystal violet. The invasive cells were observed and totaled via an inverted microscope [16].

5-Ethynyl-2’-deoxyuridine (Edu) assay

The cell proliferation was tracked with the use of Edu assay [15]. In brief, TPC-1 cells were placed on the glass coverslips in a 24-well plate (2 × 104 cells/well) for incubation under 37°C for 24 h. Thereafter, each well was added with Edu solution for 2-hour incubation of cells, followed by staining with Apollo567 for 30 min in the darkness. 4’,6-diamidino-2-phenylindole (DAPI) was subsequently applied to stain the nuclear. Finally, a fluorescence microscope (Olympus, Tokyo, Japan) was employed to capture the stained cells.

Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay

The influence of KAP-1 silence on cell apoptosis was evaluated by TUNEL assay [17]. After the cells were rinsed with PBS, the fixation and permeation were carried out with 4% paraformaldehyde and 0.1 Triton X-100, individually. Subsequently, cells were fostered with a TUNEL reaction mixture (Roche, Germany) in the darkness, followed by incubation with DAPI for 10 min. Finally, the apoptotic cells were tracked with the help of a fluorescence microscope (Olympus, Tokyo, Japan).

Quantitative real-time polymerase chain reaction (qRT-PCR)

The RNA isolated by Trizol reagent (Invitrogen) was reversely transcribed into cDNA with PrimerScript RT Reagent Kit (Takara, Dalian, China). Subsequently, the qRT-PCR analysis was conducted using a SYBR RT-PCR kit on a Light Cycler (Roche, Co., Penzberg, Germany). The primers used were listed as follows: KAP-1, forward, 5'-AAGTCTCGGGATGGTGAACG-3' and reverse, 5'-CAGACACCTGGCGGATTGA-3'; DDX5, forward, 5'- GCCGGGACCGAGGGTTTGGT-3' and reverse, 5'-CTTGTGCTGTGCGCCTAGCCA-3'; β-actin, 5'- CGGGAAATCGTGCGTGAC-3', and reverse, 5'-CAGGAAGGAAGGCTGGAAG-3'. The mRNA level was determined by 2−ΔΔCt and normalized to β-actin [18].

Western blot

The proteins isolated by RIPA lysis buffer (Beyotime Biotech, Shanghai, China) were then quantified with a bicinchoninic acid (BCA) protein assay kit (Thermo Fisher Scientific, Wilmington, USA). After exposure to 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the proteins were transferred onto polyvinylidene fluoride (PVDF) membranes. Before probing with primary antibodies against KAP-1 (dilution 1:10,000; ab109545, Abcam), MMP9 (dilution 1:1,000; ab76003, Abcam), MMP12 (dilution 1:1,000; ab52897, Abcam), DDX5 (dilution 1:10,000; ab126730, Abcam), β-catenin (dilution 1:1,000; ab16051, Abcam), c-myc (dilution 1:1,000; ab32072, Abcam), cyclin D1 (dilution 1:200; ab16663, Abcam), and GAPDH (dilution 1:2,500; ab9485, Abcam) at 4°C overnight, the membranes were impeded with 5% skimmed milk. On the following day, the membranes were exposure to horse radish peroxidase (HRP)-labeled secondary antibody (dilution 1:5,000; ab6721, Abcam) for 2 h. An enhanced chemiluminescence-detection kit (Thermo Fisher Scientific, Wilmington, USA) was adopted to observe the immune signals and the protein expression was normalized to endogenous GAPDH [16].

Co-immunoprecipitation (Co-IP) assay

TPC-1 cells were lysed in lysis buffer, and the cellular protein was extracted as aforementioned. After quantification, equal amount of proteins was incubated with anti-IgG or anti-KAP-1/anti-DDX5 at 4°C overnight. Subsequently, the immune complex was obtained by protein A-Sepharose (Amersham, Uppsala, Sweden). The precipitated complex was then subjected to SDS-PAGE for western blot assay as aforementioned [16].

Statistical analysis

Data that analyzed by SPSS 17.0 software (SPSS Inc., Chicago, USA) were displayed as mean ± standard deviation (SD). Statistical difference that analyzed by one-way ANOVA followed by Tukey’s post hoc test indicated statistically significant when p value was less than 0.05.

Results

KAP-1 was upregulated in thyroid cancer cells

Firstly, to confirm the basic role of KAP-1 in thyroid cancer, the expression level of KAP-1 was detected in normal thyroid epithelial Nthy-ori 3–1 cells and human thyroid cancer cell lines (TPC-1, IHH-4, and B-CPAP). As Figure 1a,b vividly showed, both of the mRNA level and protein expression of KAP-1 were greatly upregulated in thyroid cancer cell lines in comparison with that in Nthy-ori 3–1 cells, suggesting that KAP-1 was universally highly expressed in thyroid cancer.

