Cloning of the cDNA encoding the myosin heavy chain of a vertebrate cellular myosin

Changes in the expression and functional activities of Myosin II isoforms in human hyperplastic prostate

Benign prostatic hyperplasia (BPH) is a common disease among aging males with the etiology remaining unclear. We recently found myosin II was abundantly expressed in rat and cultured human prostate cells with permissive roles in the dynamic and static components. The present study aimed to explore the expression and functional activities of myosin II isoforms including smooth muscle (SM) myosin II (SMM II) and non-muscle myosin II (NMM II) in the hyperplastic prostate. Human prostate cell lines and tissues from normal human and BPH patients were used. Hematoxylin and Eosin (H&E), Masson's trichrome, immunohistochemical staining, in vitro organ bath, RT-polymerase chain reaction (PCR) and Western-blotting were performed. We further created cell models with NMM II isoforms silenced and proliferation, cycle, and apoptosis of prostate cells were determined by cell counting kit-8 (CCK-8) assay and flow cytometry. Hyperplastic prostate SM expressed more SM1 and LC17b isoforms compared with their alternatively spliced counterparts, favoring a slower more tonic-type contraction and greater force generation. For BPH group, blebbistatin (BLEB, a selective myosin II inhibitor), exhibited a stronger effect on relaxing phenylephrine (PE) pre-contracted prostate strips and inhibiting PE-induced contraction. Additionally, NMMHC-A and NMMHC-B were up-regulated in hyperplastic prostate with no change in NMMHC-C. Knockdown of NMMHC-A or NMMHC-B inhibited prostate cell proliferation and induced apoptosis, with no changes in cell cycle. Our novel data demonstrate that expression and functional activities of myosin II isoforms are altered in human hyperplastic prostate, suggesting a new pathological mechanism for BPH. Thus, the myosin II system may provide potential new therapeutic targets for BPH/lower urinary tract symptoms (LUTS).

Scribble, Lgl1, and myosin II form a complex in vivo to promote directed cell migration

Scribble (Scrib) and Lethal giant larvae 1 (Lgl1) are conserved polarity proteins that play important roles in different forms of cell polarity. The roles of Scrib and Lgl1 in apical-basal cell polarity have been studied extensively, but little is known about their roles in the cell polarity of migrating cells. Furthermore, the effect of Scrib and Lgl1 interaction on cell polarity is largely unknown. In this study, we show that Scrib, through its leucine-rich repeat domain, forms a complex in vivo with Lgl1. Scrib also forms a complex with myosin II, and Scrib, Lgl1, and myosin II colocalize at the leading edge of migrating cells. The cellular localization and the cytoskeletal association of Scrib and Lgl1 are interdependent, as depletion of either protein affects its counterpart. In addition, depletion of either Scrib or Lgl1 disrupts the cellular localization of myosin II. We show that depletion of either Scrib or Lgl1 affects cell adhesion through the inhibition of focal adhesion disassembly. Finally, we show that Scrib and Lgl1 are required for proper cell polarity of migrating cells. These results provide new insights into the mechanism regulating the cell polarity of migrating cells by Scrib, Lgl1, and myosin II.

Non-Muscle Myosin 2A (NM2A): Structure, Regulation and Function

Non-muscle myosin 2A (NM2A) is a motor cytoskeletal enzyme with crucial importance from the early stages of development until adulthood. Due to its capacity to convert chemical energy into force, NM2A powers the contraction of the actomyosin cytoskeleton, required for proper cell division, adhesion and migration, among other cellular functions. Although NM2A has been extensively studied, new findings revealed that a lot remains to be discovered concerning its spatiotemporal regulation in the intracellular environment. In recent years, new functions were attributed to NM2A and its activity was associated to a plethora of illnesses, including neurological disorders and infectious diseases. Here, we provide a concise overview on the current knowledge regarding the structure, the function and the regulation of NM2A. In addition, we recapitulate NM2A-associated diseases and discuss its potential as a therapeutic target.

Blebbistatin modulates prostatic cell growth and contrapctility through myosin II signaling

To investigate the effect of blebbistatin (BLEB, a selective myosin inhibitor) on regulating contractility and growth of prostate cells and to provide insight into possible mechanisms associated with these actions. BLEB was incubated with cell lines of BPH-1 and WPMY-1, and intraprostatically injected into rats. Cell growth was determined by flow cytometry, and in vitro organ bath studies were performed to explore muscle contractility. Smooth muscle (SM) myosin isoform (SM1/2, SM-A/B, and LC_17a/b) expression was determined via competitive reverse transcriptase PCR. SM myosin heavy chain (MHC), non-muscle (NM) MHC isoforms (NMMHC-A and NMMHC-B), and proteins related to cell apoptosis were further analyzed via Western blotting. Masson's trichrome staining was applied to tissue sections. BLEB could dose-dependently trigger apoptosis and retard the growth of BPH-1 and WPMY-1. Consistent with in vitro effect, administration of BLEB to the prostate could decrease rat prostatic epithelial and SM cells via increased apoptosis. Western blotting confirmed the effects of BLEB on inducing apoptosis through a mechanism involving MLC₂₀ dephosphorylation with down-regulation of Bcl-2 and up-regulation of BAX and cleaved caspase 3. Meanwhile, NMMHC-A and NMMHC-B, the downstream proteins of MLC₂₀, were found significantly attenuated in BPH-1 and WPMY-1 cells, as well as rat prostate tissues. Additionally, BLEB decreased SM cell number and SM MHC expression, along with attenuated phenylephrine-induced contraction and altered prostate SMM isoform composition with up-regulation of SM-B and down-regulation of LC_17a, favoring a faster contraction. Our novel data demonstrate BLEB regulated myosin expression and functional activity. The mechanism involved MLC₂₀ dephosphorylation and altered SMM isoform composition.

Multiple polyadenylation signals and 3' untranslated sequences are conserved between chicken and human cellular myosin II transcripts

We have isolated a chicken cellular myosin II heavy chain isoform cDNA clone that overlaps the published sequence for MHC-A (Shohet et al., 1989, Proc Natl Acad Sci 86, 7726-7730) and contains three canonical AAUAAA-polyadenylation signals in an additional 374 nucleotides at its 3' end. S1 nuclease protection analysis and PCR-amplification of MHC-A cDNA 3' ends have confirmed that all three of the signals are used in vivo. Differential usage of these signals without differential splicing in this region yields three messages that differ at their 3' ends but appear to encode the same protein. Comparison of the new chicken sequence with the homologous human MHC-A cDNA sequence (Saez et al., 1990, Proc Natl Acad Sci 87, 1164-1168) has revealed a number of similarities at this end of their long 3' untranslated regions (3'-UTRs). The three chicken polyadenylation signals reported here are positioned similarly to three signals evident in the human sequence. This region also contains distinct stretches of identity that are interspersed with regions of little homology. Within these regions of identity are a number of conserved sequence motifs, some of which have been demonstrated to be involved in mRNA metabolism in other systems. The pattern of mRNA sequence conservation demonstrated here suggests that the mechanisms for regulating MHC-A mRNA metabolism have been conserved between chickens and humans.

The expression and functional activities of smooth muscle myosin and non-muscle myosin isoforms in rat prostate

Benign prostatic hyperplasia (BPH) is mainly caused by increased prostatic smooth muscle (SM) tone and volume. SM myosin (SMM) and non-muscle myosin (NMM) play important roles in mediating SM tone and cell proliferation, but these molecules have been less studied in the prostate. Rat prostate and cultured primary human prostate SM and epithelial cells were utilized. In vitro organ bath studies were performed to explore contractility of rat prostate. SMM isoforms, including SM myosin heavy chain (MHC) isoforms (SM1/2 and SM-A/B) and myosin light chain 17 isoforms (LC_17a/b ), and isoform ratios were determined via competitive RT-PCR. SM MHC and NM MHC isoforms (NMMHC-A, NMMHC-B and NMMHC-C) were further analysed via Western blotting and immunofluorescence microscopy. Prostatic SM generated significant force induced by phenylephrine with an intermediate tonicity between phasic bladder and tonic aorta type contractility. Correlating with this kind of intermediate tonicity, rat prostate mainly expressed LC_17a and SM1 but with relatively equal expression of SM-A/SM-B at the mRNA level. Meanwhile, isoforms of NMMHC-A, B, C were also abundantly present in rat prostate with SMM present only in the stroma, while NMMHC-A, B, C were present both in the stroma and endothelial. Additionally, the SMM selective inhibitor blebbistatin could potently relax phenylephrine pre-contracted prostate SM. In conclusion, our novel data demonstrated the expression and functional activities of SMM and NMM isoforms in the rat prostate. It is suggested that the isoforms of SMM and NMM could play important roles in BPH development and bladder outlet obstruction.

Differential role of nonmuscle myosin II isoforms during blebbing of MCF-7 cells

One molecular cue that regulates cellular protrusions such as blebbing and lamellipodia in tumor cells has been less explored than other environmental factors. NM II-A induces blebbing and NM II-C1 induces lamellipodia in tumor cells. NM-II isoforms can change the protrusive activity of a tumor cell.

