Comparative studies of human smooth and striated muscle myosins

Characterization of a mammalian smooth muscle myosin heavy chain cDNA clone and its expression in various smooth muscle types

A cDNA clone, SMHC-29, encoding the light meromyosin of smooth muscle myosin heavy chain (MHC), was isolated from a rabbit uterus cDNA library constructed in phage lambda gt11. This smooth muscle MHC cDNA demonstrates significant nucleotide and amino acid sequence homologies with known sarcomeric MHC genes from rabbit, rat skeletal, and nematode body wall myosin, and even with nonmuscle MHC gene from a slime mold (Dictyostelium discoideum), suggesting that smooth muscle, striated muscle, and nonmuscle MHC genes diverged from a common ancestor. The deduced amino acid sequences of the smooth muscle light meromyosin show very similar periodic distributions of hydrophobic and charged residues as found for the light meromyosin of striated muscle MHCs together with a high potential for alpha-helical formation, indicating an alpha-helical coiled-coil structure for the smooth muscle light meromyosin sequences. Furthermore, S1 nuclease mapping has revealed that this smooth muscle MHC gene for SMHC-29 is specifically expressed in smooth muscles of vascular and nonvascular types but not in the striated muscles or nonmuscle cells.

Morphologic characterization of cultured smooth muscle cells isolated from the tracheas of adult dogs

The goals of our study were to isolate smooth muscle cells from the trachealis muscle of adult dogs and to characterize the cells morphologically when they were maintained in primary culture. Enzymatic digestion of the muscle yielded 4.8 +/- 1.8 X 10(6) viable smooth muscle cells per gram of tissue. When placed in culture, these cells rapidly proliferated until confluence was reached. The proliferating cells in culture differed from the cells in the intact tissue in that they stained less intensely for smooth muscle myosin, developed immunofluorescent staining for the intermediate filament protein vimentin, and lost many of the ultrastructural properties of the intact muscle. Only within nodules of cells in the confluent cultures were these ultrastructural properties preserved. Cultures of canine tracheal fibroblasts differed from these smooth muscle cell cultures in that the fibroblasts did not stain for smooth muscle myosin and did not form nodules at confluence. We concluded that adult canine airway smooth muscle cells may be maintained in primary culture, that the confluent cultures contain nodules of cells with many morphologic characteristics of the intact muscle, and that these preparations may be distinguished from cultured canine tracheal fibroblasts on specific morphologic grounds.

The identification of myoepithelial cells in human salivary glands. A review and comparison of light microscopical methods

Myoepithelial cells have frequently been implicated in salivary gland tumour histogenesis. A major problem has been the reliable identification of these cells at the light microscopical level, both in tumours and in normal salivary glands. Many methods have been advocated, often with comparatively little evaluation in normal human tissue and with limited comparison between techniques. This paper reviews the application of histological staining techniques, enzyme histochemistry and immunocytochemistry with antibodies to actin, myosin and keratins. The only reliable method was immunocytochemistry with an antibody to smooth muscle myosin, with immunofluorescence on frozen tissue and immunoenzyme labelling on methacarn-fixed/paraffin-processed material. Formalin fixation did not permit successful staining. Monoclonal antibodies to specific keratin polypeptides may prove to be a useful label of myoepithelial cells but at the present time the available cytokeratin antibodies preferentially stain duct cell populations.

Dissociation of actomyosin complex by monovalent fragments of polyclonal antibodies to myosin

The monovalent fragments of antibodies specific for skeletal muscle myosin inhibit myosin ATPase activity and dissociate the actomyosin complex, as shown by analytical ultracentrifugation and viscosity measurements.

Degradation of smooth-muscle myosin by trypsin-like serine proteinases

1. Hydrolysis of the myosins from smooth and from skeletal muscle by a rat trypsin-like serine proteinase and by bovine trypsin at pH 7 is compared. 2. Proteolysis of the heavy chains of both myosins by the rat enzyme proceeds at rates approx. 20 times faster than those obtained with bovine trypsin. Whereas cleavage of skeletal-muscle myosin heavy chain by both enzymes results in the generation of conventional products i.e. heavy meromyosin and light meromyosin, the heavy chain of smooth-muscle myosin is degraded into a fragment of mol. wt. 150000. This is dissimilar from heavy meromyosin and cannot be converted into heavy meromyosin. It is shown that proteolysis of the heavy chain takes place in the head region. 3. The 'regulatory' light chain (20kDa) of smooth-muscle myosin is degraded very rapidly by the rat proteinase. 4. The ability of smooth-muscle myosin to have its ATPase activity activated by actin in the presence of a crude tropomyosin fraction on introduction of Ca2+ is diminished progressively during exposure to the rat proteinase. The rate of loss of the Ca2+-activated actomyosin ATPase activity is very similar to the rate observed for proteolysis of the heavy chain and 3-4 times slower than the rate of removal of the so-called 'regulatory' light chain. 5. The significance of these findings in terms of the functional organization of the smooth muscle myosin molecule is discussed. 6. Since the degraded myosin obtained after exposure to very small amounts of the rat proteinase is no longer able to respond to Ca2+, i.e. the functional activity of the molecule has been removed, the implications of a similar type of proteolysis operating in vivo are considered for myofibrillar protein turnover in general, but particularly with regard to the initiation of myosin degradation, which is known to take place outside the lysosome (i.e. at neutral pH).

