Tropomyosin heterogeneity in human cells

Polyelectrolyte properties of filamentous biopolymers and their consequences in biological fluids

Anionic polyelectrolyte filaments are common in biological cells. DNA, RNA, the cytoskeletal filaments F-actin, microtubules, and intermediate filaments, and polysaccharides such as hyaluronan that form the pericellular matrix all have large net negative charge densities distributed over their surfaces. Several filamentous viruses with diameters and stiffnesses similar to those of cytoskeletal polymers also have similar negative charge densities. Extracellular protein filaments such collagen, fibrin and elastin, in contrast, have notably smaller charge densities and do not behave as highly charged polyelectrolytes in solution. This review summarizes data that demonstrate generic counterion-mediated effects on four structurally unrelated biopolymers of similar charge density: F-actin, vimentin, Pf1 virus, and DNA, and explores the possible biological and pathophysiological consequences of the polyelectrolyte properties of biological filaments.

Cryo-EM structures of the actin:tropomyosin filament reveal the mechanism for the transition from C- to M-state

Tropomyosin (Tm) is a key factor in the molecular mechanisms that regulate the binding of myosin motors to actin filaments (F-Actins) in most eukaryotic cells. This regulation is achieved by the azimuthal repositioning of Tm along the actin (Ac):Tm:troponin (Tn) thin filament to block or expose myosin binding sites on Ac. In striated muscle, including involuntary cardiac muscle, Tm regulates muscle contraction by coupling Ca(2+) binding to Tn with myosin binding to the thin filament. In smooth muscle, the switch is the posttranslational modification of the myosin. Depending on the activation state of Tn and the binding state of myosin, Tm can occupy the blocked, closed, or open position on Ac. Using native cryogenic 3DEM (three-dimensional electron microscopy), we have directly resolved and visualized cardiac and gizzard muscle Tm on filamentous Ac in the position that corresponds to the closed state. From the 8-Å-resolution structure of the reconstituted Ac:Tm filament formed with gizzard-derived Tm, we discuss two possible mechanisms for the transition from closed to open state and describe the role Tm plays in blocking myosin tight binding in the closed-state position.

Comparative proteomics analysis of Barrett metaplasia and esophageal adenocarcinoma using two-dimensional liquid mass mapping

Esophageal adenocarcinoma, currently the seventh leading cause of cancer-related death, has been associated with the presence of Barrett metaplasia. The malignant potential of Barrett metaplasia is evidenced by ultimate progression of this condition to invasive adenocarcinoma. We utilized liquid phase separation of proteins with chromatofocusing in the first dimension and nonporous reverse phase HPLC in the second dimension followed by ESI-TOF mass spectrometry to identify proteins differentially expressed in six Barrett metaplasia samples as compared with six esophageal adenocarcinoma samples; all six Barrett samples were obtained from the identical six patients from whom we obtained the esophageal adenocarcinoma tissue. Approximately 300 protein bands were detected by mass mappings, and 38 differentially expressed proteins were identified by microLC-MS/MS. The false positive rates of the peptide identifications were evaluated by reversed database searching. Among the proteins that were identified, Rho GDP dissociation inhibitor 2, alpha-enolase, Lamin A/C, and nucleoside-diphosphate kinase A were demonstrated to be up-regulated in both mRNA and protein expression in esophageal adenocarcinomas relative to Barrett metaplasia. Candidate proteins were examined at the mRNA level using high density oligonucleotide microarrays. The cellular expression patterns were verified in both esophageal adenocarcinomas and in Barrett metaplasia by immunohistochemistry. These differentially expressed proteins may have utility as useful candidate markers of esophageal adenocarcinoma.