Bleb formation has been correlated with nonmuscle myosin II (NM-II) activity. Whether three isoforms of NM-II (NM-IIA, -IIB and -IIC) have the same or differential roles in bleb formation is not well understood. Here we report that ectopically expressed, GFP-tagged NM-II isoforms exhibit different types of membrane protrusions, such as multiple blebs, lamellipodia, combinations of both, or absence of any such protrusions in MCF-7 cells. Quantification suggests that 50% of NM-IIA-GFP–, 29% of NM-IIB-GFP–, and 19% of NM-IIC1-GFP–expressing MCF-7 cells show multiple bleb formation, compared with 36% of cells expressing GFP alone. Of interest, NM-IIB has an almost 50% lower rate of dissociation from actin filament than NM-IIA and –IIC1 as determined by FRET analysis both at cell and bleb cortices. We induced bleb formation by disruption of the cortex and found that all three NM-II-GFP isoforms can reappear and form filaments but to different degrees in the growing bleb. NM-IIB-GFP can form filaments in blebs in 41% of NM-IIB-GFP–expressing cells, whereas filaments form in only 12 and 3% of cells expressing NM-IIA-GFP and NM-IIC1-GFP, respectively. These studies suggest that NM-II isoforms have differential roles in the bleb life cycle.

The tumor suppressor Lgl1 forms discrete complexes with NMII-A and Par6α-aPKCζ that are affected by Lgl1 phosphorylation

Non-muscle myosin IIA (NMII-A) and the tumor suppressor lethal giant larvae 1 (Lgl1) play a central role in the polarization of migrating cells. Mammalian Lgl1 interacts directly with NMII-A, inhibiting its ability to assemble into filaments in vitro. Lgl1 also regulates the cellular localization of NMII-A, the maturation of focal adhesions and cell migration. In Drosophila, phosphorylation of Lgl affects its association with the cytoskeleton. Here we show that phosphorylation of mammalian Lgl1 by aPKCζ prevents its interaction with NMII-A both in vitro and in vivo, and affects its inhibition of NMII-A filament assembly. Phosphorylation of Lgl1 affects its cellular localization and is important for the cellular organization of the acto-NMII cytoskeleton. We further show that Lgl1 forms two distinct complexes in vivo, Lgl1-NMIIA and Lgl1-Par6α-aPKCζ, and that the formation of these complexes is affected by the phosphorylation state of Lgl1. The complex Lgl1-Par6α-aPKCζ resides in the leading edge of the cell. Finally, we show that aPKCζ and NMII-A compete to bind directly to Lgl1 at the same domain. These results provide new insights into the mechanism regulating the interaction between Lgl1, NMII-A, Par6α and aPKCζ in polarized migrating cells.

The tumor suppressor Lgl1 regulates NMII-A cellular distribution and focal adhesion morphology to optimize cell migration

The Drosophila tumor suppressor Lethal (2) giant larvae (Lgl) regulates the apical-basal polarity in epithelia and asymmetric cell division. However, little is known about the role of Lgl in cell polarity in migrating cells. In this study we show direct physiological interactions between the mammalian homologue of Lgl (Lgl1) and the nonmuscle myosin II isoform A (NMII-A). We demonstrate that Lgl1 and NMII-A form a complex in vivo and provide data that Lgl1 inhibits NMII-A filament assembly in vitro. Furthermore, depletion of Lgl1 results in the unexpected presence of NMII-A in the cell leading edge, a region that is not usually occupied by this protein, suggesting that Lgl1 regulates the cellular localization of NMII-A. Finally, we show that depletion of Lgl1 affects the size and number of focal adhesions, as well as cell polarity, membrane dynamics, and the rate of migrating cells. Collectively these findings indicate that Lgl1 regulates the polarity of migrating cells by controlling the assembly state of NMII-A, its cellular localization, and focal adhesion assembly.

LPA(1) -induced migration requires nonmuscle myosin II light chain phosphorylation in breast cancer cells

The enhanced migration found in tumor cells is often caused by external stimuli and the sequential participation of cytoskeleton-related signaling molecules. However, until now, the molecular connection between the lysophosphatidic acid (LPA) receptor and nonmuscle myosin II (NM II) has not been analyzed in detail for LPA-induced migration. Here, we demonstrate that LPA induces migration by activating the LPA(1) receptor which promotes phosphorylation of the 20 kDa NM II light chain through activation of Rho kinase (ROCK). We show that LPA-induced migration is insensitive to pertussis toxin (PTX) but does require the LPA(1) receptor as determined by siRNA and receptor antagonists. LPA activates ROCK and also increases GTP-bound RhoA activity, concomitant with the enhanced membrane recruitment of RhoA. LPA-induced migration and invasion are attenuated by specific inhibitors including C3 cell-permeable transferase and Y-27632. We demonstrate that NM II plays an important role in LPA-induced migration and invasion by inhibiting its cellular function with blebbistatin and shRNA lentivirus directed against NM II-A or II-B. Inhibition or loss of either NM II-A or NM II-B in 4T1 cells results in a decrease in migration and invasion. Restoration of the expression of NM II-A or NM II-B also rescued LPA-induced migration. Taken together, these results suggest defined pathways for signaling through the LPA(1) receptor to promote LPA-mediated NM II activation and subsequent cell migration in 4T1 breast cancer cells.

Enucleation of human erythroblasts involves non-muscle myosin IIB

Mammalian erythroblasts undergo enucleation, a process thought to be similar to cytokinesis. Although an assemblage of actin, non-muscle myosin II, and several other proteins is crucial for proper cytokinesis, the role of non-muscle myosin II in enucleation remains unclear. In this study, we investigated the effect of various cell-division inhibitors on cytokinesis and enucleation. For this purpose, we used human colony-forming unit-erythroid (CFU-E) and mature erythroblasts generated from purified CD34(+) cells as target cells for cytokinesis and enucleation assay, respectively. Here we show that the inhibition of myosin by blebbistatin, an inhibitor of non-muscle myosin II ATPase, blocks both cell division and enucleation, which suggests that non-muscle myosin II plays an essential role not only in cytokinesis but also in enucleation. When the function of non-muscle myosin heavy chain (NMHC) IIA or IIB was inhibited by an exogenous expression of myosin rod fragment, myosin IIA or IIB, each rod fragment blocked the proliferation of CFU-E but only the rod fragment for IIB inhibited the enucleation of mature erythroblasts. These data indicate that NMHC IIB among the isoforms is involved in the enucleation of human erythroblasts.

Precipitation of kidney myosin IIA and IIB by freezing

Actomyosin precipitation is a critical step in the purification of myosins. In this work, the objective was to precipitate rat kidney actomyosin and isolate myosin by freezing and thawing the soluble fraction. Kidney was homogenized in imidazole buffer, centrifuged at 45000 g for 30 min, and the supernatant was frozen at -20°C for 48 h. The supernatant was thawed at 4°C, centrifuged at 45000 g for 30 min and the precipitate washed twice with imidazole buffer pH 7.0 (with and without Triton X-100, respectively). The resulting precipitate presented a polypeptide profile in SDS/PAGE characteristic of actomyosin and expressed Mg- and K/EDTA-ATPase activity. The actomyosin complex was solubilized with ATP and Mg, and the main polypeptide, p200, was purified in a DEAE-Sepharose column. p200 was marked with anti-myosin II, co-sedimented with F-actin in the absence, but not in the presence, of ATP and was identified by MS/MS with a high Mascot score for myosin IIA. The analysis identified peptides exclusive of myosin IIB, but detected no peptides exclusive of myosin IIC.

Dynamic assembly properties of nonmuscle myosin II isoforms revealed by combination of fluorescence correlation spectroscopy and fluorescence cross-correlation spectroscopy

Myosin II molecules assemble into filaments through their C-terminal rod region, and are responsible for several cellular motile activities. Three isoforms of nonmuscle myosin II (IIA, IIB and IIC) are expressed in mammalian cells. However, little is known regarding the isoform composition in filaments. To obtain new insight into the assembly properties of myosin II isoforms, especially regarding the isoform composition in filaments, we performed a combination analysis of fluorescence correlation spectroscopy (FCS) and fluorescence cross-correlation spectroscopy (FCCS), which enables us to acquire information on both the interaction and the size of each molecule simultaneously. Using C-terminal rod fragments of IIA and IIB (ARF296 and BRF305) labelled with different fluorescent probes, we demonstrated that hetero-assemblies were formed from a mixture of ARF296 and BRF305, and that dynamic exchange of rod fragments occurred between preformed homo-assemblies of each isoform in an isoform-independent manner. We also showed that Mts1 (S100A4) specifically stripped ARF296 away from the hetero-assemblies, and consequently, homo-assemblies of BRF305 were formed. These results suggest that IIA and IIB can form hetero-filaments in an isoform-independent manner, and that a factor like Mts1 can remove one isoform from the hetero-filament, resulting in a formation of homo-filaments consisting of another isoform.

