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Oncology Reports Jun 2016In humans, four tropomyosin genes (TPM1, TPM2, TPM3, and TPM4) are known to produce a multitude of isoforms via alternate splicing and/or using alternate promoters....
In humans, four tropomyosin genes (TPM1, TPM2, TPM3, and TPM4) are known to produce a multitude of isoforms via alternate splicing and/or using alternate promoters. Expression of tropomyosin has been shown to be modulated at both the transcription and the translational levels. Tropomyosins are known to make up some of the stress fibers of human epithelial cells and differences in their expression has been demonstrated in malignant breast epithelial cell lines compared to 'normal' breast cell lines. We have recently reported the expression of four novel TPM1 isoforms (TPM1λ, TPM1µ, TPM1ν, and TPM1ξ) from human malignant tumor breast cell lines that are not expressed in adult and fetal cardiac tissue. Also, we evaluated their expression in relation to the stress fiber formation. In this study, nine malignant breast epithelial cell lines and three 'normal' breast cell lines were examined for stress fiber formation and expression of tropomyosin 2 (TPM2) isoform-specific RNAs and proteins. Stress fiber formation was assessed by immunofluorescence using Leica AF6000 Deconvolution microscope. Stress fiber formation was strong (++++) in the 'normal' cell lines and varied among the malignant cell lines (negative to +++). No new TPM2 gene RNA isoforms were identified, and TPM2β was the most frequently expressed TPM2 RNA and protein isoform. Stress fiber formation positively correlated with TPM2β RNA or protein expression at high, statistically significant degrees. Previously, we had shown that TPM1δ and TPM1λ positively and inversely, respectively, correlated with stress fiber formation. The most powerful predictor of stress fiber formation was the combination of TPM2β RNA, TPM1δ RNA, and the inverse of TPM1λ RNA expression. Our results suggest that the increased expression of TPM1λ and the decreased expression of TPM1δ RNA and TPM2β may lead to decreased stress fiber formation and malignant transformation in human breast epithelial cells.
Topics: Alternative Splicing; Cell Transformation, Neoplastic; Female; Gene Expression; Humans; MCF-7 Cells; Protein Isoforms; RNA, Messenger; Stress Fibers; Tropomyosin
PubMed: 27108600
DOI: 10.3892/or.2016.4732 -
Cytoskeleton (Hoboken, N.J.) Jun 2015Tropomyosin is an elongated α-helical coiled coil that binds to seven consecutive actin subunits along the long-pitch helix of actin filaments. Once bound, tropomyosin...
Tropomyosin is an elongated α-helical coiled coil that binds to seven consecutive actin subunits along the long-pitch helix of actin filaments. Once bound, tropomyosin polymerizes end-to-end and both stabilizes F-actin and regulates access of various actin-binding proteins including myosin in muscle and nonmuscle cells. Single tropomyosin molecules bind weakly to F-actin with millimolar Kd , whereas the end-to-end linked tropomyosin associates with about a 1000-fold greater affinity. Despite years of study, the assembly mechanism of tropomyosin onto actin filaments remains unclear. In this study, we used total internal reflection fluorescence microscopy to directly monitor the cooperative binding of fluorescently labeled tropomyosin molecules to phalloidin-stabilized actin filaments. We find that tropomyosin molecules assemble from multiple growth sites after random low-affinity binding of single molecules to actin. As the length of the tropomyosin chain increases, the probability of detachment decreases, which leads to further chain growth. Tropomyosin chain extension is linearly dependent on the concentration of tropomyosin, occurring at approximately 100 monomers/(μM*s). The random tropomyosin binding to F-actin leads to discontinuous end-to-end association where gaps in the chain continuity smaller than the required seven sequential actin monomers are available. Direct observation of tropomyosin detachment revealed the number of gaps in actin-bound tropomyosin, the time course of gap annealing, and the eventual filament saturation process.