Phosphorylation-dependent translocation of glycogen synthase to a novel structure during glycogen resynthesis

Glycogen metabolism has been the subject of extensive research, but the mechanisms by which it is regulated are still not fully understood. It is well accepted that the rate-limiting enzymes in glycogenesis and glycogenolysis are glycogen synthase (GS) and glycogen phosphorylase (GPh), respectively. Both enzymes are regulated by reversible phosphorylation and by allosteric effectors. However, evidence in the literature indicates that changes in muscle GS and GPh intracellular distribution may constitute a new regulatory mechanism of glycogen metabolism. Already in the 1960s, it was proposed that glycogen was present in dynamic cellular organelles that were termed glycosomas but no such cellular entities have ever been demonstrated. The aim of this study was to characterize muscle GS and GPh intracellular distribution and to identify possible translocation processes of both enzymes. Using in situ stimulation of rabbit tibialis anterior muscle, we show GS and GPh intracellular redistribution at the beginning of glycogen resynthesis after contraction-induced glycogen depletion. We identify a new "player," a new intracellular compartment involved in skeletal muscle glycogen metabolism. They are spherical structures that were not present in basal muscle, and we present evidence that indicate that they are products of actin cytoskeleton remodeling. Furthermore, for the first time, we show a phosphorylation-dependent intracellular distribution of GS. Here, we present evidence of a new regulatory mechanism of skeletal muscle glycogen metabolism based on glycogen enzyme intracellular compartmentalization.

Contractile proteins in human fetoplacental vessels

OBJECTIVE

Our purpose was to compare the protein isoform composition of the contractile apparatus at different levels of the fetoplacental vessel musculature at term.

STUDY DESIGN

Umbilical, chorionic, and stem villi vessel protein extracts were run on one- and two-dimensional gel electrophoresis; previously characterized human myometrium proteins were used as the smooth muscle proteins of reference.

RESULTS

Fetoplacental vessel musculature exhibited a high actin/myosin ratio. The presence, in varying quantities, of myosin heavy chain and actin isoforms of smooth muscle type in the different vessels reflected their degree of differentiation. The presence of nonmuscle protein isoforms, particularly in stem villi vessels, indicated a certain degree of immaturity.

CONCLUSIONS

The presence of smooth muscle contractile protein isoforms indicates that fetoplacental vessel musculature is highly differentiated. Regional modulation of fetoplacental blood flow could be, in part, the result of local differences in contractile apparatus protein composition.

Polyacrylamide gel electrophoretic methods in the separation of structural muscle proteins

Polyacrylamide gel electrophoresis plays a major role in analyzing the function of muscle structural proteins. This review describes one- and two-dimensional gel electrophoretic methods for qualitative and quantitative investigation of the muscle proteins, with special emphasis on determination of protein phosphorylation. The electrophoretic studies established the subunit structures of the muscle proteins, characterized their multiple forms, revealed changes in subunit composition or shifts in isoform distribution of specific proteins during development, upon stimulation or denervation of the muscle. Protein phosphorylation during muscle contraction is preferentially studied by two-dimensional gel electrophoresis. The same method demonstrated protein alterations in human neuromuscular diseases.

Caldesmon and low Mr isoform of tropomyosin are localized in neuronal growth cones

Neuronal growth cones move actively, accompanying changes in intracellular Ca2+ concentration. The movement of growth cones may partly depend on the actomyosin system, considering the presence of actin and myosin II. Yet, Ca(2+)-sensitive regulatory proteins for the actomyosin system have not been identified in growth cones. In the present study, caldesmon, an inhibitory protein on actin-myosin interaction, was detected in the growth cone fraction isolated from embryonic rat brain, using immunoblotting with the antibody to chicken gizzard caldesmon. Morphological evidence of caldesmon in growth cones of cultured rat neurons was obtained using the indirect immunofluorescence method. Since inhibition of caldesmon on actin-myosin interaction can be overcome by calmodulin and Ca2+, caldesmon may be involved in the Ca(2+)-dependent regulation in growth cone motility. Tropomyosin is another member of the actomyosin system whose function may be regulated by caldesmon in smooth and nonmuscle cells. A low Mr isoform of tropomyosin was distributed in the growth cone fraction. Using specific antibodies against tropomyosin isoforms, we further clarified morphologically that the low Mr isoform was localized in growth cones, but not the high Mr isoform. High Mr isoforms of tropomyosin were present in nonneuronal cells. Actin filaments in growth cones may be unstable, since low Mr tropomyosin binds to actin filaments with a lower affinity than high Mr isoforms. The instability of actin filaments may be suitable for the rapid movement and shape changes of growth cones.