Immunological cross-reactivity between chicken slow skeletal and ventricular muscle myosin

Antibodies elicited in rabbits against chicken slow skeletal anterior latissimus dorsi and ventricular myosin were analyzed by double immunodiffusion for their ability to react with homologous and heterologous antigen at different stages of immunization (1--12 months). Each anti myosin antiserum formed a single, strong precipitin line with its immunogen after short time of immunization. This reaction was specific for myosin heavy chains as determined by GEDELISA (gel electrophoresis derived enzyme lined immunosorbent assay) test. In rabbits injected with ventricular myosin after long time of immunization a second, fainter precipitin line has generally been observed. The antigenic determinants responsible for this precipitin line have been localized on the light myosin subunits. By comparing the two types of anti myosin antisera with heterologous antigen we have obtained evidence for partial immunological cross-reactivity between slow skeletal and ventricular muscle myosins. In particular, all anti ventricular myosin antisera displayed a marked immunological reactivity with anterior latissimus dorsi myosin whereas most of anti anterior latissimus dorsi myosin antisera showed absence of reciprocity. By means of immunofluorescence and immunoabsorption techniques both common and unique slow skeletal and ventricular antigenic determinants have been demonstrated.

Isomyosins in human type 1 and type 2 skeletal muscle fibres

Human myosin from different skeletal muscles was analysed in a non-denaturing gel system, and the isoenzyme composition correlated with the histochemical composition of the muscle. Two components (SM1 and SM2) were associated with type 1 (slow-twitch) fibres, and three (FM1, FM2 and FM3) with type 2 (fast-twitch) fibres. Light-chain analysis was performed in sodium dodecyl sulphate/polyacrylamide gels. There are three light chains (LCs1a, LCS1b and LCs2) in type 1 fibres, and three (LCf1, LCf2 and LCf3) in type 2 fibres. LCf1 and LCs1b co-migrate in sodium dodecyl sulphate gels. The ratio of LCf3/LCf2 is correlated with the distribution of the individual fast isoenzymes. These results explain apparent discrepancies in the literature concerning the light-chain distribution of human myosin.

Turtledove: a new source of P1-like material cross-reacting with the human erythrocyte antigen

An antigen cross-reacting with the human blood group P1 has been discovered in turtledove's blood an egg-white. In egg-white, this P1 antigenicity is carried by a glycoprotein called ovomucoid, which is particularly rich in galactose residues and which has been successfully used to produce specific anti-P1 antibodies in rabbits.

Use of antibodies against dodecylsulfate-denatured heavy meromyosins to probe structural differences between muscular myosin isoenzymes

Heavy meromyosin, a tryptic myosin fragment, was purified from rabbit fast twitch muscles and rat cardiac ventricles. Both types of heavy meromyosin were denatured by sodium dodecylsulfate and used to immunize guinea-pigs after chromatography on Sephadex G-10 to remove excess dodecylsulfate. Micro-complement fixation analysis showed that the antisera were specific to a denatured configuration of heavy meromyosin and myosin, and hardly recognized the native proteins. Cross-reactions performed with both rabbit skeletal and rat cardiac antisera indicated that the antigenic structures of denatured myosins varied according both to species (man, rabbit, rat or mouse), and to muscle-type (red skeletal slow twitch, while skeletal fast twitch, cardiac atria or cardiac ventricles). Denatured heavy meromyosin chromatography on Sephadex G-200 in the presence of 0.1% sodium dodecylsulfate enabled separation of several polypeptides groups. Of these, a polypeptide of Mr 29000 was the most reactive and exhibited the same immunological specificities as the whole myosin molecule. The use of antibodies against denatured heavy meromyosin in conjunction with micro-complement fixation therefore provides a discriminant means, not only for estimating the structural relationship between several myosin isoenzymes, but also for localizing constant and variable regions in the heavy chains of these isoenzymes.

