Transcription upregulation via force-induced direct stretching of chromatin

Abstract

Mechanical forces play critical roles in the function of living cells. However, the underlying mechanisms of how forces influence nuclear events remain elusive. Here, we show that chromatin deformation as well as force-induced transcription of a green-fluorescent-protein (GFP) tagged bacterial-chromosome dihydrofolate reductase (DHFR) transgene can be visualized in a living cell by using three-dimensional magnetic twisting cytometry to apply local stresses on the cell surface via an Arg-Gly-Asp-coated magnetic bead. Chromatin stretching depended on loading direction. DHFR transcription upregulation was sensitive to load direction and proportional to the magnitude of chromatin stretching. Disrupting filamentous actin or inhibiting actomyosin contraction abrogated or attenuated force-induced DHFR transcription, whereas activating endogenous contraction upregulated force-induced DHFR transcription. Our findings suggest that local stresses applied to integrins propagate from the tensed actin cytoskeleton to the LINC complex and then through lamina-chromatin interactions to directly stretch chromatin and upregulate transcription.

Mechanical forces direct stem cell behaviour in development and regeneration

“…1B), altering chromatin structure, for example inducing stretching and opening, which regulates ttranscription factor accessibility. 76 LMNA expression and assembly of the nuclear lamina increases with tissue stiffness. 75 Extrinsic forces may also directly upregulate transcription by deforming the nucleus.…”

“…76 Magnetic probes can generate localized and repeatable extrinsic forces on the cortex of individual cells in a high-throughput and scalable manner. 77 Microfluidics [G] can be used to deform single cells by extensional flow to measure their mechanical properties in a cytometer.…”

Techniques to stimulate and interrogate cell–cell adhesion mechanics

“…This method was developed in 1950 [150] and has been used in a variety of studies, including applying cyclic loadings to cells [33,151–154]. The technique has been mostly applied to investigate the mechanical properties, especially viscoelasticity, of cells [151], but was also applied to fundamental studies of the role of membrane forces in gene regulation [155]. Two main advantages of MTC are the ability to apply torque to cells and the ability to easily apply cyclic loadings through control of the magnetic field.…”

Cellular mechanosensing of the biophysical microenvironment: A review of mathematical models of biophysical regulation of cell responses

“…Stress-activated ion channels are also known to sense membrane tension [35, 36]. Cytoskeletal elements connect to the LINC (linker of nucleoskeleton and cytoskeleton) complex and possibly enable mechanical forces to affect gene expression and transcription directly via nuclear deformation [37, 38]. All of these result mechanical transduction to activate intracellular signaling [39–42] and to thereby enable cells to respond to microenvironmental biophysical cues [43, 44].…”