Topics: Actin Cytoskeleton; Actins; Protein Binding; Tropomyosin
PubMed: 26033920
DOI: 10.1002/cm.21225 -
The Journal of Biological Chemistry May 1984Two polypeptides of Mr approximately 29,000 and 27,000 have been identified in human erythrocyte membranes that cross-react specifically with affinity purified...
Two polypeptides of Mr approximately 29,000 and 27,000 have been identified in human erythrocyte membranes that cross-react specifically with affinity purified antibodies to chicken gizzard tropomyosin. The cross-reacting polypeptides are quantitatively retained on the membrane after cell lysis if millimolar concentrations of magnesium are included in the lysis and wash buffers, indicating that they are membrane-bound proteins under physiological conditions. Milligram quantities of these immunoreactive polypeptides have been purified to greater than 95% purity from a low salt extract of membranes by DEAE-chromatography, precipitation at pH 4.4, and heating to 85 degrees C to denature contaminants. Physical similarities of the erythrocyte protein to other tropomyosins include (a) amino acid composition (b) anomalous migration of the Mr approximately 29,000 and 27,000 polypeptides on sodium dodecyl sulfate-gels in the presence of 6 M urea to apparent Mr approximately 43,000 and 38,000, respectively (c) arrangement of chains as dimers of Mr approximately 60,000 based on cross-linking studies and calculation of molecular weight from hydrodynamic values (Rs = 5.9 nm, sedimentation coefficient = 2.5 S; partial specific volume = 0.72 cm3/g) and (d) highly asymmetric shape, based on a frictional ratio of 2.07. Binding of erythrocyte tropomyosin to muscle F-actin saturates at one tropomyosin molecule (Mr approximately 60,000) to 6-7 actin monomers and is highly cooperative with a Hill coefficient of about 2.8, similar to muscle tropomyosins. Binding also exhibits a high degree of cooperativity as a function of the magnesium concentration with a transition between no binding and complete binding between 1 and 2 mM MgCl2. Increasing the magnesium concentration from 2 to 10 mM increases the apparent affinity of tropomyosin for actin from approximately 2.6 X 10(6) M-1 to approximately 2.7 X 10(7) M-1 without effect on the Hill coefficient. The tropomyosin polypeptides comprise about 1% of the erythrocyte membrane protein and are present in a ratio of one Mr approximately 60,000 tropomyosin molecule to 7-8 actin monomers, an amount almost sufficient to coat all of the F-actin on the membrane. These data are consistent with the association of two tropomyosin molecules with each of the short actin filaments (12-17 monomers long) thought to exist in the erythrocyte membrane cytoskeleton. The erythrocyte tropomyosin could function to mechanically stabilize these actin filaments as well as play a role in regulating the interaction of spectrin with actin.(ABSTRACT TRUNCATED AT 400 WORDS)
Topics: Actins; Amino Acids; Animals; Chickens; Erythrocyte Membrane; Gizzard, Avian; Humans; Magnesium; Molecular Weight; Muscle, Smooth; Protein Binding; Protein Conformation; Tropomyosin
PubMed: 6715382
DOI: No ID Found -
The Biochemical Journal Aug 19731. Free thiol groups were shown to be essential for tropomyosin to effect maximum inhibition of the Ca(2+)-stimulated ATPase (adenosine triphosphatase) of desensitized...
1. Free thiol groups were shown to be essential for tropomyosin to effect maximum inhibition of the Ca(2+)-stimulated ATPase (adenosine triphosphatase) of desensitized actomyosin but not for its activity in the regulatory-protein system. 2. The activity of tropomyosin on the Mg(2+)-stimulated ATPase in the regulatory-protein system was more susceptible to enzymic digestion and thermal denaturation than its effect on the Ca(2+)-stimulated ATPase of actomyosin. 3. Rabbit skeletal tropomyosin migrated as two distinct electrophoretic components in the presence of sodium dodecyl sulphate and urea and as four components on isoelectric focusing in urea. 4. The two main subunits present in rabbit skeletal tropomyosin, which have been named the alpha- and beta-chains, were separated by chromatography on CM-cellulose in urea at pH4.0. They were shown to be virtually identical in amino acid composition, except for their cysteine contents. The alpha(2) and beta(2) forms of tropomyosin possessed all the biological activities characteristic of normal tropomyosin preparations. 5. In skeletal muscle the alpha and beta components of tropomyosin were present in the proportion of 4:1. Somewhat lower ratios were obtained in skeletal muscle of sheep, pig and cow. 6. Tropomyosin isolated from cardiac muscle and Pecten maximus adductor muscle migrated as one band only. These tropomyosins possessed similar biological activities to those isolated from skeletal muscle.
