IQGAP3 Overexpression Correlates With Poor Prognosis and Radiation Therapy Resistance in Breast Cancer

Abstract

Background: IQ motif-containing GTPase activating protein 3 (IQGAP3), the latest identified member of the IQGAP family, may act as a crucial factor in cancer development and progression; however, its clinical value in breast cancer remains unestablished. We explored the correlation between IQGAP3 expression profile and the clinicopathological features in breast cancer. Methods: IQGAP3 mRNA and protein levels were detected in breast cancer cell lines and tumor tissues by real-time PCR and western blotting and compared to the normal control groups. Protein expression of IQGAP3 was also evaluated immunohistochemically in archived paraffin-embedded specimens from 257 breast cancer patients, and the associations between IQGAP3 expression level, clinical characteristics, and prognosis were analyzed. We assessed the relationship between IQGAP3 expression and sensitivity to radiation therapy which was determined by subgroup analysis. Results: IQGAP3 was significantly upregulated in breast cancer cell lines and human tumor tissues at both the mRNA and protein level compared to controls. Additionally, high levels of IQGAP3 expression were detected in 110/257 (42.8%) of archived paraffin-embedded breast cancer specimens. High IQGAP3 expression level was significantly related to clinical stage (p = 0.001), T category (p = 0.002), N category (p = 0.001), locoregional recurrence (p = 0.002), distant metastasis (p = 0.001), and vital status (p = 0.001). Univariate and multivariate statistical analysis showed that IQGAP3 expression was an independent prognostic factor among all 257 breast cancer patients in our cohort (p = 0.003, p = 0.001). Subgroup analysis revealed IQGAP3 expression correlated with radioresistance and was also an independent predictor of radiotherapy outcome. Conclusion: Our findings suggest that high IQGAP3 expression predicts poor prognosis and radioresistance in breast cancer. Therefore, IQGAP3 may be a reliable prognostic biomarker in breast cancer and could be used to identify patients who may benefit from radiotherapy.

Keywords: IQGAP3; breast cancer; prognosis; radiation therapy; resistance.

FIGURE 1

Microarray data reveals IQGAP3 is upregulated in breast cancer patients and in cases that are resistant to radiotherapy (RT). (A) Expression of IQGAP3 in TCGA (breast invasive carcinoma) tumor and normal tissue data (Mann–Whitney test; p < 0.01). (B) Expression of IQGAP3 in TCGA (breast invasive carcinoma) including RT-resistant and RT-sensitive cases (Mann–Whitney test; p < 0.05).

FIGURE 2

IQGAP3 is upregulated in breast cancer cell lines and tissues. (A) Quantitative real-time PCR analysis of IQGAP3 mRNA expression in MCF-10A immortalized breast epithelial cells and twelve cultured breast cancer cell lines. GAPDH was used as a loading control. *p < 0.05. (B) Real-time PCR analysis of IQGAP3 mRNA expression in six paired breast cancer tumor tissues and adjacent normal tissues (ANT). GAPDH was used as a loading control. *p < 0.05. (C) Western blotting analysis of IQGAP3 protein expression in MCF-10A immortalized breast epithelial cells and twelve cultured breast cancer cell lines. α-tubulin was used as a loading control. (D) Western blotting analysis of IQGAP3 protein expression in six paired breast cancer tumor tissues and adjacent normal tissues (ANT). α-tubulin was used as a loading control.

FIGURE 3

Immunohistochemical detection of IQGAP3 expression in paraffin-embedded breast cancer tissues. Representative images of immunohistochemical staining for IQGAP3 in normal breast tissues (controls) and breast tumor tissues are shown.

FIGURE 4

IQGAP3 protein expression is associated with clinical outcomes in the whole cohort of breast cancer cases and in the radiotherapy (RT) subgroup (A and B,C). Kaplan–Meier overall survival (A), locoregional recurrence-free survival (B), and distant metastasis-free survival (C) curves for all 257 patients with breast cancer stratified by high IQGAP3 expression (n = 110) vs. low IQGAP3 expression (n = 147) (D and E,F). Kaplan–Meier overall survival (D), locoregional recurrence-free survival (E), and distant metastasis free survival (F) curves for RT subgroup of 201 patients stratified by high IQGAP3 expression (n = 87) vs. low IQGAP3 expression (n = 114). p values were calculated using the log-rank test.

FIGURE 5

Immunohistochemical (IHC) detection of IQGAP3 expression in paraffin-embedded breast cancer tissues in the radiotherapy- (RT-) sensitive and RT-resistant subgroups. Left panel: representative images of IHC staining for IQGAP3 in the RT-resistant and RT-sensitive tissues. Right panel: average IHC score of IQGAP3 in the RT-resistant (n = 19) and RT-sensitive tissues (n = 140).

FIGURE 6

Gene Set Enrichment Analysis (GSEA) plots showing that IQGAP3 expression correlates positively with DNA repair gene signatures (HALLMARK_DNA_REPAIR) and PI3K signaling-activated gene signatures (HALLMARK_PI3K_AKT_MTOR_SIGNALING) in the published Cancer Genome Atlas (TCGA) breast invasive carcinoma gene expression profiles.