Incorporation of microinjected mutant and wildtype recombinant tropomyosins into stress fibers in fibroblasts

The structural requirements for assembly of tropomyosin into stress fibers were investigated by microinjecting wildtype and four mutant striated chicken muscle alpha-tropomyosins expressed in E. coli as fusion and nonfusion proteins into cultured rat embryo fibroblasts, followed by localization of tropomyosin using indirect immunofluorescence. The results show that the determinants for stress fiber incorporation in living cells correlate with the in vitro actin affinity of these tropomyosins. Wildtype recombinant protein incorporated into stress fibers both when the amino terminus was unacetylated and when it was blocked with an 80-residue fusion protein [Hitchcock-DeGregori, S.E., and Heald, R.W. (1987): J. Biol. Chem. 262:9730-9735]. The pattern of incorporation was indistinguishable from that of tropomyosin isolated from chicken pectoral muscle. The striated alpha-tropomyosin incorporated into stress fibers, even though this isoform is not found in nonmuscle cells. Three recombinant mutant tropomyosins in which one-half, two-thirds, or one actin binding site was deleted were tested [Hitchcock-DeGregori, S.E., and Varnell, T.A. (1990): J. Mol. Biol. 214:885-896]. Only the fusion protein with a full actin binding site deleted incorporated into stress fibers. However, the unacetylated, nonfusion proteins with one half and one actin binding site deleted incorporated into stress fibers, consistent with the ability of troponin to promote the actin binding in vitro. A fourth mutant, in which the conserved amino-terminal nine residues were deleted, did not incorporate into stress fibers, consistent with the complete loss of function of this mutant [Cho, Y.J., Liu, J., and Hitchcock-DeGregori, S.E. (1990): J. Biol. Chem. 265:538-545].

Gene expression patterns in the black blowfly (Phormia regina) as revealed by two-dimensional electrophoresis of proteins. I. Developmental stage-specific and sex-specific differences

The black blowfly, Phormia regina, has been implicated in human myiasis and as a contact vector of viral and bacterial diseases present in carrion to which female flies are attracted for egg deposition. Inbred strains of P. regina are an excellent model system for studying gene expression in the developmental stages of such holometabolous dipteran parasites. However, information regarding gene and protein expression patterns in P. regina is limited. We used ISO-DALT high-resolution, two-dimensional electrophoresis with silver staining to establish fundamental protein maps for examination of the stage-specific gene expression patterns in the 615 most abundant proteins of the eggs, first- and third-instar larvae, pupae, and male and female adults. We also used a differential extraction technique to identify the major cuticular proteins of the adults. The results show 48 clearly identifiable stage-specific and sex-specific proteins. Thus, approximately 8% of the most abundant proteins exhibit developmental changes. These analyses serve as an initial data base for further studies of ontogenetic regulation, organellar origin, and physiologic function of the stage-specific proteins in the life cycle of these opportunistically parasitic dipterans.

Simple harmonic motion of tropomyosin: proposed mechanism for length-dependent regulation of muscle active tension

A simple harmonic theory is proposed to describe the regulatory mechanism of tropomyosin in the activation of muscle contraction. The theory proposes that activation-associated displacement of tropomyosin is inherent to tropomyosin, a consequence of the molecule's large-scale vibrational motion (5-10 A root mean square displacement). In association with thin filament the vibrational motion may become less complex, approaching the ideal case of simple harmonic motion. The degree of activation increases as the amplitude of the simple harmonic motion increases, causing tropomyosin to shorten lengthwise, shiftings its position from the periphery of thin filament (OFF) to the actin groove (ON). The amplitude may be regulated in a rectilinear manner by the thick filament electrostatic force, the thin filament hydrophobic force, and the Ca(2+)-dependent force of the troponin complex. The radial and tangenital components of the resultant force may vary as the muscle is stretched, regulating maximum active tension and Ca2+ sensitivity, respectively. This may represent the molecular basis for Starling's law of the heart. The mechanism may be important for describing the regulatory mechanism of tropomyosin in smooth muscle and nonmuscle cells and may facilitate a clinically relevant understanding of the effects of pH, Mg2+ concentration, ionic strength, and ethanol on the regulation of active tension.