Figure 1.

KAP-1 was upregulated in thyroid cancer cells. (a) The mRNA level and (b) protein expression of KAP-1 in normal thyroid epithelial Nthy-ori 3–1 cells and human thyroid cancer cell lines (TPC-1, IHH-4, B-CPAP) was detected by qRT-PCR and western blot, respectively. ***p < 0.001 vs Nthy-ori 3–1.

KAP-1 knockdown suppressed cell proliferation, migration and invasion

Next, to figure out the player that KAP-1 acts in thyroid cancer, TPC-1 and IHH-4 cell lines with relatively high level of KAP-1 were applied for the following experiments. Firstly, cell transfection was successfully conducted to achieve the inhibition of KAP-1 on mRNA level and protein expression (Figure 2a,b). Subsequently, a series of cellular function was detected. A reduced proliferation ability, presented as the decreased cell viability and the decline of EDU-positive cells, could be observed in TPC-1 cells or IHH-4 cells upon KAP-1 knockdown (Figure 2c,d). Additionally, more TUNEL-positive cells in shRNA-KAP-1 group revealed that KAP-1 knockdown induced higher cell apoptosis (Figure 2e). Moreover, results in Figure 3a-c revealed that the migrated cells and invaded cells were remarkably reduced upon KAP-1 knockdown in both TPC-1 and IHH-4 cell lines, indicating that KAP-1 knockdown hugely hindered the cell migration and invasion rate, which were consistent with the following downregulated protein expression of MMP12 and MMP9 in TPC-1 cells and IHH-4 cells (Figure 3d).

Figure 2.

KAP-1 knockdown suppressed cell proliferation and promoted apoptosis. TPC-1 cells and IHH-4 cells were transfected with shRNA-NC or shRNA-KAP-1-1/shRNA-KAP-1-2, and the (a) mRNA level and (b) protein expression of KAP-1 was detected by qRT-PCR and western blot, respectively. (c) cell viability was measured by CCK-8 assay. (d) EdU staining was conducted to evaluate cell proliferation. (e) TUNEL assay was performed to assess cell apoptosis. **p < 0.01, ***p < 0.001 vs shRNA-NC.

Figure 3.

KAP-1 knockdown suppressed cell migration and invasion. TPC-1 and IHH-4 cells cells were transfected with shRNA-NC or shRNA-KAP-1, then (a) wound-healing assay and (b) Transwell assay was conducted, respectively, to assess cell migration and invasion. (c) Relative cell migration rate and relative cell invasion rate were quantified. (d) protein expression of MMP12 and MMP9 was measured by western blot. ***p < 0.001 vs shRNA-NC.

KAP-1 interacted with DDX5 and regulated DDX5 expression

To clarify the connection between KAP-1 and DDX5, DDX5 expression in thyroid cancer was initially measured. As Figure 4a,b depicted, the mRNA level and the protein expression of DDX5 were higher in thyroid cancer cell lines than that in Nthy-ori 3–1 cells, especially in TPC-1 cells. Considering the high expression of KAP-1 and DDX5 in TPC-1 cells, TPC-1 cells were employed for the next research. The following Co-IP assay demonstrated that KAP-1 and DDX5 could interact with each other (Figure 4c). Furthermore, DDX5 expression was greatly decreased upon KAP-1 knockdown (Figure 4d,e). The results above suggested that KAP-1 could interact with DDX5 and positively regulated DDX5 expression in TPC-1 cells.

Figure 4.

KAP-1 interacted with DDX5 and regulated DDX5 expression. (a) The mRNA level and (b) protein expression of DDX5 in normal thyroid epithelial Nthy-ori 3–1 cells and human thyroid cancer cell lines (TPC-1, IHH-4, B-CPAP) was detected by qRT-PCR and western blot, respectively. ***p < 0.001 vs Nthy-ori 3–1. (c) CoIP assay was conducted to assess the interaction between KAP-1 and DDX5. TPC-1 cells were transfected with shRNA-NC or shRNA-KAP-1, and the (d) mRNA level and (e) protein expression of DDX5 was detected by qRT-PCR and western blot, respectively. ***p < 0.001 vs shRNA-NC.