Topics: Actomyosin; Adenosine Triphosphatases; Amino Acids; Animals; Calcium; Carbon Radioisotopes; Cattle; Chromatography; Cysteine; Electrophoresis; Electrophoresis, Polyacrylamide Gel; Isoelectric Focusing; Magnesium; Mollusca; Muscles; Myocardium; Papain; Rabbits; Sodium Dodecyl Sulfate; Temperature; Tropomyosin; Urea
PubMed: 4270662
DOI: 10.1042/bj1330765 -
Cell Reports Jan 2023The actin cytoskeleton is critical for cell migration, morphogenesis, endocytosis, organelle dynamics, and cytokinesis. To support diverse cellular processes, actin...
The actin cytoskeleton is critical for cell migration, morphogenesis, endocytosis, organelle dynamics, and cytokinesis. To support diverse cellular processes, actin filaments form a variety of structures with specific architectures and dynamic properties. Key proteins specifying actin filaments are tropomyosins. Non-muscle cells express several functionally non-redundant tropomyosin isoforms, which differentially control the interactions of other proteins, including myosins and ADF/cofilin, with actin filaments. However, the underlying molecular mechanisms have remained elusive. By determining the cryogenic electron microscopy structures of actin filaments decorated by two functionally distinct non-muscle tropomyosin isoforms, Tpm1.6 and Tpm3.2, we reveal that actin filament conformation remains unaffected upon binding. However, Tpm1.6 and Tpm3.2 follow different paths along the actin filament major groove, providing an explanation for their incapability to co-polymerize on actin filaments. We also elucidate the molecular basis underlying specific roles of Tpm1.6 and Tpm3.2 in myosin II activation and protecting actin filaments from ADF/cofilin-catalyzed severing.
Topics: Tropomyosin; Protein Binding; Protein Isoforms; Actin Cytoskeleton; Actin Depolymerizing Factors; Actins
PubMed: 36586407
DOI: 10.1016/j.celrep.2022.111900 -
Molecular Biology and Evolution Jul 2010Nature contains a tremendous diversity of forms both at the organismal and genomic levels. This diversity motivates the twin central questions of molecular evolution:...
Nature contains a tremendous diversity of forms both at the organismal and genomic levels. This diversity motivates the twin central questions of molecular evolution: what are the molecular mechanisms of adaptation, and what are the functional consequences of genomic diversity. We report a 22-species comparative analysis of tropomyosin (PPM) genes, which exist in a variety of forms and are implicated in the emergence of a wealth of cellular functions, including the novel muscle functions integral to the functional diversification of bilateral animals. TPM genes encode either or both of long-form [284 amino acid (aa)] and short-form (approximately 248 aa) proteins. Consistent with a role of TPM diversification in the origins and radiation of bilaterians, we find evidence that the muscle-specific long-form protein arose in proximal bilaterian ancestors (the bilaterian 'stem'). Duplication of the 5' end of the gene led to alternative promoters encoding long- and short-form transcripts with distinct functions. This dual-function gene then underwent strikingly parallel evolution in different bilaterian lineages. In each case, recurrent tandem exon duplication and mutually exclusive alternative splicing of the duplicates, with further association between these alternatively spliced exons along the gene, led to long- and short-form-specific exons, allowing for gradual emergence of alternative "internal paralogs" within the same gene. We term these Mutually exclusively Alternatively spliced Tandemly duplicated Exon sets "MATEs". This emergence of internal paralogs in various bilaterians has employed every single TPM exon in at least one lineage and reaches striking levels of divergence with up to 77% of long- and short-form transcripts being transcribed from different genomic regions. Interestingly, in some lineages, these internal alternatively spliced paralogs have subsequently been "externalized" by full gene duplication and reciprocal retention/loss of the two transcript isoforms, a particularly clear case of evolution by subfunctionalization. This parallel evolution of TPM genes in diverse metazoans attests to common selective forces driving divergence of different gene transcripts and represents a striking case of emergence of evolutionary novelty by alternative splicing.
