The nesprin-cytoskeleton interface probed directly on single nuclei is a mechanically rich system

The cytoskeleton provides structure and plays an important role in cellular function such as migration, resisting compression forces, and transport. The cytoskeleton also reacts to physical cues such as fluid shear stress or extracellular matrix remodeling by reorganizing filament associations, most commonly focal adhesions and cell-cell cadherin junctions. These mechanical stimuli can result in genome-level changes, and the physical connection of the cytoskeleton to the nucleus provides an optimal conduit for signal transduction by interfacing with nuclear envelope proteins, called nesprins, within the LINC (linker of the nucleus to the cytoskeleton) complex. Using single-molecule on single nuclei assays, we report that the interactions between the nucleus and the cytoskeleton, thought to be nesprin-cytoskeleton interactions, are highly sensitive to force magnitude and direction depending on whether cells are historically interfaced with the matrix or with cell aggregates. Application of ~10-30 pN forces to these nesprin linkages yielded structural transitions, with a base transition size of 5-6 nm, which are speculated to be associated with partial unfoldings of the spectrin domains of the nesprins and/or structural changes of histones within the nucleus.
This research work was funded and supported by NSF DMR BMAT under 1506717 and NIH EB under 019509 (D.A.B. and H.J.S.). H.J.S. was also supported by the Faculty Research Assistance Program of Yonsei University College of Medicine for 2000 (6–2016–0031). U.H.K was supported by the National Research Foundation of Korea (NRF) under MEST-2015M3A9B3028216. This work was also supported, in part, by Singapore-MIT Alliance for Research and Technology – BioSym, NSF under 1330792, and GAANN under P200A090323 (S.K.B and M.J.L).