Mechanoaccumulative Elements of the Mammalian Actin Cytoskeleton

Abstract

To change shape, divide, form junctions, and migrate, cells reorganize their cytoskeletons in response to changing mechanical environments [ 1 -4 ]. Actin cytoskeletal elements, including myosin II motors and actin crosslinkers, structurally remodel and activate signaling pathways in response to imposed stresses [5][6][7][8][9]. Recent studies demonstrate the importance of force-dependent structural rearrangement of α-catenin in adherens junctions [ 10 ] and vinculin's molecular clutch mechanism in focal adhesions [ 11 ]. However, the complete landscape of cytoskeletal mechanoresponsive proteins and the mechanisms by which these elements sense and respond to Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Author Contributions E.S.S., T.L., E.G., V.S., and D.N.R. conceived experiments. E.S.S., T.L., V.S. and X.Q. performed experiments. K.M. and P.A.I. developed the model and carried out the simulations. E.S.S. and T.L. wrote the manuscript, V.S., K.M., E.G., P.A.I., and D.N.R. edited the manuscript. , Tables S1 and S2, Figures S1-S4, and Supplemental References. Supplementary Information Supplemental Information includes Supplemental Materials and Procedures HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript force remain to be elucidated. To find mechanosensitive elements in mammalian cells, we examined protein relocalization in response to controlled external stresses applied to individual cells. Here, we show that non-muscle myosin II, α-actinin, and filamin accumulate to mechanically stressed regions in cells from diverse lineages. Using reaction-diffusion models for force-sensitive binding, we successfully predicted which mammalian α-actinin and filamin paralogs would be mechanoaccumulative. Furthermore, a Goldilocks zone must exist for each protein where the actin-binding affinity must be optimal for accumulation. In addition, we leveraged genetic mutants to gain a molecular understanding of the mechanisms of α-actinin and filamin catch-bonding behavior. Two distinct modes of mechanoaccumulation can be observed: a fast, diffusion-based accumulation and a slower, myosin II-dependent cortical flow phase that acts on proteins with specific binding lifetimes. Finally, we uncovered cell-type and cell-cycle-stagespecific control of the mechanosensation of myosin IIB, but not myosin IIA or IIC. Overall, these mechanoaccumulative mechanisms drive the cell's response to physical perturbation during proper tissue development and disease. Results and DiscussionTo identify mechanosensitive elements, we examined protein relocalization i...

Binding dynamics of alpha-actinin-4 in dependence of actin cortex tension

“…Previous studies put forward that the actin cross-linker α-actinin-4 forms catch bonds: Yao et al showed stressenhanced gelation of in vitro actin networks cross-linked by α-actinin-4 indicating catch bond behaviour. Previous studies with Dictyostelium cells demonstrated slowed α-actinin-4 turnover in the actin cytoskeleton in response to compressive stress 6 and accumulation of α-actinin-4 in response to suction pressure from micropipette aspiration 7 . However, to date, there is no study that showed a quantitative relation between α-actinin-4 cross-linking lifetimes and mechanical tension in the cytoskeleton.…”

Mechanochemical Signaling Directs Cell-Shape Change

“…3 A). Similarly, the actin cross-linking protein filamin can accumulate in response to shear stress in multiple cell types (18,49). However, the mammalian paralog filamin B shows higher mechanosensitive accumulation than filamin A (Fig.…”

“…At higher forces, these bonds then slip so that they display a catch-slip behavior, depending on the force regime. The catch-slip bond also accounts for the mechanosensitive accumulation (the accumulation of a protein in response to applied stress) of the actin cross-linking protein a-actinin (18,49) and its recruitment to focal adhesions under high tension (50). In mammalian cells, mechanoaccumulation is unique to the a-actinin 4 paralog, and is not observed for a-actinin 1 (49) (Fig.…”

“…3, C and D) for force-dependent binding can predict which paralog will accumulate based on the intrinsic difference in actin-binding affinity of the paralogs (49). These models utilize parameters for cross-linker concentration, diffusion rates, on-and off-rates for actin binding measured in Dictyostelium and mammalian cells, and the catch-slip characteristics of the bonds (18,49,51). The models recapitulate the kinetics of protein accumulation over time, capturing a sigmoidal rise for filamin and an exponential rise for a-actinin.…”

“…PKC's phosphorylation of the myosin IIA heavy chain at S1916 is essential for a cell's ability to sense and respond to the mechanical input of substrate stiffness at focal adhesions (57). Myosin IIB shows differential mechanoresponsiveness across cell types, and within a cell type, myosin IIB shows differential mechanoaccumulation across the phases of the cell cycle (49). As myosin IIB's subcellular localization is regulated primarily by a single site of heavy-chain phosphorylation (58), this myosin's mechanoaccumulative ability may be readily tuned by heavy-chain phosphorylation.…”