Expression of cell cycle regulatory proteins in epithelial components of dental follicles

Dental follicle is a component of tooth germs, which remain adjacent to the crown of unerupted or impacted teeth. Under the influence of pathologic changes, however, dental follicles that possess reduced epithelium can proliferate into stratified squamous epithelium as far as originate dental cysts. In order to clarify the role of apoptosis and cellular proliferation herein, expression of p53 and PCNA was examined in epithelial components of dental follicles associated with impacted third molars by means of immunohistochemistry. A total of 40 cases was included in this study being 22 cases with reduced epithelium and 18 cases with stratified epithelium. Expression of p53 expression was weak or not detected in dental follicles with reduced and stratified squamous epithelium. By contrast, PCNA positive cells were evidenced in basal and supra basal layers of the stratified squamous epithelium and in reduced epithelium of dental follicles, but without any significant statistically differences between them (P > 0.05). In conclusion, these data suggest that dental follicles possess proliferative activity as depicted by PCNA-positive nuclei in some epithelial cells. However, the biological behavior of dental follicles during the late stage of dental eruptive process may not be associated with deregulation of death and/or cell proliferation.     

Intracellular accumulation of cell cycle regulatory proteins and nucleolin re-localization are associated with pre-lethal ultrastructural lesions in circulating T lymphocytes: The HIV-induced cell cycle dysregulation revisited

The HIV-induced demise of CD4-T cells is thought to be a result of the execution of genetically programmed cell death that occurs in lymphoid tissue, where many resident T cells are chronically hyperactivated. Since HIV-induced alterations of cell cycle control has been often indicated as prominent mechanism of immune hyper activation and cause of apoptotic death, the signal pathway involved in cell cycle dysregulation of T lymphocytes from HIV infected patients was extensively studied.

Here, we also demonstrate that circulating T lymphocytes leave lymphoid tissues with diffused regressive lesions (vacuolization, blebbing, nuclear evanescence and organelle swelling). Equally diffused are biochemical anomalies that accompany the overall disarrangement of cell structure, particularly the fragmentation and diffusion into the cytoplasm of C23/nucleolin, the intracellular accumulation of short lived regulatory proteins and the decrease in expression of membrane proteins.

All this is something more than a cell cycle-related remodelling of cell morphology and biochemical mechanisms, and rather recalls a necrotic/oncotic cell damage. Since these changes are associated with adaptive mechanisms to hypoxia, we give evidence for alteration of cell cycle control developing in conditions of scarce energy supply.     

Induction of apoptosis and expression of cell cycle regulatory proteins in response to a phytosphingosine derivative in HaCaT human keratinocyte cells

Ceramide, a compound derived from sphingomyelin, a sphingolipid precursor, affects cell functions such as growth, differentiation, cell division and apoptosis. We have shown that the phytosphingosine derivative, tetra-acetyl phytosphingosine (TAPS), inhibits the growth of HaCaT cells mainly by inducing apoptosis. In this study, we investigated its effect on the cell cycle and on cell cycle regulatory proteins. We showed by flow cytometry and staining for BrdU and phosphorylated histone H3 that the cells accumulated in S phase and arrested in G2 phase and did not divide before undergoing apoptosis. The level of the pro-apoptotic regulator Bax peaked after 6 h and then returned to normal, whereas the level of the anti-apoptotic regulator Bcl-xL, which is presumably induced in order to inhibit apoptosis, started to increase at 6 h, and remained high for 24 h. Phosphorylation of Cdc2 on Tyr-15 greatly increased while p21 rose to a plateau at 8 h. Levels of p53 and Mad2 proteins were unchanged. Our observations suggest that TAPS induces apoptosis of the HaCaT cells at least in part via transient G2 arrest.     

The effect of environmental micropollutant (DEET) on the expression of cell cycle and apoptosis regulatory proteins in human cells

N,N-diethyl-m-toluamide (DEET) is an insect repellent used worldwide, and a common micropollutant in aquatic environments. However, few studies have addressed the molecular mechanism of DEET toxicity and its effects on cell growth and apoptosis. The purpose of this study was to investigate the effect of DEET on the expression of the cell cycle and apoptosis regulatory proteins in human BE(2)-M17 cells. The results showed that DEET significantly decreased the cell viability (40.6 ∼ 68.9% of control) at concentrations of 500 ∼ 4,000 mg/L. Also, DEET significantly decreased the expressions of CDK 2, CDK 4, and cyclin D1 (3.9 ∼ 86.6% of control), at concentrations of 50 ∼ 400 mg/L but from 100 mg/L for cyclin E. Furthermore, DEET significantly increased the expression of caspase-3 (223.1 ∼ 1,770.6% of control), but significantly decreased Bcl-2 expression (46.1 ∼ 86.3% of control) at all concentrations tested. In conclusion, DEET partially affected the expression of CDK/cyclin molecules, but fully affected the expressions of caspase-3 and Bcl-2 in BE(2)-M17 cells.     

Expression and function of cell cycle proteins in rheumatoid arthritis synovial tissue

Rheumatoid Arthritis (RA) is a chronic disease characterised by synovial lining hyperplasia and progressive destruction of joint tissues. Experimental data suggests that abnormal alterations in the expression of proteins involved in maintaining homeostatic control of the cell cycle is involved in disease progression in RA. By contributing to the overgrowth of synovial tissue, factors such as dysregulated proliferation or reduced apoptosis of cells can directly influence the pathological outcome of RA.     

