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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. The role of actin/tropomyosin filaments in the assembly of cell–substrate adhesions has been investigated and it is now shown by cryo-electron tomography that they are essential for adhesion assembly and also regulate mechanosensing, matrix remodelling and transformation of cells towards a cancer phenotype.

1- and 1,5-Aminoalkylamine substituted anthraquinones (AAQs, 1C3 and 1,5C3) were peptide coupled to 1-, 2-, and 3-pyrrole lexitropsins to generate compounds that incorporated both DNA minor groove and intercalating moieties. The corresponding platinum(II) amidine complexes were synthesized through a synthetically facile amine-to-platinum mediated nitrile 'Click' reaction. The precursors as well as the corresponding platinum(II) complexes were biologically evaluated in 2D monolayer cells and 3D tumour cell models. Despite having cellular accumulation levels that were up to five-fold lower than that of cisplatin, the platinum complexes had cytotoxicities that were only three-fold lower. Accumulation was lowest for the complexes with two or three pyrrole groups, but the latter was the most active of the complexes exceeding the activity of cisplatin in the MDA-MB-231 cell line. All compounds showed moderate to good penetration into spheroids of DLD-1 cells with the distributions being consistent with active uptake of the pyrrole containing complexes in regions of the spheroids starved of nutrients.

Tropomyosins are elongated alpha-helical proteins that form co-polymers with most actin filaments within a cell and play important roles in the structural and functional diversification of the actin cytoskeleton. How the assembly of tropomyosins along an actin filament is regulated and the kinetics of tropomyosin association with an actin filament is yet to be fully determined. A recent series of publications have used total internal reflection fluorescence (TIRF) microscopy in combination with advanced surface and protein chemistry to visualise the molecular assembly of actin/tropomyosin filaments in vitro. Here, we review the use of the in vitro TIRF assay in the determination of kinetic data on tropomyosin filament assembly. This sophisticated approach has enabled generation of real-time single-molecule data to fill the gap between in vitro bulk assays and in vivo assays of tropomyosin function. The in vitro TIRF assays provide a new foundation for future studies involving multiple actin-binding proteins that will more accurately reflect the physiological protein-protein interactions in cells.

Increasing evidence suggests that an inflammatory microenvironment promotes invasion by glioblastoma (GBM) cells. Together with p38 mitogen-activated protein kinase (MAPK) activation being regarded as promoting inflammation, we hypothesized that elevated inflammatory cytokine secretion and p38 MAPK activity contribute to expansion of GBMs. Here we report that IL-1β, IL-6, and IL-8 levels and p38 MAPK activity are elevated in human glioblastoma specimens and that p38 MAPK inhibitors attenuate the secretion of pro-inflammatory cytokines by microglia and glioblastoma cells. RNAi knockdown and immunoprecipitation experiments suggest that the p38α MAPK isoform drives inflammation in GBM cells. Importantly, p38 MAPK inhibition strongly reduced invasion of U251 glioblastoma cells in an inflammatory microenvironment, providing evidence for a p38 MAPK-regulated link between inflammation and invasiveness in GBM pathophysiology.