Quantitation of human leukocyte proteins after silver staining: a study with two-dimensional electrophoresis

The quantitative attributes of human leukocyte proteins detected by silver staining two-dimensional electrophoresis (2-DE) gels were studied by using computer-assisted data analysis. Experiments included (a) analysis of replicate patterns of the same sample, (b) analysis of different dilutions of the same sample, and (c) analysis of samples from different individuals. Over 200 proteins were observed to have coefficients of variation (CV) less than or equal to 15% when data from replicate patterns were analyzed. In contrast, 8 proteins had CV values of less than or equal to 15% when data from different samples were analyzed. The dilution experiment showed that a majority of the proteins detected with some consistency (i.e., observed in at least 80% of the patterns) have a linear relationship between the amount of protein loaded onto a 2-DE gel and the spot volume in the final 2-DE pattern. The slope of the curves and the deviation from linearity were found to be quite protein-specific. These results indicate that optimization of sample purity and minimization of staining protocol variables are required to limit the background quantitative variability between and within 2-DE runs to a level that will allow detection of quantitative changes indicative of biological responses.

Expression of tropomyosin genes during the development of the rat cerebellum

The expression of the tropomyosin genes in the rat nervous system was examined during the postnatal development of the cerebellum, using human-specific alpha-, beta-, gamma-, and delta-tropomyosin cDNA probes and rat-specific alpha-, beta-, and delta-tropomyosin oligonucleotide probes. The beta- and gamma-genes do not seem to be expressed in the rat brain. The delta-tropomyosin gene produces two mRNAs: a major one of 2.4 kb, which is highly concentrated during the first postnatal week and then decreases fourfold in level until the age of 35 days, and a minor one of 2 kb, with the same developmental profile as the 2.4-kb mRNA. A 3-kb mRNA is expressed by the alpha-tropomyosin gene and is characteristic of the mature rat. The expression of the tropomyosin genes during the development of the rat cerebellum does not seem to be regulated through alternative splicing but rather implies the differential expression of two different isogenes. The multiple isoforms of tropomyosin produced during neuronal differentiation may be intimately involved in the regulation of the organization and function of actin microfilaments.

Generation of skeletal, smooth and low molecular weight non-muscle tropomyosin isoforms from the chicken tropomyosin 1 gene

We have determined the organization of the chicken tropomyosin 1 gene by sequencing the cloned genomic DNA. The single-copy gene spans approximately 11,000 bases and includes 12 exons. Comparison of cDNA and genomic sequences demonstrates that three tissue-specific tropomyosins are encoded by the gene: a 284 amino acid skeletal muscle beta-tropomyosin, a 284 amino acid smooth muscle tropomyosin, and a 248 amino acid non-muscle (fibroblast) beta-tropomyosin. Skeletal and smooth muscle transcripts use the same putative promoter and transcription initiation site. However, they are alternatively spliced to generate mRNAs that differ in the region giving rise to amino acids 188 to 213 and 258 through the poly(A) site. The fibroblast transcript uses a promoter, initiation site and first exon that is distinct from that used for both the smooth and the skeletal muscle transcripts. However, beyond the first exon the fibroblast transcript undergoes splicing and polyadenylation that is identical with the smooth muscle transcript.

