Background
Breast cancer is the leading cause of cancer-related death in Southeast Asian women, and is second only to gastric cancer in East Asian women [
1]. Breast cancer incidence rates have been increasing annually, and in some countries, breast cancer is the most common cause of death among women [
2,
3].
In recent years, several members of the kinesin family of motor proteins have been identified in mammalian cells. In particular, it has been shown that the kinesin-13 class of proteins, which includes KIF2A, KIF2B, and KIF2C/MCAK, play an important role in mitosis [
4,
5]. These proteins modulate intracellular transport, cell division, and bipolar spindle assembly during spindle formation [
5‐
7]. During cancer cell proliferation, the chromosome appears to be unstable as a result of continuous chromosomal missegregation during mitosis [
8,
9]. As a critical cytoskeleton, microtubules (MTs) are not only essential for mitotic activity of malignant cells but also for invading neighboring tissues and for the distant metastasis. The KIFs participate in spindle orientation and chromosomal movements during mitosis and cytoskeletal reorganization [
10‐
13]. KIF2A has been shown to have microtubule depolymerizing activities
in vitro[
14,
15]. Monopolar spindles in the cells could cause the gain or loss of chromosomes in daughter cells [
16]. Any interference with this process can lead to chromosome missegregation, resulting in significant changes in the proliferation and migration of tumor cells. Among kinesin family members, the function of KIF2C/MCAK in gastric, colorectal and breast cancers has been studied. However, the role of KIF2A in breast cancer remains unknown. The goal of this study was to explore the function of KIF2A in human breast cancer, and to determine its effects on the proliferation and invasion of breast cancer cells.
Discussion
In this study, we found that the mitotic centromere-associated Kinesin-13 protein KIF2A mRNA and protein levels in breast cancer tissue were highly expressed compared to adjacent normal tissue. The increase in KIF2A expression was associated with a decrease in patient survival time indicating that KIF2A is a potential novel prognosis biomarker for breast cancer. We also demonstrated that patients with lymph node metastasis had high frequency of KIF2A overexpression.
As the key components of the cytoskeleton, MTs play important roles in mitosis, cell migration, trafficking and cell signaling [
20]. Kinesin is one family of motor protein associated with MT transport. The Kinesin-13 proteins (KIF2A, KIF2B, and KIF2C/MCAK) are MT depolymerases that depolymerize the ends of MTs [
21,
22] and have important functions in mitosis, including the catalysis of microtubule disassembly, which is important for normal chromosome movement [
23]. KIF2A was found to specifically localize in centrosomes during the process of cellular mitosis, and possesses microtubule-depolymerizing activity for spindle bipolarity [
14,
16]. The overexpression of these proteins causes a moderate increase in the frequency of multipolar and monopolar spindles [
24,
25], which may further contribute to the gain or loss of chromosomes in daughter cells. In a study by Ganem et al. [
16]
, the cell cycle was inhibited in cells with RNAi-induced knockdown of KIF2A, and these cells formed monopolar spindles instead of bipolar spindles, leading to chromosome mis-segregation in cells.
Human osteosarcoma (U2OS) cells transfected with non-sense siRNA typically had bipolar spindles but 90% of cells transfected with KIF2A-specific siRNA had monopolar spindles [
16]. KIF2B showed a similar effect as KIF2A in the study conducted by [
5] and KIF2C is overexpressed in gastric cancer cells [
26], which may enhance cellular proliferation by increasing the rate of cancer cell mitosis. To demonstrate the function of KIF2C in cancer cell proliferation, Shimo et al. knocked down endogenous KIF2C/MACK in breast cancer cells [
7], which led to a significant decrease in cell proliferation. These results illustrated the contribution of KIF2C to the aggressive behavior of KIF2C-overexpressing breast tumors. The formation of monopolar spindles and inhibition of cellular proliferation were also observed in human cancer cells treated with anti-KIF2A siRNA or Xenopus eggs with a KIF2A antibody [
27,
28]. We reported that the migratory ability of KIF2A–siRNA transfected oral cancer cells decreased significantly compared to the control group [
29]. In the current study using MDA-MB-231 breast cancer cell, we found that upon transfection with KIF2A-siRNA, cell proliferation was inhibited, as was cell migration and invasion. Cells transfected with KIF2A-siRNA showed up to 55% reduction in cell growth, the migration decreased by 41%, and the invasion decreased by 66%. These findings suggest that the overexpression of KIF2A in breast cancer tissues may alter key features of the cells leading to uncontrolled proliferation, migration and invasion. KIF2A is likely to be an important growth factor and might be associated with the malignant phenotype of breast cancer cells. The fact that patients with lymph node metastasis had KIF2A overexpression in our study suggests that KIF2A overexpression correlates with an aggressive phenotype (Figure
2, Table
1). The follow-up results suggested that patients with KIF2A-overexpression had a poorer survival than patients without KIF2A-overexpressing.
Our current study demonstrated a relationship between HER2 and KIF2A expression in cancer cells (P < 0.05), which needs further investigation. HER2-positive breast cancers represent a unique subtype that are often associated with poorly differentiated, high-grade tumors, and have a poorer prognosis than HER2-negative type [
17]. Histological grading provides important prognostic information, and patients with low grade tumors have a significantly better survival time than those with high grade tumors.
Conclusions
In summary, metastasis. Patients with higher KIF2A expression have poorer survival. Cells with silenced KIF2A gene in vitro showed reduced cell proliferation, migration and invasion function, in agreement with the findings in vivo. The study provides clear evidence for the significant role of KIF2A in breast cancer development, using both patient data and a cell line model in vitro. The results indicate that KIF2A could potentially be an important novel prognostic marker for breast cancer.
Acknowledgments
This work was supported by Shandong Provincial Foundation for Scientific Research (No.ZR2010HM131). We especially thank Jinbo Feng, Haiting Mao Yongmei Yang, and Xiaoying Zhang for excellent technical assistance and advice, and pathologist Qinghui Zhang for selection of tissue and scoring the IHC section.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
WJL and MSQ were responsible for implementing cell culture. LWJ and ZS were responsible for IHC and following-up. WJL and LCX were responsible for data analyses. QX and GYY were responsible for experimental design. WJL and MR were responsible for the overall experimental design, data analysis, and implementation of the project. All authors read and approved the final manuscript.