ABSTRACT
Breast cancer pathogenesis is known to be propagated by the differential expression of a group of proteins called the Kinesin Superfamily (KIFs), which are instrumental in the intracellular transport of chromosomes along microtubules during mitosis. During mitosis, KIFs are strictly regulated through temporal synthesis so that they are only present when needed. However, their misregulation may contribute to uncontrolled cell growth due to premature sister chromatid separation, highlighting their involvement in tumorigenesis. One particular KIF, KIF21A, was recently found to promote the survival of human breast cancer cells in vitro. However, how KIF21A influences other cancerous phenotypes is currently unknown. This study therefore aimed to consolidate the in vitro role of KIF21A in breast cancer metastasis, while also analysing KIF21A expression in human breast cancer tissue to determine its prognostic value. This was achieved by silencing KIF21A in MCF-7 and MDA-MB-231 breast cancer cell lines via siRNA transfection. Migration, invasion, proliferation, and adhesion assays were then performed to measure the effects of KIF21A silencing on oncogenic behaviour. Immunohistochemistry was also conducted in 263 breast cancer tissue samples to compare KIF21A expression levels against various prognostic outcomes and clinicopathological parameters. KIF21A knockdown reduced cell migration (by 42.8% [MCF-7] and 69.7% [MDA-MB-231]) and invasion (by 72.5% [MCF-7] and 42.5% [MDA-MB-231]) in both cell lines, but had no effect on adhesion or proliferation, suggesting that KIF21A plays an important role in the early stages of breast cancer metastasis. Unexpectedly however, KIF21A was shown to negatively correlate with various pro-malignant clinicopathological parameters, including tumour size and histological grade, and high KIF21A expression predicted better breast cancer survival (hazard ratio = 0.45), suggesting that KIF21A is a tumour suppressor. The conflicting outcomes of in vitro and in vivo data may be due to the possible multi-functionality of KIF21A or study limitations, and means no definitive conclusions can be drawn about the role of KIF21A in breast cancer. This warrants further investigation, which may prove pivotal to the development of novel chemotherapeutic strategies to mediate KIF21A’s function and enhance prognostic outcomes.