Proteins of the rat prostate. III. Effect of testosterone on protein synthesis by the ventral prostate of castrated rats

Protein synthetic activities in the ventral prostate were assessed by two-dimensional electrophoresis in either four-day or seven-day castrated rats at different intervals following subcutaneous implantation of testosterone-filled silastic tubings for a period of up to four days. Prostatic tissues were cut into one to two mm. pieces and incubated in tissue culture medium containing S35-methionine (100 microCi/ml.) at 37C under 95% oxygen and 5% carbon dioxide for four hours. The incubated tissues were subjected to two-dimensional electrophoresis and radiofluorography. Analysis of protein spots detected in the fluorograms by computer-assisted densitometry revealed temporal changes in the synthesis of individual proteins by the ventral prostate of castrated rats following androgen treatment. Changes in two groups of proteins were evaluated: castration-induced proteins and androgen-dependent proteins. The level of synthesis of three castration-induced proteins (spots G, H, and I) declined rapidly upon testosterone treatment and reached a non-detectable level for spots G and H and a low level of synthesis for spot I by three days following androgen treatment. Synthesis of androgen-dependent proteins (spots D, E, and F) was activated by testosterone treatment. However, the time interval required to activate the synthesis of these proteins is different. Synthesis of protein spot D (prostatic binding protein) was detected as soon as half hour after the treatment. Synthesis of spots E and F, on the other hand, was not activated until 24 and 48 hours after the treatment, respectively. These changes in patterns of protein synthesis represent the characteristics of cellular responses to testosterone stimulation by the regressed prostate.

Papillomavirus-associated inductions of cellular proteins in mouse C127 cells: correlation with the presence of open reading frame E2

Bovine papillomavirus type 1 (BPV-1) readily transforms mouse C127 cells, conferring the ability to grow in soft agar and to form tumors in athymic (nu/nu) mice. Electrophoresis of total cellular proteins from these BPV-transformed lines on ultra-high resolution, giant two-dimensional gels displays the presence of novel, papillomavirus-related protein phenotypes. Analysis of the established BPV-1-transformed C127 cell lines, ID13 and ID14, reveals a set of six proteins which are either absent or synthesized at extremely low levels in the parental cell line. One of these proteins is also present in v-ras-transformed C127 cells, but none of the others are found in cells transformed by a variety of viral oncogenes, including the polyomavirus middle T, v-mos, or v-fes. The genome of BPV-1 contains two separate open reading frames (ORFs), E5 and E6, which can act independently to transform C127 cells. In addition, trans-activator and repressor proteins encoded respectively by the full-length and carboxy-terminal E2 ORF regulate the level of expression of other BPV-1 genes. We examined 34 cell lines transformed by intact and subgenomic recombinant DNAs of BPV-1. Cells harboring BPV-1 DNAs engineered to eliminate the expression of ORFs E4, E5, E6, or E7 display five of the PV-associated proteins, but these proteins are not seen in lines lacking the full E2 ORF. Moreover, G418-selected nontransformed cells expressing E2 cDNA from an SV40 promoter exhibit these proteins at high levels. Surprisingly, these proteins are also present in cells containing BPV-1 DNAs with amino-terminal E2 deletions, suggesting that these PV-associated proteins represent novel cellular responses to a factor encoded within the E2-C gene region.

Specific polypeptide differences in normal versus malignant breast tissue by two-dimensional electrophoresis

High resolution two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) in combination with computer-assisted densitometry was used to analyze 800-1000 silver stained postmitochrondrial and 600-800 cytosolic polypeptides extracted from malignant and nonmalignant human breast tissues. The 2D-PAGE patterns of polypeptides from malignant and normal tissues were similar, although both qualitative and quantitative polypeptide differences were noted. Six cytosolic polypeptides (pI/molecular mass x 10(-3), 5.20/80, 5.75/43, 6.20/40, 5.43/35, 5.46/34.5, and 5.50/34 were detected exclusively in malignant tissues. One constitutive polypeptide, p52 (7.25/52), was not detected in tumor samples. Marked quantitative differences in spot density were noted in polypeptides localized mainly in the molecular weight ranges of 22-40 kDa and pI of 5.65-7.00. An overall increase in polypeptide expression was noted in this region of 2D-PAGE gels of malignant tissues as compared to normal. Twenty-two acidic and 19 polypeptides separated under nonequilibrium isoelectric focusing conditions were significantly increased in tumor samples while one polypeptide was decreased. One polypeptide, p24 (6.15/24), was expressed in greatest concentrations in tumors which also expressed the greatest estrogen receptor content. Expression of p24 was markedly reduced in normal tissue and in malignant tissues expressing low levels of estrogen and progesterone receptors. No significant differences in the expression of the Yb and Ya subunits of glutathione-S-transferases (GST)-A, -B and ligandin were observed between normal and malignant breast tissue. None of the Yp subunits of the placental isoform of GST were detected in either normal or malignant breast tissues.

