AREL1 E3 ubiquitin ligase inhibits TNF-induced necroptosis via the ubiquitination of MTX2.

Previously, we reported on a novel anti-apoptotic E3 ubiquitin ligase, apoptosis-resistant E3 ubiquitin protein ligase 1 (AREL1), that ubiquitinates inhibitors of apoptosis proteins antagonists. The present study demonstrated that AREL1 ubiquitinated Metaxin 2 (MTX2), which was involved in TNF-induced necroptosis. MTX2 has been identified as a protein that belongs to the Metaxin family.

Repression of the F-box protein Skp2 is essential for actin damage-induced tetraploid G1 arrest.

We previously reported that p53 plays a role as a key regulator in the tetraploid G1 checkpoint, which is activated by actin damage-induced cytokinesis blockade and then prevents uncoupled DNA replication and nuclear division without cytokinesis. In this study, we investigated a role of Skp2, which targets CDK2 inhibitor p27/Kip1, in actin damage-induced tetraploid G1 arrest. Expression of Skp2 was reduced, but p27/Kip1 was increased, after actin damage-induced cytokinesis blockade.

Inhibition of senescence and promotion of the proliferation of chondrocytes from articular cartilage by CsA and FK506 involves inhibition of p38MAPK.

Cyclosporine A (CsA) and tacrolimus (FK506) are the most important immunosuppressive compounds that block the activation of helper T-cells. In this study, we investigated the effects of CsA and FK506 on growth and senescence of articular chondrocytes. Chondrocytes from young rabbit cartilage entered senescence after 8.

Identification of a novel anti-apoptotic E3 ubiquitin ligase that ubiquitinates antagonists of inhibitor of apoptosis proteins SMAC, HtrA2, and ARTS.

Identification of new anti-apoptotic genes is important for understanding the molecular mechanisms underlying apoptosis and tumorigenesis. The present study identified a novel anti-apoptotic gene named AREL1, which encodes a HECT (homologous to E6-AP carboxyl terminus) family E3 ubiquitin ligase. AREL1 interacted with and ubiquitinated IAP antagonists such as SMAC, HtrA2, and ARTS.

DNA damage induces the IL-6/STAT3 signaling pathway, which has anti-senescence and growth-promoting functions in human tumors.

IL-6 is a multifunctional cytokine that is important for immune responses, cell survival, apoptosis, and proliferation. However, little is known about the correlation between the IL-6 signaling pathway and DNA damage in human tumors. The present study demonstrates the role of the IL-6/STAT3 signaling pathway in human tumor cells exposed to DNA damage.

p53 and DNA-dependent protein kinase catalytic subunit independently function in regulating actin damage-induced tetraploid G1 arrest.

We previously reported that the p53 tumor suppressor protein plays an essential role in the induction of tetraploid G1 arrest in response to perturbation of the actin cytoskeleton, termed actin damage. In this study, we investigated the role of p53, ataxia telangiectasia mutated protein (ATM), and catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in tetraploid G1 arrest induced by actin damage. Treatment with actin- damaging agents including pectenotoxin-2 (PTX-2) increases phosphorylation of Ser-15 and Ser-37 residues of p53, but not Ser-20 residue.

NF-Y binds to both G1- and G2-specific cyclin promoters; a possible role in linking CDK2/Cyclin A to CDK1/Cyclin B.

We previously reported that CDK2/Cyclin A can phosphorylate and activate the transcription factor NF-Y. In this study, we investigated a potential regulatory role for NF-Y in the transcription of Cyclin A and other cell cycle regulatory genes. Gel-shift assays demonstrate that NF-Y binds to CCAAT sequences in the Cyclin A promoter, as well as to those in the promoters of cell cycle G2 regulators such as CDC2, Cyclin B and CDC25C.

p41-Arc, a regulatory subunit of Arp2/3 complex, can induce premature senescence in the absence of p53 and Rb.

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-β-galactosidase (SA-β-gal). Despite the potential biological importance of cellular senescence, little is known of the mechanisms leading to the senescent phenotype.

p53 prevents immature escaping from cell cycle G2 checkpoint arrest through inhibiting cdk2-dependent NF-Y phosphorylation.

Purpose: Recent studies have suggested that p53 regulates the G2 checkpoint in the cell cycle and this function is required for the maintenance of genomic integrity. In this study, we addressed a role of p53 in escaping from cell cycle G2 arrest following DNA damage.

Materials And Methods: Cell cycle checkpoint arrest in the human colon cancer cell line HCT116 and its derivatives carry p53 or p21 deletions, were examined by FACS analysis, immunoprecipitation, Western blot and IP-kinase assay.

