Mediate Cell Cycle Progression Research Articles

Adenoviral RB2/p130 gene transfer inhibits smooth muscle cell proliferation and prevents restenosis after angioplasty.

Smooth muscle cell (SMC) proliferation that results in neointima formation is implicated in the pathogenesis of atherosclerotic plaques and accounts for the high rates of restenosis that occur after percutaneous transluminal coronary angioplasty, a widespread treatment for coronary artery disease. Endothelial lesions trigger intense proliferative signals to the SMCs of the subintima, stimulating their reentry into the cell cycle from a resting G(0) state, resulting in neointima formation and vascular occlusion. Cellular proliferation is negatively controlled by growth-regulatory or tumor-suppressor genes, or both, such as the retinoblastoma gene family members (RB/p105, p107, RB2/p130). In the present study, we show that RB2/p130 inhibited SMC proliferation in vitro and in vivo. We used the rat carotid artery model of restenosis to demonstrate that adenovirus-mediated localized arterial transduction of RB2/p130 at the time of angioplasty significantly reduced neointimal hyperplasia and prevented restenosis. Furthermore, the ability of pRb2/p130 to block proliferation correlated with its ability to bind and sequester the E2F family of transcription factors, which are important mediators of cell cycle progression. These results imply that RB2/p130 could be an important target for vascular gene therapy.

Mutations in the PILZ group genes disrupt the microtubule cytoskeleton and uncouple cell cycle progression from cell division in Arabidopsis embryo and endosperm

Organised cell division and expansion play important roles in plant embryogenesis. To address their cellular basis, we have analysed Arabidopsis abnormal-embryo mutants which were isolated for their characteristic phenotype: mutant embryos are small, mushroom-shaped ("pilz") and consist of only one or few large cells each containing one or more variably enlarged nuclei and often cell wall stubs. These 23 mutants represent four genes, PFIFFERLING, HALLIMASCH, CHAMPIGNON, and PORCINO, which map to different chromosomes. All four genes have very similar mutant phenotypes although porcino embryos often consisted of only one large cell. The endosperm did not cellularise and contained a variably reduced number of highly enlarged nuclei. By contrast, genetic evidence suggests that these genes are not required for gametophyte development. Expression of cell cycle genes, Cdc2a, CyclinA2 and CyclinB1, and the cytokinesis-specific KNOLLE gene was not altered in mutant embryos. However, KNOLLE syntaxin accumulated in patches but no KNOLLE-positive structure resembling a forming cell plate occurred in mitotic cells. A general defect in microtubule assembly was observed in all mutants. Interphase cells lacked cortical microtubules, and spindles were absent from mitotic nuclei although in rare cases, short stubs of microtubules were attached to partially condensed chromosomes. Our results suggest that the cellular components affected by the pilz group mutations are necessary for continuous microtubule organisation, mitotic division and cytokinesis but do not mediate cell cycle progression.

Induction of DNA synthesis and apoptosis are separable functions of E2F-1.

The family of E2F transcription factors have an essential role in mediating cell cycle progression, and recently, one of the E2F protein family, E2F-1, has been shown to participate in the induction of apoptosis. Cooperation between E2F and the p53 tumor suppressor protein in this apoptotic response had led to the suggestion that cell cycle progression induced by E2F-1 expression provides an apoptotic signal when placed in conflict with an arrest to cell cycle progression, such as provided by p53. We show here that although apoptosis is clearly enhanced by p53, E2F-1 can induce significant apoptosis in the absence of p53. Furthermore, this apoptotic function of E2F-1 is separable from the ability to accelerate entry into DNA synthesis. Analysis of E2F-1 mutants indicates that although DNA-binding is required, transcriptional transactivation is not necessary for the induction of apoptosis by E2F-1, suggesting that it may be mediated through alleviation of E2F-dependent transcriptional repression. These results indicate that E2F-1 can show independent cell cycle progression and apoptotic functions, consistent with its putative role as a tumor suppressor.

