Cellular senescence is a tumor-suppressive process instigated by proliferation in the absence of telomere replication, by cellular stresses such as oncogene activation, or by activation of the tumor suppressor proteins, such as Rb or p53. This process is characterized by an irreversible cell cycle exit, a unique morphology, and expression of senescence-associated-beta-galactosidase (SA-beta-gal). Despite the potential biological importance of cellular senescence, little is known of the mechanisms leading to the senescent phenotype. p41-Arc has been known to be a putative regulatory component of the mammalian Arp2/3 complex, which is required for the formation of branched networks of actin filaments at the cell cortex. In this study, we demonstrate that p41-Arc can induce senescent phenotypes when it is overexpressed in human tumor cell line, SaOs-2, which is deficient in p53 and Rb tumor suppressor genes, implying that p41 can induce senescence in a p53-independent way. p41-Arc overexpression causes a change in actin filaments, accumulating actin filaments in nuclei. Therefore, these results imply that a change in actin filament can trigger an intrinsic senescence program in the absence of p53 and Rb tumor suppressor genes.
Actin Cytoskeleton/metabolism ; Actin-Related Protein 2-3 Complex/*metabolism ; *Cell Aging ; Cell Cycle Proteins/metabolism ; Cell Line, Tumor ; Cell Nucleus/metabolism ; Fibroblasts/physiology ; Humans ; Recombinant Proteins/genetics/*metabolism ; Retinoblastoma Protein/*deficiency/genetics ; Tumor Suppressor Protein p53/*deficiency/genetics

The baculovirus-induced actin polymerization is mainly associated with the virus nucleocapsid protein P78/83, which is homologous with WASP proteins that can activate Arp2/3 complex and induce the actin polymerization. In order to explore the role of Arp2/3 complex in the baculovirus replication, the P40 subunit of Arp2/3 complex from Sf9 (Spodoptera frugiperda 9) cell line was cloned and characterized. Immunofluorescent microscopy assay indicated that P40 was recruited to the inner-side of nuclear membrane during virus infection, which was in accordance with nuclear F-actin distribution in virus-infected cells as documented in our previous research, suggesting P40 could be used to track Arp2/3 complex subcellular distribution changes during virus infection. In addition, co-immunoprecipitation assay demonstrated that P40 interacted with P78/83 only in virus-infected cells, suggesting that actin polymerization induced by P78/83-Arp2/3 complex during baculovirus infection was regulated by some unidentified virus factors.
Actin-Related Protein 2-3 Complex ; chemistry ; genetics ; metabolism ; Amino Acid Sequence ; Animals ; Capsid Proteins ; genetics ; metabolism ; Cell Line ; Cloning, Molecular ; Humans ; Insect Proteins ; chemistry ; genetics ; metabolism ; Molecular Sequence Data ; Nucleopolyhedrovirus ; genetics ; metabolism ; Phylogeny ; Protein Binding ; Sequence Alignment ; Sf9 Cells ; Spodoptera ; chemistry ; genetics ; metabolism ; virology

This study was aimed to investigate the effect of low dose radiation (LDR) on human bone marrow mesenchymal stem cells (MSCs) by using proteomic analysis. The bidirectional gel electrophoresis was used to establish the two-dimensional gel electrophoresis patterns of proteome in group of MSCs exposed to LDR and in group of sham irradiated MSCs, the matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) was used to identify the differentially expressed proteins in two groups. The results showed that among the differentially expressed proteins in the two groups, the expressions of 12 proteins were up-regulated, the expressions of 12 protein were down-regulated, 3 proteins disappeared after LDR, 12 proteins had been identified by MALDI-TOF-MS. In conclusion, the identified 12 proteins, such as prolyl 4-hydroxylase, dihydropyrimidinase-like 2 variant, ARP3 (actin-related protein 3, yeast) homolog, guanine nucleotide binding protein (G protein), phosphoglycerate mutase 1 may be related to mechanism of LDR effect. The study provides some new explanation for the mechanism of low dose radiation injury.
Actin-Related Protein 3 ; analysis ; Bone Marrow Cells ; radiation effects ; Dose-Response Relationship, Radiation ; GTP-Binding Proteins ; analysis ; Humans ; Mesenchymal Stromal Cells ; metabolism ; radiation effects ; Procollagen-Proline Dioxygenase ; analysis ; Proteins ; analysis ; Proteomics ; methods ; Radiation Dosage ; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

Human telomerase reverse transcriptase (hTERT) plays a central role in telomere lengthening for continuous cell proliferation, but it remains unclear how extracellular cues regulate telomerase lengthening of telomeres. Here we report that the cytokine bone morphogenetic protein-7 (BMP7) induces the hTERT gene repression in a BMPRII receptor- and Smad3-dependent manner in human breast cancer cells. Chonic exposure of human breast cancer cells to BMP7 results in short telomeres, cell senescence and apoptosis. Mutation of the BMPRII receptor, but not TGFbRII, ACTRIIA or ACTRIIB receptor, inhibits BMP7-induced repression of the hTERT gene promoter activity, leading to increased telomerase activity, lengthened telomeres and continued cell proliferation. Expression of hTERT prevents BMP7-induced breast cancer cell senescence and apoptosis. Thus, our data suggest that BMP7 induces breast cancer cell aging by a mechanism involving BMPRII receptor- and Smad3-mediated repression of the hTERT gene.
Actin-Related Protein 2 ; genetics ; metabolism ; Activin Receptors, Type II ; genetics ; metabolism ; Bone Morphogenetic Protein 7 ; genetics ; metabolism ; Bone Morphogenetic Protein Receptors, Type II ; genetics ; metabolism ; Breast Neoplasms ; genetics ; metabolism ; Cellular Senescence ; Female ; HeLa Cells ; Humans ; MCF-7 Cells ; Neoplasm Proteins ; genetics ; metabolism ; Protein-Serine-Threonine Kinases ; genetics ; metabolism ; Receptor, Transforming Growth Factor-beta Type II ; Receptors, Transforming Growth Factor beta ; genetics ; metabolism ; Smad3 Protein ; genetics ; metabolism ; Telomerase ; genetics ; metabolism ; Telomere Homeostasis