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Smith L, Su X, Lin P, Zhi G, Stull JT. Identification of a novel actin binding motif in smooth muscle myosin light chain kinase. J Biol Chem 1999; 274:29433-8. [PMID: 10506206 DOI: 10.1074/jbc.274.41.29433] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of the 20-kDa regulatory light chain of myosin catalyzed by a Ca(2+)/calmodulin-dependent myosin light chain kinase is important in the initiation of smooth muscle contraction and other contractile processes in non-muscle cells. It has been previously shown that residues 1-142 of smooth muscle myosin light chain kinase are necessary for high-affinity binding to actin-containing filaments in cells (1). To further localize the region of the kinase required for binding, a series of N-terminal deletion mutants as well as several N-terminal glutathione S-transferase fusion proteins were constructed. Cosedimentation assays showed that a peptide containing residues 1-75 binds to purified smooth muscle myofilaments. Furthermore, the N-terminal peptide was sufficient for high-affinity binding to actin stress fibers in smooth muscle cells in vivo. Alanine scanning mutagenesis in the fusion protein identified residues Asp-30, Phe-31, Arg-32, and Leu-35 as important for binding in vitro. There are two additional DFRXXL motifs located at residues 2-7 and 58-63. The DFR residues in these three motifs were individually replaced by alanine residues in the full-length kinase. Each of these mutations significantly decreased myosin light chain kinase binding to myofilaments in vitro, and each abolished high-affinity binding to actin-containing filaments in smooth muscle cells in vivo. These results identify a unique structural motif comprised of three repeat consensus sequences in the N terminus of myosin light chain kinase necessary for high-affinity binding to actin-containing filaments.
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Affiliation(s)
- L Smith
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235-9040, USA
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52
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Nolan K, Lacoste J, Parsons JT. Regulated expression of focal adhesion kinase-related nonkinase, the autonomously expressed C-terminal domain of focal adhesion kinase. Mol Cell Biol 1999; 19:6120-9. [PMID: 10454559 PMCID: PMC84535 DOI: 10.1128/mcb.19.9.6120] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Focal adhesion kinase (FAK) has been implicated in cellular processes that control cell adhesion, migration, cell cycle progression, and apoptosis. FRNK (FAK-related nonkinase) is the autonomously expressed, noncatalytic C-terminal portion of FAK. When ectopically expressed in cells, FRNK has been shown to act as a negative regulator of FAK activity, inhibiting cell spreading, migration, and cell cycle progression. The mechanisms that regulate FRNK expression during embryonic development and the functional role of FRNK in normal cell homeostasis remain poorly understood. Herein we show that FRNK expression in chicken cells is directed by an alternative promoter residing within an intron of FAK, positioned 3' of the exon encoding sequences for the catalytic domain and 5' of the exon encoding sequences for the C-terminal domain of FAK (e.g., FRNK). Using probes specific for FRNK, we show that FRNK expression occurs early in chicken embryogenesis, being readily detected at day 3, 6, or 9. Late in embryogenesis, at day 18, FRNK is expressed in a tissue-specific manner, predominately in lung and intestine cells. Western blot analysis of mouse tissues with a FAK-specific antibody revealed the expression of FRNK in the mouse lung. Reverse transcriptase PCR analysis of mouse lung RNA revealed the presence of spliced FRNK mRNAs containing 5' untranslated sequences derived from a positionally conserved exon present in the mouse genome. FAK is the first example of a tyrosine kinase regulated by a domain under the control of an alternative intronic promoter. It is also the first example of a focal adhesion-associated protein regulated by such a mechanism and thus represents a novel means for the modulation of cell adhesion signaling.
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Affiliation(s)
- K Nolan
- Department of Microbiology, Health Sciences Center, University of Virginia, Charlottesville, Virginia 22908, USA
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53
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Benian GM, Ayme-Southgate A, Tinley TL. The genetics and molecular biology of the titin/connectin-like proteins of invertebrates. Rev Physiol Biochem Pharmacol 1999; 138:235-68. [PMID: 10396143 DOI: 10.1007/bfb0119629] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Affiliation(s)
- G M Benian
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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54
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Ye LH, Kishi H, Nakamura A, Okagaki T, Tanaka T, Oiwa K, Kohama K. Myosin light-chain kinase of smooth muscle stimulates myosin ATPase activity without phosphorylating myosin light chain. Proc Natl Acad Sci U S A 1999; 96:6666-71. [PMID: 10359769 PMCID: PMC21972 DOI: 10.1073/pnas.96.12.6666] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/1999] [Accepted: 04/12/1999] [Indexed: 11/18/2022] Open
Abstract
Myosin light-chain kinase (MLCK) of smooth muscle is multifunctional, being composed of N-terminal actin-binding domain, central kinase domain, and C-terminal myosin-binding domain. The kinase domain is the best characterized; this domain activates the interaction of smooth-muscle myosin with actin by phosphorylating the myosin light chain. We have recently shown that the Met-1-Pro-41 sequence of MLCK binds to actin to inhibit this interaction. However, it is not known whether the myosin-binding domain modifies the actin-myosin interaction. We designed MLCK.cDNA to overexpress the Asp-777-Glu-972 sequence in Escherichia coli. The purified Asp-777-Glu-972 fragment, although devoid of the kinase activity, exerted a stimulatory effect on the ATPase activity of dephosphorylated myosin (Vmax = 7.36 +/- 0.44-fold, Km = 1.06 +/- 0. 20 microM, n = 4). When the N-terminal 39 residues of the fragment were deleted from the fragment, the resultant fragment, Met-816-Glu-972, lost the stimulatory activity. We synthesized the Ala-777-Ser-815 peptide that was deleted from the fragment and confirmed its stimulatory effect of the peptide (Vmax = 3.03 +/- 0. 22-fold, Km = 6.93 +/- 1.61 microM, n = 3). When this peptide was further divided into Asp-777-Met-795 and Ala-796-Ser-815 peptides, the stimulatory activity was found in the latter. We confirmed that the myosin phosphorylation did not occur during the experiments with the above fragments and peptides. Therefore, we suggest that phosphorylation is not obligatory for smooth-muscle myosin not to be active.
