Yuji Yamanashi

Impaired proliferation of peripheral B cells and indication of autoimmune disease in lyn-deficient mice.

The Src family protein-tyrosine kinase Lyn associates physically with the BCR and has been suggested to play an important role in BCR-mediated signaling. Studies with lyn-/- mice showed that the number of B cells decreased by half in their peripheral tissues. In addition, these B cells do not respond normally to a number of stimuli, including BCR cross-linking and CD40 ligand. Induction of tyrosine phosphorylation on a variety of cellular proteins, such as Vav, Cbl, and HS1, upon BCR cross-linking was also abolished in these B cells. Despite the impaired BCR-mediated signaling, concentrations of IgM and IgA in sera were remarkably elevated, and production of autoantibodies was detected in lyn-/- mice. Histological study showed splenomegaly and enlargement of lymph nodes that became evident with age in the mutant mice. The spleen contained significant number of plasma cells as well as unusual lymphoblast-like cells carrying Mac1 antigen and cytoplasmic IgM. These cells spontaneously secreted a large amount of IgM in vitro. Finally, significant number of lyn-/- mice show glomerulonephritis, an indication of autoimmune disease. From these data, we conclude that Lyn plays a role in signal transduction for not only clonal expansion and terminal differentiation of peripheral B cells but also elimination of autoreactive B cells.

The Muscle Protein Dok-7 Is Essential for Neuromuscular Synaptogenesis

The formation of the neuromuscular synapse requires muscle-specific receptor kinase (MuSK) to orchestrate postsynaptic differentiation, including the clustering of receptors for the neurotransmitter acetylcholine. Upon innervation, neural agrin activates MuSK to establish the postsynaptic apparatus, although agrin-independent formation of neuromuscular synapses can also occur experimentally in the absence of neurotransmission. Dok-7, a MuSK-interacting cytoplasmic protein, is essential for MuSK activation in cultured myotubes; in particular, the Dok-7 phosphotyrosine-binding domain and its target in MuSK are indispensable. Mice lacking Dok-7 formed neither acetylcholine receptor clusters nor neuromuscular synapses. Thus, Dok-7 is essential for neuromuscular synaptogenesis through its interaction with MuSK.

Autoantibodies to low‐density lipoprotein receptor–related protein 4 in myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease of the neuromuscular junction, where acetylcholine receptor (AChR), muscle‐specific kinase (MuSK), and low‐density lipoprotein (LDL) receptor‐related protein 4 (Lrp4) are essential. About 80% and 0% to 10% of patients with generalized MG have autoantibodies to AChR and MuSK, respectively, but pathogenic factors are elusive in others. Here we show that a proportion of AChR antibody‐negative patients have autoantibodies to Lrp4. These antibodies inhibit binding of Lrp4 to its ligand and predominantly belong to the immunoglobulin G1 (IgG1) subclass, a complement activator. These findings together indicate the involvement of Lrp4 antibodies in the pathogenesis of AChR antibody‐negative MG. Ann Neurol 2011

Construction of an Excisable Bacterial Artificial Chromosome Containing a Full-Length Infectious Clone of Herpes Simplex Virus Type 1: Viruses Reconstituted from the Clone Exhibit Wild-Type Properties In Vitro and In Vivo

ABSTRACT In recent years, several laboratories have reported on the cloning of herpes simplex virus type 1 (HSV-1) genomes as bacterial artificial chromosomes (BACs) in Escherichia coli and on procedures to manipulate these genomes by using the bacterial recombination machinery. However, the HSV-BACs reported so far are either replication incompetent or infectious, with a deletion of one or more viral genes due to the BAC vector insertion. For use as a multipurpose clone in research on HSV-1, we attempted to generate infectious HSV-BACs containing the full genome of HSV-1 without any loss of viral genes. Our results were as follows. (i) E. coli (YEbac102) harboring the full-length HSV-1 genome (pYEbac102) in which a BAC flanked by loxP sites was inserted into the intergenic region between UL3 and UL4 was constructed. (ii) pYEbac102 was an infectious molecular clone, given that its transfection into rabbit skin cells resulted in production of infectious virus (YK304). (iii) The BAC vector sequence was almost perfectly excisable from the genome of the reconstituted virus YK304 by coinfection of Vero cells with YK304 and a recombinant adenovirus, AxCANCre, expressing Cre recombinase. (iv) As far as was examined, the reconstituted viruses from pYEbac102 could not be phenotypically differentiated from wild-type viruses in vitro and in vivo. Thus, the viruses grew as well in Vero cells as did the wild-type virus and exhibited wild-type virulence in mice on intracerebral inoculation. (v) The infectious molecular clone pYEbac102 is in fact useful for mutagenesis of the HSV-1 genome by bacterial genetics, and a recombinant virus carrying amino acid substitutions in both copies of the α0 gene was generated. pYEbac102 will have multiple applications to the rapid generation of genetically engineered HSV-1 recombinants in basic research into HSV-1 and in the development of HSV vectors in human therapy.