Actin stress fiber disruption and tropomyosin isoform switching in normal thyroid epithelial cells stimulated by thyrotropin and phorbol esters

Thyrotropin (TSH), through cyclic AMP, promotes both proliferation and differentiation expression in dog thyroid epithelial cells in primary culture, whereas the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) also stimulates proliferation but antagonizes differentiating effects of TSH. In this study, within 20 min both factors triggered the disruption of actin-containing stress fibers. This process preceded distinct morphological changes: cytoplasmic retraction and arborization in response to TSH and cyclic AMP, cell shape distortion, and increased motility in response to TPA and cyclic AMP, cell shape distortion, and increased motility in response to TPA and diacylglycerol. TSH and TPA also induced a marked decrease in the synthesis of three high Mr tropomyosin isoforms, which were not present in dog thyroid tissue but appeared in culture during cell spreading and stress fiber formation. In contrast, the synthesis of two low Mr forms of tropomyosin that were already present in thyroid tissue remained unchanged after treatment with TSH or TPA. Epidermal growth factor, another mitogenic and dedifferentiating factor for these cells, did not induce acute morphological changes, nor modification of tropomyosin synthesis. The tropomyosin isoform switching observed here closely resembled similar processes in various cells transformed by oncogenic viruses. However, it did not correlate with differentiation or mitogenic activation. Contrasting with current hypothesis on this process in transformed cells, tropomyosin isoform switching in normal thyroid cells was preceded and thus might be caused by early disruption of stress fibers.

Computerized, comprehensive databases of cellular and secreted proteins from normal human embryonic lung MRC-5 fibroblasts: identification of transformation and/or proliferation sensitive proteins

Databases of protein information from human embryonal lung fibroblasts (MRC-5) have been established using computer analyzed two-dimensional gel electrophoresis. One thousand four hundred and eighty-two cellular proteins (1060 with isoelectric focusing and 422 with nonequilibrium pH gradient electrophoresis, in the first dimension) ranging in molecular mass between 8 and 234 kDa were separated and numbered. Information entered in the database (in most cases for major proteins) includes: protein name, HeLa protein catalog number, mouse protein catalog number, proteins matched in transformed human epithelial amnion cells (AMA) and peripheral blood mononuclear cells (PBMC), transformation and/or proliferation sensitive proteins, synthesis in quiescent cells, cell cycle regulated proteins, mitochondrial and heat shock proteins, cytoskeletal proteins and proteins whose synthesis is affected by interferons. Additional information entered for a few transformation-sensitive proteins that have been selected for future studies includes levels of synthesis and amounts in fetal human tissues. A total of four hundred and seventy-six [35S]methionine labeled polypeptides (258 isoelectric focusing; 218, nonequilibrium pH gradient electrophoresis) secreted by MRC-5 fibroblasts were separated and recorded (J. E. Celis et al., Leukemia 1987, 1, 707-717). Information entered in this database includes molecular weight and transformation sensitive proteins. These databases, as well as those of epithelial and lymphoid cell proteins (J. E. Celis et al., Leukemia 1988, 9, 561-601), represent the initial stages of a systematic effort to establish comprehensive databases of human protein information. In the long run, these databases are expected to offer a useful framework in which to focus the human genome sequencing effort.