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Affiliation(s)
- L H Ye
- Department of Pharmacology, Gunma University School of Medicine, Maebashi, Gunma 371-8511, Japan
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55
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Gunst SJ. Applicability of the sliding filament/crossbridge paradigm to smooth muscle. Rev Physiol Biochem Pharmacol 1999; 134:7-61. [PMID: 10087907 DOI: 10.1007/3-540-64753-8_2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Affiliation(s)
- S J Gunst
- Indiana University School of Medicine, USA
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56
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Somlyo AP, Wu X, Walker LA, Somlyo AV. Pharmacomechanical coupling: the role of calcium, G-proteins, kinases and phosphatases. Rev Physiol Biochem Pharmacol 1999; 134:201-34. [PMID: 10087910 DOI: 10.1007/3-540-64753-8_5] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The concept of pharmacomechanical coupling, introduced 30 years ago to account for physiological mechanisms that can regulate contraction of smooth muscle independently of the membrane potential, has since been transformed from a definition into what we now recognize as a complex of well-defined, molecular mechanisms. The release of Ca2+ from the SR by a chemical messenger, InsP3, is well known to be initiated not by depolarization, but by agonist-receptor interaction. Furthermore, this G-protein-coupled phosphatidylinositol cascade, one of many processes covered by the umbrella of pharmacomechanical coupling, is part of complex and general signal transduction mechanisms also operating in many non-muscle cells of diverse organisms. It is also clear that, although the major contractile regulatory mechanism of smooth muscle, phosphorylation/dephosphorylation of MLC20, is [Ca2+]-dependent, the activity of both the kinase and the phosphatase can also be modulated independently of [Ca2+]i. Sensitization to Ca2+ is attributed to inhibition of SMPP-1M, a process most likely dominated by activation of the monomeric GTP-binding protein RhoA that, in turn, activates Rho-kinase that phosphorylates the regulatory subunit of SMPP-1M and inhibits its myosin phosphatase activity. It is likely that the tonic phase of contraction activated by a variety of excitatory agonists is, at least in part, mediated by this Ca(2+)-sensitizing mechanism. Desensitization to Ca2+ can occur either through inhibitory phosphorylation of MLCK by other kinases or autophosphorylation and by activation of SMPP-1M by cyclic nucleotide-activated kinases, probably involving phosphorylation of a phosphatase activator. Based on our current understanding of the complexity of the many cross-talking signal transduction mechanisms that operate in cells, it is likely that, in the future, our current concepts will be refined, additional mechanisms of pharmacomechanical coupling will be recognized, and those contributing to the pathologenesis diseases, such as hypertension and asthma, will be identified.
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Affiliation(s)
- A P Somlyo
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville 22906-0011, USA
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57
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Arner A, Pfitzer G. Regulation of cross-bridge cycling by Ca2+ in smooth muscle. Rev Physiol Biochem Pharmacol 1999; 134:63-146. [PMID: 10087908 DOI: 10.1007/3-540-64753-8_3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- A Arner
- Department of Physiology and Neuroscience, Lund University, Sweden
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58
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Szymanski PT, Goyal RK. Calponin binds to the 20-kilodalton regulatory light chain of myosin. Biochemistry 1999; 38:3778-84. [PMID: 10090767 DOI: 10.1021/bi981394y] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Calponin (CaP) is a 34 kDa smooth muscle-specific protein that has been implicated in regulation of smooth muscle contractility. Two CaP binding sites on smooth muscle myosin rod have been recently described [Szymanski and Tao (1997) J.Biol.Chem. 272, 11142-11146]. We used a combination of cosedimentation, overlay, and fluorescence assays to determine the interaction between CaP and both subfragment 1 of myosin and isolated 20 kDa regulatory light chain of myosin (RLC). Subfragment 1, which was generated by cleavage of myosin with Staphylococcus aureus protease (myosin S1SA) inhibits cosedimentation of CaP with myosin filaments. Fluorescence assay showed that CaP labeled with fluorescent label (DAN-CaP) interacts with myosin S1SA in solution via a single class of binding sites. The binding constant (kaff) of this interaction at 50 mM NaCl is (2. 1 +/- 0.2) x 10(6) M-1 (n = 3). The interaction between DAN-CaP and myosin S1SA depends on ionic strength, and the EC50 of inhibition of this interaction occurs at about 130 mM NaCl. In contrast, the subfragment 1 that was generated by papain digestion (myosin S1PA), which cleaves RLC 4 kDa away from the NH2-terminal end of the molecule, does not interact with DAN-CaP. Overlay and fluorescent assay in solution showed that CaP binds to isolated RLC, suggesting that the interaction between CaP and subfragment 1 of myosin is due to a direct binding of CaP to RLC. CaP binding to myosin S1SA is stronger than to subfragment 2 in physiological salt concentrations. CaP binding to myosin head strengthened upon phosphorylation of RLC by Ca2+/calmodulin-dependent myosin light chain kinase. We suggest that CaP binds to subfragment 1 of myosin, exclusively via the NH2-terminal end of RLC, and this interaction could play a role in regulation of the actin-myosin interaction in smooth muscle contractility.
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Affiliation(s)
- P T Szymanski
- Center for Swallowing and Motility Disorders, VA Medical Center, West Roxbury, Massachusetts 02132, USA
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59
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Abstract
Myosin light chain kinase binds to actin-containing filaments from cells with a greater affinity than to F-actin. However, it is not known if this binding in cells is regulated by Ca2+/calmodulin as it is with F-actin. Therefore, the binding properties of the kinase to stress fibers were examined in smooth muscle-derived A7r5 cells. Full-length myosin light chain kinase or a truncation mutant lacking residues 2-142 was expressed as chimeras containing green fluorescent protein at the C terminus. In intact cells, the full-length kinase bound to stress fibers, whereas the truncated kinase showed diffuse fluorescence in the cytoplasm. After permeabilization with saponin, the fluorescence from the truncated kinase disappeared, whereas the fluorescence of the full-length kinase was retained on stress fibers. Measurements of fluorescence intensities and fluorescence recovery after photobleaching of the full-length myosin light chain kinase in saponin-permeable cells showed that Ca2+/calmodulin did not dissociate the kinase from these filaments. However, the filament-bound kinase was sufficient for Ca2+-dependent phosphorylation of myosin regulatory light chain and contraction of stress fibers. Thus, dissociation of myosin light chain kinase from actin-containing thin filaments is not necessary for phosphorylation of myosin light chain in thick filaments. We note that the distance between the N terminus and the catalytic core of the kinase is sufficient to span the distance between thin and thick filaments.
