The actin cytoskeleton is the primary driver of cellular adhesion and mechanosensing due to its ability to generate force and sense the stiffness of the environment. At the cell’s leading edge, severing of the protruding Arp2/3 actin network generates a specific actin/tropomyosin (Tpm) filament population that controls lamellipodial persistence. The interaction between these filaments and adhesion to the environment is unknown. Using cellular cryo-electron tomography we resolve the ultrastructure of the Tpm/actin copolymers and show that they specifically anchor to nascent adhesions and are essential for focal adhesion assembly. Re-expression of Tpm1.8/1.9 in transformed and cancer cells is sufficient to restore cell–substrate adhesions. We demonstrate that knock-out of Tpm1.8/1.9 disrupts the formation of dorsal actin bundles, hindering the recruitment of α-actinin and non-muscle myosin IIa, critical mechanosensors. This loss causes a force-generation and proliferation defect that is notably reversed when cells are grown on soft surfaces. We conclude that Tpm1.8/1.9 suppress the metastatic phenotype, which may explain why transformed cells naturally downregulate this Tpm subset during malignant transformation.
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The authors declare that all the data supporting the findings of this study are available within the article and the Supplementary Information. Requests for resources including plasmids should be directed to and will be fulfilled by the corresponding author. The publicly available mRNA sequence of mouse Tpm1.8/1.9 used in this study has the access code NCBI M_001164253.1. Source data are provided with this paper.
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We would like to thank the Katharina Gaus Light Microscopy Facility, the Flow Cytometry Facility and the Electron Microscopy Unit of the Mark Wainwright Analytical Centre at UNSW, and the Cryo Electron Microscopy Facility through the Victor Chang Innovation Centre for their valuable help. Thanks to J. Hook and Y. Yao for their technical assistance. P.W.G. and E.C.H. were supported by grants from the ARC (DP160101623), the Australian NHMRC (APP1100202, APP1079866) and The Kid’s Cancer Project. N.A. was supported by the Australian NHMRC (APP1102730).
The authors declare no competing interests.
Peer review information Nature Materials thanks the anonymous reviewers for their contribution to the peer review of this work.
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Cagigas, M.L., Bryce, N.S., Ariotti, N. et al. Correlative cryo-ET identifies actin/tropomyosin filaments that mediate cell–substrate adhesion in cancer cells and mechanosensitivity of cell proliferation. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-01087-z