Myosin motor proteins in the cell biology of axons and other neuronal compartments

Most neurons of both the central and peripheral nervous systems express multiple members of the myosin superfamily that include nonmuscle myosin II, and a number of classes of unconventional myosins. Several classes of unconventional myosins found in neurons have been shown to play important roles in transport processes. A general picture of the myosin-dependent transport processes in neurons is beginning to emerge, although much more work still needs to be done to fully define these roles and establish the importance of myosin for axonal transport. Myosins appear to contribute to three types of transport processes in neurons; recycling of receptors or other membrane components, dynamic tethering of vesicular components, and transport or tethering of protein translational machinery including mRNA. Defects in one or more of these functions have potential to contribute to disease processes.

Conventional myosins - unconventional functions

While the discovery of unconventional myosins raised expectations that their actions were responsible for most aspects of actin-based cell motility, few anticipated the wide range of cellular functions that would remain the purview of conventional two-headed myosins. The three nonsarcomeric, cellular myosins-M2A, M2B and M2C-participate in diverse roles including, but not limited to: neuronal dynamics, axon guidance and synaptic transmission; endothelial cell migration; cell adhesion, polarity, fusion and cytokinesis; vesicle trafficking and viral egress. These three conventional myosins each take on specific, differing functional roles during development and maturity, characteristic of each cell lineage; exact roles depend on the developmental stage of the cell, cellular location, upstream regulatory controls, relative isoform expression, orientation and associated state of the actin cytoscaffolds in which these myosins operate. Here, we discuss the separate yet related roles that characterise the actions of M2A, M2B and M2C in various cell types and show that these conventional myosins are responsible for functions as unconventional as any performed by unconventional myosins.

TLRR (lrrc67) interacts with PP1 and is associated with a cytoskeletal complex in the testis

BACKGROUND INFORMATION

Spermatozoa are formed via a complex series of cellular transformations, including acrosome and flagellum formation, nuclear condensation and elongation and removal of residual cytoplasm. Nuclear elongation is accompanied by the formation of a unique cytoskeletal structure, the manchette. We have previously identified a leucine-rich repeat protein that we have named TLRR (testis leucine-rich repeat), associated with the manchette that contains a PP1 (protein phosphatase-1)-binding site. Leucine-rich repeat proteins often mediate protein-protein interactions; therefore, we hypothesize that TLRR acts as a scaffold to link signalling molecules, including PP1, to the manchette near potential substrate proteins important for spermatogenesis.

RESULTS

TLRR and PP1 interact with one another as demonstrated by co-immunoprecipitation and the yeast two-hybrid assay. TLRR binds more strongly to PP1 gamma 2 than it does to PP1 alpha. Anti-phosphoserine antibodies immunoprecipitate TLRR from testis lysate, indicating that TLRR is a phosphoprotein. TLRR is part of a complex in testis that includes cytoskeletal proteins and constituents of the ubiquitin-proteasome pathway. The TLRR complex purified from 3T3 cells contains similar proteins, co-localizes with microtubules and is enriched at the microtubule-organizing centre. TLRR is also detected near the centrosome of elongated, but not mid-stage, spermatids.

CONCLUSION

We demonstrate here that TLRR interacts with PP1, particularly the testis-specific isoform, PP1 gamma 2. Immunoaffinity purification confirms that TLRR is associated with the spermatid cytoskeleton. In addition, proteins involved in protein stability are part of the TLRR complex. These results support our hypothesis that TLRR links signalling molecules to the spermatid cytoskeleton in order to regulate important substrates involved in spermatid transformation. The translocation of TLRR from the manchette to the centrosome region suggests a possible role for this protein in tail formation. Our finding that TLRR is associated with microtubules in cultured cells suggests that TLRR may play a common role in modulating the cytoskeleton in other cell types besides male germ cells.

The positively charged region of the myosin IIC non-helical tailpiece promotes filament assembly

The motor protein, non-muscle myosin II (NMII), must undergo dynamic oligomerization into filaments to participate in cellular processes such as cell migration and cytokinesis. A small non-helical region at the tail of the long coiled-coil region (tailpiece) is a common feature of all dynamically assembling myosin II proteins. In this study, we investigated the role of the tailpiece in NMII-C self-assembly. We show that the tailpiece is natively unfolded, as seen by circular dichroism and NMR experiments, and is divided into two regions of opposite charge. The positively charged region (Tailpiece(1946-1967)) starts at residue 1946 and is extended by seven amino acids at its N terminus from the traditional coiled-coil ending proline (Tailpiece(1953-1967)). Pull-down and sedimentation assays showed that the positive Tailpiece(1946-1967) binds to assembly incompetent NMII-C fragments inducing filament assembly. The negative region, residues 1968-2000, is responsible for NMII paracrystal morphology as determined by chimeras in which the negative region was swapped between the NMII isoforms. Mixing the positive and negative peptides had no effect on the ability of the positive peptide to bind and induce filament assembly. This study provides molecular insight into the role of the structurally disordered tailpiece of NMII-C in shifting the oligomeric equilibrium of NMII-C toward filament assembly and determining its morphology.

Myosin II tailpiece determines its paracrystal structure, filament assembly properties, and cellular localization

Non muscle myosin II (NMII) is a major motor protein present in all cell types. The three known vertebrate NMII isoforms share high sequence homology but play different cellular roles. The main difference in sequence resides in the C-terminal non-helical tailpiece (tailpiece). In this study we demonstrate that the tailpiece is crucial for proper filament size, overcoming the intrinsic properties of the coiled-coil rod. Furthermore, we show that the tailpiece by itself determines the NMII filament structure in an isoform-specific manner, thus providing a possible mechanism by which each NMII isoform carries out its unique cellular functions. We further show that the tailpiece determines the cellular localization of NMII-A and NMII-B and is important for NMII-C role in focal adhesion complexes. We mapped NMII-C sites phosphorylated by protein kinase C and casein kinase II and showed that these phosphorylations affect its solubility properties and cellular localization. Thus phosphorylation fine-tunes the tailpiece effects on the coiled-coil rod, enabling dynamic regulation of NMII-C assembly. We thus show that the small tailpiece of NMII is a distinct domain playing a role in isoform-specific filament assembly and cellular functions.

Identification and characterization of Myosin from rat testicular peritubular myoid cells

In the mammalian testis, peritubular myoid cells (PMCs) surround seminiferous tubules. These cells are contractile, express the cytoskeletal markers of true smooth muscle-alpha-isoactin and F-actin-and participate in the contraction of seminiferous tubules during the transport of spermatozoa and testicular fluid to the rete testis. Myosin from PMCs (PMC-myosin) was isolated from adult rat testis and purified by cycles of assembly-disassembly and sucrose gradient centrifugation. PMC-myosin was recognized by a monoclonal anti-smooth muscle myosin antibody, and the peptide sequence shared partial homology with rat smooth muscle myosin-II, MYH11 (also known as SMM-II). Most PMC-myosin (95%) was soluble in the PMC cytosol, and purified PMC-myosin did not assemble into filaments in the in vitro salt dialysis assay at 4 degrees C, but did at 20 degrees C. PMC-myosin filaments are stable to ionic strength to the same degree as gizzard MYH11 filaments, but PMC-myosin filaments were more unstable in the presence of ATP. When PMCs were induced to contract by endothelin 1, a fraction of the PMC-myosin was found to be involved in the contraction. From these results we infer that PMCs express an isoform of smooth muscle myosin-II that is characterized by solubility at physiological ionic strength, a requirement for high temperature to assemble into filaments in vitro, and instability at low ATP concentrations. PMC-myosin is part of the PMC contraction apparatus when PMCs are stimulated with endothelin 1.

