Identification and Characterization of Nonmuscle Myosin II-C, a New Member of the Myosin II Family
Shaare Zedek Medical Center, Yerushalayim, Jerusalem, Israel Journal of Biological Chemistry
(Impact Factor: 4.57).
02/2004; 279(4):2800-8. DOI: 10.1074/jbc.M309981200
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.
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- "Striated muscles use different isoforms of the dimeric myosin II subgroup to perform 'external' mechanical work. Most mammals express up to a dozen myosin II isoforms, each from a separate gene (Golomb et al., 2003;Schiaffino and Reggiani, 2011;Weiss and Leinwand, 1996). Nomenclature for the isoforms can be confusing, as the isoforms are known historically by the muscle fibre type or tissue initially associated with the isoform, and more recently by the systematic naming of the gene coding for the protein. "
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- "The multimeric, bipolar structure of NMII determines its ability to crosslink and contract actin filaments (Pollard, 1982). There are three NMII isoforms (A, B and C; see Box 2), which consist of different NMII heavy chains and shared essential and regulatory light chains (ELCs and RLCs; see Box 1) (D'Apolito et al., 2002; Golomb et al., 2004; Simons et al., 1991). The heavy chain is comprised of a globular head domain, which binds both actin and adenosine triphosphate (ATP) (Rayment et al., 1993a,b); a neck region, which binds both the ELC and RLC (Winkelmann et al., 1984); and a tail region, which homodimerizes in a helical fashion (Côté et al., 1984) (Fig. 1). "
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ABSTRACT: The actin motor protein non-muscle myosin II (NMII) acts as a master regulator of cell morphology, with a role in several essential cellular processes, including cell migration and post-synaptic dendritic spine plasticity in neurons. NMII also generates forces that alter biochemical signaling, by driving changes in interactions between actin-associated proteins that can ultimately regulate gene transcription. In addition to its roles in normal cellular physiology, NMII has recently emerged as a critical regulator of diverse, genetically complex diseases, including neuronal disorders, cancers and vascular disease. In the context of these disorders, NMII regulatory pathways can be directly mutated or indirectly altered by disease-causing mutations. NMII regulatory pathway genes are also increasingly found in disease-associated copy-number variants, particularly in neuronal disorders such as autism and schizophrenia. Furthermore, manipulation of NMII-mediated contractility regulates stem cell pluripotency and differentiation, thus highlighting the key role of NMII-based pharmaceuticals in the clinical success of stem cell therapies. In this Review, we discuss the emerging role of NMII activity and its regulation by kinases and microRNAs in the pathogenesis and prognosis of a diverse range of diseases, including neuronal disorders, cancer and vascular disease. We also address promising clinical applications and limitations of NMII-based inhibitors in the treatment of these diseases and the development of stem-cell-based therapies.
Available from: Sarah Escuin
- "In fact, enhanced actin crosslinking by myosin II could also contribute to the postulated increase in neuroepithelial tension in embryos that fail in spinal closure. Of the three myosin II heavy chains, MHCB is the predominant isoform expressed in neuroepithelial cells (Wang et al., 2011) and fetal brain (Golomb et al., 2004), whereas MHCA and MHCC (also known as MYH9 and MYH14, respectively) are present at only low levels. MHCB is characterized by a high 'duty ratio', with strong ADP-binding and propensity to exist in a rigor state, tightly bound to actin (Rosenfeld et al., 2003; Wang et al., 2003). "
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ABSTRACT: The cytoskeleton is widely considered essential for neurulation, yet the mouse spinal neural tube can close despite genetic and non-genetic disruption of the cytoskeleton. To investigate this apparent contradiction, we applied cytoskeletal inhibitors to mouse embryos in culture. Preventing actomyosin cross-linking, F-actin assembly or myosin II contractile activity did not disrupt spinal closure. In contrast, inhibiting Rho kinase or blocking F-actin disassembly prevented closure, with apical F-actin accumulation and adherens junction disturbance in the neuroepithelium. Cofilin 1-null embryos yielded a similar phenotype, supporting a key role for actin turnover. Co-exposure to Blebbistatin rescued the neurulation defects caused by RhoA inhibition, whereas an inhibitor of myosin light chain kinase, ML-7, had no such effect. We conclude that regulation of RhoA/Rho kinase/LIM kinase/cofilin signalling is necessary for spinal neural tube closure through precise control of neuroepithelial actin turnover and actomyosin disassembly. In contrast, actomyosin assembly and myosin ATPase activity are not limiting for closure.
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