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Affiliation(s)
- P Lin
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA
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60
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Kishi H, Ye LH, Nakamura A, Okagaki T, Iwata A, Tanaka T, Kohama K. Structure and function of smooth muscle myosin light chain kinase. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 453:229-34. [PMID: 9889833 DOI: 10.1007/978-1-4684-6039-1_26] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Myosin light chain kinase (MLCK) plays a central role in regulating the actin-myosin interaction of smooth muscle. MLCK phosphorylates the light chain of myosin in the presence of Ca2+ and calmodulin (CaM) thereby activating myosin so that it can interact with actin. Besides this kinase activity, MLCK shows i) actin-binding activity that can assemble actin filaments into their bundles and ii) myosin-binding activity that can form myosin filaments. To localize the actin- and myosin-binding activities in the MLCK molecule and to examine their possible role in regulating the actin-myosin interaction, we expressed various fragments of cDNA encoding MLCK in Escherichia coli as recombinant proteins. We found that MLCK consists of an N-terminal actin-binding domain, a central kinase domain, and a C-terminal myosin-binding domain. The Met1-Pro41 sequence is responsible for Ca2+/CaM-sensitive binding to actin. This binding site exerts an inhibitory effect on the actin-myosin interaction only when myosin is phosphorylated. MLCK binds to myosin at the C-terminal domain, the sequence of which is identical to telokin, an abundant myosin-binding protein in smooth muscle cells. This domain itself has no regulatory role in the interaction. However, the interaction was stimulated when this domain was extended to include the sequence known to regulate the activity of the kinase domain. The stimulation was observed only when myosin was unphosphorylated.
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Affiliation(s)
- H Kishi
- Department of Pharmacology, Gunma University School of Medicine, Japan
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61
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The genetics and molecular biology of the titin/connectin-like proteins of invertebrates. Rev Physiol Biochem Pharmacol 1999. [DOI: 10.1007/bf02346665] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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62
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Butler TM, Siegman MJ. Control of cross-bridge cycling by myosin light chain phosphorylation in mammalian smooth muscle. ACTA PHYSIOLOGICA SCANDINAVICA 1998; 164:389-400. [PMID: 9887963 DOI: 10.1046/j.1365-201x.1998.00450.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
This review focuses on experiments in which the single turnover of myosin-bound ADP is used to characterize the regulation of the cross-bridge cycle by myosin light chain phosphorylation in mammalian smooth muscle. Under isometric conditions, at rest, when the myosin light chain is not phosphorylated, myosin cycles very slowly (about 0.004 s-1), while phosphorylation of the light chain results in a 50-fold increase in cycling rate of 0.2 s-1. Experiments consistently show that some myosin does not increase its cycling rate although its light chain is phosphorylated. Studies at low levels of myosin light chain phosphorylation show that phosphorylation also induces an increase in the cycling rate of unphosphorylated myosin. The fast cycling phosphorylated myosin is the main determinant of suprabasal myosin ATPase activity, while the cycling rate of cooperatively activated unphosphorylated myosin is slow and appears to depend on the extent of phosphorylation of the entire thick filament. Single turnover experiments measuring the rate of phosphorylation and dephosphorylation of myosin light chain show that the turnover of light chain phosphate can be very rapid (0.3-0.4 s-1) at suprabasal calcium concentrations. The expected effect of such a rapid turnover of light chain phosphorylation on the turnover of myosin-bound ADP is not observed. The effects of low levels of myosin light chain phosphorylation on the single turnover of myosin suggest that the same small pool of myosin remains phosphorylated for relatively long periods of time rather than the entire pool of myosin spending a small fraction of its cycle time in the phosphorylated state.
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Affiliation(s)
- T M Butler
- Department of Physiology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA
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63
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Stull JT, Lin PJ, Krueger JK, Trewhella J, Zhi G. Myosin light chain kinase: functional domains and structural motifs. ACTA PHYSIOLOGICA SCANDINAVICA 1998; 164:471-82. [PMID: 9887970 DOI: 10.1111/j.1365-201x.1998.tb10699.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Conventional myosin light chain kinase found in differentiated smooth and non-muscle cells is a dedicated Ca2+/calmodulin-dependent protein kinase which phosphorylates the regulatory light chain of myosin II. This phosphorylation increases the actin-activated myosin ATPase activity and is thought to play major roles in a number of biological processes, including smooth muscle contraction. The catalytic domain contains residues on its surface that bind a regulatory segment resulting in autoinhibition through an intrasteric mechanism. When Ca2+/calmodulin binds, there is a marked displacement of the regulatory segment from the catalytic cleft allowing phosphorylation of myosin regulatory light chain. Kinase activity depends upon Ca2+/calmodulin binding not only to the canonical calmodulin-binding sequence but also to additional interactions between Ca2+/calmodulin and the catalytic core. Previous biochemical evidence shows myosin light chain kinase binds tightly to actomyosin containing filaments. The kinase has low-affinity myosin and actin binding sites in Ig-like motifs at the N- and C-terminus, respectively. Recent results show the N-terminus of myosin light chain kinase is responsible for filament binding in vivo. However, the apparent binding affinity is greater for smooth muscle myofilaments, purified thin filaments, or actin-containing filaments in permeable cells than for purified smooth muscle F-actin or actomyosin filaments from skeletal muscle. These results suggest a protein on actin thin filaments that may facilitate kinase binding. Myosin light chain kinase does not dissociate from filaments in the presence of Ca2+/calmodulin raising the interesting question as to how the kinase phosphorylates myosin in thick filaments if it is bound to actin-containing thin filaments.