PGE2-mediated podosome loss in dendritic cells is dependent on actomyosin contraction downstream of the RhoA-Rho-kinase axis

Podosomes are dynamic adhesion structures found in dendritic cells (DCs) and other cells of the myeloid lineage. We previously showed that prostaglandin E2 (PGE2), an important proinflammatory mediator produced during DC maturation, induces podosome disassembly within minutes after stimulation. Here, we demonstrate that this response is mediated by cAMP elevation, occurs downstream of Rho kinase and is dependent on myosin II. Whereas PGE2 stimulation leads to activation of the small GTPase RhoA, decreased levels of Rac1-GTP and Cdc42-GTP are observed. These results show that PGE2 stimulation leads to activation of the RhoA-Rho-kinase axis to promote actomyosin-based contraction and subsequent podosome dissolution. Because podosome disassembly is accompanied by de novo formation of focal adhesions, we propose that the disassembly/formation of these two different adhesion structures is oppositely regulated by actomyosin contractility and relative activities of RhoA, Rac1 and Cdc42.

cDNA cloning and characterization of temperature-acclimation-associated light meromyosins from grass carp fast skeletal muscle

The three types of cDNA clones, previously defined as the 10 degrees C, intermediate and 30 degrees C-types [Tao, Y., Kobayashi, M., Liang, C.S., Okamoto, T., Watabe, S., 2004. Temperature-dependent expression patterns of grass carp fast skeletal myosin heavy chain genes. Comp. Biochem. Physiol. B 139, 649-656], were determined for their 5'-regions which encoded at least the C-terminal half of myosin rod, light meromyosin (LMM), in fast skeletal muscles of grass carp Ctenopharyngodon idella. The deduced amino acid sequence identity was 91.1% between the 10 degrees C and 30 degrees C-types and 91.4% between the 10 degrees C and intermediate-types, whereas a high sequence identity of 97.8% was found between the intermediate and 30 degrees C-types. These three grass carp LMMs all had a characteristic seven-residue (heptad) repeat (a, b, c, d, e, f, g)(n), where positions a and d were normally occupied by hydrophobic residues, and positions b, c and f by charged residues. However, the ratios of hydrophobic residues to the total were higher for the intermediate- and 30 degrees C- than 10 degrees C-type LMM, suggesting that the former both types may form more stable coiled-coils of alpha-helices than the latter type. These differences in the primary structures of LMM isoforms might be partially implicated in differences in the thermostabilities and gel-forming profiles of myosins from grass carp in different seasons reported previously [Tao, Y., Kobayashi, M., Fukushima, H., Watabe, S., 2005. Changes in enzymatic and structural properties of grass carp fast skeletal myosin induced by the laboratory-conditioned thermal acclimation and seasonal acclimatization. Fish. Sci. 71, 195-204; Tao, Y., Kobayashi, M., Fukushima, H., Watabe, S., 2007. Changes in rheological properties of grass carp fast skeletal myosin induced by seasonal acclimatization. Fish. Sci. 73, 189-196].

Purification and partial characterization of myosin II from rat testis

The intent, in this work, was to isolate rat testis myosin II. Testis 40,000 x g x 40' supernatant was frozen at -20 degrees C for 48 h and, after it was thawed and centrifuged. The precipitate, after washed twice, was enriched in three polypeptides bands: p205, p43 and one that migrated together with the front of the gel. These polypeptides were solubilized in pH 10.8 at 27 degrees C and separated in Sephacryl S-400 column. Three low weight polypeptides co-eluted together with p205. The p205 was marked with anti-myosin II, possess actin-stimulated Mg-ATPase activity and co-sedimented with F-actin in the absence, but not in the presence, of ATP. In the present study, we have been developing a method for purification of myosin II from rat testis.

Replacement of nonmuscle myosin II-B with II-A rescues brain but not cardiac defects in mice

The purpose of these studies was to learn whether one isoform of nonmuscle myosin II, specifically nonmuscle myosin II-A, could functionally replace a second one, nonmuscle myosin II-B, in mice. To accomplish this, we used homologous recombination to ablate nonmuscle myosin heavy chain (NMHC) II-B by inserting cDNA encoding green fluorescent protein (GFP)-NMHC II-A into the first coding exon of the Myh10 gene, thereby placing GFP-NMHC II-A under control of the endogenous II-B promoter. Similar to B(-)/B(-) mice, most B(a*)/B(a*) mice died late in embryonic development with structural cardiac defects and impaired cytokinesis of the cardiac myocytes. However, unlike B(-)/B(-) mice, 15 B(a*)/B(a*) mice of 172 F2 generation mice survived embryonic lethality but developed a dilated cardiomyopathy as adults. Surprisingly none of the B(a*)/B(a*) mice showed evidence for hydrocephalus that is always found in B(-)/B(-) mice. Rescue of this defect was due to proper localization and function of GFP-NMHC II-A in place of NMHC II-B in a cell-cell adhesion complex in the cells lining the spinal canal. Restoration of the integrity and adhesion of these cells prevents protrusion of the underlying cells into the spinal canal where they block circulation of the cerebral spinal fluid. However, abnormal migration of facial and pontine neurons found in NMHC II-B mutant and ablated mice persisted in B(a*)/B(a*) mice. Thus, although NMHC II-A can substitute for NMHC II-B to maintain integrity of the spinal canal, NMHC II-B plays an isoform-specific role during cytokinesis in cardiac myocytes and in migration of the facial and pontine neurons.

Myosin II isoforms in smooth muscle: heterogeneity and function

Both smooth muscle (SM) and nonmuscle class II myosin molecules are expressed in SM tissues comprising hollow organ systems. Individual SM cells may express one or more of multiple myosin II isoforms that differ in myosin heavy chain (MHC) and myosin light chain (MLC) subunits. Although much has been learned, the expression profiles, organization within contractile filaments, localization within cells, and precise roles in various contractile functions of these different myosin molecules are still not well understood. However, data supporting unique physiological roles for certain isoforms continues to build. Isoform differences located in the S1 head region of the MHC can alter actin binding and rates of ATP hydrolysis. Differences located in the MHC tail can alter the formation, stability, and size of the myosin thick filament. In these distinct ways, both head and tail isoform differences can alter force generation and muscle shortening velocities. The MLCs that are associated with the lever arm of the S1 head can affect the flexibility and range of motion of this domain and possibly the motion of the S2 and motor domains. Phosphorylation of MLC(20) has been associated with conformational changes in the S1 and/or S2 fragments regulating enzymatic activity of the entire myosin molecule. A challenge for the future will be delineation of the physiological significance of the heterogeneous expression of these isoforms in developmental, tissue-specific, and species-specific patterns and or the intra- and intercellular heterogeneity of myosin isoform expression in SM cells of a given organ.

Non-muscle myosin-II-B filament regulation of paracellular resistance in cervical epithelial cells is associated with modulation of the cortical acto-myosin

OBJECTIVE

To understand myosin regulation of epithelial permeability.

METHODS

This was an experimental study, using human cervical epithelial cells CaSki. End points were paracellular permeability (determined in terms of transepithelial electrical resistance); non-muscle myosin-II-B (NMM-II-B) cellular localization; NMM-II-B phosphorylation status; NMM-II-B-actin interaction (determined in vitro by the immunoprecipitation-immunoreactivity method); and NMM-II-B filamentation (determined in vitro using purified NMM-II-B filaments in terms of filaments disassembly/assembly ratios.

RESULTS

Treatment of cells with the Rho-associated kinase (ROCK) inhibitor Y-27632 or with the phosphatase inhibitor okadaic acid decreased the resistance of the lateral intercellular space (R(LIS)), and increased phosphorylation of NMM-II-B on threonine and serine residues. Y-27632 induced disorganization of the cortical acto-myosin and decreased co-immunoprecipitation of actin with NMM-II-B. Homodimerization assays using NMM-II-B filaments from cells treated with Y-27632 or okadaic acid revealed decreased filamentation compared to control cells. However, okadaic acid blocked Y-27632 decreased filamentation. Treatment with DRB, a casein kinase-II (CK2) inhibitor, induced opposing effects to those of Y-27632 and okadaic acid. Treatment with 5,6-dichloro-1-beta-(D)-ribofuranosylbenzimidazole (DRB) did not involve modulation of actin depolymerization, suggesting that NMM-II-B regulation of the R(LIS) was independent of actin polymerization status. Exposure of NMM-II-B filaments to CK2 increased filamentation, regardless of prior treatments in vivo with Y-27632, okadaic acid, or DRB.

CONCLUSIONS

The results suggest that NMM-II-B filaments are in steady-state equilibrium of phosphorylation-dephosphorylation mediated by CK2 and by ROCK-regulated myosin heavy chain phosphatase, respectively. Increased phosphorylation would tend to inhibit assembly of NMM-II-B filaments and lead to decreased actin-myosin interaction, which would tend to decrease the R(LIS) and increase the paracellular permeability.

A Specific Isoform of Nonmuscle Myosin II-C Is Required for Cytokinesis in a Tumor Cell Line

Nonmuscle myosin IIs play an essential role during cytokinesis. Here, we explore the function of an alternatively spliced isoform of nonmuscle myosin heavy chain (NMHC) II-C, called NMHC II-C1, in the A549 human lung tumor cell line during cytokinesis. NMHC II-C1 contains an insert of 8 amino acids in the head region of NMHC II-C. First, we show that there is a marked increase in both the mRNA encoding NMHC II-C1 and protein in tumor cell lines compared with nontumor cell lines derived from the same tissue. Quantification of the amount of myosin II isoforms in the A549 cells shows that the amounts of NMHC II-A and II-C1 protein are about equal and substantially greater than NMHC II-B. Using specific siRNAs to decrease NMHC II-C1 in cultured A549 cells resulted in a 5.5-fold decrease in the number of cells at 120 h, whereas decreasing NMHC II-A with siRNA does not affect cell proliferation. This decreased proliferation can be rescued by reintroducing NMHC II-C1 but not NMHC II-A or II-B into A549 cells, although noninserted NMHC II-C does rescue to a limited extent. Time lapse video microscopy revealed that loss of NMHC II-C1 leads to a delay in cytokinesis and prolongs it from 2 to 8-10 h. These findings are consistent with the localization of NMHC II-C1 to the intercellular bridge that attaches the two dividing cells during the late phases of cytokinesis. The results suggest a specific function for NMHC II-C1 in cytokinesis in the A549 tumor cell line.