Parvalbumins from the lungfish (Protopterus dolloi)

Five parvalbumins have been isolated from the white muscles of the lungfish. They can be divided into two sub families showing typical amino acid compositions, C-terminal amino acid residues, peptide maps and immuno-reactivity. The red muscles including the cardiac muscle also contain parvalbumins in amounts roughly inversely related to the concentration of myoglobin in the muscle. Parvalbumins have also been detected in the brain and kidney.

An electrophoretic study of native myosin isozymes and of their subunit content

Myosin polymorphism in muscles has been studied by a variety of electrophoretic techniques, in non-dissociating and in dissociating conditions. The analysis of myosin isozymes in the native state was achieved in pyrophosphate buffer and required only minute amounts of protein; identical results were obtained with purified or crudely extracted myosin. The determination of the subunit content of each isozyme was done in the presence of sodium dodecyl sulphate or urea for light chain, and in a phenol, acetic acid and urea system for heavy chain screening. Electrophoresis in non-dissociating conditions has led to the separation of up to a dozen of myosin isozymes, differing in mobilities by as much as 30%. Muscle specificity of myosin was clearly established. Apart from a few exceptions, all the muscles tested were shown to contain more than one myosin species; fast-twitch muscles for instance all contained the same three isozymes, but in variable ratios. Class specificity of myosin appeared related to the relative proportions of isozymes in a given muscle. A second electrophoresis in dissociating solvents of the myosin bands first resolved in pyrophosphate buffer has then allowed a further characterization of the various isozymes. The differences in mobilities observed in the native state were shown to come either from the light chains, or from the heavy chains, or from both. The first case was illustrated by the three species present in fast muscles, which were shown to correspond to three alkali light-chain isozymes, the heterodimer representing in some instances up to 40% of the total. Next to light-chain muscle type specificity, electrophoresis in the phenol, acetic acid, urea system has led to the detection of differences in the heavy chains of fast, slow and cardiac myosins. The application of these various electrophoretic techniques to the analysis of the modification of myosin isozymes during development or in pathology studies can be considered.

Inhibition of energy-dependent Ca2+ accumulation in fibroblasts by smooth muscle antibodies

An antibody prepared against smooth muscle myosin interferes with active Ca2+ accumulation of fibroblasts. This provides further evidence for the existence of myosin at the cell surface.

Characterization of the intermediate (10 nm) filaments of cultured cells using an autoimmune rabbit antiserum

An antiserum has been found in a nonimmunized rabbit which reacts strongly with a system of filaments in various fibroblasts, epithelial cells, macrophages and neuroblastoma. These filaments are distinct from the actin microfilament bundles visualized by an antibody against actin, and they are not affected by brief treatment with cytochalasin B. The pattern of these filaments somewhat resembles that described for microtubules, but the filaments could be clearly distinguished from microtubules by a comparison of their respective immunofluorescent patterns during cell division. In response to the drugs colcemid and vinblastine, the filaments reacting with this preimmune serum condense to form a compact perinuclear coil of fibers, a distribution and behavior in agreement with that previously described for the 10 nm or intermediate filaments studied by electron microscopy. Further evidence supporting our conclusion that this antiserum reacts with intermediate filaments is provided by a comparison of electron micrographs and the immunofluorescent patterns from parallel cell cultures. To identify the antigens reacting with this antiserum we have used the new technique of immuno-autoradiography on SDS gels of whole cell extracts. Two reactive polypeptide chains have been identified with apparent molecular weights of 56,000 and 30,000 daltons.

Immunochemical evidence for the species-specificity of mammalian cardiac myosin and heavy meromyosin

Structural differences between various myosins were investigated by means of antibodies to heavy meromyosin, a tryptic subfragment of myosin. Heavy meromyosin was purified from rabbit white skeletal and from pig and human cardiac muscles by gel filtration, and antisera were produced in guinea pigs. Analyses, carried out with the quantitative micro-complement fixation technique, indicated that the antibodies were specific to heavy meromyosin and myosin and not to other contractile proteins. For each muscle type, the corresponding intact myosin reacted, and the degree of dixation was always lower than with heavy meromyosin (50 and 70% fixation respectively). This vertical shift was the same for the three muscle types, indicating that the heavy meromyosin represent corresponding fragments of the myosin molecule from one muscle to the other. Antisera to pig or human cardiac heavy meromyosin clearly distinguished antigens (heavy meromyosins, myosins, or crude extracts) from the ventricles of various heterologous species. Relative to pig, the immunological distances were 50 for the rabbit, 73 for the rat and greater than 100 for human and mice. Relative to human, these values were 20 for the rat, 60 for the rabbit, 72 for the pig. These data provide direct evidence that mammalian cardiac myosin is species-specific.

