IQGAP1‑siRNA inhibits proliferation and metastasis of U251 and U373 glioma cell lines.

IQ motif containing GTPase activating protein 1 (IQGAP1) is a scaffold protein, which is aberrantly expressed in several tumor types and is closely associated with the development, metastasis and prognosis of cancer. Several studies have demonstrated that IQGAP1 has broad prospects in the basic and clinical research of tumors. The present study aimed to explore the effects of IQGAP1‑small interfering (si) NA on the proliferation and metastasis of U251 and U373 glioma cell lines, which markedly expressed IQGAP1. The human glioma cell lines (U251 and U373) were transfected with siRNA and transfection efficacy was confirmed by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blot analysis. Cell proliferation was detected using the Cell Counting kit‑8, and cell metastasis capabilities were detected using cell adhesion, migration and invasion assays. In addition, the expression levels of several tumor‑associated genes were determined by RT‑qPCR and western blotting. The results indicated that IQGAP1 was expressed at higher levels in glioma tissues compared with in normal brain tissues. IQGAP1‑siRNA significantly inhibited cell proliferation, and cell adhesion, migration and invasion. Furthermore, the expression levels of matrix metalloproteinase (MMP)2, Snail, MMP9, fibronectin 1 and Twist were suppressed, and E‑cadherin was upregulated in response to siRNA‑IQGAP1. The present study identified the function of IQGAP1 in glioma cell biology, and indicated that it may be considered a novel target for glioma treatment.

Introduction

Glioma a primary tumor of the central nervous system that is associated with the highest levels of morbidity and mortality, and accounts for ~45% of intracranial malignant tumors (1). Glioma exhibits increased levels of invasive growth, and is prone to invasion and metastasis (2,3). At present, it is impossible to achieve total removal of the tumor, and following resection, poor prognosis and high recurrence rates are common (3). Due to its resistance to radiotherapy and chemotherapy, the 5-year survival rate of glioma is <5%. Glioma cannot be completely cured and available treatment options are also a concern (4,5).

IQ motif containing GTPase activating protein 1 (IQGAP1) was initially cloned in 1994. It is a 189-kDa scaffolding protein, which belongs to the IQGAP family, alongside its homologs IQGAP2 and IQGAP3 (6). IQGAP1 contains several protein-interacting domains, including one polyproline-binding domain, one calponin homology domain, one Ras-GTPase-activating protein (GAP)-related domain and four calmodulin-binding motifs (7,8). Numerous proteins, including the GTP-bound forms of Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division cycle 42 (Cdc42), and the GDP-bound form of GTPases, are able to bind to IQGAP1 (9,10). IQGAP1 increases the levels of active Rac1 in cells (11). Notably, despite one domain of IQGAP1 that presents sequence similarity to GAP, IQGAP1 does not possess GAP activity (12). In addition, IQGAP1 binds directly to E-cadherin (13,14); a previous study reported that IQGAP1 is associated with the modulation of several cellular functions and various signaling pathways (7). Notably, numerous IQGAP1 binding partners have well-defined roles in tumorigenesis (15). Overexpression of IQGAP1 has been demonstrated to increase proliferation of MCF-7 cells (16) and reduce E-cadherin-mediated adhesion (14). Conversely, silencing of IQGAP1 inhibits the invasion of HO-8910PM ovarian cancer cells (17), and small interfering (si)RNA-induced knockdown of IQGAP1 reduces the migration of U87MG human glioblastoma cells (18). These previous studies indicated that IQGAP1 expression levels are frequently altered in neoplasia; therefore, IQGAP1 has been proposed as an oncogene (16).

The present study explored the effects of IQGAP1 on the proliferation and metastasis of U251 and U373 glioma cell lines. IQGAP1 was shown to be more highly expressed in glioma tissues compared with in normal tissues. Conversely, IQGAP1-siRNA significantly inhibited cell proliferation. Furthermore, cell adhesion, migration and invasion were markedly suppressed following IQGAP1-siRNA transfection. The expression levels of matrix metalloproteinase (MMP)2, Snail, MMP9, fibronectin 1 (FN1) and Twist were suppressed, and E-cadherin was upregulated. The present study provided insight into the function of IQGAP1 in glioma cell biology, and indicated that it may be considered an oncogene and a novel target for glioma treatment.

