Tropomyosin isoforms support actomyosin biogenesis to generate contractile tension at the epithelial zonula adherens

Caldwell, Benjamin J.; Lucas, Christine A.; Kee, Anthony J.; Gaus, Katharina; Gunning, Peter W.; Hardeman, Edna C.; Yap, Alpha S.; Gómez, Guillermo A.

doi:10.1002/cm.21202

Cited by 28 publications

(24 citation statements)

References 55 publications

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“…Tropomyosin Co-localizes with Most Actin Structures Tropomyosins have been implicated in a variety of different actin structures, including stress fibers [6], lamellipodia [7], granules [11], endosomes [12], cortical actin [13], the epithelial zonula adherens [14], podosomes [15], the cleavage furrow of dividing cells [16,17], mitotic spindles [16], actin ruffles [18], short microfilaments associated with the Golgi [16,19], filopodia [8], and the endoplasmic reticulum [20]. Mammalian cells can produce over 40 different splice variants using four different tropomyosin genes, TPM1-4, and the resulting gene products can be divided into low-molecular-weight (LMW) isoforms that span six actin monomers and high-molecular-weight (HMW) isoforms that span seven actin monomers.…”

Section: Resultsmentioning

confidence: 99%

Co-polymers of Actin and Tropomyosin Account for a Major Fraction of the Human Actin Cytoskeleton

et al. 2018

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Tropomyosin proteins form stable coiled-coil dimers that polymerize along the α-helical groove of actin filaments [1]. The actin cytoskeleton consists of both co-polymers of actin and tropomyosin and polymers of tropomyosin-free actin [2]. The fundamental distinction between these two types of filaments is that tropomyosin determines the functional capability of actin filaments in an isoform-dependent manner [3-9]. However, it is unknown what portion of actin filaments are associated with tropomyosin. To address this deficit, we have measured the relative distribution between these two filament populations by quantifying tropomyosin and actin levels in a variety of human cell types, including bone (U2OS); breast epithelial (MCF-10A); transformed breast epithelial (MCF-7); and primary (BJpar), immortalized (BJeH), and Ras-transformed (BJeLR) BJ fibroblasts [10]. Our measurements of tropomyosin and actin predict the saturation of the actin cytoskeleton, implying that tropomyosin binding must be inhibited in order to generate tropomyosin-free actin filaments. We find the majority of actin filaments to be associated with tropomyosin in four of the six cell lines tested and the portion of actin filaments associated with tropomyosin to decrease with transformation. We also discover that high-molecular-weight (HMW), unlike low-molecular-weight (LMW), tropomyosin isoforms are primarily co-polymerized with actin in untransformed cells. This differential partitioning of tropomyosins is not due to a lack of N-terminal acetylation of LMW tropomyosins, but it is, in part, explained by the susceptibility of soluble HMW tropomyosins to proteasomal degradation. We conclude that actin-tropomyosin co-polymers make up a major fraction of the human actin cytoskeleton.

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Section: Resultsmentioning

confidence: 99%

Co-polymers of Actin and Tropomyosin Account for a Major Fraction of the Human Actin Cytoskeleton

et al. 2018

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“…Tpm1.7 promotes the formation of filopodia in B35 cells (Creed et al, 2011), which is dependent on the availability of active cofilin. In epithelial cells, Tpm3.1 is necessary for the stability of cell-cell junctions, and its deletion in mice greatly reduces the levels of junctional E-cadherin in the kidney (Caldwell et al, 2014). In addition to neurons, Tpm1.9 (also known as Tm5b) was shown to be essential for morphogenesis in a cell model of mammary gland differentiation (Zucchi et al, 2001), and Tpm1.1 (also known as alpha-Tm) is essential for development of the heart (Rethinasamy et al, 1998) Cell trafficking and cytokinesis…”

Section: Morphogenesismentioning

confidence: 99%

Tropomyosin – master regulator of actin filament function in the cytoskeleton

Gunning

Hardeman

Lappalainen

et al. 2015

Journal of Cell Science

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Tropomyosin (Tpm) isoforms are the master regulators of the functions of individual actin filaments in fungi and metazoans. Tpms are coiled-coil parallel dimers that form a head-to-tail polymer along the length of actin filaments. Yeast only has two Tpm isoforms, whereas mammals have over 40. Each cytoskeletal actin filament contains a homopolymer of Tpm homodimers, resulting in a filament of uniform Tpm composition along its length. Evidence for this 'master regulator' role is based on four core sets of observation. First, spatially and functionally distinct actin filaments contain different Tpm isoforms, and recent data suggest that members of the formin family of actin filament nucleators can specify which Tpm isoform is added to the growing actin filament. Second, Tpms regulate wholeorganism physiology in terms of morphogenesis, cell proliferation, vesicle trafficking, biomechanics, glucose metabolism and organ size in an isoform-specific manner. Third, Tpms achieve these functional outputs by regulating the interaction of actin filaments with myosin motors and actin-binding proteins in an isoform-specific manner. Last, the assembly of complex structures, such as stress fibers and podosomes involves the collaboration of multiple types of actin filament specified by their Tpm composition. This allows the cell to specify actin filament function in time and space by simply specifying their Tpm isoform composition.

