Cofilin phosphorylation and actin polymerization by NRK/NESK,a member of the germinal center kinase family

Nck-interacting kinase (NIK)-related kinase (NRK)/NIK-like embryo-specific kinase (NESK) is a protein kinase that belongs to the germinal center kinase family, and activates the c-Jun N-terminal kinase (JNK) signaling pathway. In this study, we examined the effect of NRK/NESK on actin cytoskeletal organization. Overexpression of NRK/NESK in COS7 cells induced accumulation of polymerized actin at the perinuclear. Phosphorylation of cofilin, an actin-depolymerizing factor, was increased in NRK/NESK-expressing HEK 293T cells. In addition, in vitro phosphorylation of cofilin was observed on NRK/NESK immunoprecipitates from HEK 293T cells expressing the kinase domain of NRK/NESK. The cofilin phosphorylation occurred at the serine residue of position 3 (Ser-3). Since the phosphorylation at Ser-3 inactivates the actin-depolymerizing activity of cofilin, these results suggest that NRK/NESK induces actin polymerization through cofilin phosphorylation. The cofilin phosphorylation did not appear to be mediated through activation of LIM-kinasel, a cofilin-phosphorylating kinase, or through the activation of JNK. Thus, cofilin is likely to be a direct substrate of NRK/NESK. NRK/NESK is predominantly expressed in skeletal muscle during the late stages of mouse embryogenesis. Thus, NRK/NESK may be involved in the regulation of actin cytoskeletal organization in skeletal muscle cells through cofilin phosphorylation.     

The PIR domain of Grb14 is an intrinsically unstructured protein: implication in insulin signaling

Grb14 belongs to the Grb7 family of adapter proteins and was identified as a negative regulator of insulin signal transduction. Its inhibitory effect on the insulin receptor kinase activity is controlled by a newly discovered domain called PIR. To investigate the biochemical and biophysical characteristics of this new domain, we cloned and purified recombinant PIR-SH2, PIR, and SH2 domains. The isolated PIR and PIR-SH2 domains were physiologically active and inhibited insulin-induced reinitiation of meiosis in the Xenopus oocytes system. However, NMR experiments on (15)N-labelled PIR revealed that it did not present secondary structure. These results suggest that the PIR domain belongs to the growing family of intrinsically unstructured proteins.     

A repressor element in the 5'-untranslated region of human Pax5 exon 1A

Five members of the RecQ helicase family, RECQL, WRN, BLM, RTS and RECQL5, have been found in human and three of them (WRN, BLM and RTS) were disclosed to be the genes responsible for Werner, Bloom and Rothmund–Thomson syndromes, respectively. RECQL5 (RecQ helicase protein-like 5) was isolated as the fifth member of the family in humans through a search of homologous expressed sequence tags. The gene is expressed with at least three alternative splicing products, , β and γ. Here, we isolated mouse RECQL5β and determined the DNA sequence of full-length cDNA as well as the genome organization and chromosome locus. The mouse RECQL5β gene consists of 2949 bp coding 982 amino acid residues. Comparison of amino acid sequence among human (Homo sapiens), mouse (Mus musculus), Drosophila melanogaster and Caenorhabditis elegans RECQL5β homologs revealed three portions of highly conserved regions in addition to the helicase domain. Nineteen exons are dispersed over 40 kbp in the genome and all of the acceptor and donor sites for the splicing of each exon conform to the GT/AG rule. The gene is localized to the mouse chromosome 11E2, which has a syntenic relation to human 17q25.2-q25.3 where human RECQL5β exists. Our genetic characterizations of the mouse RECQL5β gene will contribute to functional studies on the RECQL5β products.     

Low-density lipoprotein receptor family: endocytosis and signal transduction

The low-density lipoprotein receptor (LDLR) family is composed of a class of single transmembrane glycoproteins, generally recognized as cell surface endocytic receptors, which bind and internalize extracellular ligands for degradation by lysosomes. Structurally, members of the LDLR family share homology within their extracellular domains, which are highlighted by the presence of clusters of ligand-binding repeats. Recently, information regarding the structural and functional elements within their cytoplasmic tails has begun to emerge, which suggests that members of the LDLR family function not only in receptor-mediated endocytosis, but also in transducing signals that are important during embryonic development and the pathogenesis of Alzheimer's disease. This review focuses on recent knowledge of the structural and functional aspects of LDLR family members in endocytosis and signal transduction. The relationship of these functions to the development of the neuronal system and in the pathogenesis of Alzheimer's disease is specifically discussed.     

A novel two-step mechanism for removal of a mitochondrial signal sequence involves the mAAA complex and the putative rhomboid protease Pcp1

The yeast protein cytochrome c peroxidase (Ccp1) is nuclearly encoded and imported into the mitochondrial intermembrane space, where it is involved in degradation of reactive oxygen species. It is known, that Ccp1 is synthesised as a precursor with a N-terminal pre-sequence, that is proteolytically removed during transport of the protein. Here we present evidence for a new processing pathway, involving novel signal peptidase activities. The mAAA protease subunits Yta10 (Afg3) and Yta12 (Rca1) were identified both to be essential for the first processing step. In addition, the Pcp1 (Ygr101w) gene product was found to be required for the second processing step, yielding the mature Ccp1 protein. The newly identified Pcp1 protein belongs to the rhomboid-GlpG superfamily of putative intramembrane peptidases. Inactivation of the protease motifs in mAAA and Pcp1 blocks the respective steps of proteolysis. A model of coupled Ccp1 transport and N-terminal processing by the mAAA complex and Pcp1 is discussed. Similar processing mechanisms may exist, because the mAAA subunits and the newly identified Pcp1 protein belong to ubiquitous protein families.     

The role of astroglia on the survival of dopamine neurons

Glial cells play a key role in the function of dopamine (DA) neurons and regulate their differentiation, morphology, physiological and pharmacological properties, survival, and resistance to different models of DA lesion. Several studies suggest that glial cells may be important in the pathogenesis of Parkinson’s disease (PD), a common neurodegenerative disorder characterized by degeneration of the nigrostriatal DA system. In this disease the role of glia could be due to the excessive production of toxic products such as nitric oxide (NO) or cytokines characteristic of inflammatory process, or related to a defective release of neuroprotective agents, such as small antioxidants with free radical scavenging properties or peptidic neurotrophic factors.     

The PRINTS database: a resource for identification of protein families

The PRINTS database houses a collection of protein fingerprints, which may be used to assign family and functional attributes to uncharacterised sequences, such as those currently emanating from the various genome-sequencing projects. The April 2002 release includes 1,700 family fingerprints, encoding approximately 10,500 motifs, covering a range of globular and membrane proteins, modular polypeptides and so on. Fingerprints are groups of conserved motifs that, taken together, provide diagnostic protein family signatures. They derive much of their potency from the biological context afforded by matching motif neighbours; this makes them at once more flexible and powerful than single-motif approaches. The technique further departs from other pattern-matching methods by readily allowing the creation of fingerprints at superfamily-, family- and subfamily-specific levels, thereby allowing more fine-grained diagnoses. Here, we provide an overview of the method of protein fingerprinting and how the results of fingerprint analyses are used to build PRINTS and its relational cousin, PRINTS-S.