Downregulation of lumican enhanced mitotic defects and aneuploidy in lung cancer cells.

Lumican is overexpressed in lung cancer cells and has been implicated in the pathogenesis of tumorigenesis and regulation of cancer cell invasion. Lumican is robustly associated with the binding of p120-catenin protein to modulate cell metastasis. However, its role in cancer cell proliferation is still unclear. This study investigated the effect of lumican on the cell division including mitosis and cytokinesis in non-small lung cancer cells. We found that the downregulation of lumican prolonged the doubling time of cells and retarded the cell growth in H460 and A549 cells. Along with tubulin, lumican localized to the mitotic spindle and centrosome during the metaphase-anaphase stage. The cell cycle was retained in the G2/M phase after the downregulation of lumican. Interestingly, lumican was found to play important roles in central spindle and midbody formation during cytokinesis. Lumican interacted with the midbody-associated proteins such as MKLP1, Aurora B, and ECT2. Notably, the downregulation of lumican decreased the level of MKLP1 accompanied by the retention of midbody-residual that resulted in multi-nucleated cells. Downregulation of lumican promoted the chromosome missegregation and the increment of the bi-/multinucleated cells. The results of this study indicated that lumican associated with tubulin is crucial for spindle fiber formation and midbody assembly in cell division. Downregulation of lumican displayed the defects in mitotic spindle assembly/dynamics and improper kinetochore-microtubules attachment that led to increase aneuploidy. This emerging property of lumican is suggested to tightly control chromosome segregation during cell division in lung cancer cells.Abbreviations: ESCRT: endosomal sorting complex required for transport; PRC1: protein regulator of cytokinesis 1; Nci: negative control siRNA; Lumi: lumican siRNAs; MKLP1: mitotic kinesin-like protein 1; H460LD and A549LD: H460 and A549 cell lines with less expressed lumican.