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“…Tropomyosin (Tpm) was identified as a major component in integrin contractile units, and cells were incapable of forming contractions or sensing rigidity when Tpm2.1 protein levels were downregulated 14 . Recent discoveries have indicated that several types of tropomyosin, notably Tpm2.1 and Tpm3, were involved in E-cadherin adhesion integrity 41,42 . We found that Tpm2.1 accumulated in between E-cadherin-coated pillars in newly spread areas where CCs formed in the periphery of Cos-7 cells, which resembled its localization in integrin contractile units 14 .…”

Section: Myosin Iib and Tpm21 Mediate Cadherin Contractionmentioning

confidence: 99%

Local Contractions Regulate E-Cadherin Adhesions, Rigidity Sensing and Epithelial Cell Sorting

Yang

Nguyen

Narayana

et al. 2018

Preprint

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30 31 E-cadherin is a major cell-cell adhesion molecule involved in mechanotransduction at cell-32 cell contacts in tissues. Since epithelial cells respond to rigidity and tension in the tissue 33 through E-cadherin, there must be active processes that test and respond to the mechanical 34 properties of these adhesive contacts. Using sub-micrometer, E-cadherin-coated PDMS 35 pillars, we find that cells generate local contractions between E-cadherin adhesions and 36 pull to a constant distance for a constant duration, irrespective of pillar rigidity. These 37 cadherin contractions require non-muscle myosin IIB, tropomyosin 2.1, α-catenin and 38 binding of vinculin to α-catenin; plus, they are correlated with rigidity-dependent cell 39 spreading. Without contractions, cells fail to spread to different areas on soft and rigid 40 surfaces and to maintain monolayer integrity. We further observe that cadherin 41contractions enable cells to test myosin IIA-mediated tension of neighboring cells, and sort 42 out myosin IIA-depleted cells. Thus, we suggest that epithelial cells test and respond to the 43 mechanical characteristics of neighboring cells through cadherin contractions.For the proper organization of tissues, cells need to probe the mechanical properties of their 63 micro-environment including both extracellular matrix and neighboring cells through 64 adhesive contacts. These mechanical properties are then transduced into biochemical 65 information to regulate cell functions 1 , including single and collective cell motility 2, 3 , 66 proliferation 4 or differentiation 5 . Of the many mechanical properties that cells control, 67 stiffness appears to be an important parameter that is distinctive for a tissue and is reflected 68 in the cells that constitute the tissue 6 . It follows that cells should be able to measure the 69 stiffness of their neighbors to enable them to regulate their cell-cell contacts, cytoskeletal 70 rigidity and organize cell monolayers. Thus, it is important to understand how E-cadherin 71 rigidity might be sensed. Recent studies have indeed found that epithelial cells spread to 72 larger areas on rigid cadherin-coated surfaces than soft 7 . The testing of cadherin adhesion 73 rigidity 8 shares similarities with the testing of matrix rigidity described for fibroblasts 9 . In 74 the context of epithelial cell dynamics, this mechanism may allow cells to adapt to changes 75 in the local stiffness of their neighbors due to cytoskeleton remodeling and reinforcement 10-76 12 . 77 78 Cadherin rigidity is a complex mechanical parameter since it is defined as the force per 79 unit area needed to displace a cadherin adhesion by a given distance. In the case of matrix 80 rigidity sensing, cells pull matrix contacts to a constant deflection and measure the force 81 generated [13][14][15] . The local matrix rigidity sensor is a sarcomere-like contraction complex (2 82 micrometers in length) that contracts matrix adhesions by 120 nm and if the force exceeds 83 25 pN, then a rigid-matrix signal is activate...

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Tropomyosin isoforms support actomyosin biogenesis to generate contractile tension at the epithelial zonula adherens

Cited by 28 publications

References 55 publications

Co-polymers of Actin and Tropomyosin Account for a Major Fraction of the Human Actin Cytoskeleton

Co-polymers of Actin and Tropomyosin Account for a Major Fraction of the Human Actin Cytoskeleton

Tropomyosin – master regulator of actin filament function in the cytoskeleton

Local Contractions Regulate E-Cadherin Adhesions, Rigidity Sensing and Epithelial Cell Sorting

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