Interphase microtubule disassembly is a signaling cue that drives cell rounding at mitotic entry

Abstract

Reorganization of the cortical actin cytoskeleton at mitotic entry is essential to increase membrane tension for cell rounding. This spherical shape is necessary for the biogenesis and organization of the mitotic spindle. Proteins of the Ezrin, Radixin, Moesin (ERM) family play essential roles in mitotic morphogenesis by linking actomyosin forces to the plasma membrane. While ERMs drive metaphase cell rounding, the cell-cycle signals that prompt their conformational activation in mitosis are unknown. We screened a library of small molecules using novel ERM biosensors and we unexpectedly found that drugs that disassemble microtubules promote ERM activation. Remarkably, cells disassemble their interphase microtubules while entering mitosis. We further discovered that this disassembly of microtubules acts as a cell-cycle signal that directs ERM activation and metaphase cell rounding. We show that GEF-H1, a Rho-GEF inhibited by microtubule binding, acts downstream of microtubule disassembly to activate ERMs via RhoA and its kinase effector SLK. In addition, we demonstrate that GEF-H1 and Ect2, another Rho-GEF responsible for the generation of mitotic actomyosin forces, act together to drive metaphase ERM activation and cell rounding. In summary, we report microtubule disassembly as a cell cycle signal that triggers a signaling network ensuring that actomyosin forces are efficiently integrated at the plasma membrane to promote cell rounding at mitotic entry.

Dynamics of cell rounding during detachment

“…This was the case even though LOK/SLK siRNA cells in suspension had a markedly reduced ratio of cortical to cytoplasmic pERM ( Figure 2 L) and diminished levels of cortical pERM ( Figure 2 M). Taken together these data suggest that pERM levels become elevated as cells round in a manner that depends on LOK/SLK, but which is independent of the trigger (partial disassembly of adhesions or entry into mitosis 23 ).…”

Hypoxia enhances interactions between Na+/H+ exchanger isoform 1 and actin filaments via ezrin in pulmonary vascular smooth muscle

“…Via regulation of cell stiffness, actin polymerization or cytoskeletal regulation, NHE1/actin interactions might also contribute to promoting cell movement or shape change, both of which are required for migration and proliferation. For example, recent work in Drosophila indicates a role for ezrin-mediated actin/plasma membrane tethering in mitotic rounding (Leguay et al, 2022), suggesting a mechanical mechanism by which NHE1/ezrin/actin interactions could potentially modulate proliferation. Further experiments will be needed to delineate the exact mechanisms by which the proposed pathway control migration and proliferation.…”

Crosstalk between the plasma membrane and cell-cell adhesion maintains epithelial identity for correct polarised cell divisions

“…During mitosis, cells transduce external cues to reorganise F-actin and microtubules at the cell cortex to control cell shape and balance intracellular tensions, thereby creating an optimal space for mitotic spindle formation and facilitate the subsequent correct alignment of the metaphase chromosomes [14][15][16][17][18][19][20] . While most of our knowledge of the mechanics of mitosis in mammalian cells comes from studies in non-polarised cells or cells grown in isolation on adhesive micropatterns 16,17,21 , increasing evidence shows that mitotic epithelial cells must maintain their native polarity and geometry to ensure correct mitotic spindle dynamics and chromosome segregation fidelity [22][23][24] .…”