Materials and methods

Tissue samples

Human normal brain tissues (n=21) and glioma tissues (n=26) were provided by the Department of Neurosurgery, Wuhan General Hospital of Guangzhou Command (Wuhan, China). Sample acquisitions were approved by the Medical Ethics Committee, Hospital. All samples were cut into small pieces, and were quickly placed in cryotubes with liquid nitrogen. All glioma tissues were histopathologically confirmed, and the pathological diagnosis and classification was determined in accordance with the World Health Organization classification of tumors of the nervous system (19). Normal brain tissues were depressurized resection specimens. The current study was approved by the ethics committee of Wuhan General Hospital of Guangzhou Command (Wuhan, China).

Cell culture

The following five human glioma cell lines: U251, T98G, SHG44, U87 and U373 were obtained from the Shanghai Cell Bank, Chinese Academy of Science (Shanghai, China). All cells were cultured in Dulbecco's modified Eagle's medium (DMEM; Hyclone; GE Healthcare, Logan, UT, USA), supplemented with 100 µg/ml streptomycin, 10% heat-inactivated fetal bovine serum (FBS; Gibco; Thermo Fisher Scientific, Inc., Waltham, MA, USA) and 100 U/ml penicillin. The cells were cultured in an incubator (Thermo Fisher Scientific, Inc.) at 37°C in an atmosphere containing 100% humidity and 5% CO2.

siRNA transfection

U251 and U373 cells in the logarithmic growth phase were collected, trypsin-digested, counted and plated into 6-well culture plates (1 ml/well, 5×105 cells/ml). The cells were then seeded in antibiotic-free medium the day prior to transfection. Subsequently, cells were transfected with 400 nmol/l IQGAP1-siRNA or negative control (NC) siRNA (Shanghai GenePharma Co., Ltd., Shanghai, China) using Lipofectamine® 2000 (Invitrogen; Thermo Fisher Scientific, Inc.) according to the manufacturer's protocol. For IQGAP1-siRNA, RNA oligomers were synthesized in the sense and anti-sense directions, containing 19 nucleotides, corresponding to human IQGAP1 at nucleotides 1,620–1,642 (5′-GGCACAUGCAGAGAAUAAU-3′). After 24, 48 and 72 h, the cells were collected; cells were also collected at 0 h as a control for the proliferation assay. Cells collected 48 h post-transfection were used to conduct the subsequent cell adhesion assay, Transwell assay, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis.

Cell growth and proliferation assay

Cell Counting kit (CCK)-8 (Shanghai Tongren Pharmaceutical Co., Ltd., Shanghai, China) was used to assess the effects of IQGAP1-siRNA on the viability of U251 and U373 cells. Briefly, after transfcetion for 0, 24, 48 and 72 h, CCK-8 reagent [1:10 (v/v) per 100 µl medium] was added to each well and incubated for 4 h at 37°C. Following incubation, optical density (OD) of the supernatants was determined at 450 nm using a microplate reader. Experiments were performed at least three times, each in triplicate. Cell viability was exhibited by the OD value. Cell proliferation rate (%) was calculated as follows: (OD value of NC or IQGAP1-siRNA group/OD value of control group) ×100.

Adhesion assays

Adhesion assays, as well as Transwell assays, were performed to detect the effects of IQGAP1-siRNA on the metastasis of U251 and U373 cells. Suspensions of transfected cells were added to a 12-well plate (1×105 cells/well), incubated for 1 h at 37°C and 5% CO2, and centrifuged at 1,000 × g for 5 min at room temperature. Subsequently, the supernatant was discarded, the cells were washed twice with PBS, and the adherent cells were fixed with 4% methanol for 15 min and stained with crystal violet for 30 min at room temperature. The number of adherent cells from three random fields was counted and images were captured under a microscope (x200 magnification).

