Nobuyuki Kanzawa

Specific knockdown of m-calpain blocks myogenesis with cDNA deduced from the corresponding RNAi

Fusion of mononuclear myoblast to multinucleated myotubes is crucial for myogenesis. Both mu- and m-calpain are ubiquitously expressed in most cells and are particularly abundant in muscle cells. Knockout of calpain-1 (catalytic subunit of mu-calpain) induced moderate platelet dysaggregation, preserving the normal development and growth, although knockout of calpain-2 (m-calpain) is lethal in mice. Therefore, there should be muscle-specific function of m-calpain per se. Previous methods lack direct evidence for the involvement of m-calpain, because the specific inhibitor to m-calpain has not been developed yet and the inhibition was less potent. Here, we show that screened RNA interference (RNAi) specifically blocked the m-calpain expression by 95% at both the protein and the activity levels. After transfection of adenovirus vector-mediated cDNA corresponding to the RNAi-induced short hairpin RNA, m-calpain in C(2)C(12) myoblasts was knocked down with no compensatory overexpression of mu-calpain or calpain-3. The specific knockdown strongly inhibited the fusion to multinucleated myotubes. In addition, the knockdown modestly blocked ubiquitous effects, including cell migration, cell spreading, and alignment of central stress fiberlike structures. These results may indicate that m-calpain requiring millimolar Ca(2+) level for the full activation plays specific roles in myogenesis, independent of mu-calpain, and leave us challenging problems in the future.

CHARACTERIZATION OF MYOSIN AND PARAMYOSIN FROM CRAYFISH FAST AND SLOW MUSCLES

Myosin and paramyosin were purified to homogeneity from deep abdominal flexor and extensor, and claw closer and opener muscles of crayfish. Myosins from fast muscle (deep abdominal flexor and extensor) consisted of one species of heavy chain and two species of light chains, Lf21 and Lf18. Myosin from slow muscle (opener) consisted of two species of heavy chains and three species of light chains, Ls31, Ls21 and Ls18. Closer myosin containing both fast and slow types of muscles contained Lf21, Lf18, Ls31, Ls21 and Ls18. The actin-Mg2+-activated, Ca2+-activated, and K+-EDTA-activated ATPase activities of the fast muscle type of myosins were much higher than those of the slow muscle type of myosin. The ATPase activities of closer myosin were in-between. The optimal KCI concentration of the K+-EDTA-activated ATPase activity of crayfish myosins was around 0.4 M as compared to 1 M in rabbit skeletal muscle. Opener myosin was contaminated with a 130 kDa protein. The latter turned out to be a paramyosin isoform. Slow type of muscle including closer muscle contained both 130 kDa and 105 kDa paramyosin isoforms. On the other hand, fast muscle expressed 110 kDa paramyosin isoform.

Sea anemone (Actinia equina) myosin

Abstract 1. 1. Myosin was purified to homogeneity from both tentacle and body of the sea anemone, Actinia equina . 2. 2. Sea anemone myosin was two-headed myosin (Type II), approximately 160 nm long. 3. 3. The tail tended to bend at about 60 nm from the tip of the tail. 4. 4. Sea anemone myosin consisted of heavy chain (about 230 kDa) and two species of light chains: 18 and 19 kDa for tentacle myosin; 17 and 22 kDa for body myosin. 5. 5. The K + -EDTA-activated and Ca 2+ -activated ATPase activities were approximately 0.40 and 0.07 (tentacle), 0.39 and 0.06 (body) μmol mg −1 min −1 , respectively. 6. 6. In both myosins, the Mg 2+ -actin activated ATPase activities were as low as 0.02 μmol mg −1 min −1 . 7. 7. However, it was elevated to 0.055 μmol mg −1 min −1 , when myosin light chain was phosphorylated by myosin light chain kinase from chicken gizzard. 8. 8. It appears that sea anemone myosin-actin interaction was regulated by myosin light chain phosphorylation.