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Affiliation(s)
- J T Stull
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, USA
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64
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Somlyo AV, Matthew JD, Wu X, Khromov AS, Somlyo AP. Regulation of the cross-bridge cycle: the effects of MgADP, LC17 isoforms and telokin. ACTA PHYSIOLOGICA SCANDINAVICA 1998; 164:381-8. [PMID: 9887962 DOI: 10.1111/j.1365-201x.1998.tb10695.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
This review summarizes the role of MgADP in force maintenance by dephosphorylated cross-bridges in smooth muscle and a potential physiological role for telokin. In tonic, compared with phasic, smooth muscles the affinity of cross-bridges in approximately 5 times higher for MgADP and the apparent second-order rate constant for MgATP is approximately 3 times lower. This gives rise to a large population of dephosphorylated cross-bridges in tonic smooth muscle. Such cross-bridges are thought to be major determinants of the different relaxation kinetics of the two types of smooth muscle and contribute to force maintenance at low levels of MLC20 phosphorylation, termed 'catch-like state' (Somlyo & Somlyo 1967) or 'latch' (Dillon et al. 1981). The molecular basis of the different affinities for MgADP and MgATP between tonic and phasic smooth muscle myosin was explored by exchange of essential myosin light chain (LC17) isoforms. In phasic bladder smooth muscle the exchange of LC17b for LC17a caused a significant decrease in the unloaded shortening velocity of non-phosphorylated, slowly cycling cross-bridges, suggesting that the LC17 isoforms contribute to the nucleotide affinity of latch bridges. The role of telokin in Ca(2+)-desensitization in phasic smooth muscle is reviewed. Telokin, the independently expressed C-terminus of myosin light chain kinase, is extensively phosphorylated during forskolin- and 8-br-cGMP-induced relaxation in situ. Telokin accelerated dephosphorylation of the regulatory myosin light chain and relaxed rabbit ileum smooth muscle. The results suggest that telokin contributes to cAMP and/or cGMP kinase-mediated Ca(2+)-desensitization of phasic smooth muscles.
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Affiliation(s)
- A V Somlyo
- Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Centre, Charlottesville 22906-0011, USA
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65
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Birukov KG, Schavocky JP, Shirinsky VP, Chibalina MV, Van Eldik LJ, Watterson DM. Organization of the genetic locus for chicken myosin light chain kinase is complex: Multiple proteins are encoded and exhibit differential expression and localization. J Cell Biochem 1998. [DOI: 10.1002/(sici)1097-4644(19980901)70:3<402::aid-jcb13>3.0.co;2-m] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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66
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Smith AF, Bigsby RM, Word RA, Herring BP. A 310-bp minimal promoter mediates smooth muscle cell-specific expression of telokin. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C1188-95; discussion C1187. [PMID: 9612204 DOI: 10.1152/ajpcell.1998.274.5.c1188] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A cell-specific promoter located in an intron of the smooth muscle myosin light chain kinase gene directs transcription of telokin exclusively in smooth muscle cells. Transgenic mice were generated in which a 310-bp rabbit telokin promoter fragment, extending from -163 to +147, was used to drive expression of simian virus 40 large T antigen. Smooth muscle-specific expression of the T-antigen transgene paralleled that of the endogenous telokin gene in all smooth muscle tissues except uterus. The 310-bp promoter fragment resulted in very low levels of transgene expression in uterus; in contrast, a transgene driven by a 2.4-kb fragment (-2250 to +147) resulted in high levels of transgene expression in uterine smooth muscle. Telokin expression levels correlate with the estrogen status of human myometrial tissues, suggesting that deletion of an estrogen response element (ERE) may account for the low levels of transgene expression driven by the 310-bp rabbit telokin promoter in uterine smooth muscle. Experiments in A10 smooth muscle cells directly showed that reporter gene expression driven by the 2.4-kb, but not 310-bp, promoter fragment could be stimulated two- to threefold by estrogen. This stimulation was mediated through an ERE located between -1447 and -1474. Addition of the ERE to the 310-bp fragment restored estrogen responsiveness in A10 cells. These data demonstrate that in addition to a minimal 310-bp proximal promoter at least one distal cis-acting regulatory element is required for telokin expression in uterine smooth muscle. The distal element may include an ERE between -1447 and -1474.
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Affiliation(s)
- A F Smith
- Department of Physiology, Indiana University School of Medicine, Indianapolis 46202-5120, USA
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67
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Wu X, Haystead TA, Nakamoto RK, Somlyo AV, Somlyo AP. Acceleration of myosin light chain dephosphorylation and relaxation of smooth muscle by telokin. Synergism with cyclic nucleotide-activated kinase. J Biol Chem 1998; 273:11362-9. [PMID: 9556631 DOI: 10.1074/jbc.273.18.11362] [Citation(s) in RCA: 120] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Incorporation of 32P into telokin, a smooth muscle-specific, 17-18-kDa, acidic (pI 4.2-4.4) protein, was increased by forskolin (20 microM) in intact rabbit ileum smooth muscle (ileum) and by 8-bromo-cyclic GMP (100 microM) in alpha-toxin-permeabilized ileum. Native telokin (5-20 microM), purified from turkey gizzard, and recombinant rabbit telokin, expressed in Escherichia coli and purified to >90% purity, induced dose-dependent relaxation, associated with a significant decrease in regulatory myosin light chain phosphorylation, without affecting the rate of thiophosphorylation of regulatory myosin light chain of ileum permeabilized with 0.1% Triton X-100. Endogenous telokin was lost from ileum during prolonged permeabilization (>20 min) with 0.1% Triton X-100, and the time course of loss was correlated with the loss of 8-bromo-cyclic GMP-induced calcium desensitization. Recombinant and native gizzard telokins were phosphorylated, in vitro, by the catalytic subunit of cAMP-dependent protein kinase, cGMP-dependent protein kinase, and p42/44 mitogen-activated protein kinase; the recombinant protein was also phosphorylated by calmodulin-dependent protein kinase II. Exogenous cGMP-dependent protein kinase (0.5 microM) activated by 8-bromo-cyclic GMP (50 microM) phosphorylated recombinant telokin (10 microM) when added concurrently to ileum depleted of its endogenous telokin, and their relaxant effects were mutually potentiated. Forskolin (20 microM) also increased phosphorylation of telokin in intact ileum. We conclude that telokin induces calcium desensitization in smooth muscle by enhancing myosin light chain phosphatase activity, and cGMP- and/or cAMP-dependent phosphorylation of telokin up-regulates its relaxant effect.