WR-1065, an active metabolite of the cytoprotector amifostine, affects phosphorylation of topoisomerase IIalpha leading to changes in enzyme activity and cell cycle progression in CHO AA8 cells

The effects of WR-1065 (2-((aminopropyl)amino)ethanethiol) on cell cycle progression, topoisomerase (topo) IIα activity, and topo IIα phosphorylation in Chinese hamster ovary (CHO) cells have been investigated. Exposure of CHO cells to 0.4 μm of WR-1065 for 30 min did not effect cell cycle progression nor topo IIaL activity and phosphorylation status. However, concentrations ranging from 4 μm to 4 mm were equally effective in significantly altering these three end points. Cell cycle progression was analysed by flow cytometry. Following a 30 min exposure to this range of concentrations, cells redistributed throughout the cell cycle with the most prominent changes being an accumulation of cells in G2. Topo IIα activity was measured using a kinetoplast DNA (kDNA) decatenation assay. Enzyme activity was reduced by 50% relative to control levels throughout the 4 μm to 4 mm dose range tested. Likewise, topo IIα phosphorylation levels, analysed using an immuno-precipitation assay and an antibody specific to the 170 kDa band of topo II, decreased between 42% to 48% of control levels. Inhibition of topo IIα activity in cells exposed to WR-1065 is consistent with the associated observation of WR-1065 mediated cell cycle progression delay and build-up of cells in the G2 phase of the cell cycle.

WR‐1065, an active metabolite of the cytoprotector amifostine, affects phosphorylation of topoisomerase IIα leading to changes in enzyme activity and cell cycle progression in CHO AA8 cells

The effects of WR-1065 (2-((aminopropyl)amino)ethanethiol) on cell cycle progression, topoisomerase (topo) II alpha activity, and topo II alpha phosphorylation in Chinese hamster ovary (CHO) cells have been investigated. Exposure of CHO cells to 0.4 microM of WR-1065 for 30 min did not effect cell cycle progression nor topo II alpha activity and phosphorylation status. However, concentrations ranging from 4 microM to 4 mM were equally effective in significantly altering these three end points. Cell cycle progression was analysed by flow cytometry. Following a 30 min exposure to this range of concentrations, cells redistributed throughout the cell cycle with the most prominent changes being an accumulation of cells in G2. Topo II alpha activity was measured using a kinetoplast DNA (kDNA) decatenation assay. Enzyme activity was reduced by 50% relative to control levels throughout the 4 microM to 4 mM dose range tested. Likewise, topo II alpha phosphorylation levels, analysed using an immunoprecipitation assay and an antibody specific to the 170 kDa band of topo II, decreased between 42% to 48% of control levels. Inhibition of topo II alpha activity in cells exposed to WR-1065 is consistent with the associated observation of WR-1065 mediated cell cycle progression delay and build-up of cells in the G2 phase of the cell cycle.

Integrin-dependent activation of MAP kinase: a link to shape-dependent cell proliferation.

Adhesion to extracellular matrix mediates cell cycle progression in mid-late G1; this effect involves an integrin-dependent organization of the cytoskeleton and a consequent change in cell shape. In an effort to identify potential signal-transducing agents that are associated with integrin-dependent shape changes, we looked for kinase activities that were stimulated by long-term adhesion of G0-synchronized NIH-3T3 cells to fibronectin-coated dishes. Several kinase activities were stimulated by this procedure, two of which migrated at 42 and 44 kDa and phosphorylated myelin basic protein in vitro. Blotting with anti-phosphotyrosine and anti-mitogen-activated protein (MAP) kinase antibodies identified these enzymes as ERK 1 and ERK 2. In contrast to the rapid and transient activation of these MAP kinases by platelet-derived growth factor, stimulation of MAP kinase activity by fibronectin was gradual, persistent, and associated with cell spreading rather than cell attachment itself. Cytochalasin D blocked the activation of MAP kinase activity that was induced by the binding of cells to fibronectin. Moreover, MAP kinase was also activated by adhesion of cells to vitronectin and type IV collagen; these effects were also associated with cell spreading. These results distinguish the regulation of G1 phase MAP kinase activity by soluble mitogens and extracellular matrix. They also implicate MAP kinase in shape-dependent cell cycle progression.