Oxygen Dependent Regulation of DNA Replication of Ehrlich Ascites Cells In Vitro and In Vivo

Probst, Hans; Gekeler, Volker

doi:10.1007/978-3-642-83444-8_6

Cited by 28 publications

(65 citation statements)

References 21 publications

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“…DNA synthesis in AG1522 cells immediately after reoxygenation occurred both in cells emerging from G1 phase and also in cells that had a greater than GI-phase content of DNA, indicating that under hypoxia, some cells in S phase stopped synthesizing DNA and, upon reoxygenation, restarted where they had stopped. This is consistent with previously published results and is thought to reflect a lack of replicon initiation under hypoxia (20,62). GM02184B cells differed from AG1522 cells in that they lacked any DNA synthesis in the first 4 h following reoxygenation (Fig.…”

Section: Resultssupporting

confidence: 82%

Hypoxia induces accumulation of p53 protein, but activation of a G1-phase checkpoint by low-oxygen conditions is independent of p53 status.

et al. 1994

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function. In addition, cells expressing the human papillomavirus E6 gene, which show increased degradation of p53 by ubiquitination and fail to accumulate p53 in response to DNA-damaging agents, do increase their p53 levels following heat and hypoxia. These results suggest that hypoxia is an example of a "nongenotoxic" stress which induces p53 activity by a different pathway than DNA-damaging agents.

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Section: Resultssupporting

confidence: 82%

Hypoxia induces accumulation of p53 protein, but activation of a G1-phase checkpoint by low-oxygen conditions is independent of p53 status.

et al. 1994

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“…This is, however, a slowlyacting regulation and even in cells with functional pRB the immediate arrest in S-phase after the onset of moderate hypoxia is believed to be a consequence of blocking de novo synthesis of pyrimidine deoxynucleotides due to inhibition of the two oxygendependent enzymes, dihydroorotate dehydrogenase and ribonucleotide reductase (Probst et al, 1989;Loffler, 1992;Amellem et al, 1994;Brischwein et al, 1997). An additional explanation proposed by Probst et al (1988) suggests that hypoxia inhibits the initiation of new replicones, whereas DNA chain elongation and termination proceed during hypoxia. They further demonstrated that replicon initiation depends on one or several short-lived proteins that are also formed under hypoxic conditions, suggesting that hypoxic cells in S-phase are arrested in a state fully prepared for entering DNA replication (Riedinger et al, 1992).…”

Section: Discussion Cell Cycle Regulation During Moderate Hypoxia In mentioning

confidence: 99%

The retinoblastoma protein-associated cell cycle arrest in S-phase under moderate hypoxia is disrupted in cells expressing HPV18 E7 oncoprotein

Åmellem

Sandvik²,

Stokke³

et al. 1998

Br J Cancer

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Summary We have studied the role of the oxygen-dependent pyrimidine metabolism in the regulation of cell cycle progression under moderate hypoxia in human cell lines containing functional (T-47D) or non-functional (NHIK 3025, SAOS-2) retinoblastoma gene product (pRB). Under aerobic conditions, pRB exerts its growth-regulatory effects during early G, phase of the cell cycle, when all pRB present has been assumed to be in the underphosphorylated form and bound in the nucleus. We demonstrate that pRB is dephosphorylated and re-bound in the nucleus in approximately 90% of T-47D cells located in S and G2 phases under moderately hypoxic conditions. Under these conditions, no T-47D cells entered S-phase, and no progression through S-phase was observed. Progression of cells through G2 and mitosis seems independent of their functional pRB status. The p21 WAF1/CIP1 protein level was significantly reduced by moderate hypoxia in p53-deficient T-47D cells, whereas p1 6INK4a was not expressed in these cells, suggesting that the hypoxia-induced cell cycle arrest is independent of these cyclindependent kinase inhibitors. The addition of pyrimidine deoxynucleosides did not release T-47D cells, containing mainly underphosphorylated pRB, from the cell cycle arrest induced by moderate hypoxia. However, NHIK 3025 cells, in which pRB is abrogated by expression of the HPV18 E7 oncoprotein, and SAOS-2 cells, which lack pRB expression, continued cell cycle progression under moderate hypoxia provided that excess pyrimidine deoxynucleosides were present. NHIK 3025 cells express high levels of p16INK4a under both aerobic and moderately hypoxic conditions, suggesting that the inhibitory function of p1 6INK4a would not be manifested in such pRB-deficient cells. Thus, pRB, a key member of the cell cycle checkpoint network, seems to play a major role by inducing growth arrest under moderate hypoxia, and it gradually overrides hypoxia-induced suppression of pyrimidine metabolism in the regulation of progression through S-phase under such conditions.