Purification and Biochemical Characterization of a Novel Ecto-Apyrase, MP67, from Mimosa pudica

We have previously reported the presence of an apyrase in Mimosa pudica. However, only limited information is available for this enzyme. Thus, in this study, the apyrase was purified to homogeneity. The purified enzyme had a molecular mass of around 67 kD and was able to hydrolyze both nucleotide triphosphate and nucleotide diphosphate as substrates. The ratio of ATP to ADP hydrolysis velocity of the purified protein was 0.01 in the presence of calcium ion, showing extremely high substrate specificity toward ADP. Thus, we designated this novel apyrase as MP67. A cDNA clone of MP67 was obtained using primers designed from the amino acid sequence of trypsin-digested fragments of the protein. In addition, rapid amplification of cDNA ends-polymerase chain reaction was performed to clone a conventional apyrase (MpAPY2). Comparison of the deduced amino acid sequences showed that MP67 is similar to ecto-apyrases; however, it was distinct from conventional apyrase based on phylogenetic classification. MP67 and MpAPY2 were expressed in Escherichia coli, and the recombinant proteins were purified. The recombinant MP67 showed high substrate specificity toward ADP rather than ATP. A polyclonal antibody raised against the recombinant MP67 was used to examine the tissue distribution and localization of native MP67 in the plant. The results showed that MP67 was ubiquitously distributed in various tissues, most abundantly in leaves, and was localized to plasma membranes. Thus, MP67 is a novel ecto-apyrase with extremely high substrate specificity for ADP.

Identification and characterization of Tetrahymena myosin

Abstract Myosin was partially purified from ciliated protozoan Tetrahymena pyriformis. Tetrahymena myosin has a fibrous tail with two globular heads at one end and contains 220-kDa heavy chains. The tail length of the molecule (200 nm) is longer than that of myosins from other animals (approximately 160 nm). A sample after HPLC column chromatography containing 220-kDa peptide showed a myosin-specific K + -/NH 4 + -EDTA-ATPase activity. Polyclonal anti-crayfish myosin heavy chain antibody reacted with Tetrahymena 220-kDa myosin heavy chain, and monoclonal anti-pan myosin antibody reacted with Tetrahymena 180-kDa peptide. The isolated 180-kDa peptide was identified as a clathrin heavy chain.

Mutagenesis of apyrase conserved region 1 alters the nucleotide substrate specificity

Two apyrases having different substrate specificity, MP67 and MpAPY2, are present in Mimosa pudica. The substrate specificity of MP67 is quite high against ADP, and is distinct from any other apyrase. This might be attributed to the nucleotide binding motif (DXG) in apyrase conserved region 1. We performed a single amino acid substitution at position X in the motif. The ratio of the velocity of ATP/ADP hydrolysis was higher (approximately 1) for the S63A-MP67 mutant than for wild type-MP67 (0.19). Binding affinity for ADP of A75S-MpAPY2 mutant was increased to a level higher than that of the wild type MpAPY2. Thus, the residue at position X in the DXG motif plays an important role in determining nucleotide preference.

Comparative expression and tissue distribution analyses of astacin-like squid metalloprotease in squid and cuttlefish.

Abstract Astacin-like squid metalloprotease (ALSM) is a member of the astacin family of metalloproteases. In the present study, we investigated the expression and tissue distribution of ALSM in bigfin reef squid (Sepioteuthis lessoniana) and golden cuttlefish (Sepia esculenta). Myosin heavy chain hydrolysis tests showed ALSM-I-like activity in both species. We isolated partial cDNA clones showing high sequence similarity to ALSM-I and -III, suggesting that ALSM is common to squid and cuttlefish. Phylogenetic analysis showed that ALSMs are classified into two clades: ALSM-I forms one clade, and ALSM-II and -III form the other. ALSM was expressed in several tissues in bigfin reef squid, though expression was confined to the liver in cuttlefish. ALSMs are distributed in digestive organs but not in mantle muscle of squid and cuttlefish. Immunofluorescence analysis further showed that cellular localization of ALSM is evident not only in hepatic cells but also in pancreatic cells of bigfin reef squid. Thus, ALSM is commonly expressed in squid and cuttlefish, but its expression levels and distribution are distinct.