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Affiliation(s)
- X Wu
- Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22906-0011, USA
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68
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Ye LH, Hayakawa K, Kishi H, Imamura M, Nakamura A, Okagaki T, Takagi T, Iwata A, Tanaka T, Kohama K. The structure and function of the actin-binding domain of myosin light chain kinase of smooth muscle. J Biol Chem 1997; 272:32182-9. [PMID: 9405419 DOI: 10.1074/jbc.272.51.32182] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
In addition to its kinase activity, the myosin light chain kinase (MLCK) of smooth muscle has an actin binding activity through which it can regulate the actin-myosin interaction of smooth muscle (Kohama, K., Okagaki, T., Hayakawa, K., Lin, Y., Ishikawa, R., Shimmen, T., and Inoue, A. (1992) Biochem. Biophys. Res. Commun. 184, 1204-1211). In this study, we have analyzed the actin binding activity of MLCK and related it to its amino acid sequence by producing native and recombinant fragments of MLCK. Parent MLCK exhibited both calcium ion (Ca2+) and calmodulin (Ca2+/CaM)-sensitive and Ca2+/CaM-insensitive binding to actin filaments. The native fragment, which consists of the Met1-Lys114 sequence (Kanoh, S., Ito, M., Niwa, E., Kawano, Y., and Hartshorne, D. J. (1993) Biochemistry 32, 8902-8907), and the recombinant NN fragment, which contains this 1-114 sequence, showed only Ca2+/CaM-sensitive binding. An inhibitory effect of the NN fragment on the actin-myosin interaction was observed by assaying in vitro motility and by measuring the actin-activated ATPase activity of myosin. The recombinant NN/41 fragment, which is constructed without the Met1-Pro41 sequence of the NN fragment, lost both the actin binding activity and the inhibitory effect. We confirmed the importance of the 1-41 sequence by using a few synthetic peptides to compete against the NN fragment in binding to actin filaments. The experiments using recombinant fragments and synthetic peptides also revealed that the site for CaM-binding is the Pro26-Pro41 sequence. The site for the Ca2+/CaM-insensitive binding, which is shown to be localized between the Ca2+/CaM-sensitive site and the central kinase domain of MLCK, exerted no regulatory effects on the actin-myosin interaction.
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Affiliation(s)
- L H Ye
- Department of Pharmacology, Gunma University School of Medicine, Maebashi, Gunma 371 Japan
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69
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Silver DL, Vorotnikov AV, Watterson DM, Shirinsky VP, Sellers JR. Sites of interaction between kinase-related protein and smooth muscle myosin. J Biol Chem 1997; 272:25353-9. [PMID: 9312155 DOI: 10.1074/jbc.272.40.25353] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Kinase-related protein, also known as KRP or telokin, is an independently expressed protein product derived from a gene within the gene for myosin light chain kinase (MLCK). KRP binds to unphosphorylated smooth muscle myosin filaments and stabilizes them against ATP-induced depolymerization in vitro. KRP competes with MLCK for binding to myosin, suggesting that both proteins bind to myosin by the KRP domain (Shirinsky, V. P., Vorotnikov, A. V., Birukov, K. G., Nanaev, A. K., Collinge, M., Lukas, T. J., Sellers, J. R., and Watterson, D. M. (1993) J. Biol. Chem. 268, 16578-16583). In this study, we investigated which regions of myosin and KRP interact in vitro. Using cosedimentation assays, we determined that KRP binds to unphosphorylated myosin with a stoichiometry of 1 mol of KRP/1 mol of myosin and an affinity of 5.5 microM. KRP slows the rate of proteolytic cleavage of the head-tail junction of heavy meromyosin by papain and chymotrypsin, suggesting it is binding to this region of myosin. In addition, competition experiments, using soluble headless fragments of nonmuscle myosin, confirmed that KRP interacts with the regulatory light chain binding region of myosin. The regions important for KRP's binding to myosin were investigated using bacterially expressed KRP truncation mutants. We determined that the acid-rich sequence between Gly138 and Asp151 of KRP is required for high affinity myosin binding, and that the amino terminus and beta-barrel regions weakly interact with myosin. All KRP truncations, at concentrations comparable to their KD values, exhibited some stabilization of myosin filaments against ATP depolymerization in vitro, suggesting that KRP's ability to stabilize myosin filaments is commensurate with its myosin binding affinity. KRP weakened the Km but not the Vmax of phosphorylation of myosin by MLCK, demonstrating that bound KRP does not prevent MLCK from activating myosin.
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Affiliation(s)
- D L Silver
- Laboratory of Molecular Cardiology, NHLBI, Bethesda, Maryland 20892, USA
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70
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Rusconi F, Potier MC, Le Caer JP, Schmitter JM, Rossier J. Characterization of the chicken telokin heterogeneity by time-of-flight mass spectrometry. Biochemistry 1997; 36:11021-6. [PMID: 9283094 DOI: 10.1021/bi970752e] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Chicken gizzard telokin was purified to apparent homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This preparation yielded upon mass spectrometry analysis seven mass peaks spanning from 15 858 to 17 100 Da. Anion exchange-high performance liquid chromatography of the purified telokin revealed a high diversity of telokin molecules. By combining protein chemistry to chromatography and mass spectrometry, the telokin heterogeneity was analyzed. Three acetylated N-termini were found, AMI, MIS, and SGR. Cyanogen bromide cleavage of telokin yielded six different C-terminal peptides corresponding to the removal of one to six C-terminal glutamyl residues from the protein sequence deduced from the cDNA. Phosphorylation of telokin was detected, thus increasing the heterogeneity of the telokin preparation. In addition, peptide sequencing has shown that telokin contained either an aspartyl or a glutamyl residue at position 27, probably resulting from chicken polymorphism.