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“…Some studies have suggested that DNA initiation is affected by hypoxia and is most apparent at low oxygen tensions (21,42,43,46,47). Alternatively, deoxynucleotide depletion, which would be expected to affect DNA initiation, as well as elongation, has also been suggested to occur in hypoxic cells (9,37).…”

Section: Discussionmentioning

confidence: 99%

Anoxic Fibroblasts Activate a Replication Checkpoint That Is Bypassed By E1a

Gardner

Yang

et al. 2003

Molecular and Cellular Biology

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Little is known about cell cycle regulation in hypoxic cells, despite its significance. We utilized an experimentally tractable model to study the proliferative responses of rat fibroblasts when rendered hypoxic (0.5% oxygen) or anoxic (<0.01% oxygen). Hypoxic cells underwent G 1 arrest, whereas anoxic cells also demonstrated S-phase arrest due to suppression of DNA initiation. Upon reoxygenation, only those cells arrested in G 1 were able to resume proliferation. The oncoprotein E1a induced p53-independent apoptosis in anoxic cells, which when suppressed by Bcl-2 permitted proliferation despite anoxia. E1a expression led to marked increases in the transcription factor E2F, and overexpression of E2F-1 allowed proliferation in hypoxic cells, although it had minimal effect on the anoxic suppression of DNA initiation. We thus demonstrate two distinct cell cycle responses to low oxygen and suggest that alterations that lead to increased E2F can overcome hypoxic G 1 arrest but that additional alterations, promoted by E1a expression, are necessary for neoplastic cells to proliferate despite anoxia.Cellular hypoxia is common in many physiological and pathophysiological states, including cancer. Poor and disordered vascularization and rapid tumor cell proliferation lead to areas of significant hypoxia in the tumor microenvironment. Direct measurements of oxygen tension reveal that oxygenation may vary widely in tumors, with some areas approaching anoxia (55). Hypoxic tumors are poorly responsive to radiation and chemotherapy and appear to be more aggressive than nonhypoxic tumors (30). This may be partly related to the observation that some oncogenes, such as c-myc, selectively promote apoptosis in hypoxic p53 wild-type cells; thus, hypoxia can select for cells with mutant p53 (24, 25, 52). The role of hypoxia in tumor proliferation may also have important consequences in therapy resistance and tumor progression. However, the regulation of growth in hypoxia, and how oncogenes may affect this proliferation, is still poorly understood despite its importance in tumor biology and cancer treatment.Normal cell cycle progression is regulated by the coordinated actions of cyclins, cyclin-dependent kinases (CDKs), cyclin-dependent kinase inhibitors (CDKIs), and the E2F family of transcription factors (22). Exit from G 1 is mediated by CDK-mediated phosphorylation of the retinoblastoma protein (Rb) and its related pocket proteins, including p107. This phosphorylation releases members of the E2F family, which may then promote the transcription of genes necessary for S phase, including cyclin E enzymes necessary for deoxynucleotide synthesis and members of the DNA initiation complex, CDC6 and MCM6 (5, 11, 40). CDK2-mediated phosphorylation is important for other steps required for DNA synthesis, including the assembly and activation of the DNA initiation complex (11,12,40). CDK2 activity is dependent on the formation of cyclin A or cyclin E complexes and can be inhibited by the CDKIs p27 and p21. Many neoplasms have deregulated cel...

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Oxygen Dependent Regulation of DNA Replication of Ehrlich Ascites Cells In Vitro and In Vivo

Cited by 28 publications

References 21 publications

Hypoxia induces accumulation of p53 protein, but activation of a G1-phase checkpoint by low-oxygen conditions is independent of p53 status.

Hypoxia induces accumulation of p53 protein, but activation of a G1-phase checkpoint by low-oxygen conditions is independent of p53 status.

The retinoblastoma protein-associated cell cycle arrest in S-phase under moderate hypoxia is disrupted in cells expressing HPV18 E7 oncoprotein

Anoxic Fibroblasts Activate a Replication Checkpoint That Is Bypassed By E1a

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