Tension-induced cytokinetic abscission in human fibroblasts

Abstract

Previous studies have shown that cytokinetic abscission at the end of mitosis is executed by the ESCRT machinery in mammalian cells, and that the process is dependent on adhesion-induced integrin signalling via a FAK-PLK1-CEP55-TSG101/Alix-CHMP4B pathway. The present study identified an alternative abscission mechanism driven by mechanical force. In the absence of integrin signals (non-adherent conditions), cytokinesis in non-transformed human fibroblasts proceeds to CEP55 accumulation at the midbody, but after prolonged time (>3 hours) the major midbody components Aurora B, MKLP1 and CEP55 were no longer detected in the area. Upon adhesion to fibronectin, such cells were able to complete abscission without re-appearance of midbody proteins. Live-cell imaging revealed that re-plating on stiff fibronectin matrix (64 KPa) allowed >95% of the cells to complete abscission within 9 hours while the corresponding number was 40% on soft fibronectin matrix (0.5 KPa). The cells re-plated on poly-L-lysine were not able to generate tension and did not divide. Thus, mechanical tension can cause cytokinetic abscission by stretching of the intercellular bridge between the two daughter cells until it eventually ruptures without the involvement of ESCRT complexes. Importantly, regression of the cleavage furrow and formation of bi-nucleated cells did not occur in most of the suspension-treated mitotic cells after re-plating on fibronectin. Septin, which stabilizes the membrane associated with the midbody, was found to remain along the ingressed membrane, suggesting that this filament system maintains the membrane bridge although the midbody had dissolved, thereby preventing regression and allowing tension to act on the narrow intercellular bridge.

Septin and Ras regulate cytokinetic abscission in detached cells

“…To analyze if the passage of the critical CEP55-ALIX step led to completion of abscission in non-adherent BJ-LT-Ras cells, the cells were followed by time-lapse microscopy and compared with BJ and BJ-LT cells. In agreement with our previous studies [4, 6, 15], M-phase BJ cells in suspension underwent karyokinesis and cleavage furrow ingression but failed to divide and remained as bi-lobular cells even after 25 h. Similarly, BJ-LT cells did not complete cytokinesis, but after 24–25 h, each of the two nuclei divided and the bi-lobular cells became tetra-lobular [Fig. 2a, b, Additional file 6: Movies S3 (BJ) and Additional file 7: Movie S4, Additional file 8: Movie S5 (BJ-LT)].…”

“…However, the septin rings were found to remain longer at the ICB and thereby prevent the attached plasma membrane from regressing. If such cells are allowed to re-adhere to a fibronectin surface, most of them, but not all, will divide in the absence of MB by traction force (“cytofission”) [15]. Identification of the conditions and mechanisms that determine whether regression will happen or not is important to understand the fate of detached cells in the body and their possible contribution to tumor formation and/or progression.…”

Cep55 promotes cytokinesis of neural progenitors but is dispensable for most mammalian cell divisions

“…One factor potentially affecting the different abscission requirements in fibroblasts and neural progenitors is the relative stiffness of the originating tissues, which would enable greater exertion of traction forces in fibroblasts compared with NPCs in vivo. Traction forces at the cell-substrate interface have been proposed to promote abscission in fibroblasts [41][42][43]60 , whereas neural progenitors have been reported to proliferate maximally on low-stiffness substrates 61 . MBs from neural epithelial cells and HeLa cells have a very similar lipid composition 62,63 , and altered plasma membrane lipid composition during abscission in HeLa has been suggested to increase mechanical resistance to rupture 62 .…”

“…As attachment to different substrates influences the ability of cells to complete abscission [41][42][43] , we tested whether Cep55knockout TTFs can complete abscission when cultured on dishes coated with poly-L-lysine (PLL) and custom-made soft (0.5 kPa) and stiff (64 kPa) fibronectin matrices (Methods). Cep55 −/− TTFs efficiently completed cell division under all these conditions ( Supplementary Fig.…”

Molecular mechanisms of contractile-ring constriction and membrane trafficking in cytokinesis

“…Tension in the membrane has also been shown to aid abscission. This tension relies on integrin proteins, and cells that do not have adequate tension are unable to resolve the midbody (Gupta et al 2018).…”