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PUBLISHED ONLINE: 22 AUGUST 2016 | DOI: http://dx.doi.org/10.1038/nmat4729
Web End =10.1038/NMAT4729
Arash Tajik1,2, Yuejin Zhang1, Fuxiang Wei1, Jian Sun2, Qiong Jia1, Wenwen Zhou1, Rishi Singh2, Nimish Khanna3, Andrew S. Belmont3* and Ning Wang1,2*
Mechanical forces play critical roles in the function of living cells. However, the underlying mechanisms of how forces inuence nuclear events remain elusive. Here, we show that chromatin deformation as well as force-induced transcription of a green uorescent 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 lamentous actin or inhibiting actomyosin contraction abrogated or attenuated force-induced DHFR transcription, whereas activating endogenous contraction upregulated force-induced DHFR transcription. Our ndings suggest that local stresses applied to integrins propagate from the tensed actin cytoskeleton to the LINC complex and then through laminachromatin interactions to directly stretch chromatin and upregulate transcription.
It is increasingly evident that both soluble growth factor-mediated chemical signalling and the physical microenvironment and niche-mediated mechanical signalling play critical roles in living
cells and tissues1,2. Yet we still know relatively little about how mechanotransduction actually regulates gene expression, protein synthesis, and other vital biological functions. One major challenge in understanding the role of mechanotransduction inside the nucleus is the intrinsic diculty in separating direct force-induced changes in proteins and genes from intracellular biochemical cascades induced by force-induced conformational change or unfolding of proteins such as integrin, talin and vinculin at the cell surface36. From the findings of force-induced surface molecule activation and the presumed model that a local force induces only a local deformation, it is generally accepted that direct force impacts occur at the cell surface2, and that deep cytoplasmic or nuclear mechanotransduction occurs only via intermediate biochemical activities or regulatory proteins in the cytoplasm/nucleus. One example of such a biochemical pathway connecting cell surface deformation with nuclear biochemical signalling is the discovery of the matrix rigidity responsive element YAP/TAZ as a cytoplasmic mechanotransducer which translocates to the nucleus to regulate dierentiation and proliferation7.
However, the activation of Src molecules on the endosomal...