Vertebrate nonmuscle myosin II isoforms rescue small interfering RNA-induced defects in COS-7 cell cytokinesis

RNA interference (RNAi) treatment of monkey COS-7 cells, a cell line that lacks nonmuscle myosin heavy chain II-A (NMHC II-A) but contains NMHC II-B and II-C, was used to investigate the participation of NMHC isoforms in cytokinesis. We specifically suppressed the expression of NMHC II-B or II-C using 21 nucleotide small interfering RNA (siRNA) duplexes. Down-regulation of NMHC II-B protein expression to 10.2 +/- 0.7% inhibited COS-7 cell proliferation by 50% in the RNAi-treated cells compared with control cells. Moreover, whereas 8.7 +/- 1.0% of control cells were multinucleated, 62.4 +/- 8.8% of the NMHC II-B RNAi-treated cells were multinucleated 72 h after transfection. The RNAi-treated cells had increased surface areas and, unlike control cells, lacked actin stress fibers. Treatment of the COS-7 cells with NMHC II-C siRNA decreased NMHC II-C expression to 5.2 +/- 0.1% compared with the endogenous content of II-C; however, down-regulation of NMHC II-C did not cause increased multinucleation. Immunoblot analysis using a pan-myosin antibody showed that the content of NMHC II-C was less than one-twentieth the amount of NMHC II-B, thereby explaining the lack of response to II-C siRNA. Introducing green fluorescent protein (GFP)-tagged NMHC II isoforms into II-B siRNA-treated cells resulted in reduction of multinucleation from 62.4 +/- 8.8% to 17.8 +/- 2.2% using GFP-NMHC II-B, to 29.8 +/- 7.4% using GFP-NMHC II-A, and to 34.1 +/- 8.6% using NMHC II-C-GFP. These studies have shown that expression of endogenous NMHC II-C in COS-7 cells is insufficient for normal cytokinesis and that exogenous NMHC II-A and NMHC II-C can, at least partially, rescue the defect in cytokinesis due to the loss of NMHC II-B.

Basic mechanism of three-dimensional collagen fibre transport by fibroblasts

Collagen remodelling by fibroblasts has a crucial role in organizing tissue structures that are essential to motility during wound repair, development and regulation of cell growth. However, the mechanism of collagen fibre movement in three-dimensional (3D) matrices is not understood. Here, we show that fibroblast lamellipodia extend along held collagen fibres, bind, and retract them in a 'hand-over-hand' cycle, involving alpha2beta1 integrin. Wild-type fibroblasts move collagen fibres three to four times farther per cycle than fibroblasts lacking myosin II-B (myosin II-B(-/-)). Similarly, myosin II-B(-/-) fibroblasts contract 3D collagen gels threefold less than controls. On two-dimensional (2D) substrates, however, rates of collagen bead and cell movement are not affected by loss of myosin II-B. Green fluorescent protein (GFP)-tagged myosin II-B, but not II-A, restores normal function in knockout cells and localizes to cell processes, whereas myosin II-A is more centrally located. Additionally, GFP-myosin II-B moves out to the periphery and back during hand-over-hand fibre movement, whereas on 2D collagen, myosin II-B is more centrally distributed. Thus, we suggest that cyclic myosin II-B assembly and contraction in lamellipodia power 3D fibre movements.

Identification and characterization of nonmuscle myosin II-C, a new member of the myosin II family

A previously unrecognized nonmuscle myosin II heavy chain (NMHC II), which constitutes a distinct branch of the nonmuscle/smooth muscle myosin II family, has recently been revealed in genome data bases. We characterized the biochemical properties and expression patterns of this myosin. Using nucleotide probes and affinity-purified antibodies, we found that the distribution of NMHC II-C mRNA and protein (MYH14) is widespread in human and mouse organs but is quantitatively and qualitatively distinct from NMHC II-A and II-B. In contrast to NMHC II-A and II-B, the mRNA level in human fetal tissues is substantially lower than in adult tissues. Immunofluorescence microscopy showed distinct patterns of expression for all three NMHC isoforms. NMHC II-C contains an alternatively spliced exon of 24 nucleotides in loop I at a location analogous to where a spliced exon appears in NMHC II-B and in the smooth muscle myosin heavy chain. However, unlike neuron-specific expression of the NMHC II-B insert, the NMHC II-C inserted isoform has widespread tissue distribution. Baculovirus expression of noninserted and inserted NMHC II-C heavy meromyosin (HMM II-C/HMM II-C1) resulted in significant quantities of expressed protein (mg of protein) for HMM II-C1 but not for HMM II-C. Functional characterization of HMM II-C1 by actin-activated MgATPase activity demonstrated a V(max) of 0.55 + 0.18 s(-1), which was half-maximally activated at an actin concentration of 16.5 + 7.2 microm. HMM II-C1 translocated actin filaments at a rate of 0.05 + 0.011 microm/s in the absence of tropomyosin and at 0.072 + 0.019 microm/s in the presence of tropomyosin in an in vitro motility assay.

Myofibrillogenesis in the first cardiomyocytes formed from isolated quail precardiac mesoderm

De novo assembly of myofibrils was investigated in explants of precardiac mesoderm from quail embryos to address a controversy about different models of myofibrillogenesis. The sequential expression of sarcomeric components was visualized in double- and triple-stained explants before, during, and just after the first cardiomyocytes began to beat. In explants from stage 6 embryos, cultured for 10 h, ectoderm, endoderm, and the precardiac mesoderm displayed arrays of stress fibers with alternating bands of the nonmuscle isoforms of alpha-actinin and myosin IIB. With increasing time in culture, mesoderm cells contained fibrils composed of actin, nonmuscle myosin IIB, and sarcomeric alpha-actinin. Several hours later, before beating occurred, both nonmuscle and muscle myosin II localized in some of the fibrils in the cells. Concentrations of muscle myosin began as thin bundles, dispersed in the cytoplasm, often overlapping one another, and progressed to small, aligned A-band-sized aggregates. The amount of nonmuscle myosin decreased dramatically when Z-bands formed, the muscle myosin became organized into A-bands, and the cells began beating. The sequential changes in protein composition of the fibrils in the developing muscle cells supports the model of myofibrillogenesis in which assembly begins with premyofibrils and progresses through nascent myofibrils to mature myofibrils.

Myosin II in retinal pigmented epithelial cells: evidence for an association with membranous vesicles

The goal of this study was to further characterize and identify possible functions for a cytoplasmic myosin II protein which we have isolated from retinal pigmented epithelial (RPE) cells. The nucleotide and deduced amino acid sequences are highly identical to non-muscle myosin heavy chain II-A (NMMHC II-A). However, this RPE myosin displays characteristics that are atypical of other myosins, including an affinity for carbohydrate and a C-terminal sequence extension, suggesting it may have a specialized function. In this study, reverse transcriptase-PCR using isoform-specific primers demonstrated that the RPE myosin and conventional NMMHC II-A have overlapping but distinguishable tissue expression profiles. To gain clues to function, subcellular distribution was determined in motile RPE cells using indirect immunofluorescence. In addition to subtle differences in localization that appeared to further distinguish this molecule from NMMHC II-A, these studies revealed a colocalization with phagocytosed intracellular vesicles. In vitro experiments suggest that the association in situ was not simply coincidental, because isolated vesicles interacted with the protein in cosedimentation assays. Taken together, our observations suggest the RPE myosin exhibits characteristics different from conventional myosin II-A and may function in intracellular vesicle transport.

Induction of nonmuscle myosin heavy chain II-C by butyrate in RAW 264.7 mouse macrophages

RAW 264.7 macrophages express nonmuscle myosin heavy chain II-A as the only significant nonmuscle myosin heavy chain isoform, with expression of nonmuscle myosin heavy chain II-B and II-C low or absent. Treatment of the cells with sodium butyrate, an inhibitor of histone deacetylase, led to the dose-dependent induction of nonmuscle myosin heavy chain II-C. Trichostatin A, another inhibitor of histone deacetylase, also induced nonmuscle myosin heavy chain II-C. Induction of nonmuscle myosin heavy chain II-C in response to these histone deacetylase inhibitors was attenuated by mithramycin, an inhibitor of Sp1 binding to GC-rich DNA sequences. Bacterial lipopolysaccharide alone had no effect on basal nonmuscle myosin heavy chain II-C expression, but attenuated butyrate-mediated induction of nonmuscle myosin heavy chain II-C. The effects of lipopolysaccharide were mimicked by the nitric oxide donors sodium nitroprusside and spermine NONOate, suggesting a role for nitric oxide in the lipopolysaccharide-mediated down-regulation of nonmuscle myosin heavy chain II-C induction. This was supported by experiments with the inducible nitric-oxide synthase inhibitor 1400W, which partially blocked the lipopolysaccharide-mediated attenuation of nonmuscle myosin heavy chain induction. 8-Bromo-cGMP had no effect on nonmuscle myosin heavy chain induction, consistent with a cGMP-independent mechanism for nitric oxide-mediated inhibition of nonmuscle myosin heavy chain II-C induction.