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Affiliation(s)
- F Rusconi
- Centre National de la Recherche Scientifique Unité de Recherche Associée 2054, Ecole Supérieure de Physique et de Chimie Industrielles de la Ville de Paris, Paris, France.
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71
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Abstract
Kinase-related protein (telokin) is a small myosin-binding protein which has recently been discovered in smooth muscle. The KRP messenger RNA is transcribed from within the myosin light chain kinase (MLCK) gene, a rare example in vertebrates of two proteins coded for by a single gene. Owing to a separate transcription unit and a common reading frame, kinase-related protein is expressed as an independent protein which consists of the C-terminal 156 amino acids of the kinase. It binds specifically to dephosphorylated smooth muscle myosin and inhibits myosin phosphorylation by MLCK in vitro, suggesting that it might modify the rate of myosin activation and consequently the rate of tension development in the muscle. KRP also stabilizes an extended conformation of dephosphorylated myosin which can polymerize, and thereby stabilizes myosin in the filamentous state against the dissociating effect of ATP. Thus, kinase-related protein may have a function in regulating the assembly of myosin filaments into the contractile apparatus in the cell.
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Affiliation(s)
- A V Vorotnikov
- Laboratory of Molecular Endocrinology, Russian Cardiology Research Centre, Moscow, Russia
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72
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Szymanski PT, Tao T. Localization of protein regions involved in the interaction between calponin and myosin. J Biol Chem 1997; 272:11142-6. [PMID: 9111011 DOI: 10.1074/jbc.272.17.11142] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Calponin is a 33-kDa smooth muscle-specific protein that has been suggested to play a role in muscle contractility. It has previously been shown to interact with actin, tropomyosin, and calmodulin. More recently we showed that calponin also interacts with myosin (Szymanski, P. T., and Tao, T. (1993) FEBS Lett. 331, 256-259). In the present study we used a combination of co-sedimentation and fluorescence assays to localize the regions in myosin and calponin that are involved in the interaction between these two proteins. We found that recombinant chicken gizzard alpha-calponin co-sediments with myosin rod and, to a lesser extent, with light meromyosin. Fluorescently labeled recombinant calponin shows interaction with heavy meromyosin and myosin subfragment 2 but not subfragment 1. A fragment comprising residues 7-182 and a synthetic peptide spanning residues 146-176 of calponin co-sediment with myosin, but fragments comprising residues 7-144 and 183-292 do not. Our results indicate that there are calponin binding sites in the subfragment 2 and light meromyosin regions of myosin, and that the region comprising residues 145-182 of calponin mediates its interaction with myosin.
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Affiliation(s)
- P T Szymanski
- Muscle Research Group, Boston Biomedical Research Institute, Boston, Massachusetts 02114, USA
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73
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Lin PJ, Luby-Phelps K, Stull JT. Binding of myosin light chain kinase to cellular actin-myosin filaments. J Biol Chem 1997; 272:7412-20. [PMID: 9054442 DOI: 10.1074/jbc.272.11.7412] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Myosin light chain kinase binds to the actomyosin-containing filaments in smooth and nonmuscle cells. However, the region of the kinase necessary for this high affinity binding in vivo is not known, although it has been proposed that the N and C termini bind to actin and myosin in vitro, respectively. Truncated myosin light chain kinases containing the catalytic core and calmodulin-binding domain but lacking N (amino acids 1-655) and/or C (amino acids 1004-1147) termini were expressed in the baculovirus system and purified. All enzymes were catalytically active and Ca2+/calmodulin-dependent. The C-terminal truncated myosin light chain kinase bound to detergent-washed smooth muscle contractile proteins similar to recombinant full-length myosin light chain kinase or enzyme purified from smooth muscle. The apparent affinity of the full-length kinase was greater for the actomyosin-containing filaments with associated proteins than for purified smooth muscle F-actin or actomyosin filaments from skeletal muscle. In contrast, truncations at the N terminus alone or at both N and C termini resulted in no significant binding. Similar effects were observed by two other assays: binding of fluorescently labeled myosin light chain kinases to actin-containing stress fibers in detergent-treated fibroblasts and localization of fluorescently labeled kinases after microinjection into primary smooth muscle cells in culture. The full-length and the C-terminal truncated myosin light chain kinases, but not myosin light chain kinases truncated at the N terminus or both N and C termini, associated with filaments in cells. Thus, the N terminus and not the C terminus of myosin light chain kinase is necessary for high affinity binding to actomyosin-containing filaments in smooth and nonmuscle cells.
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Affiliation(s)
- P j Lin
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA
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74
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Trybus KM, Freyzon Y, Faust LZ, Sweeney HL. Spare the rod, spoil the regulation: necessity for a myosin rod. Proc Natl Acad Sci U S A 1997; 94:48-52. [PMID: 8990159 PMCID: PMC19234 DOI: 10.1073/pnas.94.1.48] [Citation(s) in RCA: 124] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Regulation of a variety of cellular contractile events requires that vertebrate smooth and non-muscle myosin II can achieve an "off" state. To examine the role of the myosin rod in this process, we determined the minimal size at which a myosin molecule is capable of regulation via light chain phosphorylation. Expressed smooth muscle myosin subfragments with as many as 100 amino acids of the coiled-coil rod sequence did not dimerize and were active independently of phosphorylation. To test whether dimerization per se restores regulation of ATPase activity, mutants were expressed with varying lengths of rod sequence, followed by C-terminal leucine zippers to stabilize the coiled-coil. Dimerization restored partial regulation, but the presence of a length of rod approximately equal to the myosin head was necessary to achieve a completely off state. Partially regulated short dimers could be converted into fully regulated molecules by addition of native rod sequence after the zipper. These results suggest that the myosin rod mediates specific interactions with the head that are required to obtain the completely inactive state of vertebrate smooth and non-muscle myosins. If these interactions are prohibited under cellular conditions, unphosphorylated crossbridges can slowly cycle.
