Abstract
Tumor cell aggregation is critical for cell survival following the loss of extracellular matrix attachment and dissemination. However, the underlying mechanotransduction of clustering solitary tumor cells is poorly understood, especially in non-small cell lung cancers (NSCLC). Here, we examined whether cell surface protrusions played an important role in facilitating the physical contact between floating cells detached from a substrate. We employed poly-2-hydroxyethyl methacrylate-based 3D culture methods to mimic in vivo tumor cell cluster formation. The suprastructural analysis of human NSCLC A549 cell spheroids showed that finger-like protrusions clung together via the actin cytoskeleton. Time-lapse holotomography demonstrated that the finger-like protrusions of free-floating cells in 3D culture displayed exploratory coalescence. Global gene expression analysis demonstrated that the genes in the organic hydroxyl transport were particularly enriched in the A549 cell spheroids. Particularly, the knockdown of the water channel aquaporin 3 gene (AQP3) impaired multicellular aggregate formation in 3D culture through the rearrangement of the actomyosin cytoskeleton. Moreover, the cells with reduced levels of AQP3 decreased their transmigration. Overall, these data indicate that cell detachment-upregulated AQP3 contributes to cell surface protrusions through actomyosin cytoskeleton remodeling, causing the aggressive aggregation of free-floating cells dependent on the property of the substratum and collective metastasis.
Highlights
Lung cancer is the leading cause of cancer-related death worldwide; approximately 85% of all lung cancers are non-small cell lung cancers (NSCLC) [1,2,3,4]
We report that the clustering of free-floating NSCLC A549 cells in nonadhesive 3D poly-HEMA culture depends on actin-rich protrusions, which is intensely studied for cell migration under 2D culture conditions [18]
We identified the underlying structure organizing the spheroids by analyzing the cell surfaces at the nanometer resolution with a transmission electron microscope (TEM)
Summary
Lung cancer is the leading cause of cancer-related death worldwide; approximately 85% of all lung cancers are non-small cell lung cancers (NSCLC) [1,2,3,4]. Even after complete primary tumor resection, about 45% of the early-stage NSCLC patients develop local recurrences or distant metastases within 8 to 18 months [6]. Cancer metastasis is manifested by a highly complex cascade of processes, starting with the invasion of the tumor cells from a primary site into the surrounding tissues and continuing as intravasation into the circulatory system and extravasation to a distant organ, where the disseminated tumor cells that survive may initiate the progressive outgrowth of secondary tumors in a metastasis-receptive niche. Millions of cells per gram are disseminated from the primary tumors per day, but only a few become capable of transmigrating and surviving in a distant organ. One key limitation to successful metastasis is the death of the cells that occurs as they become detached from the extracellular matrix (ECM), which is known as anoikis, and from the neighboring cells, and undergo cell rounding, which is known as amorphosis [7,8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
