Knockdown of IQGAP1 inhibits proliferation and epithelial-mesenchymal transition by Wnt/β-catenin pathway in thyroid cancer

Abstract

Background: Thyroid cancer is the most common endocrine malignant disease with a high incidence rate. The expression of IQGAP1 is upregulated in various cancers, including thyroid cancer. However, the role and underlying mechanism of IQGAP1 in thyroid cancer are still not clear.

Materials and methods: The expression of IQGAP1 in thyroid cancer tissues and cells was determined by reverse transcription polymerase chain reaction and Western blot analysis. Cells were transfected with different siRNAs using Lipofectamine 2000 or were treated with various concentrations of XAV939. The effects of IQGAP1 knockdown on proliferation and epithelial-mesenchymal transition (EMT) of thyroid cancer cells were determined by MTT assay and Western blot analysis. Animal experiments were performed to investigate the effects of IQGAP1 knockdown on the growth of tumors in vivo.

Results: High IQGAP1 expression is found in thyroid cancer tissues and cells. Knockdown of IQGAP1 had inhibitory effects on cell proliferation and EMT, as well as on the Wnt/β-catenin pathway. Additionally, inactivation of the Wnt/β-catenin pathway by XAV939 or si-β-catenin suppressed cell proliferation and EMT. Furthermore, suppression of the Wnt/β-catenin pathway reversed the positive effects of pcDNA-IQGAP1 on cell proliferation and EMT in vitro. Moreover, downregulation of IQGAP1 suppressed tumor growth and EMT in SW579 tumor xenografts through the Wnt/β-catenin pathway in vivo.

Conclusion: Our study demonstrated that knockdown of IQGAP1 inhibited cell proliferation and EMT through blocking the Wnt/β-catenin pathway in thyroid cancer.

Keywords: IQGAP1; Wnt/β-catenin; epithelial–mesenchymal transition; proliferation; thyroid cancer.

Figure 1

mRNA and protein levels of IQGAP1 expression are significantly upregulated in thyroid cancer tissues (n=35) and thyroid cancer cell lines. Notes: (A) qRT-PCR analysis of IQGAP1 mRNA level in thyroid cancer tissues. (B) Western blot analysis of IQGAP1 protein in thyroid cancer tissues. (C) qRT-PCR analysis of IQGAP1 mRNA level in SW579 and TPC-1 cells. (D) Western blot analysis of IQGAP1 protein level in SW579 and TPC-1 cells. *P<0.05. Abbreviations: qRT-PCR, quantitative real-time polymerase chain reaction; N, normal; T, tumor.

Figure 2

Knockdown of IQGAP1 inhibited proliferation and EMT of thyroid cancer cells. Notes: SW579 and TPC-1 cells transfected with si-control, si-IQGAP1-1 or si-IQGAP1-2 were cultured for 48 h. (A) qRT-PCR analysis of IQGAP1 mRNA level in transfected cells. (B) Western blot analysis of IQGAP1 protein in transfected cells. (C) MTT assay was performed to detect viability in transfected cells. (D and E) Western blot analysis of E-cadherin, N-cadherin, Vimentin and Twist in transfected cells. *P<0.05. Abbreviations: EMT, epithelial–mesenchymal transition; qRT-PCR, quantitative real-time polymerase chain reaction; OD, optical density.

Figure 3

Knockdown of IQGAP1 suppressed activation of the Wnt/β-catenin pathway in thyroid cancer cells. Notes: (A and B) Western blot analysis was used to detect β-catenin, cyclin D1 and c-myc in SW579 cells transfected with si-IQGAP1-1 or si-IQGAP1-2 at 48 h. (C and D) Western blot analysis was used to determine β-catenin, cyclin D1 and c-myc in TPC-1 cells transfected with si-IQGAP1-1 or si-IQGAP1-2 at 48 h. *P<0.05. Abbreviation: NC, negative control.

Figure 4

Inactivation of the Wnt/β-catenin pathway suppressed cell proliferation and EMT in thyroid cancer cells. Notes: SW579 cells were treated with different concentrations of Wnt/β-catenin signaling inhibitor XAV939 (5, 10 and 20 μM), and TPC-1 cells were transfected with si-β-catenin-1 or si-β-catenin-2. (A and B) Western blot analysis of β-catenin, cyclin D1 and c-myc in SW579 cells at 48 h. (C and D) Western blot analysis of E-cadherin, N-cadherin, Vimentin and Twist in SW579 cells at 48 h. (E and F) Western blot analysis was performed to test the expression of β-catenin, cyclin D1 and c-myc in TPC-1 cells at 48 h. (G and H) Western blot analysis was applied to determine the level of E-cadherin, N-cadherin, Vimentin and Twist in TPC-1 cells at 48 h. (I) MTT assay was applied to examine the viability of SW579 cells at 48 h. (J) MTT assay was carried out to measure the viability of TPC-1 cells at 48 h. *P<0.05. Abbreviations: EMT, epithelial–mesenchymal transition; OD, optical density; NC, negative control.

Figure 4

Inactivation of the Wnt/β-catenin pathway suppressed cell proliferation and EMT in thyroid cancer cells. Notes: SW579 cells were treated with different concentrations of Wnt/β-catenin signaling inhibitor XAV939 (5, 10 and 20 μM), and TPC-1 cells were transfected with si-β-catenin-1 or si-β-catenin-2. (A and B) Western blot analysis of β-catenin, cyclin D1 and c-myc in SW579 cells at 48 h. (C and D) Western blot analysis of E-cadherin, N-cadherin, Vimentin and Twist in SW579 cells at 48 h. (E and F) Western blot analysis was performed to test the expression of β-catenin, cyclin D1 and c-myc in TPC-1 cells at 48 h. (G and H) Western blot analysis was applied to determine the level of E-cadherin, N-cadherin, Vimentin and Twist in TPC-1 cells at 48 h. (I) MTT assay was applied to examine the viability of SW579 cells at 48 h. (J) MTT assay was carried out to measure the viability of TPC-1 cells at 48 h. *P<0.05. Abbreviations: EMT, epithelial–mesenchymal transition; OD, optical density; NC, negative control.

Figure 5

Inactivation of the Wnt/β-catenin pathway reversed the effects of IQGAP1 overexpression on thyroid cancer cells. Notes: (A and B) Effects of combination of pcDNA-IQGAP1 and XAV939 on E-cadherin, N-cadherin, Vimentin and Twist in SW579 cells. (C) MTT assay was used to detect the effects of combination of pcDNA-IQGAP1 and XAV939 on proliferation in SW579 cells. (D and E) Effects of co-transfection with pcDNA-IQGAP1 and XAV939 on E-cadherin, N-cadherin, Vimentin and Twist in TCP-1 cells. (F) MTT assay was used to measure the effects of co-transfection with pcDNA-IQGAP1 and XAV939 on proliferation in TPC-1 cells. *P<0.05. Abbreviations: OD, optical density; NC, negative control.

Figure 6

Downregulation of IQGAP1 suppressed the growth of SW579 tumor xenografts in vivo. Notes: When the tumor volume reached the required size (50–100 mm³), 5 μg siRNA (si-control or si-IQGAP1-2) was injected into tumor cavity daily for 21 days. The mice were euthanized at day 21. (A) Effects of IQGAP1 knockdown on the growth of SW579 xenografts. (B) Tumor weights were measured at day 21. (C and D) Western blot analysis of β-catenin, cyclin D1 and c-myc in resected tumor tissues. (E and F) Western blot analysis of E-cadherin, N-cadherin, Vimentin and Twist excised in tumor tissues. n=5 and *P<0.05.