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Affiliation(s)
- K M Trybus
- Rosenstiel Research Center, Brandeis University, Waltham, MA 02254-9110, USA.
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75
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Olney JJ, Sellers JR, Cremo CR. Structure and function of the 10 S conformation of smooth muscle myosin. J Biol Chem 1996; 271:20375-84. [PMID: 8702773 DOI: 10.1074/jbc.271.34.20375] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Smooth myosin regulatory light chain (RLC) was exchanged with RLC labeled with benzophenone-4-iodoacetamide at Cys-108. Irradiation under conditions that favor the folded (10 S) conformation resulted in 10 S cross-linked myosin that could not unfold. Purified 10 S cross-linked myosin was cross-linked between the RLC of one head to light meromyosin between leucine 1554 and glutamate 1583, adjacent to a predicted noncoiled region, approximately 60 nm from the tip of the tail. At high ionic strength without actin, product release from one-half of the heads was slow (like 10 S) whereas the other half were activated. This suggests that tail binding to the RLC carboxyl-terminal domain stabilizes ionic interactions important to slow nucleotide release. With actin, product release from both (un)phosphorylated 10 S cross-linked myosin was from one slow population similar to unphosphorylated filaments. 10 S cross-linked myosin weakly bound actin (dissociation constant > 500 microM) and did not move actin in vitro. Single-headed myosin did not fold or trap nucleotide. These and other data suggest that "trapping" occurs only with both heads and the tail binds to a newly formed site, which includes the RLC carboxyl-terminal domain, once trapping has occurred.
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Affiliation(s)
- J J Olney
- Department of Biochemistry and Biophysics, Washington State University, Pullman, Washington 99164-4660, USA
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76
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Herring BP, Smith AF. Telokin expression is mediated by a smooth muscle cell-specific promoter. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C1656-65. [PMID: 8764148 DOI: 10.1152/ajpcell.1996.270.6.c1656] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The carboxy terminus of the smooth muscle myosin light chain kinase (smMLCK) is expressed as an independent protein, telokin. Western and Northern blotting analyses demonstrated that telokin protein and mRNA are expressed at high levels only in adult and embryonic smooth muscle tissues and cells. In vitro transfection assays in A10 smooth muscle cells identified a functional promoter located in an intron in the 3' region of the smMLCK gene that directs the smooth muscle cell-specific transcription of telokin. To test the cell specificity of the telokin promoter in vivo, transgenic mice were generated in which the telokin promoter was used to drive expression of SV40 large T-antigen. Expression of T-antigen in the transgenic mice paralleled that of the endogenous telokin gene. High levels of T-antigen expression were observed in smooth muscle tissues of the digestive, urinary, and reproductive tracts, with lower levels of expression in airway and vascular smooth muscle. Expression was restricted to smooth muscle cells, with no expression detected in any other cell type.
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Affiliation(s)
- B P Herring
- Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202-5120, USA
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77
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Richardson A, Parsons T. A mechanism for regulation of the adhesion-associated proteintyrosine kinase pp125FAK. Nature 1996; 380:538-40. [PMID: 8606775 DOI: 10.1038/380538a0] [Citation(s) in RCA: 411] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Focal adhesion kinase (pp125FAK) is a member of a growing family of structurally distinct protein tyrosine kinases that includes the recently identified FakB and PYK2/CAKbeta/RAFTK. Activation of pp125FAK has been functionally linked to the formation of focal adhesions, integrin-mediated sites of contact between the cell and the extracellular matrix. The carboxy-terminal domain of pp125FAK is also expressed as a separate protein called pp41/43FRNK (where FRNK represents pp125FAK-related non-kinase). Here we show that pp41/43FRNK acts as an inhibitor of pp125FAK by transiently blocking the formation of focal adhesions on fibronectin and constitutively reducing tyrosine phosphorylation of both pp125FAK and two focal adhesion proteins, tensin and paxillin. These inhibitory effects of pp41/43FRNK are reversed by co-expression of pp125FAK, suggesting that pp125FAK and pp41/43 FRNK compete for a common binding protein(s) whose association with pp125FAK is necessary for signalling by pp125FAK. We propose that pp41/43FRNK functions as an endogenous regulator of pp125FAK, thus providing an unusual means to regulate both tyrosine kinase activity and cellular adhesion to the extracellular matrix.
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Affiliation(s)
- A Richardson
- Department of Microbiology, Health Science Center, University of Virginia, Charlottesville 22908, USA
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78
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Twitchin and related giant Ig superfamily members of C. elegans and other invertebrates. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/0065-227x(96)81674-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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79
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Kemp BE, Barden JA, Kobe B, House C, Parker MW. Intrasteric regulation of calmodulin-dependent protein kinases. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 1996; 36:221-49. [PMID: 8783562 DOI: 10.1016/s1054-3589(08)60584-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- B E Kemp
- St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia
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80
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Gallagher PJ, Garcia JG, Herring BP. Expression of a novel myosin light chain kinase in embryonic tissues and cultured cells. J Biol Chem 1995; 270:29090-5. [PMID: 7493932 PMCID: PMC2836784 DOI: 10.1074/jbc.270.49.29090] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
A novel, 208-kDa myosin light chain kinase (MLCK) distinct from smooth muscle and non-muscle MLCK has been identified by cross-reaction to two antibodies raised against smooth muscle MLCK. Additional antibodies directed against the amino and carboxyl termini of the smooth muscle MLCK do not react with the 208-kDa MLCK, suggesting these regions are distinct. 208-kDa MLCK phosphorylates 20-kDa myosin light chains in a Ca2+/calmodulin-dependent manner, consistent with it being a member of the MLCK family. Expression of 208-kDa MLCK and smooth muscle MLCK appears to be inversely regulated, with 208-kDa MLCK being most abundant during early development and declining at birth. In contrast, expression of smooth muscle MLCK is relatively low early during development and increases to become the predominant MLCK detected in all adult smooth and non-muscle tissues. The developmental expression pattern of the 208-kDa MLCK suggests this form be named, embryonic MLCK.