DDX5 overexpression hindered the suppressive effects of KAP-1 knockdown on cell proliferation, migration and invasion

Subsequently, the regulatory role of DDX5 during KAP-1-mediated thyroid cancer development was explored. At first, cell transfection was successfully conducted to achieve the overexpression of DDX5 (Figure 5a,b). Then, TPC-1 cells were transfected with shRNA-KAP-1 alone or co-transfected with shRNA-KAP-1 and Ov-NC/Ov-DDX5. It was revealed that the reduced mRNA level and protein expression of DDX5 following KAP-1 knockdown were greatly reversed by additional DDX5 overexpression (Figure 5c,d). The following cellular behavior analysis revealed that the co-transfection with shRNA-KAP-1 and Ov-DDX5 greatly improved cell viability, EDU-positive cells and reduced TUNEL-positive cells, compared to co-transfection with shRNA-KAP-1 and Ov-NC (Figure 5e-g), indicating DDX5 overexpression could partly abolish the suppressive effect of KAP-1 knockdown on cell proliferation. Elsewhere, DDX5 overexpression accelerated migration, increased invasive cells as well as elevated the protein expressions of MMP12 and MMP9 compared with that in shRNA-KAP-1+ Ov-NC group (Figure 6a-d), disclosed that the suppressive effects of KAP-1 knockdown on cell migration and invasion in TPC-1 cells were weakened by DDX5 overexpression.

Figure 5.

DDX5 overexpression hindered the suppressive effects of KAP-1 knockdown on cell proliferation. TPC-1 cells were transfected with Ov-NC or Ov-DDX5, and the (a) mRNA level and (b) protein expression of DDX5 was detected by qRT-PCR and western blot, respectively. ***p < 0.001 vs Ov-NC. Subsequently, TPC-1 cells were transfected with shRNA-KAP-1 alone or co-transfected with shRNA-KAP-1 and Ov-NC/Ov-DDX5, and the (c) mRNA level and (d) protein expression of DDX5 was detected by qRT-PCR and western blot, respectively. (e) cell viability was measured by CCK-8 assay. (f) EdU staining was conducted to evaluate cell proliferation. (g) TUNEL assay was performed to assess cell apoptosis. **p < 0.01, ***p < 0.001 vs control; ##p < 0.01 vs shRNA-KAP-1+ Ov-NC.

Figure 6.

DDX5 overexpression hindered the suppressive effects of KAP-1 knockdown on cell migration and invasion. TPC-1 cells were transfected with shRNA-KAP-1 alone or co-transfected with shRNA-KAP-1 and Ov-NC/Ov-DDX5, then (a) wound-healing assay and (b) Transwell assay was conducted, respectively, to assess cell migration and invasion. (c) Relative cell migration rate and relative cell invasion rate were quantified. (d) protein expression of MMP12 and MMP9 was measured by western blot. ***p < 0.001 vs control; ##p < 0.01, ###p < 0.001 vs shRNA-KAP-1+ Ov-NC.

Wnt/β-catenin signaling was regulated by KAP-1/DDX5 axis

To discover the potential mechanism underlying the regulatory role of KAP-1/DDX5 in thyroid cancer, we also investigated Wnt/β-catenin signaling that was a classical pathway involved in tumorigenesis. Results in Figure 7 indicated that KAP-1 knockdown significantly reduced the protein expression of β-catenin, c-Myc, and cyclin D1, suggesting that Wnt/β-catenin signaling activity was impaired by KAP-1 knockdown. Nevertheless, additional DDX5 overexpression partly reversed the change induced by KAP-1 knockdown, indicating that Wnt/β-catenin signaling might be regulated by KAP-1/DDX5 axis during their bio-function in thyroid cancer development.

Figure 7.

Wnt/β-catenin signaling was regulated by KAP-1/DDX5 axis. TPC-1 cells were transfected with shRNA-KAP-1 alone or co-transfected with shRNA-KAP-1 and Ov-NC/Ov-DDX5, then the protein expression of β-catenin, c-Myc, and cyclin D1 was detected using western blot. ***p < 0.001 vs control; ##p < 0.01, ###p < 0.001 vs shRNA-KAP-1+ Ov-NC.

Activation of Wnt/β-catenin signaling retarded the anti-tumor activity of KAP-1 knockdown

Finally, to verify the importance of Wnt/β-catenin signaling underlying the critical role of KAP-1 in thyroid cancer, the rescue experiment was conducted. As shown in Figure 8a-e, TPC-1 cells were transfected with shRNA-KAP-1 with or without treatment of SKL2001, an agonist of Wnt/β-catenin signaling, and a series of assays, including CCK-8, TUNEL, wound-healing and Transwell assays, revealed that the decreased cell proliferation, migration, and invasion, as well as the increased apoptosis, following KAP-1 knockdown were partially abolished by SKL2001, verifying that KAP-1 knockdown suppressed the progression of thyroid cancer by inhibiting Wnt/β-catenin signaling.

Figure 8.

Activation of Wnt/β-catenin signaling retarded the anti-tumor activity of KAP-1 knockdown. TPC-1 cells were transfected with shRNA-KAP-1 with or without treatment of SKL2001, an agonist of Wnt/β-catenin signaling. (a) cell viability was measured by CCK-8 assay. (b) TUNEL assay was performed to assess cell apoptosis. (c) wound-healing assay and (d) Transwell assay was conducted, respectively, to assess cell migration and invasion. (e) Relative cell migration rate and relative cell invasion rate were quantified. *p < 0.05, ***p < 0.001 vs control; #p < 0.05, ###p < 0.001 vs shRNA-KAP-1.

