Carcinoma of the uterine cervix is one of the most common malignancies among women worldwide. Human papillomaviruses (HPV) have been identified as the major etiological factor in cervical carcinogenesis. However, the time lag between HPV infection and the diagnosis of cancer indicates that multiple steps, as well as multiple factors, may be necessary for the development of cervical cancer. The development and progression of cervical carcinoma have been shown to be dependent on various genetic and epigenetic events, especially alterations in the cell cycle checkpoint machinery. In mammalian cells, control of the cell cycle is regulated by the activity of cyclin-dependent kinases (CDKs) and their essential activating coenzymes, the cyclins. Generally, CDKs, cyclins, and CDK inhibitors function within several pathways, including the p16INK4A-cyclin D1-CDK4/6-pRb-E2F, p21WAF1-p27KIP1-cyclinE-CDK2, and p14ARF-MDM2-p53 pathways. The results from several studies showed aberrant regulation of several cell cycle proteins, such as cyclin D, cyclin E, p16 INK4A, p21WAF1, and p27KIP1, as characteristic features of HPV- infected and HPV E6/E7 oncogene-expressing cervical carcinomas and their precursors. These data suggested further that interactions of viral proteins with host cellular proteins, particularly cell cycle proteins, are involved in the activation or repression of cell cycle progression in cervical carcinogenesis.
Uterine Cervical Neoplasms/*pathology ; Tumor Suppressor Protein p53/physiology ; Tumor Suppressor Protein p14ARF/physiology ; Retinoblastoma Protein/physiology ; Proto-Oncogene Proteins c-mdm2/physiology ; Humans ; Female ; E2F Transcription Factors/physiology ; Cyclin-Dependent Kinase Inhibitor p27/physiology ; Cyclin-Dependent Kinase Inhibitor p21/physiology ; Cyclin-Dependent Kinase Inhibitor p16/physiology ; Cyclin-Dependent Kinase 4/physiology ; Cyclin-Dependent Kinase 2/physiology ; Cyclin E/physiology ; Cyclin D1/physiology ; Cell Cycle/*physiology

MDM2 is a substrate of caspase-3 in p53-mediated apoptosis. In addition, MDM2 mediates its own ubiquitination in a RING finger-dependent manner. Thus, we investigated whether MDM2 is degraded through a ubiquitin-dependent proteasome pathway in the absence of p53. When HL-60 cells, p53 null, were treated with etoposide, MDM2 was markedly decreased prior to caspase-3-dependent retinoblastoma tumor suppressor protein (pRb) and poly (ADP- ribose) polymerase (PARP) cleavages. Moreover, down-regulation of MDM2 level was not coupled with its mRNA down-regulation. However, the level of MDM2 was partially restored by proteasome inhibitors such as LLnL and lactacystin, even in the presence of etoposide. Our results suggest that, in the p53 null status, MDM2 protein level is decreased by proteasome-mediated proteolysis prior to caspase-3-dependent PARP and pRb cleavages.
Antineoplastic Agents, Phytogenic/pharmacology ; Apoptosis/drug effects/physiology ; Caspases/*metabolism ; Cysteine Endopeptidases/*metabolism ; Down-Regulation (Physiology)/physiology ; Etoposide/pharmacology ; HL-60 Cells ; Human ; Multienzyme Complexes/*metabolism ; NAD+ ADP-Ribosyltransferase/*metabolism ; Proto-Oncogene Proteins/*metabolism ; Retinoblastoma Protein/*metabolism

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

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

OBJECTIVETo investigate the role of HPV16E6 and E7 during the transformation of oral epithelial cells.

METHODSAn human immortalized oral epithelial cell line (HIOEC) was established by transfecting HPV16E6, E7 open reading frames using recombinant retroviral system plxsn to human normal oral epithelial cells. Expression of HPV16E6, E7, Rb, P16 and Cycin D1 were analyzed by Western blot in HIOEC and human normal oral epithelial cells. Formation of complex of HPV16E7 and Rb were analyzed by Immunoprecipitation-western blot. Human normal oral epithelial cells and the oral epithelial cells transfected with plxsn were used as control groups.