Transwell assay

Cell migration and invasion were assessed using Transwell assays. For the cell migration assay, the various U251 and U373 cell groups were starved in serum-free DMEM for 24 h. Prior to seeding, cells were digested with 0.25% trypsin (Gibco; Thermo Fisher Scientific, Inc.), resuspended in DMEM containing 1% FBS and diluted to 1×105 cells/ml; the lower chamber of the Transwell contained DMEM with 5% FBS. After a 48 h incubation at 37°C in the upper chamber of the Transwell in a 24-well plate, cells were fixed for 10 min using 1 ml/well 4% paraformaldehyde [JRDUN Biotechnology (Shanghai) Co., Ltd., Shanghai, China], stained with Giemsa [JRDUN Biotechnology (Shanghai) Co., Ltd.] for 30 min at room temperature and washed three times with 1X PBS. Subsequently, the Transwell chamber was wiped carefully to remove non-migrated cells using a cotton swab. The chambers were then visualized under a microscope [Olympus (China) Co., Ltd., Shanghai, China; ×200 magnification] and the number of cells was counted.

For the cell invasion assay, prior to assessment, the Transwell chamber (pore size, 8 µm; 24-wells; Sigma-Aldrich; Merck Millipore, Darmstadt, Germany) was washed with 1X PBS for 5 min, and the inserts were coated with 80 µl Matrigel (1:2 dilution; BD Biosciences, Franklin Lakes, NJ, USA). The cells (1×105 cells/ml density) were then added to the upper Transwell chamber in 0.5 ml serum-free medium; whereas 0.75 ml complete medium containing 10% FBS was added to the lower chamber as a chemoattractant. Subsequently, the cells were incubated at 37°C for 48 h. Cells with the ability to pass through the filter were fixed and stained with 1 ml 0.5% crystal violet for 30 min. Finally, the number of invasive cells in five randomly selected high power fields was counted under a microscope.

RT-qPCR assay

The mRNA expression levels of IQGAP1 were detected in U251 and U373 cells, and glioma and normal tissues, using RT-qPCR. Total RNA was isolated from the samples using TRIzol® reagent (Invitrogen; Thermo Fisher Scientific, Inc.) and the obtained mRNA was detected by 0.8% agarose gel electrophoresis. cDNA was synthesized from ~5 µg RNA using AMV reverse transcriptase (Fermentas; Thermo Fisher Scientific, Inc.) with a reaction mixture of 1 µl forward primer, 1 µl reverse primer, 12.5 µl 2X Supermix, 2 µl cDNA and 8.5µl ddH2O. qPCR reactions were performed in a 25 µl total volume using SYBR® Green 10X Supermix (Takara Bio, Inc., Otsu, Japan) on a Roche Light Cycler® 480II system (Roche Diagnostics, Basel, Switzerland). Primer Express Software v3 (Applied Biosystems; Thermo Fisher Scientific, Inc.) was used to design IQGAP1 primer pairs. GAPDH was used as an internal control. The PCR cycling conditions were as follows: 95°C for 10 min, followed by 40 cycles at 95°C for 15 sec and 60°C for 45 sec; one cycle at 95°C for 15 sec, 60°C for 1 min; one cycle at 95°C for 15 sec and 60°C for 15 sec. The sequences of the IQGAP1 primer pairs were as follows: IQGAP1, forward 5′-CAGAGACGTGCTATCCGTGATG-3′, reverse 5′-CTCCGCTGATTCCGAATATCCC-3′; and GAPDH, forward 5′-CGGAGTCAACGGATTTGGTCGTAT-3′, reverse 5′-AGCCTTCTCCATGGTGGTGAAGAC-3′. The size of the amplified IQGAP1 product was 209 bp. The relative expression levels in the various groups were calculated using the ΔΔCq method by normalizing to the mRNA expression levels of GAPDH (20). All PCR reactions were performed in triplicate.