Effects of combined radiofrequency radiation exposure on the cell cycle and its regulatory proteins

The aim of this study was to investigate whether single or combined radio frequency (RF) radiation exposure has effects on the cell cycle and its regulatory proteins. Exposure of MCF7 cells to either single (837 MHz) or combined (837 and 1950 MHz) RF radiation was conducted at specific absorption rate values of 4 W/kg for 1 h. During the exposure period, the chamber was made isothermal by circulating water through the cavity. After RF radiation exposure, DNA synthesis rate and cell cycle distribution were assessed. The levels of cell cycle regulatory proteins, p53, p21, cyclins, and cyclin‐dependent kinases were also examined. The positive control group was exposed to 0.5 and 4 Gy doses of ionizing radiation (IR) and showed changes in DNA synthesis and cell cycle distribution. The levels of p53, p21, cyclin A, cyclin B1, and cyclin D1 were also affected by IR exposure. In contrast to the IR‐exposed group, neither the single RF radiation‐ nor the combined RF radiation‐exposed group elicited alterations in DNA synthesis, cell cycle distribution, and levels of cell cycle regulatory proteins. These results indicate that neither single nor combined RF radiation affect cell cycle progression. Bioelectromagnetics 32:169–178, 2011. © 2010 Wiley‐Liss, Inc.     

Poriferan survivin exhibits a conserved regulatory role in the interconnected pathways of cell cycle and apoptosis

Survivin orchestrates intracellular pathways during cell division and apoptosis. Its central function as mitotic regulator and inhibitor of cell death has major implications for tumor cell proliferation. Analyses in early-branching Metazoa so far propose an exclusive role of survivin as a chromosomal passenger protein, whereas only later during evolution a complementary antiapoptotic function might have arisen, concurrent with increased organismal complexity. To lift the veil on the ancestral function(s) of this key regulator, a survivin-like protein (SURVL) of one of the earliest-branching metazoan taxa was identified and functionally characterized. SURVL of the sponge Suberites domuncula shares considerable similarities with its metazoan homologs, ranging from conserved exon/intron structure to presence of protein-interaction domains. Whereas sponge tissue shows a low steady-state level, SURVL expression was significantly upregulated in rapidly proliferating primmorph cells. In addition, challenge of tissue and primmorphs with heavy metal or lipopeptide stimulated SURVL expression, concurrent with the expression of a newly discovered caspase. Complementary functional analyses in transfected HEK-293 cells revealed that heterologous expression of a SURVL–EFGP fusion not only promotes proliferation but also enhances resistance to cadmium-induced cell death. Taken together, these results suggest both a deep evolutionary conserved dual role of survivin and an equally conserved central position in the interconnected pathways of cell cycle and apoptosis.     

Folding and association of the human cell cycle regulatory proteins ckshs1 and ckshs2.

The two human proteins ckshs1 and ckshs2 are each 79 amino acids in length and consist of a four-stranded beta-sheet capped at one end by two alpha-helices. They are members of the cks family of essential cell cycle regulatory proteins that can adopt two native states, a monomer and a domain-swapped dimer formed by exchange of a C-terminal beta-strand. ckshs1 and ckshs2 both have marginal thermodynamic stability (the free energies of unfolding at 25 degrees C are 3.0 and 2.5 kcal/mol, respectively) and low kinetic stability (the rates of unfolding in water are approximately 1 s(-1)). Refolding of their denatured states to the monomeric forms of the proteins is slowed by transient oligomerization that is likely to occur via domain swapping. The folding behavior of ckshs1 and ckshs2 is markedly different from that of suc1, the cks protein from Schizosaccharomyces pombe, but the domain swapping propensities are similar. The greater thermodynamic and kinetic stability of suc1 and the population of a folding intermediate are most likely a consequence of its larger size (113 residues). The similarity in the domain swapping propensities, despite the contrast in other biophysical properties, may be attributable to the common double-proline motif in the hinge loop that connects the swapped domain to the rest of the protein. The motif was shown previously for suc1 to control the equilibrium between the monomer and the domain-swapped dimer. Finally, according to our model, the kinetic barrier separating the monomer and the domain-swapped dimer arises because the protein must unfold for beta-strand exchange to occur. Consistent with this, interconversion between the two states is much faster in the human proteins than it is for suc1, reflecting the faster unfolding rates of the former.     

Human base excision repair complex is physically associated to DNA replication and cell cycle regulatory proteins

It has been hypothesized that a replication associated repair pathway operates on base damage and single strand breaks (SSB) at replication forks. In this study, we present the isolation from the nuclei of human cycling cells of a multiprotein complex containing most of the essential components of base excision repair (BER)/SSBR, including APE1, UNG2, XRCC1 and POLβ, DNA PK, replicative POLα, δ and , DNA ligase 1 and cell cycle regulatory protein cyclin A. Co-immunoprecipitation revealed that in this complex DNA repair proteins are physically associated to cyclin A and to DNA replication proteins including MCM7. This complex is endowed with DNA polymerase and protein kinase activity and is able to perform BER of uracil and AP sites. This finding suggests that a preassembled DNA repair machinery is constitutively active in cycling cells and is ready to be recruited at base damage and breaks occurring at replication forks.     

Telomeres and telomerase dance to the rhythm of the cell cycle

The stability of the ends of linear eukaryotic chromosomes is ensured by functional telomeres, which are composed of short, species-specific direct repeat sequences. The maintenance of telomeres depends on a specialized ribonucleoprotein (RNP) called telomerase. Both telomeres and telomerase are dynamic entities with different physical behaviors and, given their substrate-enzyme relation, they must establish a productive interaction. Regulatory mechanisms controlling this interaction are key missing elements in our understanding of telomere functions. Here, we review the dynamic properties of telomeres and the maturing telomerase RNPs, and summarize how tracking the timing of their dance during the cell cycle will yield insights into chromosome stability mechanisms. Cancer cells often display loss of genome integrity; therefore, these issues are of particular interest for our understanding of cancer initiation or progression.