Topics: Alternative Splicing; Amino Acid Sequence; Animals; Base Sequence; Evolution, Molecular; Exons; Gene Duplication; Molecular Sequence Data; Phylogeny; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid; Tropomyosin
PubMed: 20147436
DOI: 10.1093/molbev/msq018 -
Familial Cancer Jan 2022Bloom syndrome (BS) is a genomic and chromosomal instability disorder with prodigious cancer predisposition caused by pathogenic variants in BLM. We report the clinical...
Bloom syndrome (BS) is a genomic and chromosomal instability disorder with prodigious cancer predisposition caused by pathogenic variants in BLM. We report the clinical and genetic details of a boy who first presented with infantile fibrosarcoma (IFS) at the age of 6 months and subsequently was diagnosed with BS at the age of 9 years. Molecular analysis identified the pathogenic germline BLM sequence variants (c.1642C>T and c.2207_2212delinsTAGATTC). This is the first report of IFS related to BS, for which we show that both BLM alleles are maintained in the tumor and demonstrate a TPM3-NTKR1 fusion transcript in the IFS. Our communication emphasizes the importance of long-term follow up after treatment for pediatric neoplastic conditions, as clues to important genetic entities might manifest later, and the identification of a heritable tumor predisposition often leads to changes in patient surveillance and management.
Topics: Alleles; Bloom Syndrome; Child; Fibrosarcoma; Genetic Predisposition to Disease; Genotype; Humans; Infant; Male; RecQ Helicases; Tropomyosin
PubMed: 33219493
DOI: 10.1007/s10689-020-00221-1 -
Journal of Structural Biology Mar 2017The structures of muscle thin filaments reconstituted using skeletal actin and cardiac troponin and tropomyosin have been determined with and without bound Ca using...
The structures of muscle thin filaments reconstituted using skeletal actin and cardiac troponin and tropomyosin have been determined with and without bound Ca using electron microscopy and reference-free single particle analysis. The resulting density maps have been fitted with atomic models of actin, tropomyosin and troponin showing that: (i) the polarity of the troponin complex is consistent with our 2009 findings, with large shape changes in troponin between the two states; (ii) without Ca the tropomyosin pseudo-repeats all lie at almost equivalent positions in the 'blocked' position on actin (over subdomains 1 and 2); (iii) in the active state the tropomyosin pseudo-repeats are all displaced towards subdomains 3 and 4 of actin, but the extent of displacement varies within the regulatory unit depending upon the axial location of the pseudo-repeats with respect to troponin. Individual pseudo-repeats with Ca bound to troponin can be assigned either to the 'closed' state, a partly activated conformation, or the 'M-state', a fully activated conformation which has previously been thought to occur only when myosin heads bind. These results lead to a modified view of the steric blocking model of thin filament regulation in which cooperative activation is governed by troponin-mediated local interactions of the pseudo-repeats of tropomyosin with actin.
Topics: Actin Cytoskeleton; Actins; Calcium; Microscopy, Electron; Protein Binding; Tropomyosin; Troponin
PubMed: 28161413
DOI: 10.1016/j.jsb.2017.01.004 -
Electron microscopy and persistence length analysis of semi-rigid smooth muscle tropomyosin strands.Biophysical Journal Aug 2010The structural mechanics of tropomyosin are essential determinants of its affinity and positioning on F-actin. Thus, tissue-specific differences among tropomyosin...