A new type of neuronal cytoplasmic inclusion: histological, ultrastructural, and immunocytochemical studies

A novel type of non-viral cytoplasmic inclusion is described, which was seen in virtually every neuron in the brain and spinal cord of a child with a presumed metabolic disorder whose clinical picture and CNS pathology were compatible with Leigh Syndrome. The ovoid to round inclusions were sharply demarcated, measuring up to 11 microns in diameter. They showed no distinctive staining with a battery of routine histological techniques. The ultrastructural features are unique, comprising non-membrane-bounded aggregates of randomly oriented plate-like structures with parallel linear densities depicting a periodicity of 11-16 nm. Immunocytochemical studies revealed strong staining with antisera to tropomyosin and weaker staining with antisera to actin. There was no reactivity with antibodies against neurofilaments, microtubules and their associated proteins, paired helical filaments, ubiquitin, vinculin or alpha-actinin. It is postulated that the metabolic disorder resulted in a neurodegenerative condition which manifested pathologically with lesions compatible with those of Leigh Syndrome. Associated with the condition was the discrete accumulation of cytoplasmic proteinaceous components, including tropomyosin, in the form of neuronal cytoplasmic inclusions possibly resulting from an alteration of the neuronal cytoskeleton.

Organization of the hTMnm gene. Implications for the evolution of muscle and non-muscle tropomyosins

We have isolated clones of human genomic DNA which contain the structural elements of the hTMnm gene. In non-muscle tissue this gene produces a 2.5 kb (1 kb = 10(3) bases or base-pairs) mRNA encoding TM30nm, a 248 amino acid cytoskeletal tropomyosin. In muscle, alternative splicing of this gene results in the expression of a 1.3 kb mRNA encoding a 285 amino acid skeletal muscle alpha-tropomyosin. The hTMnm gene spans at least 42 kb of DNA and consists of 13 exons, only five of which are common to both the 2.5 kb and 1.3 kb transcripts. The boundaries of the exons giving rise to the muscle-specific isoform are identical to the base to those of other genes encoding muscle tropomyosins. A comparison of the structures of exons encoding the amino-terminal sequences of the muscle and non-muscle isoforms suggests that the hTMnm gene has evolved by a specific pattern of exon duplication with alternative splicing.

Evolution of tropomyosin functional domains: differential splicing and genomic constraints

We have cloned and determined the nucleotide sequence of a complementary DNA (cDNA) encoded by a newly isolated human tropomyosin gene and expressed in liver. Using the least-square method of Fitch and Margoliash, we investigated the nucleotide divergences of this sequence and those published in the literature, which allowed us to clarify the classification and evolution of the tropomyosin genes expressed in vertebrates. Tropomyosin undergoes alternative splicing on three of its nine exons. Analysis of the exons not involved in differential splicing showed that the four human tropomyosin genes resulted from a duplication that probably occurred early, at the time of the amphibian radiation. The study of the sequences obtained from rat and chicken allowed a classification of these genes as one of the types identified for humans. The divergence of exons 6 and 9 indicates that functional pressure was exerted on these sequences, probably by an interaction with proteins in skeletal muscle and perhaps also in smooth muscle; such a constraint was not detected in the sequences obtained from nonmuscle cells. These results have led us to postulate the existence of a protein in smooth muscle that may be the counterpart of skeletal muscle troponin. We show that different kinds of functional pressure were exerted on a single gene, resulting in different evolutionary rates and different convergences in some regions of the same molecule. Codon usage analysis indicates that there is no strict relationship between tissue types (and hence the tRNA precursor pool) and codon usage. G + C content is characteristic of a gene and does not change significantly during evolution.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteins of the rat prostate. II. Synthesis of new proteins in the ventral lobe during castration-induced regression