Western blot analysis

The association between IQGAP1 and tumor-related protein expression was determined by western blot analysis. Transfected cells were harvested, washed twice with PBS, lysed in ice-cold radioimmunoprecipitation assay buffer (Beyotime Institute of Biotechnology, Shanghai, China) containing 0.01% protease and phosphatase inhibitor (Sigma-Aldrich; Merck Millipore), and were incubated on ice for 30 min. The lysates were then centrifuged at 12,000 × g for 10 min at 4°C. Proteins in the supernatant were obtained and quantified using the bicinchoninic acid protein quantification kit (Thermo Fisher Scientific, Inc.). Protein samples (20–30 µg) were then separated by 10% SDS-PAGE, and were electrophoretically transferred to a polyvinylidene fluoride membrane (Merck Millipore). The membranes were blocked with 5% bovine serum albumin (Beyotime Institute of Biotechnology) in PBS-0.1% Tween, and were incubated with primary antibodies against IQGAP1 (cat. no. ab133490; 1:1,000 dilution; Abcam, Cambridge, UK), FN1 (cat. no. ab32419; 1:1,000 dilution; Abcam), Snail (cat. no. 3879s; 1:1,000 dilution; Cell Signaling Technology, Inc., Danvers, MA, USA), Twist (cat. no. ab175430; 1:500 dilution; Abcam), MMP2 (cat. no. ab92536; 1:1,000 dilution; Abcam), MMP9 (cat. no. ab119906; 1:500 dilution; Abcam), E-cadherin (cat. no. 14472; 1:1,000 dilution; Cell Signaling Technology, Inc.) and GAPDH (cat. no. 5174; 1:1,500 dilution; Cell Signaling Technology, Inc.). Blots were then incubated for 1 h at 37°C with goat anti-mouse or anti-rabbit secondary antibodies (cat. nos. A0192 and A0208, respectively; 1:3,000 dilution; Beyotime Institute of Biotechnology) and intensities were measured using enhanced chemiluminescence (Thermo Fisher Scientific, Inc.).

Statistical analysis

All data are presented as the mean ± standard deviation. All statistical analyses were conducted using GraphPad Prism 6.0 software (GraphPad Software, Inc., La Jolla, CA, USA). Data were analyzed by one-way analysis of variance without interaction terms, followed by Dunnett's or Duncan's test for multiple comparisons. P<0.05 was considered to indicate a statistically significant difference.

Results

IQGAP1 is highly expressed in glioma tissues and cell lines

In order to determine the expression levels of IQGAP1 in normal human brain tissues and glioma tissues, an RT-qPCR assay was performed; the results indicated that the mRNA expression levels of IQGAP1 were significantly higher in glioma tissues compared with in normal tissues (Fig. 1A) (n=3, P<0.01). The mRNA and protein expression levels of IQGAP1 in the following five glioma cell lines: U251, T98G, SHG44, U87 and U373, were detected by RT-qPCR and western blotting, respectively. Notably, IQGAP1 was more highly expressed in U251 and U373 cell lines compared with the others (Fig. 1B and C) (n=3, P<0.01). These findings suggest that IQGAP1 is highly expressed in glioma tissues and cell lines. U251 and U373 cell lines were used to conduct the subsequent assays.

Figure 1.

High expression of IQGAP1 in glioma tissues and cell lines. (A) mRNA expression levels of IQGAP1 in glioma tissues were significantly higher compared with in normal tissues (n=3). Data are presented as the mean ± standard deviation. ***P<0.001 vs. normal tissues. (B and C) IQGAP1 was more highly expressed in U251 and U373 cell lines compared with the others (n=3). Data are presented as the mean ± standard deviation. **P<0.05, ***P<0.001 vs. T98G and U87. IQGAP1, IQ motif containing GTPase activating protein 1.

IQGAP1 expression in U251 and U373 cells post-transfection

In order to detect whether IQGAP1-siRNA and NC-siRNA were transfected successfully, RT-qPCR and western blotting were performed. As shown in Fig. 2A and B, in the IQGAP1-siRNA group, the relative mRNA expression levels of IQGAP1 were markedly decreased in U251 and U373 cells. Similarly, the protein expression levels of IQGAP1 were downregulated in the IQGAP1-siRNA U251 and U373 cell groups (Fig. 2C and D). These results indicate that IQGAP1 expression was successfully knocked down.