Parvalbumins from frog skeletal muscle (Rana temporaria L.). Isolation and characterization. Structural modifications associated with calcium binding

Two parvalbumins have been isolated from the skeletal muscle of Rana temporaria L. Amino acid composition, tryptic peptide maps, isoelectric points, calcium content and ultraviolet as well as circular dichroism spectra have been determined. Investigation on antigenic properties revealed no antigenic determinants common to both components. The two protein molecules appear to belong to far related gene lineages. They are also different from the parvalbumins found in Rana esculenta muscle. Modifications of physical parameters, associated with calcium binding and dissociation are described. While antigenicity remained essentially unchanged, conformational changes were revealed by alterations of circular dichroism spectra.

Myosin and actomyosin from human skeletal muscle

Human skeletal natural actomyosin contained actin, tropomyosin, troponin and myosin components as judged by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Purified human myosin contained at least three light chains having molecular weights (+/-2000) of 25 000, 18 000 and 15 000. Inhibitory and calcium binding components of troponin were identified in an actin-tropomyosin-troponin complex extracted from acetone-dried muscle powder at 37 degrees C. Activation of the Mg-ATPase activity of Ca2+-sensitive human natural or reconstituted actomyosin was half maximal at approximately 3.4 muM Ca2+ concentration (CaEGTA binding constant equals 4.4 - 10(5) at pH 6.8). Subfragment 1, isolated from the human heavy meromyosin by digestion with papain, appeared as a single peak after DEAE-cellulose chromatography. In the pH 6-9 range, the Ca2+-ATPase activity of the subfragment 1 was 1.8- and 4-fold higher that the original heavy meromyosin and myosin, respectively. The ATPase activities of human myosin and its fragments were 6-10 fold lower than those of corresponding proteins from rabbit fast skeletal muscle. Human myosin lost approximately 60% of the Ca2+-ATPase activity at pH 9 without a concomitant change in the number of distribution of its light chains. These findings indicate that human skeletal muscle myosin resembles other slow and fast mammalian muscles. Regulation of human skeletal actomyosin by Ca2+ is similar to that of rabbit fast or slow muscle.

Production of specific antibodies to contractile proteins, and their use in immunofluorescence microscopy. I. Antibodies to smooth and striated chicken muscle myosins

Antibodies prepared against actomyosins can be shown to behave similarly, if not identically to more recently prepared antibodies against highly purified myosins. Details of the purification of the antigens, and of the production of antibodies to chick myosins from smooth gizzard muscle and from striated pectoral muscle are given. The antibody specificity appears to be directed against the heavy chains of the myosin molecules, since these antibodies specifically inhibit the myosin ATPase reaction, and since in situ staining of myosin polypeptide chains on an SDS gel using the antibodies in indirect fluorescence shows staining only in the heavy band region. Use of the antibodies in immunofluorescence microscopy suggest that the antibodies are tissue, but not species, specific. Example of their use in staining tissue sections are shown.

The immunological specificity of myosins from cross-striated muscles as revealed by quantitative microcomplement fixation and enzyme inhibition by antisera

The immunological properties of myosins, especially their muscle-type, class and species specificity, are still controversial. It is the opinion of the authors that the lack of agreement might at least in part be due to the use of contaminated myosins as immunogens and inappropriate methods. We, therefore, purified myosins to a very high degree (approximately 99%) and induced antisera in guinea-pigs. Studies of quantitative microcomplement fixation and enzyme-inhibition by antisera yielded the following results: myosins of cross-striated muscle have an absolute class, a very pronounced muscle-type and a low species specificity. It can be shown that even a very small contamination of myosins with other proteins could seriously hamper the experiments and that the results obtained depend significantly on the immunological methods employed.

Editorial: Subunits of myosin. Relations to ATPase activity and mechanical function of muscle

Under certain conditions the specific ATPase activity of myosin of a given muscle can be altered. The cause of this alteration can only lie in the myosin molecule itself. To produce an enzymatic activity of myosin, an interaction between their light and heavy chains is necessary. However, the specific activity appears to be determined mainly by light chains. Hence, one ought also to look for a basis of the changed activity in changes of the subunits of myosin. There are strong indications that the alterations in specific activity are accompanied by changes in the relative stoichiometry of the essential light chains of the respective myosin preparation. They differ in their pattern of subunits. The specific activity of a given kind of myosin seems to be determined by the combination of their light chains. Thus, a close correlation exists between these two properties of myosin (ATPase activity and structure of its molecule). There are sufficient indications, that these two properties of myosin correlate also with the mechanical capabiltiy of the corresponding muscle. Particularly the results of cross innervation studies demonstrate a close correlation between these three properties in skeletal muscle. The single subunits of myosin are produced and degraded independently and at heterogenous rates. The synthetis of these subunits is significantly accelerated in response to work overload. Thus, it is quite likely that the individual chains are non-coordinately synthesized, giving rise to variations in the relationship of different molecule types of myosin with different specific ATPase activity. Hence, the control mechanism to synthesize the individual subunits could also be the regulative mechanism to produce a myosin of the specific ATPase activity appropriate to the activity pattern of tissue.