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Affiliation(s)
- P J Gallagher
- Department of Physiology, Indiana University School of Medicine, Indianapolis 46202-5120, USA
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81
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Watterson DM, Collinge M, Lukas TJ, Van Eldik LJ, Birukov KG, Stepanova OV, Shirinsky VP. Multiple gene products are produced from a novel protein kinase transcription region. FEBS Lett 1995; 373:217-20. [PMID: 7589469 DOI: 10.1016/0014-5793(95)01048-j] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The nonmuscle/smooth muscle myosin light chain kinase (MLCK) and the kinase related protein (KRP) that lacks protein kinase activity are myosin II binding proteins encoded in the vertebrate genome by a true gene within a gene relationship. The genomic organization and expression result in the same amino acid sequence in different molecular contexts from two different sizes of mRNA. We report here the identification and characterization of a third size class of gene products. The protein appears to be a higher molecular weight form of MLCK with additional amino terminal tail sequence which might provide differential subcellular targeting characteristics.
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Affiliation(s)
- D M Watterson
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, IL 60611-3008, USA
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82
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Abstract
Smooth muscle cells have developed a contractile machinery that allows them to exert tension on the surrounding extracellular matrix over their entire length. This has been achieved by coupling obliquely organized contractile filaments to a more-or-less longitudinal framework of cytoskeletal elements. Earlier structural data suggested that the cytoskeleton was composed primarily of intermediate filaments and played only a passive role. More recent findings highlight the segregation of actin isotypes and of actin-associated proteins between the contractile and cytoskeletal domains and raise the possibility that the cytoskeleton performs a more active function. Current efforts focus on defining the relative contributions of myosin cross-bridge cycling and actin-associated protein interactions to the maintenance of tension in smooth muscle tissue.
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Affiliation(s)
- J V Small
- Institute of Molecular Biology, Austrian Academy of Sciences, Salzburg, Austria
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83
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Katayama E, Scott-Woo G, Ikebe M. Effect of caldesmon on the assembly of smooth muscle myosin. J Biol Chem 1995; 270:3919-25. [PMID: 7876138 DOI: 10.1074/jbc.270.8.3919] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Smooth muscle myosin filaments are much less stable than the skeletal muscle counterpart. Smooth myosin requires higher concentration of Mg2+ than skeletal myosin to form thick filaments and addition of ATP disassembles the dephosphorylated smooth muscle myosin filaments into monomers but not phosphorylated ones. We found that the addition of caldesmon to dephosphorylated myosin induced the formation of the filaments under the conditions where myosin by itself is soluble or disassembled. Although the induced filaments were short at 1 mM Mg2+, they became medium sized and seemed like side polar filaments with prominent 14 nm periodicity at higher Mg2+ conditions (8 mM). In the presence of F-actin, myosin filaments induced by caldesmon were associated along actin filaments to form large structures. The association of actin and myosin filaments was observed only in the presence of caldesmon, suggesting that caldesmon cross-linked actin and myosin filaments. This cross-linking was disrupted by the addition of calmodulin. Caldesmon-induced filament formation of dephosphorylated myosin in the presence of Mg(2+)-ATP may explain the existence of myosin filaments in relaxed smooth muscle fibers. A similar effect of telokin on myosin filament assembly was also examined and is discussed.
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Affiliation(s)
- E Katayama
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44118
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84
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Abstract
Smooth muscle cells in the walls of many organs are vital for most bodily functions, and their abnormalities contribute to a range of diseases. Although based on a sliding-filament mechanism similar to that of striated muscles, contraction of smooth muscle is regulated by pharmacomechanical as well as by electromechanical coupling mechanisms. Recent studies have revealed previously unrecognized contractile regulatory processes, such as G-protein-coupled inhibition of myosin light-chain phosphatase, regulation of myosin light-chain kinase by other kinases, and the functional effects of smooth muscle myosin isoforms. Abnormalities of these regulatory mechanisms and isoform variations may contribute to diseases of smooth muscle, and the G-protein-coupled inhibition of protein phosphatase is also likely to be important in regulating non-muscle cell functions mediated by cytoplasmic myosin II.
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Affiliation(s)
- A P Somlyo
- Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville 22908
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85
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Lukas TJ, Collinge M, Haiech J, Watterson DM. Gain of function mutations for yeast calmodulin and calcium dependent regulation of protein kinase activity. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1223:341-7. [PMID: 7918668 DOI: 10.1016/0167-4889(94)90093-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Yeast calmodulin binds only three calcium ions in the presence of millimolar concentrations of magnesium due to a defective calcium-binding sequence in its carboxyl terminal domain. Yeast calmodulin's diminished calcium-binding activity can be restored to that of other calmodulins by the use of site-directed mutagenesis to substitute its fourth calcium-binding domain with that of a vertebrate calmodulin sequence. However, the repair of yeast calmodulin's calcium-binding activity is not sufficient to repair quantitatively yeast calmodulin's defective protein kinase activator activity. Yeast calmodulin's activator activity with smooth muscle and skeletal muscle myosin light chain kinases and brain calmodulin-dependent protein kinase II can be progressively repaired by additional substitutions of vertebrate calmodulin sequences, provided that the four calcium-binding sites remain intact. An unexpected result obtained during the course of these studies was the observation that myosin light chain kinases from smooth and skeletal muscle tissues can respond differently to mutations in calmodulin. These and previous results indicate that the binding of four calcium ions by calmodulin is necessary but not sufficient to bring about quantitative activation of protein kinases, and are consistent with the conformational selection/restriction model of the dynamic equilibrium among calcium, calmodulin and each calmodulin regulated enzyme.
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Affiliation(s)
- T J Lukas
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, IL 60611-3008
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