Figure 2.

IQGAP1 expression in U251 and U373 cells post-transfection. (A and B) mRNA expression levels of IQGAP1 were markedly decreased in the IQGAP1-siRNA U251 and U373 cell groups. (C and D) Protein expression levels of IQGAP1 were also downregulated in the IQGAP1-siRNA U251 and U373 cell groups. (n=3). Data are presented as the mean ± standard deviation. ***P<0.001 vs. the control group; ##P<0.01 vs. the NC group. IQGAP1, IQ motif containing GTPase activating protein 1; siRNA, small interfering RNA; NC, negative control.

IQGAP1-siRNA inhibits cell viability

Cell viability (OD, 450 nm) and proliferation rates were measured using the CCK-8 assay. Following transfection with IQGAP1-siRNA or NC-siRNA for 24, 48 or 72 h, the viability of U251 and U373 cells was markedly reduced in the IQGAP1-siRNA groups in a time-dependent manner (n=3, P<0.01) (Fig. 3A and B). Post-transfection for 72 h, the proliferation rates of U251 and U373 cells in the IQGAP1-siRNA group were significantly reduced compared with that of the controls (n=3, P<0.01) (Fig. 3C and D). These results indicate that IQGAP1-siRNA inhibits cell viability and proliferation.

Figure 3.

IQGAP1-siRNA inhibited cell viability. (A and B) Cell viability of U251 and U373 cells was markedly reduced post-transfection with IQGAP1-siRNA in a time-dependent manner. (C and D) Proliferation rates of U251 and U373 cells were significantly reduced post-transfection with IQGAP1-siRNA compared with the control groups. (n=3). Data are presented as the mean ± standard deviation. *P<0.05, **P<0.01, ***P<0.001 vs. the control group; ##P<0.01, ###P<0.001 vs the NC group. IQGAP1, IQ motif containing GTPase activating protein 1; siRNA, small interfering RNA; NC, negative control.

IQGAP1-siRNA inhibits adhesion of U251 and U373 cells

Cell metastasis serves a vital role in cancer progression. In order to determine whether IQGAP1-siRNA had an effect on glioma cell metastasis, cell adhesion assays (Fig. 4) and Transwell assays (Figs. 5 and 6) were performed in U251 and U373 cells. The results indicated that the number of adhesive U251 and U373 cells was significantly decreased in the IQGAP1-siRNA groups (Fig. 4A and C). In the U251 groups, the number of adhesive cells was 27±2, 25±2 and 11±1 in the control, NC and IQGAP-siRNA groups, respectively (Fig. 4B). In the U373 groups, the number of adhesive cells was 55±4, 45±3 and 20±7 in the control, NC and IQGAP1-siRNA groups, respectively (Fig. 4D). These results suggest that IQGAP1-siRNA may inhibit the adhesion of U251 and U373 cells.

Figure 4.

IQGAP1-siRNA inhibited adhesion of U251 and U373 cells. (A and B) The number of adhesive U251 cells was significantly decreased in the IQGAP1-siRNA group. (C and D) The number of adhesive U373 cells was significantly decreased in the IQGAP1-siRNA group. n=3. Data are presented as the mean ± standard deviation. Magnification, ×200. *P<0.05, **P<0.01, ***P<0.001 vs. the control group; ##P<0.01, ###P<0.001 vs. the NC group. IQGAP1, IQ motif containing GTPase activating protein 1; siRNA, small interfering RNA; NC, negative control.

Figure 5.

IQGAP1-siRNA inhibits migration of U251 and U373 cells. (A and B) Transfection with IQGAP1-siRNA markedly suppressed the migratory ability of U251 cells compared with in the NC and control groups. (C and D) Transfection with IQGAP1-siRNA markedly suppressed the migratory ability of U373 cells compared with the NC and control groups. n=3. Data are presented as the mean ± standard deviation. Magnification, ×200. ***P<0.001 vs. the control group; ###P<0.001 vs. the NC group. IQGAP1, IQ motif containing GTPase activating protein 1; siRNA, small interfering RNA; NC, negative control.

Figure 6.