RESULTSHIOEC expressed HPV16 E6 and E7; HIOEC expressed both hyperphosphorylated and underphosphorylated Rb while oral epithelial cells in two control groups only expressed hyperphosphorylated Rb. HPV16 E7 formed complex with underphosphorylated Rb; the level of P16 and Cyclin D1 had no remarkable change.

CONCLUSIONSHPV16E7 plays an important role in the immortalization of oral epithelial cells induced by HPV16.

Blotting, Western ; Cell Line ; Cell Transformation, Neoplastic ; Cyclin D1 ; analysis ; Cyclin-Dependent Kinase Inhibitor p16 ; analysis ; Humans ; Mouth Mucosa ; metabolism ; pathology ; virology ; Oncogene Proteins, Viral ; physiology ; Papillomavirus E7 Proteins ; Phosphorylation ; Repressor Proteins ; Retinoblastoma Protein ; analysis

OBJECTIVETo investigate the mechanism of all trans retinoid acid (ATRA) inhibition of cell growth and induction of apoptosis in human retinoblastoma Y79 cells.

METHODSAntiproliferating effects of ATRA on Y79 cells were studied by (3)H-thymidine incorporation. Cell cycle analysis was performed by flow cytometry, apoptosis of the ATRA-treated cells was determined by DNA fragmentation analysis and JNK phosphorylation analyzed by Western blot.

RESULTSAfter 36h treatment of 1 micro mol/L ATRA, (3)H-thymidine incorporation decreased to 40% with Y79 cells arrested in G(0)/G(1) and Sub-G(1) peak appeared. DNA ladder was observed in DNA fragmentation analysis after 36h treatment of ATRA. Curcumin, a JNK blocker, blocked the apoptosis and the growth inhibition induced by ATRA. JNK was phosphorylated in 10 to 20 min.

CONCLUSIONATRA can induce the apoptosis in Y79 cells by phosphorylation of JNK, which suggests that ATRA may have clinical application prospects for treatment of retinoblastoma.

Antineoplastic Agents ; pharmacology ; Apoptosis ; drug effects ; Cell Cycle ; drug effects ; Cell Line, Tumor ; Flow Cytometry ; Humans ; JNK Mitogen-Activated Protein Kinases ; physiology ; Phosphorylation ; Retinoblastoma ; drug therapy ; pathology ; Thymidine ; metabolism ; Tretinoin ; pharmacology

WT1 gene encodes a zinc finger transcription factor that regulates transcription of its downstream genes. Some of target genes for WT1 are involved in regulating both cell cycle and cellular proliferation and differentiation. However, WT1 itself is regulated by its upstream genes such as NF-kappaB and GATA-1. Thus there exists a pathway of transcriptional regulation mediated by WT1, which controls development of hematopoietic system. Leukemia results from disrupting the homeostasis among hematopoietic proliferation, differentiation and apoptosis, which is often the consequence of an inappropriate expression of transcription factors and subsequent disruption of the normal gene expression pattern. This article reviews the relationship between the WT1-mediated pathway of transcriptional regulation and leukemia.
Animals ; Carrier Proteins ; genetics ; Cyclin-Dependent Kinase Inhibitor p21 ; Cyclins ; genetics ; DNA-Binding Proteins ; metabolism ; Erythroid-Specific DNA-Binding Factors ; GATA1 Transcription Factor ; Gene Expression Regulation ; Humans ; Leukemia ; etiology ; genetics ; NF-kappa B ; metabolism ; Nuclear Proteins ; genetics ; Retinoblastoma-Binding Protein 7 ; Transcription Factors ; metabolism ; Transcription, Genetic ; WT1 Proteins ; physiology