The structural mechanics of tropomyosin are essential determinants of its affinity and positioning on F-actin. Thus, tissue-specific differences among tropomyosin isoforms may influence both access of actin-binding proteins along the actin filaments and the cooperativity of actin-myosin interactions. Here, 40 nm long smooth and striated muscle tropomyosin molecules were rotary-shadowed and compared by means of electron microscopy. Electron microscopy shows that striated muscle tropomyosin primarily consists of single molecules or paired molecules linked end-to-end. In contrast, smooth muscle tropomyosin is more a mixture of varying-length chains of end-to-end polymers. Both isoforms are characterized by gradually bending molecular contours that lack obvious signs of kinking. The flexural stiffness of the tropomyosins was quantified and evaluated. The persistence lengths along the shaft of rotary-shadowed smooth and striated muscle tropomyosin molecules are equivalent to each other (approximately 100 nm) and to values obtained from molecular-dynamics simulations of the tropomyosins; however, the persistence length surrounding the end-to-end linkage is almost twofold higher for smooth compared to cardiac muscle tropomyosin. The tendency of smooth muscle tropomyosin to form semi-rigid polymers with continuous and undampened rigidity may compensate for the lack of troponin-based structural support in smooth muscles and ensure positional fidelity on smooth muscle thin filaments.
Topics: Animals; Biomechanical Phenomena; Cattle; Chickens; Microscopy, Electron; Muscle, Smooth; Myocardium; Protein Multimerization; Reproducibility of Results; Tropomyosin
PubMed: 20682264
DOI: 10.1016/j.bpj.2010.05.004 -
Cancer Medicine Jan 2022Despite advances in multiple disciplinary diagnoses and treatments, the prognosis of hepatocellular carcinoma (HCC) remains poor. Some evidence has identified that the...
BACKGROUND
Despite advances in multiple disciplinary diagnoses and treatments, the prognosis of hepatocellular carcinoma (HCC) remains poor. Some evidence has identified that the aberrant expression of tropomyosins (TPMs) is involved with some cancers development. However, prognostic values of TPMs in HCC have not been thoroughly investigated.
METHODS
Original TPM1-4 mRNA expression of TCGA HCC data and GTEx was downloaded from UCSC XENA. Oncomine database and GSE46408 were used for verification. Clinical stages and survival analysis of TPM1-4 in HCC were performed by GEPIA2. cBioPortal was utilized to assess TPM1-4 gene alteration in HCC. TIMER2.0 was used for investigating the relevance of TPM1-4 to tumor-infiltrating immune cells in HCC. Additionally, we constructed a TPM1-4 prognostic model to explore the value of TPM1-4 for prognostic evaluation in HCC. LinkedOmics was applied to elucidate TPM3 co-expression networks in HCC.
RESULTS
This present study showed that TPM1-4 was upregulated in all HCC tissues, and TPM3 overexpression was correlated with poor survival outcomes in patients with HCC. Besides, TPM3 amplification was the main altered type in TPM1-4 genetic alteration, which affected the prognosis of HCC patients. The risk model revealed that TPM1, TPM2, and TPM3 were applied to risk assessment of HCC prognosis, among which TPM3 expression was significantly higher in the high-risk group than that in the low-risk group. Univariate and multivariate cox regression analyses indicated that TPM3 may be an independent prognostic factor of HCC prognosis. In addition, TPM3 co-expression genes mainly participated in the cell cycle by maintaining microtubule cytoskeleton in HCC progression. TPM1-4 was associated with some tumor-infiltrating immune cells in HCC.
CONCLUSION
Our study detected that the expression level of TPM1-4 was all remarkably elevated in HCC, suggesting that TPM1-4 may serve an important role in HCC development. High TPM3 expression was found to be correlated with poor overall survival, and TPM3 may be an independent prognostic factor for HCC.
Topics: Carcinoma, Hepatocellular; Female; Gene Expression Regulation, Neoplastic; Humans; Liver Neoplasms; Male; Middle Aged; Prognosis; Survival Analysis; Tropomyosin
PubMed: 34850589
DOI: 10.1002/cam4.4453