IQGAP1-siRNA in hibits invasion of U251 and U373 cells. (A and B) The invasive ability of U251 cells was markedly suppressed by IQGAP1-siRNA. (C and D) The invasive ability of U373 cells was markedly suppressed by IQGAP1-siRNA. n=3. Data are presented as the mean ± standard deviation. Magnification, ×200. **P<0.01, ***P<0.001 vs. the control group; ##P<0.01 vs. the NC group. IQGAP1, IQ motif containing GTPase activating protein 1; siRNA, small interfering RNA; NC, negative control.

IQGAP1-siRNA inhibits migration of U251 and U373 cells

A Transwell migration assay was performed to explore the effects of IQGAP1-siRNA on U251 and U373 cells. As shown in Fig. 5A and C, transfection with IQGAP1-siRNA markedly suppressed the migratory ability of cells compared with in the NC and control groups. The number of migratory cells in the control, NC and IQGAP1-siRNA U251 groups was 72±3, 68±1 and 33±4, respectively (Fig. 5B), and was 67±4, 61±3 and 28±5, respectively in the U373 cell groups (Fig. 5D). These results indicate that IQGAP1-siRNA inhibits the migration of U251 and U373 cells.

IQGAP1-siRNA inhibits invasion of U251 and U373 cells

A Transwell invasion assay was used to determine the effects of IQGAP1-siRNA on U251 and U373 cells. As shown in Fig. 6A and C, IQGAP1-siRNA markedly suppressed the invasive ability of cells compared with in the NC and control groups. The number of invasive U251 cells in the control, NC and IQGAP1-siRNA groups was 120±14, 107±6 and 64±11, respectively (Fig. 6B), and was 122±11, 118±11 and 58±7, respectively in the U373 cell groups (Fig. 6D). These results indicate that IQGAP1-siRNA may inhibit invasion of U251 and U373 cells.

IQGAP1-siRNA regulates the expression of tumor suppressor genes and oncogenes

In order to further determine the mechanism by which IQGAP1-siRNA inhibits glioma cell proliferation and metastasis, the mRNA and protein expression levels of several tumor-associated genes were detected in U251 and U373 cells by RT-qPCR and western blotting, respectively. As presented in Fig. 7A and B, in U251 and U373 cells, the mRNA expression levels of MMP2, Snail, MMP9, FN1 and Twist were decreased, whereas E-cadherin was increased in the IQGAP1-siRNA groups, compared with in the controls. Similarly, the protein levels corresponded with the mRNA levels, which indicated that with the exception of E-cadherin, all other proteins were downregulated by IQGAP1-siRNA (Fig. 7C and D).

Figure 7.

IQGAP1-siRNA regulated the expression of tumor suppressor genes and oncogenes. (A and B) The mRNA expression levels of MMP2, Snail, MMP9, FN1 and Twist were decreased, whereas E-cadherin was increased, in the IQGAP1-siRNA groups compared with in the control groups. (C and D) The protein expression levels of MMP2, Snail, MMP9, FN1 and Twist were downregulated, whereas E-cadherin was upregulated. n=3. Data are presented as the mean ± standard deviation. **P<0.01, ***P<0.001 vs. the control group, ##P<0.01, ###P<0.001 vs. the NC group. IQGAP1, IQ motif containing GTPase activating protein 1; siRNA, small interfering RNA; NC, negative control; MMP, matrix metalloproteinase; FN1, fibronectin 1.

Discussion

It has previously been revealed that IQGAP1 RNA and protein expression is increased in various human malignancies (15). Although an increasing number of studies has aimed to elucidate the expression of IQGAP1 in various types of cancer, including lung cancer (21), endometrial cancer (22), ovarian cancer (23), gastric cancer (24), colon cancer (25), hepatic carcinoma (26), breast cancer (27) and even glioma (28), the molecular roles of IQGAP1 remain to be understood and the correlation between clinical outcomes and IQGAP1 expression in human malignant tumors require further investigation. The present study indicated that IQGAP1-siRNA inhibited the proliferation and metastasis of U251 and U373 glioma cells. Furthermore, several tumor suppressor genes and oncogenes were modulated following IQGAP1-siRNA transfection.