Dok-7 Mutations Underlie a Neuromuscular Junction Synaptopathy

Congenital myasthenic syndromes (CMSs) are a group of inherited disorders of neuromuscular transmission characterized by fatigable muscle weakness. One major subgroup of patients shows a characteristic “limb girdle” pattern of muscle weakness, in which the muscles have small, simplified neuromuscular junctions but normal acetylcholine receptor and acetylcholinesterase function. We showed that recessive inheritance of mutations in Dok-7, which result in a defective structure of the neuromuscular junction, is a cause of CMS with proximal muscle weakness.

The yes-related cellular gene lyn encodes a possible tyrosine kinase similar to p56lck.

With v-yes DNA as the probe, a human cDNA library made from placental RNA was screened under relaxed conditions, and DNA clones derived from a novel genetic locus, termed lyn, were obtained. Nucleotide sequencing revealed that lyn could encode a novel tyrosine kinase that was very similar to mouse T-lymphocyte-specific tyrosine kinase p56lck and the v-yes protein as well as to the gene products of v-fgr and v-src. Northern hybridization analysis revealed that a 3.2-kilobase lyn mRNA was expressed in a variety of tissues of the human fetus. The pattern of lyn mRNA expression was different from those of related genes, such as yes and syn. Hybridization analysis of DNA from sorted chromosomes showed that the lyn gene is located on human chromosome 8 q13-qter.

Tyrosine phosphorylation of p62 Dok induced by cell adhesion and insulin: possible role in cell migration

Dok, a 62‐kDa Ras GTPase‐activating protein (rasGAP)‐associated phosphotyrosyl protein, is thought to act as a multiple docking protein downstream of receptor or non‐receptor tyrosine kinases. Cell adhesion to extracellular matrix proteins induced marked tyrosine phosphorylation of Dok. This adhesion‐dependent phosphorylation of Dok was mediated, at least in part, by Src family tyrosine kinases. The maximal insulin‐induced tyrosine phosphorylation of Dok required a Src family kinase. A mutant Dok (DokΔPH) that lacked its pleckstrin homology domain failed to undergo tyrosine phosphorylation in response to cell adhesion or insulin. Furthermore, unlike the wild‐type protein, DokΔPH did not localize to subcellular membrane components. Insulin promoted the association of tyrosine‐phosphorylated Dok with the adapter protein NCK and rasGAP. In contrast, a mutant Dok (DokY361F), in which Tyr361 was replaced by phenylalanine, failed to bind NCK but partially retained the ability to bind rasGAP in response to insulin. Overexpression of wild‐type Dok, but not that of DokΔPH or DokY361F, enhanced the cell migratory response to insulin without affecting insulin activation of mitogen‐activated protein kinase. These results identify Dok as a signal transducer that potentially links, through its interaction with NCK or rasGAP, cell adhesion and insulin receptors to the machinery that controls cell motility.