Temperature plasticity of contractile proteins in fish muscle

Three myosin heavy chain isoforms with different actin-activated Mg2+-ATPase activities were found in the fast skeletal muscle from carp (Cyprinus carpio) acclimated to 10 and 30°C. The composition of three types of myosin heavy chain was dependent on acclimation temperature,demonstrating the presence of temperature-specific myosin isoforms in carp. Subsequently, the temperature-dependence of the sliding velocity of fluorescent F-actin in myosins isolated from 10°C- and 30°C-acclimated carp was measured. At 8°C, the filament velocity was three times higher for myosin from 10°C- than from 30°C-acclimated fish. Activation energies (Ea) for the sliding velocity of F-actin were 63 and 111 kJ mol-1 for myosins from 10°C- and 30°C-acclimated fish, respectively. Activation energy for actin-activated Mg2+-ATPase activity was 0.46 kJ mol-1 in myosin from 10°C-acclimated fish and 0.54 kJ mol-1 in myosin from 30°C-acclimated fish. The inactivation rate constant(KD) of Ca2+-ATPase was 7.5×10-4s-1 at 30°C for myosin from 10°C-acclimated fish, which was approximately twice that for myosin from 30°C-acclimated fish. It is suggested that these differences in thermostability reflect a more flexible structure of the myosin molecule in cold-acclimated carp, which results in a reduced activation enthalpy for contraction and, hence, a higher sliding velocity at low temperatures. Structural analysis of cDNAs encoding the carp myosin heavy chain demonstrated striking differences in two surface loops of myosin subfragment-1 (S1), loops 1 and 2, between the 10°C and 30°C types, which were predominantly expressed in carp acclimated to 10°C and 30°C, respectively. Chimeric myosins composed of Dictyostelium discoideum myosin backbones with loop sequences of carp S1 heavy chain isoforms demonstrated that the diversity of the loop 2 sequence of carp S1 affected the Vmax of actin-activated Mg2+-ATPase activity.

The tip of the coiled-coil rod determines the filament formation of smooth muscle and nonmuscle myosin

Myosin II self-assembles to form thick filaments that are attributed to its long coiled-coil tail domain. The present study has determined a region critical for filament formation of vertebrate smooth muscle and nonmuscle myosin II. A monoclonal antibody recognizing the 28 residues from the C-terminal end of the coiled-coil domain of smooth muscle myosin II completely inhibited filament formation, whereas other antibodies recognizing other parts of the coiled-coil did not. To determine the importance of this region in the filament assembly in vivo, green fluorescent protein (GFP)-tagged smooth muscle myosin was expressed in COS-7 cells, and the filamentous localization of the GFP signal was monitored by fluorescence microscopy. Wild type GFP-tagged smooth muscle myosin colocalized with F-actin during interphase and was also recruited into the contractile ring during cytokinesis. Myosin with the nonhelical tail piece deleted showed similar behavior, whereas deletion of the 28 residues at the C-terminal end of the coiled-coil domain abolished this localization. Deletion of the corresponding region of GFP-tagged nonmuscle myosin IIA also abolished this localization. We conclude that the C-terminal end of the coiled-coil domain, but not the nonhelical tail piece, of myosin II is critical for myosin filament formation both in vitro and in vivo.

TFEC can function as a transcriptional activator of the nonmuscle myosin II heavy chain-A gene in transfected cells

Transcription of the human nonmuscle myosin II heavy chain-A (NMHC-A) gene is regulated via multiple elements located in intron 1, including element F which contains an E-box. In this study we have identified and characterized the factors that are capable of binding to element F. Yeast one-hybrid screening using element F allowed isolation of cDNAs encoding transcriptional factors TFEC, TFE3, and USF2, each of which contains basic helix-loop-helix and leucine zipper motifs. Furthermore, cDNA cloning by polymerase chain reaction yielded cDNAs for two TFEC isoforms, designated TFEC-l and TFEC-s, which are generated by alternative pre-mRNA splicing. In addition to these four factors, USF1, which is known to share the same DNA binding elements with USF2, was isolated for comparison. Electrophoretic mobility shift assays and cotransfection studies of the expression constructs with reporter gene constructs revealed that the above five factors have different binding activities for element F with different transactivation potencies. USF1 and USF2 demonstrate the highest binding activity to element F, yet show the lowest element F-dependent transactivation. TFE3 has a high transactivation potency but the lowest binding activity. TFEC-l demonstrates a high binding activity with the highest transactivation potency, whereas TFEC-s has the same binding activity as TFEC-l with intermediate transactivation. We also demonstrate that an N-terminal activation domain exists only in TFEC-l, whereas a C-terminal activation domain is common to both the l and s isoforms. This study provides the first evidence of TFEC being an activator of transcription, with two separate activation domains.

Characterization of sea urchin unconventional myosins and analysis of their patterns of expression during early embryogenesis

Early sea urchin development requires a dynamic reorganization of both the actin cytoskeleton and cytoskeletal interactions with cellular membranes. These events may involve the activities of multiple members of the superfamily of myosin motor proteins. Using RT-PCR with degenerate myosin primers, we identified 11 myosin mRNAs expressed in unfertilized eggs and coelomocytes of the sea urchin Strongylocentrotus purpuratus. Seven of these sea urchin myosins belonged to myosin classes Igamma, II, V, VI, VII, IX, and amoeboid-type I, and the remaining four may be from novel classes. Sea urchin myosins-V, -VI, -VII, and amoeboid-type-I were either completely or partially cloned and their molecular structures characterized. Sea urchin myosins-V, -VI, -VII, and amoeboid-type-I shared a high degree of sequence identity with their respective family members from vertebrates and they retained their class-specific structure and domain organization. Analysis of expression of myosin-V, -VI, -VII, and amoeboid-type-I mRNAs during development revealed that each myosin mRNA displayed a distinct temporal pattern of expression, suggesting that myosins might be involved in specific events of early embryogenesis. Interestingly, the onset of gastrulation appeared to be a pivotal point in modulation of myosin mRNA expression. The presence of multiple myosin mRNAs in eggs and embryos provides insight into the potential involvement of multiple specific motor proteins in the actin-dependent events of embryo development.

Cingulin contains globular and coiled-coil domains and interacts with ZO-1, ZO-2, ZO-3, and myosin

We characterized the sequence and protein interactions of cingulin, an M(r) 140-160-kD phosphoprotein localized on the cytoplasmic surface of epithelial tight junctions (TJ). The derived amino acid sequence of a full-length Xenopus laevis cingulin cDNA shows globular head (residues 1-439) and tail (1,326-1,368) domains and a central alpha-helical rod domain (440-1,325). Sequence analysis, electron microscopy, and pull-down assays indicate that the cingulin rod is responsible for the formation of coiled-coil parallel dimers, which can further aggregate through intermolecular interactions. Pull-down assays from epithelial, insect cell, and reticulocyte lysates show that an NH(2)-terminal fragment of cingulin (1-378) interacts in vitro with ZO-1 (K(d) approximately 5 nM), ZO-2, ZO-3, myosin, and AF-6, but not with symplekin, and a COOH-terminal fragment (377-1,368) interacts with myosin and ZO-3. ZO-1 and ZO-2 immunoprecipitates contain cingulin, suggesting in vivo interactions. Full-length cingulin, but not NH(2)-terminal and COOH-terminal fragments, colocalizes with endogenous cingulin in transfected MDCK cells, indicating that sequences within both head and rod domains are required for TJ localization. We propose that cingulin is a functionally important component of TJ, linking the submembrane plaque domain of TJ to the actomyosin cytoskeleton.

Developmentally regulated expression of a nonmuscle myosin heavy chain IIB inserted isoform in rat brain

The alternatively spliced isoform of the nonmuscle myosin II heavy chain B (MHC-B) with an insert of 21 amino acids at the 50- to 20-kDa junction of the globular region of myosin has been demonstrated to be expressed specifically in the central nervous system (CNS) in chicken. To explore the role of this B2 inserted isoform (MHC-B(B2)), immunoblot and immunoprecipitation analyses were performed using specific antibodies and extracts from rat tissues. MHC-B(B2) is present throughout the CNS, but is less abundant in the cerebrum and not expressed in the olfactory lobe at all. In the developing rat brain, MHC-B(B2) is expressed from postnatal day 10 (P10) in the cerebellum and increases markedly from P14. The appearance of MHC-B(B2) in the cerebrum (P28) is later than in the cerebellum. Additionally, we show that myosin IIB(B2) is homodimeric in its heavy chain subunit composition. These results suggest that myosin IIB(B2) might participate in cell motility in the neuronal cells of the mature CNS.