The expression of IQGAP1 has been explored in various types of cancer in vivo and in vitro. With regards to glioma, patients with glioblastoma and negative IQGAP1 expression have been reported to survive for >3 years (28). Studies regarding the effects of IQGAP1 on cell proliferation are increasing. It has previously been reported that IQGAP1, as a mitogen-activated protein kinase (MAPK) scaffold that responds to MAPK signaling activation, may modulate cellular functions and enhance proliferation (29). Overexpression of IQGAP1 increases the proliferation of MCF-7 cells (16), whereas knockdown of IQGAP1 with siRNA inhibits cell proliferation of umbilical vein endothelial cells, and IQGAP1 is required for vascular endothelial-derived growth factor-stimulated proliferation (30). Taken together, IQGAP1 expression appears to be upregulated in various cancer cells, and is involved in the regulation of cell proliferation. Similarly, in the present study, knockdown of IQGAP1 with siRNA inhibited the proliferation of glioma cell lines.

IQGAP1 contains several protein-interacting domains, including one polyproline-binding domain, one calponin homology domain, one Ras-GAP-related domain and four calmodulin-binding motifs (7,8). The domains possess several important interacting partners, including calmodulin, Rac1, Csc42, Rap1, β-catenin, E-cadherin and members of the MAPK pathway (7,31). IQGAP1 regulates various basic cellular activities such as cell-cell adhesion, cell migration and invasion through the aforementioned interactions (32). For example, IQGAP1 binds directly to E-cadherin (13,14) and overexpression of IQGAP1 reduces E-cadherin-mediated cell adhesion (14). In ovarian cancer, it has been reported that overexpression of IQGAP1 is significantly correlated with poor prognosis, as determined by multivariate analysis (33). In addition, IQGAP1 is strongly expressed at the invasion front; furthermore, this invasion front-associated expression pattern appeared more frequently in advanced carcinoma, compared with other carcinomas (32). Taken together, these findings suggested that IQGAP1 has a function on cancer cell metastasis, and the existing reports agree with the present study that transfection of cells with IQGAP1-siRNA may inhibit cell metastasis.

IQGAP1 may serve a critical role in pathways leading to cell proliferation and metastasis; however, the precise mechanism remains unknown. In order to explore this, the present study indicated that IQGAP1 affects the expression of several tumor-associated genes. Knockdown of IQGAP1 with siRNA resulted in upregulation of the tumor suppressor gene E-cadherin, whereas oncogenes, including MMP2, Snail, MMP9, FN1 and Twist, were downregulated. Among them, MMP2 and MMP9 are members of the MMP family (34). A previous study indicated that human prostate cancer cell invasion was inhibited by finasteride via MMP2 and MMP9 downregulation (35). Furthermore, it has been suggested that MMP2 serves a role in the migration of tumor cells (36). Snai1, E-cadherin and Twist have vital roles in the epithelial-mesenchymal transition (EMT) process (36,37), which is closely associated with tumor cell metastasis (38,39). Furthermore, Snai1 and E-cadherin regulate EMT to initiate the metastasis of several types of tumor cell (40). Twist is known to be a highly conserved basic helix-loop-helix protein transcription factor, which promotes EMT and may have prognostic significance in endometrial cancers (41). As for FN1, U94 alters gene expression of angiopoietin-like 4 and FN1 resulting in inhibition of tumorigenesis of PC3 prostate cancer cells (42). These results indicated that IQGAP1 knockdown-mediated inhibition of cell proliferation and metastasis in glioma cell lines may be associated with the expression of these tumor-associated genes. Further studies are required to determine the functional roles of IQGAP1 in cancer.

In conclusion, IQGAP1 was highly expressed in glioma tissues and cell lines. The present study indicated that IQGAP1-siRNA inhibited proliferation and metastasis of U251 and U373 glioma cell lines. Furthermore, the expression levels of several tumor suppressor genes and oncogenes were modulated. These results provide evidence regarding the functional roles of IQGAP1 in cancer.