Ventral prostates from adult Sprague-Dawley rats at different days postcastration were cut into one to two mm.3 pieces and incubated in medium containing S35-methionine (100 uCi/ml.) at 37C under 95% oxygen and 5% carbon dioxide for four hours. The incubated tissues were subjected to two-dimensional electrophoresis and radiofluorography. Over 100 spots were developed in the fluorograms. Three groups of spots, representing cytoskeletal proteins, androgen-dependent proteins and castration-induced proteins, were further evaluated by a computer-based densitometer. The level of densitometry absorption is proportional to the amount of radioactivity in each spot. The synthesis of cytoskeletal proteins, such as actin and tropomyosin, were relatively constant throughout the course of prostatic regression. The rate of synthesis of androgen-dependent proteins declined rapidly from a high level of synthesis before castration to a non-detectable level by Day 3 postcastration. However, three proteins, which were either not synthesized (spot G and spot H) or synthesized at a very low level (spot I) before castration, were the major proteins synthesized by the prostate during early stages of its regression. The rate of synthesis of these proteins reached a peak by Day 4 postcastration, declined rapidly and remained at a low level thereafter. The respective molecular weights and isoelectric points for these three proteins were 33 Kd and 7.2 for spot G, 38 Kd and 5.3 for spot H and 64 Kd and 6.0 for spot I. Previous findings showed that prostatic regression in rats was associated with a surge of activities in proteolytic enzymes which peaked five to six days postcastration. The peak of synthesis of three proteins noted in the present study, therefore, preceded the peak of activities of proteolytic enzymes in the regressing prostate by one to two days. Testosterone replacement to animals at the time of castration prevented the synthesis of these proteins in the prostate. Since the synthesis of these three proteins in the ventral prostate is induced by androgen-depletion resulted from castration, they are considered as the castration-induced proteins.

Cytochalasin D alters the rate of synthesis of some HEp-2 cytoskeletal proteins. Examination by two-dimensional gel electrophoresis

The most abundant proteins of HEp-2 cells were resolved by two-dimensional gel electrophoresis. The protein spots corresponding to several cytoskeletal proteins (vimentin, alpha-tubulin, beta-tubulin, alpha-actinin, tropomyosins, and cytokeratins) were identified by comigration with protein markers or by immunological techniques. After treatment of HEp-2 cells with 0.2 microM or 2.0 microM cytochalasin D for 20 h, radioautograms of two-dimensional gel patterns of lysates from cells pulse-labeled with [35S]methionine indicated that the drug altered the rate of synthesis of some proteins. The relative rate of synthesis of the identified cytoskeletal proteins was measured. Synthesis of alpha-actinin, the higher-molecular-mass pair of tropomyosins and actin were similarly increased with cytochalasin D treatment, suggesting coordinate induction. Vimentin and tubulin synthesis was depressed. One cytokeratin exhibited an increase in synthesis comparable to actin, another was increased to a lesser extent and one was decreased.

Isolation from bovine brain of tropomyosins that bind to actin filaments with different affinities

Tropomyosin was isolated from bovine brain using mild conditions thereby avoiding heat precipitation. Separation by DEAE ion exchange chromatography yielded a 33 kDa tropomyosin and a mixture of 30 and 32 kDa tropomyosin. Binding of the tropomyosins to actin filaments was measured by a newly developed method. The binding was assayed by the retarding effect of tropomyosin on actin polymerization. The 33 kDa tropomyosin was found to bind to actin filaments with considerably higher affinity than the 30 and 32 kDa tropomyosin.

Two different variants of the same tropomyosin polypeptide in clones from GM1386 human skin fibroblasts

A new protein observed in two-dimensional electrophoresis patterns of proteins from the human skin fibroblast line GM1386 has been identified as a charge and molecular-weight variant of the type of tropomyosin found in smooth muscle (Tm:3). This is the second variant of Tm:3 found in GM1386 and represents a second site mutation in one of the genes coding for Tm:3.

Proteins of the rat prostate: I. Preliminary characterization by two-dimensional electrophoresis

The rat prostate consists of three distinct lobes: the ventral, lateral, and dorsal. Proteins in the three lobes of the prostate were studied with the ISO-DALT system for high-resolution two-dimensional electrophoresis. Proteins were detected with ammoniacal silver stain. Comparison of patterns from the three lobes of the prostate of control, noncastrated rats revealed that while there was a remarkable overall similarity, six groups of proteins showed lobe-specific differences. When prostatic regression was induced by castration, androgen-dependent proteins showed a decrease in staining intensity. A group of proteins, with pI 5.0-6.0 and MW 65,000-70,000, was consistently observed only during the active phase of prostatic regression (days 3-7 postcastration). Their presence during this specific interval may play a role in tissue involution.