Characterization of the carp myosin heavy chain multigene family

We isolated partial coding sequences for 29 carp myosin heavy chain genes (MyoHCs) and determined the nucleotide sequences around the region encoding the loop 2 of the myosin molecule. The predicted amino acid sequences from the isolated genes all showed very high similarity to those of skeletal and cardiac muscles from higher vertebrates, but not to those of smooth and non-muscle counterparts. Among all clones isolated, carp MyoHC10, MyoHCI-1-3 and MyoHC30 showed exon-nucleotide sequences identical to those of cDNAs encoding the loop 2 region of the 10 degrees C-, intermediate- and 30 degrees C-type fast skeletal isoforms [Hirayama and Watabe, Euro. J. Biochem. 246 (1997) 380-387]. The loop 2 of 28 types of carp MyoHCs was encoded by two exons separated by an intron corresponding to that of the 16th in higher vertebrate MyoHCs, whilst this intron was not found in carp MyoHC30. Although carp MyoHC30 had a gene organization different from those of higher vertebrates and other carp MyoHCs, its predicted amino acid sequence for loop 2 showed the highest homology to those of higher vertebrates among carp MyoHCs. In the 28 carp MyoHCs containing the intron, a combination of different nucleotide sequences for the two resulted in 14 distinct series for the combined coding sequence. These different nucleotide sequences encoded nine distinct amino acid sequences. Phylogenetic analysis for the present loop 2 and light meromyosin previously reported for carp MyoHCs [Imai et al., J. Exp. Biol. 200 (1997) 27-34] revealed that carp MyoHCs have recently diverged and are more closely related to each other than to MyoHCs from other species.

Amino-acid sequence of squid myosin heavy chain

This work describes the determination of the cDNA sequence encoding the myosin heavy chain (MHC) of the squid, Loligo pealei. To date, the amino-acid sequence of the MHC of calcium-regulated myosins is known only for two closely related species of scallops. We have determined the sequence of the entire coding region of the muscle MHC of squid, a cephalopod, and compared it with the MHC of scallops, which are pelecypods, and to other regulated and non-regulated myosins. Residues present in the MHC of only regulated myosins have been identified. The 6504 base pair (bp) sequence contains an open reading frame of 5805 nucleotides, which encodes 1935 amino acids. The sequence includes 697 bps of 3' untranslated sequence and 2 bps of 5' untranslated sequence. The deduced amino-acid sequence shows the squid MHC to be 72-73% identical and 86-87% similar to the calcium-regulated scallop MHCs cloned previously. In contrast, the squid MHC sequence is only 54-55% identical and 74% similar to skeletal MHCs of non-regulated myosins such as human fast skeletal embryonic and human perinatal skeletal muscle, and 39-40% identical and 60-62% similar to smooth muscle MHC of rabbit uterus muscle and chicken gizzard muscle, respectively. We have also detected two isoforms of the MHC in squid that appear to be spliced variants of a single myosin gene. These isoforms differ in the sequence encoding the surface loop at the nucleotide binding site. Taken together, our data may help to identify more precisely the residues that are crucial in regulated myosins.

Transcriptional regulation of the human nonmuscle myosin II heavy chain-A gene. Identification of three clustered cis-elements in intron-1 which modulate transcription in a cell type- and differentiation state-dependent manner

In an attempt to identify cis-acting elements for transcriptional regulation of the human nonmuscle myosin II heavy chain (MHC)-A gene, the region extending 20 kilobases (kb) upstream and 40 kb downstream from the transcription start sites, which includes the entire 37-kb intron 1, was examined. Using transient transfection analysis of luciferase reporter constructs, a 100-base pair (bp) region (N2d) in intron 1, located 23 kb downstream from the transcriptional start sites, has been found to activate transcription in a cell type- and differentiation state-dependent manner. Maximum activity (approximately 20-fold) is seen in NIH 3T3 fibroblasts and intermediate activity (7-fold) in proliferating and undifferentiated C2C12 myoblasts. In contrast, this region is almost inactive in terminally differentiated C2C12 myotubes, in which endogenous nonmuscle MHC-A expression is down-regulated. Gel mobility shift assays and methylation interference analyses were performed using NIH 3T3 nuclear extracts to determine the protein-binding elements for transcription factors. Three binding elements have been identified within the N2d region. Antibody-supershift experiments, as well as competition experiments using consensus binding sequences for specific transcription factors, revealed that the most 5'-element, C (GGGAGGGGCC) is recognized specifically and exclusively by Sp1 and Sp3 transcriptional factors. Element C is immediately followed by a novel element, A (GTGACCC). A third element, F (GTGTCAGGTG), which contains an E-box, is located 50 bp 3' to element A. Element F can be recognized partially by upstream stimulatory factors, USF1 and/or USF2. Transfection studies with luciferase reporter constructs which include mutations in all three elements in various combinations demonstrate that the A and C binding factors cooperatively activate transcriptional activity in NIH 3T3 cells. The F binding factor shows an additive effect on transcription.

Two nonmuscle myosin II heavy chain isoforms expressed in rabbit brains: filament forming properties, the effects of phosphorylation by protein kinase C and casein kinase II, and location of the phosphorylation sites

During the course of the expression of a 47-kDa COOH-terminal fragment of brain-type nonmuscle myosin heavy chain (MIIBF47), we found two closely related forms of MIIB, designated MIIB alpha and MIIB beta, in rabbit brains. The B alpha form corresponded to SMemb, described by Kuro-o et al. [(1991) J. Biol. Chem. 266, 3768] and was the more abundant form in rabbit brain, while the B beta form was novel. MIIB beta F47 differed from MIIB alpha F47 at six positions, three of which were within the carboxyl-terminal nonhelical domain; in MIIB beta F47, Ser, Pro, and Lys replaced Pro, Ser, and Glu, respectively. MIIB alpha F47 and MIIB beta F47 differed in filament assembly properties in the presence of various concentrations of salt, and a chimera containing the helical domain of MIIB beta F47 and the nonhelical domain of MIIB alpha F47 behaved very much like MIIB beta F47. Protein kinase C (PK C) incorporated 1 and 2 mol of phosphate/mol peptide of MIIB alpha F47 and MIIB beta F47, respectively, and caused similar levels of inhibition of assembly for both isoforms. Casein kinase II (CK II) incorporated 4 and 2 mol of phosphate/mol of MIIB alpha F47 and MIIB beta F47 peptides, respectively, and this caused strong inhibition of assembly for MIIB alpha F47 but only slight inhibition for MIIB beta F47. PK C sites in MIIB alpha F47 were localized within a region containing a cluster of Ser residues near the predicted junction of the helical and nonhelical domains: P-I-S(PO4)-F-S(PO4)-S(PO4)-S(PO4)-R-S(PO4)-. Out of the five potential PK C sites, only one site seemed to be phosphorylated per peptide. The PK C sites in MIIB beta F47 were localized as S(PO4)-I-S-F-S-S-(PO4)-R-S(PO4)-, with total incorporation of about 2 mol/mol of peptide. In addition, PK C phosphorylated a Ser within the predicted helical domain, E-V-S(PO4)-T-L, in both MIIB alpha F47 and MIIB beta F47. For CK II, five sites were identified within the COOH end of MIIB alpha F47: S(PO4)-L-E-L-S(PO4)-D-D-D-T(PO4)-E-S-K-T-S(PO4)-D-V-N-E-T-Q-P-P-Q-S(PO4) -E. The same sites were phosphorylated in MIIB beta F47 except for the first Ser, which was replaced by Pro in MIIB beta F47. An average of about two of the four potential sites were phosphorylated in MIIB beta F47, while in MIIB alpha F47 all five sites could be fully phosphorylated by CK II. Our results demonstrate that (1) the helical domains dictate the intrinsic salt dependence of assembly for nonmuscle myosin, (2) the isoforms are phosphorylatable by different kinases in an isoform specific manner mostly within the COOH-terminal nonhelical domain, and (3) the effects of the phosphorylation on assembly are isoform specific.

Primary peptide sequences from squid muscle and optic lobe myosin IIs: a strategy to identify an organelle myosin

The squid giant axon provides an excellent model system for the study of actin-based organelle transport likely to be mediated by myosins, but the identification of these motors has proven to be difficult. Here the authors purified and obtained primary peptide sequence of squid muscle myosin as a first step in a strategy designed to identify myosins in the squid nervous system. Limited digestion yielded fourteen peptides derived from the muscle myosin which possess high amino acid sequence identities to myosin II from scallop (60-95%) and chick pectoralis muscle (31-83%). Antibodies generated to this purified muscle myosin were used to isolate a potential myosin from squid optic lobe which yielded 11 peptide fragments. Sequences from six of these fragments identified this protein as a myosin II. The other five sequences matched myosin II (50-60%, identities), and some also matched unconventional myosins (33-50%). A single band that has a molecular weight similar to the myosin purified from optic lobe copurifies with axoplasmic organelles, and, like the optic lobe myosin, this band is also recognized by the antibodies raised against squid muscle myosin II. Hence, this strategy provides an approach to the identification of a myosin associated with motile axoplasmic organelles.