Preparation and properties of vertebrate smooth-muscle myofibrils and actomyosin

A new technique for obtaining a myofibril-like preparation from vertebrate smooth muscle has been developed. An actomyosin can be readily extracted from these myofibrils at low ionic strength and in yields 20 times as high as previously reported. The protein composition of all preparations has been monitored using dodecylsulfate-gel electrophoresis. By this method smooth muscle actomyosin showed primarily only the major proteins, myosin, actin and tropomyosin, while the myofibrils contained, additionally, three new proteins not previously described with polypeptide chain weights of 60000, 110000 and 130000. The ATPase activities of both the myofibrils and actomyosin preparations are considerably higher than previously described for vertebrate smooth muscle. They are sensitive to micromolar Ca2+ ion concentrations to the same degree as comparable skeletal and cardiac muscle preparations, even though troponin-like proteins could not be identified in these smooth muscle preparations. From the latter observation and the presence of Ca2+-sensitivity in tropomyosin-free actomyosin it is suggested that this calcium sensitivity is, as in some invertebrate muscles, a property of the myosin molecule.

Detection and ultrastructural localization of human smooth muscle myosin-like molecules in human non-muscle cells by specific antibodies

Spectrin, a protein complex which is peripherally attached to the cytoplasmic surface of the human erythrocyte membrane, cannot be detected (by complement fixation with anti-spectrin antibodies) in homogenates of several different human non-muscle cells studied. On the other hand, a protein antigenically identical or similar to human smooth muscle myosin was detected (by complement fixation with antibodies to uterine smooth muscle myosin) in these cells. In the case of human fibroblast line WI38, this smooth muscle myosin like component was shown (by ferritin-antibody experiments in electron microscopy) to be at least partly associated with cytoplasmic surface of the plasma membrane of the cell. It is proposed that the spectrin complex of the erythrocyte membrane and the smooth muscle myosin-like component of the fibroblast membrane play similar roles in regulating the translational mobilities of integral proteins in their respective membranes.

Thick filaments in vertebrate smooth muscle

Smooth muscle cells of the mouse vas deferens fixed with 5% glutaraldehyde contained three types of filaments, namely, thin (50-80) A) filaments, intermediate (100 A) filaments and thick (120-180 A) filments. However, in 2 out of 16 experiments, under identical conditions, the cells did not contain thick filaments. With OSO4 fixation, thin filaments were not prominent, the most obvious being thick (120-250 A) and intermediate (100 A) filaments. After soaking in a modified Ringer solution under no applied tension for one hour, thick filaments (120-180 A) appeared prominently in smooth muscle cells of the mouse vas deferens and thin filaments were in ordered bundles. By 4 hours, thick filaments had increased in size and density, with thin filaments distributed randomly around them. After 8 hours in Ringer, thin filaments were diffuse and difficult to discern, while thick filaments were large (up to 300 A) and electron-dense. Intermediate (100 A) filaments were present in association with dark bodies. Physiological experiments indicated that the intracellular components responsible for the development of a mechanical response were still functional at this time. The presence of "thick filaments" is also reported in degenerating smooth muscle cells of the guinea-pig vas deferens in tissue culture.

Antibody to myosin: the specific visualization of myosin-containing filaments in nonmuscle cells

Myosin in human, rat, mouse, and chicken fibroblasts was localized by indirect immunofluorescence microscopy using antibodies prepared in rabbits against highly purified chicken gizzard myosin. Filaments containing myosin span the interior of the cells and are often parallel to each other. The majority of the fibers are concentrated toward the adhesive side of the cell. Most of the myosin-containing filaments show "interruptions" or "striations." From a comparison of these fibers in fluorescence and phase microscopy and from previous results on actin-containing fibers, we conclude that at least some of the cytoplasmic myosin can be found in the actin-containing fibers, which themselves have been shown to be very similar or identical to the microfilament bundles. The occurrence of both myosin and actin in the microfilament bundles provides a basis for the motility and contractility of the cell.