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

OBJECTIVETo investigate the role of p53 gene in serum-induced cell migration.

METHODSThe effects of p53 knockout on serum-induced formation of lamellipodia and cell migration were observed using Transwell cell migration system.

RESULTSp53(+/+) cells developed lamellipodia upon serum stimulation and showed enhanced activity of cell migration, but these effects were not observed in p53 knockout cells after serum stimulation.

CONCLUSIONp53 plays a role in serum-induced cell migration.

Animals ; Cell Line ; Cell Movement ; genetics ; Gene Expression Regulation ; Gene Knockout Techniques ; Mice ; Pseudopodia ; genetics ; metabolism ; Serum ; metabolism ; Tumor Suppressor Protein p53 ; deficiency ; genetics ; metabolism

Cellular senescence is an irreversible cell cycle arrest triggered by the activation of oncogenes or mitogenic signaling as well as the enforced expression of tumor suppressors such as p53, p16(INK4A) and promyelocytic leukemia protein (PML) in normal cells. E2F-binding protein 1 (E2FBP1), a transcription regulator for E2F, induces PML reduction and suppresses the formation of PML-nuclear bodies, whereas the down-regulation of E2FBP1 provokes the PML-dependent premature senescence in human normal fibroblasts. Here we report that the depletion of E2FBP1 induces the accumulation of PML through the Ras-dependent activation of MAP kinase signaling. The cellular levels of p16(INK4A) and p53 are elevated during premature senescence induced by depletion of E2FBP1, and the depletion of p16(INK4A), but not p53 rescued senescent cells from growth arrest. Therefore, the premature senescence induced by E2FBP1 depletion is achieved through the p16(INK4A)-Rb pathway. Similar to human normal fibroblasts, the growth inhibition induced by E2FBP1 depletion is also observed in human tumor cells with intact p16(INK4A) and Rb. These results suggest that E2FBP1 functions as a critical antagonist to the p16(INK4A)-Rb tumor suppressor machinery by regulating PML stability.
Cell Line, Tumor ; Cells, Cultured ; Cellular Senescence ; genetics ; physiology ; Cyclin-Dependent Kinase Inhibitor p16 ; antagonists & inhibitors ; genetics ; physiology ; DNA-Binding Proteins ; deficiency ; genetics ; physiology ; Down-Regulation ; Fibroblasts ; Gene Expression Regulation ; Humans ; Intranuclear Inclusion Bodies ; metabolism ; MAP Kinase Signaling System ; Nuclear Proteins ; genetics ; metabolism ; physiology ; Promyelocytic Leukemia Protein ; Protein Isoforms ; Protein Stability ; RNA Interference ; Retinoblastoma Protein ; antagonists & inhibitors ; genetics ; physiology ; Transcription Factors ; deficiency ; genetics ; metabolism ; physiology ; Transfection ; Tumor Suppressor Protein p53 ; physiology ; Tumor Suppressor Proteins ; genetics ; metabolism ; physiology ; Ubiquitination ; ras Proteins ; metabolism

Although human telomerase catalytic subunit (TERT) has several cellular functions including telomere homeostasis, genomic stability, cell proliferation, and tumorigenesis, the molecular mechanism underlying anti-apoptosis regulated by TERT remains to be elucidated. Here, we show that ectopic expression of TERT in spontaneously immortalized human fetal fibroblast (HFFS) cells, which are a telomerase- and p53-positive, leads to increases of cell proliferation and transformation, as well as a resistance to DNA damage response and inactivation of p53 function. We found that TERT and a mutant TERT (no telomerase activity) induce expression of basic fibroblast growth factor (bFGF), and ectopic expression of bFGF also allows cells to be resistant to DNA-damaging response and to suppress activation of p53 function under DNA-damaging induction. Furthermore, loss of TERT or bFGF markedly increases a p53 activity and DNA-damage sensitivity in HFFS, HeLa and U87MG cells. Therefore, our findings indicate that a novel TERT-bFGF axis accelerates the inactivation of p53 and consequent increase of resistance to DNA-damage response.
*Apoptosis ; *Catalytic Domain ; Cell Line, Transformed ; Cell Proliferation ; DNA Damage ; Fetus/cytology ; Fibroblast Growth Factor 2/*genetics/metabolism ; Fibroblasts/cytology/metabolism ; Gene Expression Regulation, Neoplastic ; Hela Cells ; Humans ; RNA, Messenger/genetics/metabolism ; Telomerase/deficiency/*metabolism ; Tumor Suppressor Protein p53/*metabolism

Germ-line mutations in BRCA2 predispose to early-onset cancer. Homozygous mutant mouse, which has Brca2 truncated in exon 11 exhibit paradoxic occurrence of growth retardation and development of thymic lymphomas. However, due to its large embryonic lethality, cohort studies on the thymic lymphomas were not feasible. With the aid of Cre-loxP system, we demonstrate here that thymus-specific disruption of Brca2 allele without crossing it to p53-mutant background leads to the development of thymic lymphomas. Varying from 16 weeks to 66 weeks after birth, 25% of mice disrupted of Brca2 in the thymus died of thymic lymphomas, whereas previous report did not observe lymphomagenesis using similar Cre-loxP system. Future analysis of thymic lymphomas from these mice presented here will provide information on the cooperative mutations that are required for the BRCA2-associated pathogenesis of cancer.
Animals ; BRCA2 Protein/deficiency/*genetics ; CD4-CD8 Ratio ; Cell Separation ; Flow Cytometry ; Integrases/*genetics/immunology ; Lymphoma/*genetics/immunology/metabolism/pathology ; Mice ; Mice, Knockout ; Organ Specificity ; *Sequence Deletion ; T-Lymphocytes/enzymology/*immunology ; Thymus Gland/immunology/metabolism/pathology ; Thymus Neoplasms/*genetics/immunology/metabolism/pathology ; Tumor Suppressor Protein p53/deficiency/genetics/immunology