Expression of smooth muscle myosin heavy chains and unloaded shortening in single smooth muscle cells

The functional significance of the variable expression of the smooth muscle myosin heavy chain (SM-MHC) tail isoforms, SM1 and SM2, was examined at the mRNA level (which correlates with the protein level) in individual permeabilized rabbit arterial smooth muscle cells (SMCs). The length of untethered single permeabilized SMCs was monitored during unloaded shortening in response to increased Ca2+ (pCa 6.0), histamine (1 microM), and phenylephrine (1 microM). Subsequent to contraction, the relative expression of SM1 and SM2 mRNAs from the same individual SMCs was determined by reverse transcription-polymerase chain reaction amplification and densitometric analysis. Correlational analyses between the SM2-to-SM1 ratio and unloaded shortening in saponin- and alpha-toxin-permeabilized SMCs (n = 28) reveal no significant relationship between the SM-MHC tail isoform ratio and unloaded shortening velocity. The best correlations between SM2/SM1 and the contraction characteristics of untethered vascular SMCs were with the minimum length attained following contraction (n = 20 and r = 0.72 for alpha-toxin, n = 8 and r = 0.78 for saponin). These results suggest that the primary effect of variable expression of the SM1 and SM2 SM-MHC tail isoforms is on the cell final length and not on shortening velocity.

Structural differences in the crossbridge head of temperature-associated myosin subfragment-1 isoforms from carp fast skeletal muscle

We determined the primary structures of the three acclimation-temperature-associated isoforms of myosin subfragment-1 heavy chain from fast skeletal muscle of thermally acclimated carp. These isoforms were cloned by extending 5'-regions of cDNAs that encode the rod part of myosin heavy chain specifically expressed in 10 degrees C- and 30 degrees C-acclimated carp, together with the region that encodes an intermediate structure [Imai, J., Hirayama, Y., Kikuchi, K., Kakinuma, M. & Watabe, S. (1997) J. Exp. Biol. 200, 27-34]. These three isoforms generally resembled each other in primary structure, showing 94.8, 90.9, and 92% similarity between the 10 degrees C- and intermediate-type, between the 10 degrees C- and 30 degrees C-type, and between the intermediate- and 30 degrees C-type myosin heavy chains, respectively. However, isoform-specific differences were clearly observed between the 10 degrees C- and 30 degrees C-type heavy chains in the first 60 amino acid residues from the N-terminus, where the intermediate-type showed an intermediate feature in its sequence compared to the 10 degrees C- and 30 degrees C-type isoforms. Other striking differences were observed in two surface loops between the 10 degrees C- and 30 degrees C-type isoform. Five amino acid residues out of sixteen were different in loop 1 near the ATP-binding pocket, and six out of twenty were different in loop 2 on the actin-binding site. The loops connecting beta-sheets that are known to surround the ATP-binding pocket were highly conserved in primary structure for the three types. In northern blot analysis, the accumulated mRNA levels of the 10 degrees C- and intermediate-type isoforms were significantly higher in carp acclimated to 10 degrees C and 20 degrees C than carp acclimated to 30 degrees C, whereas the level of the 30 degrees C-type isoform was significantly higher in carp acclimated to 30 degrees C than those acclimated to 10 degrees C and 20 degrees C.

Expression of nonmuscle myosin heavy chain-B isoform in the vessel wall of porcine coronary arteries after balloon angioplasty

Nonmuscle myosin heavy chain-B isoform (NMMHC-B) is expressed by proliferating vascular smooth muscle cells (SMCs), and its expression in primary lesions has been proposed to be predictive of restenosis after atherectomy. The present study was designed to study the time-course expression of NMMHC-B after angioplasty of porcine coronary arteries by in situ hybridization and immunohistochemistry. Domestic juvenile swine underwent percutaneous transluminal coronary angioplasty (PTCA) of the left anterior descending and circumflex coronary arteries with standard clinical angioplasty catheters. To identify proliferating cells, 5'-bromo-2'-deoxyuridine (BrdU) was administered and detected by immunohistochemistry on serial sections. Vessels were examined at 3, 7, and 14 days after balloon angioplasty, and uninjured coronary vessels were used as controls. Normal arteries showed hybridization to 35S-labeled NMMHC-B riboprobes localized mainly in the medial layer. NMMHC-B expression in the adventitia was markedly increased 3 days after balloon angioplasty. Seven and 14 days after injury, NMMHC-B mRNA-containing cells were localized in the adventitia and neointima at the arterial injury site. Cell proliferation, as indicated by BrdU staining, colocalized with NMMHC-B mRNA expression 3 and 7 days after angioplasty. These data indicate that cells proliferating in the adventitia and neointima express NMMHC-B; however, its expression is not limited to the proliferative state, since NMMHC-B mRNA was also found in quiescent SMCs of normal coronary arteries and in nonproliferating adventitial and neointimal cells 14 days after angioplasty.

A 29 residue region of the sarcomeric myosin rod is necessary for filament formation

Myosin is a motor protein whose functional unit in the sarcomere is the thick filament. The myosin molecule is capable of self-assembly into thick filaments through its alpha-helical coiled-coil rod domain. To define more precisely the sequence requirements for this assembly, segments of the human fast IId skeletal myosin rod were expressed in Escherichia coli and examined differential solubility and the formation of ordered paracrystals. We show that both properties appear to require a 29 residue sequence (residues 1874 to 1902) near the C terminus of the rod region. To test further the role of this region in assembly, a protein was constructed which consisted of this assembly competence domain (ACD) fused to the carboxy terminus of an assembly-incompetent myosin rod fragment. This chimeric fragment exhibited myosin's characteristic solubility properties and formed ordered paracrystals. To complement these in vitro experiments, both a full-length myosin heavy chain (MYH) and one from which the 29 residues were deleted were transfected into cultured mammalian cells. While the full-length construct formed the spindle-shaped structures characteristic of arrays of thick filaments, the deleted MYH showed only diffuse staining throughout the cytoplasm by light microscopy. Thus, there appears to be a specific sequence in the C-terminal region of the myosin heavy chain rod which is necessary for ordered paracrystal formation and is sufficient to confer assembly properties to an assembly-incompetent rod fragment.

MFP1, a novel plant filament-like protein with affinity for matrix attachment region DNA

The interaction of chromatin with the nuclear matrix via matrix attachment regions (MARs) on the DNA is considered to be of fundamental importance for higher order chromatin organization and regulation of gene expression. Here, we report a novel nuclear matrix-localized MAR DNA binding protein, designated MAR binding filament-like protein 1 (MFP1), from tomato. In contrast to the few animal MAR DNA binding proteins thus far identified, MFP1 contains a predicted N-terminal transmembrane domain and a long filament-like alpha-helical domain that is similar to diverse nuclear and cytoplasmic filament proteins from animals and yeast. DNA binding assays established that MFP1 can discriminate between animal and plant MAR DNAs and non-MAR DNA fragments of similar size and AT content. Deletion mutants of MFP1 revealed a novel, discrete DNA binding domain near the C terminus of the protein. MFP1 is an in vitro substrate for casein kinase II, a nuclear matrix-associated protein kinase. Its structure, MAR DNA binding activity, and nuclear matrix localization suggest that MFP1 is likely to participate in nuclear architecture by connecting chromatin with the nuclear matrix and potentially with the nuclear envelope.

Xenopus nonmuscle myosin heavy chain isoforms have different subcellular localizations and enzymatic activities

There are two isoforms of the vertebrate nonmuscle myosin heavy chain, MHC-A and MHC-B, that are encoded by two separate genes. We compared the enzymatic activities as well as the subcellular localizations of these isoforms in Xenopus cells. MHC-A and MHC-B were purified from cells by immunoprecipitation with isoform-specific peptide antibodies followed by elution with their cognate peptides. Using an in vitro motility assay, we found that the velocity of movement of actin filaments by MHC-A was 3.3-fold faster than that by MHC-B. Likewise, the Vmax of the actin-activated Mg(2+)-ATPase activity of MHC-A was 2.6-fold greater than that of MHC-B. Immunofluorescence microscopy demonstrated distinct localizations for MHC-A and MHC-B. In interphase cells, MHC-B was present in the cell cortex and diffusely arranged in the cytoplasm. In highly polarized, rapidly migrating interphase cells, the lamellipodium was dramatically enriched for MHC-B suggesting a possible involvement of MHC-B based contractions in leading edge extension and/or retraction. In contrast, MHC-A was absent from the cell periphery and was arranged in a fibrillar staining pattern in the cytoplasm. The two myosin heavy chain isoforms also had distinct localizations throughout mitosis. During prophase, the MHC-B redistributed to the nuclear membrane, and then resumed its interphase localization by metaphase. MHC-A, while diffuse within the cytoplasm at all stages of mitosis, also localized to the mitotic spindle in two different cultured cell lines as well as in Xenopus blastomeres. During telophase both isoforms colocalized to the contractile ring. The different subcellular localizations of MHC-A and MHC-B, together with the data demonstrating that these myosins have markedly different enzymatic activities, strongly suggests that they have different functions.