Conserved Protein Kinases Encoded by Herpesviruses and Cellular Protein Kinase cdc2 Target the Same Phosphorylation Site in Eukaryotic Elongation Factor 1δ

ABSTRACT Earlier studies have shown that translation elongation factor 1δ (EF-1δ) is hyperphosphorylated in various mammalian cells infected with representative alpha-, beta-, and gammaherpesviruses and that the modification is mediated by conserved viral protein kinases encoded by herpesviruses, including UL13 of herpes simplex virus type 1 (HSV-1), UL97 of human cytomegalovirus, and BGLF4 of Epstein-Barr virus (EBV). In the present study, we attempted to identify the site in EF-1δ associated with the hyperphosphorylation by the herpesvirus protein kinases. Our results are as follows: (i) not only in infected cells but also in uninfected cells, replacement of the serine residue at position 133 (Ser-133) of EF-1δ by alanine precluded the posttranslational processing of EF-1δ, which corresponds to the hyperphosphorylation. (ii) A purified chimeric protein consisting of maltose binding protein (MBP) fused to a domain of EF-1δ containing Ser-133 (MBP-EFWt) is specifically phosphorylated in in vitro kinase assays by purified recombinant UL13 fused to glutathione S-transferase (GST) expressed in the baculovirus system. In contrast, the level of phosphorylation by the recombinant UL13 of MBP-EFWt carrying an alanine replacement of Ser-133 (MBP-EFS133A) was greatly impaired. (iii) MBP-EFWt is also specifically phosphorylated in vitro by purified recombinant BGLF4 fused to GST expressed in the baculovirus system, and the level of phosphorylation of MBP-EFS133A by the recombinant BGLF4 was greatly reduced. (iv) The sequence flanking Ser-133 of EF-1δ completely matches the consensus phosphorylation site for a cellular protein kinase, cdc2, and in vitro kinase assays revealed that purified cdc2 phosphorylates Ser-133 of EF-1δ. (v) As observed with EF-1δ, the casein kinase II β subunit (CKIIβ) was specifically phosphorylated by UL13 in vitro, while the level of phosphorylation of CKIIβ by UL13 was greatly diminished when a serine residue at position 209, which has been reported to be phosphorylated by cdc2, was replaced with alanine. These results indicate that the conserved protein kinases encoded by herpesviruses and a cellular protein kinase, cdc2, have the ability to target the same amino acid residues for phosphorylation. Our results raise the possibility that the viral protein kinases mimic cdc2 in infected cells.

The roles of Dok family adapters in immunoreceptor signaling

Summary:  The mammalian Dok protein family has seven members (Dok‐1–Dok‐7). The Dok proteins share structural similarities characterized by the NH2‐terminal pleckstrin homology and phosphotyrosine‐binding domains followed by SH2 target motifs in the COOH‐terminal moiety, indicating an adapter function. Indeed, Dok‐1 was originally identified as a 62 kDa protein that binds with p120 rasGAP, a potent inhibitor of Ras, upon tyrosine phosphorylation by a variety of protein tyrosine kinases. Among the Dok family, only Dok‐1, Dok‐2, and Dok‐3 are preferentially expressed in hematopoietic/immune cells. Dok‐1 and its closest relative Dok‐2 act as negative regulators of the Ras–Erk pathway downstream of many immunoreceptor‐mediated signaling systems, and it is believed that recruitment of p120 rasGAP by Dok‐1 and Dok‐2 is critical to their negative regulation. By contrast, Dok‐3 does not bind with p120 rasGAP. However, accumulating evidence has demonstrated that Dok‐3 is a negative regulator of the activation of JNK and mobilization of Ca2+ in B‐cell receptor‐mediated signaling, where the interaction of Dok‐3 with SHIP‐1 and Grb2 appears to be important. Here, we review the physiological roles and underlying mechanisms of Dok family proteins.

Characterization of cDNA clones for the human c-yes gene

Three c-yes cDNA clones were obtained from poly(A)+ RNA of human embryo fibroblasts. Sequence analysis of the clones showed that they contained inserts corresponding to nearly full-length human c-yes mRNA, which could encode a polypeptide of 543 amino acids with a relative molecular weight (Mr) of 60,801. The predicted amino acid sequence of the protein has no apparent membrane-spanning region or suspected ligand binding domain and closely resembles pp60c-src. Comparison of the sequences of c-yes and v-yes revealed that the v-yes gene contains most of the c-yes coding sequence except the region encoding its extreme carboxyl terminus. The region missing from the v-yes protein is the part that is highly conserved in cellular gene products of the protein-tyrosine kinase family.