Discussion

Thyroid cancer has developed to a great threat to public health, companied with an increasing morbidity and mortality in women worldwide [19]. Up to date, the mechanism underlying various biological behaviors or clinical features of thyroid cancer is not fully understood, despite of the great efforts concerning about critical oncogenes or tumor suppressors, which may contribute to the occurrence and development of thyroid cancer. In previous studies KAP-1 has been shown to act as an oncogene in multiple malignant tumors, and plays an indispensable role in regulating tumor cell growth, metastasis, epithelial–mesenchymal transition, and drug resistance, thereby influencing the development and therapeutic effect of various kinds of tumors, including pancreatic cancer, lung cancer, ovarian cancer, and breast cancer [20-23]. However, little is known about the biological functions of KAP-1 and its molecular mechanism in thyroid cancer. In our study, we explored the malignant biological properties in thyroid cancer under the regulation of KAP-1, discovering that KAP-1 was markedly elevated in thyroid cancer, and that KAP-1 knockdown could effectively suppress the proliferation, migration and invasion in TPC-1 cells, disclosing a critically regulatory role during the development of thyroid cancer.

Emerging research have claimed that most proteins require interacting with other proteins in the cell to function properly, and this interaction between proteins may influence each other and form a complex regulatory network, thus exerting important effects on the biological processes of various kinds of tumor cells [24,25]. For example, Ma N et al. demonstrated that deleted in malignant brain tumors 1 (DMBT1) could interact with galectin-3 and exert suppressive effects on cell proliferation, migration and invasion in ovarian cancer cells through galectin-3-mediated PI3k/Akt signaling [26]. Cui H et al. confirmed the interaction between DTL and programmed cell death 4 (PDCD4) by Co-IP assay, and revealed that DTL enhanced the motility and proliferation of cancer cells through degrading PDCD4, thus promoting cancer progression [27]. In the present study, a potential interaction between KAP-1 and DDX5 was predicted by BioGRID Database Statistics (https://thebiogrid.org/), which was further verified using Co-IP assay. In addition, KAP-1 could positively regulate DDX5 expression, and the following rescued experiments results showed that the inhibitory effects of KAP-1 knockdown on cellular activities of thyroid cancer was partly reversed by DDX5 overexpression, suggesting that KAP-1 might exert its function in TPC-1 cells partly by interacting with and regulating DDX5.

Being a classical pathway involved in tumorigenesis, Wnt/β-catenin signaling participates in the regulation of multiple fundamental cellular processes, including cell migration and proliferation [28]. β-catenin is the key member of Wnt/β-catenin signaling pathway, inappropriate action of the β-catenin is thought to induce tumor formation at an early stage in most condition [29]. Currently, targeting the inhibition of wnt/β-catenin signaling has been proved to be a good way to prevent the progression of thyroid cancer, and the Wnt/β-catenin signaling targeted regimens have been demonstrated to represent promising candidates of clinical treatment of cancer patients [30-32]. The regulatory effect of DDX5 on Wnt/β-catenin signaling has been widely evidenced in documents. DDX5 can form a complex with β-catenin and accelerate the transcription activation of β-catenin, and promote the transcription of target pro-oncogenes, including c-Myc, cyclin D1, c-Jun, and fra-1, thereby activating β-catenin signaling pathway and facilitating carcinogenesis, and progression of endometrial cancer, lung cancer, colorectal cancer, esophageal cancer, and so on [13,33-36]. In this study, we not only observed a decreased expression level of the Wnt/β-catenin components (β-catenin, c-Myc, and cyclin D1) in TPC-1 cell upon KAP-1 knockdown, consistent with the previous study that KAP-1 knockdown suppressed the migration and invasion of ovarian carcinoma cells through down-regulating Wnt/β-catenin signaling pathway [37], but also found that simultaneous DDX5 overexpression recovered this decrease resulted from KAP-1 knockdown, suggesting that KAP-1 knockdown might exert its anti-tumor effects in TPC-1 cells by regulating DDX-5-mediated Wnt/β-catenin signaling pathway.

Conclusion

In conclusion, these results indicate that KAP-1 may be a novel potential oncogene in thyroid cancer. Notably, KAP-1 knockdown imparted repressive effects on the progression of thyroid cancer cells through the regulation of DDX5-mediated Wnt/β-catenin signaling pathway. Therefore, our study gives a new insight into the role of KAP-1 and DDX5 in thyroid cancer and enriches the potential therapeutic strategies for the treatment of thyroid cancer.

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