Inhomogeneous mechanotransduction defines the spatial pattern of apoptosis-induced compensatory proliferation.

The number of cells in tissues is controlled by cell division and cell death, and its misregulation could lead to pathological conditions such as cancer. To maintain the cell numbers, a cell-elimination process called apoptosis also stimulates the proliferation of neighboring cells. This mechanism, apoptosis-induced compensatory proliferation, was originally described more than 40 years ago. Although only a limited number of the neighboring cells need to divide to compensate for the apoptotic cell loss, the mechanisms that select cells to divide have remained elusive. Here, we found that spatial inhomogeneity in Yes-associated protein (YAP)-mediated mechanotransduction in neighboring tissues determines the inhomogeneity of compensatory proliferation in Madin-Darby canine kidney (MDCK) cells. Such inhomogeneity arises from the non-uniform distribution of nuclear size and the non-uniform pattern of mechanical force applied to neighboring cells. Our findings from a mechanical perspective provide additional insight into how tissues precisely maintain homeostasis.

Interfacial friction and substrate deformation mediate long-range signal propagation in tissues.

Tissue layers can generally slide at the interface, accompanied by the dissipation due to friction. Nevertheless, it remains elusive how force could propagate in a tissue with such interfacial friction. Here, we elaborate the force dynamics in a prototypical multilayer system in which an epithelial monolayer was cultivated upon an elastic substrate in contact with a hard surface, and discover a novel mechanism of pronounced force propagation over a long distance due to interfacial dynamics between substrate layers. We derived an analytical model for the dynamics of the elastic substrate under the shear stress provided by the cell layer at the surface boundary and the friction at bottom. The model reveals that sliding between substrate layers leads to an expanding stretch regime from a shear regime of substrate deformation in time and space. The regime boundary propagating diffusively with a speed depending on the stiffness, thickness, and slipperiness of the substrate, is a robust nature of a deformed elastic sheet with interfacial friction. These results shed new light on force propagation in tissues and our model could serve as a basis for studies of such propagation in a more complex tissue environment.

Lung Cancer Induces NK Cell Contractility and Cytotoxicity Through Transcription Factor Nuclear Localization.

Actomyosin-mediated cellular contractility is highly conserved for mechanotransduction and signalling. While this phenomenon has been observed in adherent cell models, whether/how contractile forces regulate the function of suspension cells like natural killer (NK) cells during cancer surveillance, is unknown. Here, we demonstrated in coculture settings that the evolutionarily conserved NK cell transcription factor, Eomes, undergoes nuclear shuttling during lung cancer cell surveillance. Biophysical and biochemical analyses revealed mechanistic enhancement of NK cell actomyosin-mediated contractility, which is associated with nuclear flattening, thus enabling nuclear entry of Eomes associated with enhanced NK cytotoxicity. We found that NK cells responded to the presumed immunosuppressive TGFß in the NK-lung cancer coculture medium to sustain its intracellular contractility through myosin light chain phosphorylation, thereby promoting Eomes nuclear localization. Therefore, our results demonstrate that lung cancer cells provoke NK cell contractility as an early phase activation mechanism and that Eomes is a plausible mechano-responsive protein for increased NK cytotoxicity. There is scope for strategic application of actomyosin-mediated contractility modulating drugs ex vivo, to reinvigorate NK cells prior to adoptive cancer immunotherapy in vivo (177 words).

BNIP-2 Activation of Cellular Contractility Inactivates YAP for H9c2 Cardiomyoblast Differentiation.

Rho GTPases and Hippo kinases are key regulators of cardiomyoblast differentiation. However, how these signaling axes are coordinated spatiotemporally remains unclear. Here, the central and multifaceted roles of the BCH domain containing protein, BNIP-2, in orchestrating the expression of two key cardiac genes (cardiac troponin T [cTnT] and cardiac myosin light chain [Myl2]) in H9c2 and human embryonic stem cell-derived cardiomyocytes are delineated. This study shows that BNIP-2 mRNA and protein expression increase with the onset of cTnT and Myl2 and promote the alignment of H9c2 cardiomyocytes. Mechanistically, BNIP-2 is required for the inactivation of YAP through YAP phosphorylation and its cytosolic retention. Turbo-ID proximity labeling corroborated by super-resolution analyses and biochemical pulldown data reveals a scaffolding role of BNIP-2 for LATS1 to phosphorylate and inactivate YAP in a process that requires BNIP-2 activation of cellular contractility. The findings identify BNIP-2 as a pivotal signaling scaffold that spatiotemporally integrates RhoA/Myosin II and LATS1/YAP mechanotransduction signaling to drive cardiomyoblast differentiation, by switching the genetic programming from YAP-dependent growth to YAP-silenced differentiation. These findings offer insights into the importance of scaffolding proteins in bridging the gap between mechanical and biochemical signals in cell growth and differentiation and the prospects in translational applications.

Epithelial Cell Packing Induces Distinct Modes of Cell Extrusions.

The control of tissue growth, which is a key to maintain the protective barrier function of the epithelium, depends on the balance between cell division and cell extrusion rates [1, 2]. Cells within confluent epithelial layers undergo cell extrusion, which relies on cell-cell interactions [3] and actomyosin contractility [4, 5]. Although it has been reported that cell extrusion is also dependent on cell density [6, 7], the contribution of tissue mechanics, which is tightly regulated by cell density [8-12], to cell extrusion is still poorly understood. By measuring the multicellular dynamics and traction forces, we show that changes in epithelial packing density lead to the emergence of distinct modes of cell extrusion. In confluent epithelia with low cell density, cell extrusion is mainly driven by the lamellipodia-based crawling mechanism in the neighbor non-dying cells in connection with large-scale collective movements. As cell density increases, cell motion is shown to slow down, and the role of a supracellular actomyosin cable formation and its contraction in the neighboring cells becomes the preponderant mechanism to locally promote cell extrusion. We propose that these two distinct mechanisms complement each other to ensure proper cell extrusion depending on the cellular environment. Our study provides a quantitative and robust framework to explain how cell density can influence tissue mechanics and in turn regulate cell extrusion mechanisms.