Transcription repression of a CCAAT-binding transcription factor CBF/HSP70 by p53.

NF-Y transcription factor binds to CCAAT boxes on promoters of cell cycle regulatory genes such as cdc2, cyclin B, cdc25C, and cyclin A. We previously reported that the DNA binding activity of NF-Y is regulated by p53-p21-cdk2 pathway. CBF/HSP70 was originally identified as a transcription factor binding to the CCAAT box on the hsp70 promoter and mediates transcription repression of hsp70 pro- moter by p53.

Oocyte-based screening of cytokinesis inhibitors and identification of pectenotoxin-2 that induces Bim/Bax-mediated apoptosis in p53-deficient tumors.

In this study, we demonstrate that a loss of p53 sensitizes tumor cells to actin damage. Using a novel oocyte-based screening system, we identified natural compounds that inhibit cytokinesis. Among these, pectenotoxin-2 (PTX-2), which was first identified as a cytotoxic entity in marine sponges, which depolymerizes actin filaments, was found to be highly effective and more potent to activate an intrinsic pathway of apoptosis in p53-deficient tumor cells compared to those with functional p53 both in vitro and in vivo.

Inactivation of p38 kinase delays the onset of senescence in rabbit articular chondrocytes.

Replicative senescence limits cellular proliferation in vivo and in vitro. Recently, other groups and we reported that p38 kinase plays a key role on the onset of senescence. In this study, we demonstrated that replicative senescence can be delayed in rabbit chondrocytes in vitro by that p38 kinase inactivation.

Cdk2-dependent phosphorylation of the NF-Y transcription factor is essential for the expression of the cell cycle-regulatory genes and cell cycle G1/S and G2/M transitions.

We previously reported that cdk2 phosphorylates two serine residues near the DNA-binding domain of the YA subunit of NF-Y transcription factor and this phosphorylation is essential for DNA binding of NF-Y. In this study, we examined the effects of a phosphorylation-deficient mutant form of YA, YA-aa, in which the two serine residues are replaced with alanine, on the cell cycle and expression of the NF-Y target genes. Transient transfection assays show that YA-aa inhibits transcription from the NF-Y target promoters, such as cdc2, cyclin A, and cdc25C.

Bcl-xL and E1B-19K proteins inhibit p53-induced irreversible growth arrest and senescence by preventing reactive oxygen species-dependent p38 activation.

In this study, we describe novel functions of the anti-apoptotic Bcl-2 family proteins. Bcl-x(L) and E1B-19K were found to inhibit p53-induced irreversible growth arrest and senescence, but not to inhibit transient growth arrest, implying that Bcl-x(L) and E1B-19K are specifically involved in senescence without participating in growth arrest. We provide several lines of evidences showing that the functions of Bcl-x(L) and E1B-19K to prevent generation of reactive oxygen species (ROS) are important to inhibit senescence induction.

Roscovitine sensitizes glioma cells to TRAIL-mediated apoptosis by downregulation of survivin and XIAP.

The cytotoxic effect of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is limited in many glioma cell lines. However, treatment with TRAIL in combination with subtoxic doses of roscovitine, a specific inhibitor of Cdc2 and Cdk2, induced rapid apoptosis in TRAIL-resistant glioma cells. Roscovitine could sensitize Bcl-2- or Bcl-xL-overexpressing glioma cells, but not human astrocytes, to TRAIL-induced apoptosis, offering an attractive strategy for safely treating resistant gliomas.

Cdk2-dependent phosphorylation of the NF-Y transcription factor and its involvement in the p53-p21 signaling pathway.

Recent studies have suggested that the NF-Y transcription factor is involved in transcription repression of the cell cycle regulatory genes in a response to p53 induction or DNA damage. Here we demonstrate the cdk2-dependent phosphorylation of NF-Y and its involvement in transcription repression by the p53-p21 signaling pathway. Cdk2 phosphorylates two serine residues near the DNA-binding domain of the YA subunit of NF-Y.

p38 kinase regulates nitric oxide-induced apoptosis of articular chondrocytes by accumulating p53 via NFkappa B-dependent transcription and stabilization by serine 15 phosphorylation.

Nitric oxide (NO) during primary culture of articular chondrocytes causes apoptosis via p38 mitogen-activated protein kinase in association with elevation of p53 protein level, caspase-3 activation, and differentiation status. In this study, we characterized the molecular mechanism by which p38 kinase induces apoptosis through activation of p53. We report here that NO-induced activation of p38 kinase leads to activation of NFkappaB, which in turn induces transcription of the p53 gene.