A novel lineage-tracing tool reveals that hypoxic tumor cells drive tumor relapse after radiotherapy.

Purpose: Tumor hypoxia imposes a main obstacle to the efficacy of anti-cancer therapy. Understanding the cellular dynamics of individual hypoxic cells before, during and post-treatment has been hampered by the technical inability to identify and trace these cells over time.

Methods And Materials: Here, we present a novel lineage-tracing reporter for hypoxic cells based on the conditional expression of a HIF1a-CreER-UnaG biosensor that can visualize hypoxic cells in a time-dependent manner and trace the fate of hypoxic cells over time.

Combined Inactivation of Pocket Proteins and APC/C by Cdk4/6 Controls Recovery from DNA Damage in G1 Phase.

Most Cyclin-dependent kinases (Cdks) are redundant for normal cell division. Here we tested whether these redundancies are maintained during cell cycle recovery after a DNA damage-induced arrest in G1. Using non-transformed RPE-1 cells, we find that while Cdk4 and Cdk6 act redundantly during normal S-phase entry, they both become essential for S-phase entry after DNA damage in G1.

Resistance of Hypoxic Cells to Ionizing Radiation Is Mediated in Part via Hypoxia-Induced Quiescence.

Double strand breaks (DSBs) are highly toxic to a cell, a property that is exploited in radiation therapy. A critical component for the damage induction is cellular oxygen, making hypoxic tumor areas refractory to the efficacy of radiation treatment. During a fractionated radiation regimen, these hypoxic areas can be re-oxygenated.

Quaternary structure of the human Cdt1-Geminin complex regulates DNA replication licensing.

All organisms need to ensure that no DNA segments are rereplicated in a single cell cycle. Eukaryotes achieve this through a process called origin licensing, which involves tight spatiotemporal control of the assembly of prereplicative complexes (pre-RCs) onto chromatin. Cdt1 is a key component and crucial regulator of pre-RC assembly.

P18 is a tumor suppressor gene involved in human medullary thyroid carcinoma and pheochromocytoma development.

In multiple endocrine neoplasia syndrome Type 2 (MEN2), medullary thyroid carcinoma (MTC) and pheochromocytoma (PC) are associated with hereditary activating germ-line mutations in the RET proto-oncogene. Also in a large percentage of sporadic MTCs and PCs, somatic RET mutations appear to be involved in tumor formation. In one single MEN2 family an extensive variety in disease expression may be observed, indicating that additional genetic events are responsible for progression of the disease towards a more aggressive phenotype.

Polo-like kinase-1 is activated by aurora A to promote checkpoint recovery.

Polo-like kinase-1 (PLK1) is an essential mitotic kinase regulating multiple aspects of the cell division process. Activation of PLK1 requires phosphorylation of a conserved threonine residue (Thr 210) in the T-loop of the PLK1 kinase domain, but the kinase responsible for this has not yet been affirmatively identified. Here we show that in human cells PLK1 activation occurs several hours before entry into mitosis, and requires aurora A (AURKA, also known as STK6)-dependent phosphorylation of Thr 210.

Polo-box domains confer target specificity to the Polo-like kinase family.

Polo-like kinases (Plks) contain a conserved Polo-box domain, shown to bind to phosphorylated Ser-pSer/pThr-Pro motifs. The Polo-box domain of Plk-1 mediates substrate interaction and plays an important role in subcellular localization. Intriguingly, the major interactions between the PBD and the optimal recognition peptide are mediated by highly conserved residues in the PBD, suggesting there is little target specificity conveyed by the various PBDs.

Ablation of the spindle assembly checkpoint by a compound targeting Mps1.

The spindle assembly checkpoint ensures accurate chromosome segregation by delaying anaphase initiation until all chromosomes are properly attached to the mitotic spindle. Here, we show that the previously reported c-Jun amino-terminal kinase (JNK) inhibitor SP600125 effectively disrupts spindle checkpoint function in a JNK-independent fashion. SP600125 potently inhibits activity of the mitotic checkpoint kinase monopolar spindle 1 (Mps1) in vitro and triggers efficient progression through a mitotic arrest imposed by spindle poisons.

Uncoupling anaphase-promoting complex/cyclosome activity from spindle assembly checkpoint control by deregulating polo-like kinase 1.

Polo-like kinase 1 (Plk1) plays a role in numerous events in mitosis, but how the multiple functions of Plk1 are separated is poorly understood. We studied regulation of Plk1 through two putative phosphorylation residues, Ser-137 and Thr-210. Using phospho-specific antibodies, we found that Thr-210 phosphorylation precedes Ser-137 phosphorylation in vivo, the latter occurring specifically in late mitosis.

Polo-like kinase-1 is required for bipolar spindle formation but is dispensable for anaphase promoting complex/Cdc20 activation and initiation of cytokinesis.

Polo-like kinase-1 (Plk1) performs multiple essential functions during the cell cycle. Here we show that human Plk1-deficient cells are unable to separate their centrosomes, fail to form a bipolar spindle, and undergo a Mad2/BubR1-dependent prometaphase arrest. However, electron microscopy demonstrates that kinetochore-microtubule interactions can be established in cells lacking Plk1.

Survivin is required for a sustained spindle checkpoint arrest in response to lack of tension.

Genetic evidence is mounting that survivin plays a crucial role in mitosis, but its exact role in human cell division remains elusive. We show that mammalian cells lacking survivin are unable to align their chromosomes, fail to recruit Aurora B to kinetochores and become polyploid at a very high frequency. Survivin-depleted cells enter mitosis with normal kinetics, but are delayed in prometaphase in a BubR1/Mad2-dependent fashion.

Cell cycle inhibition by FoxO forkhead transcription factors involves downregulation of cyclin D.

The FoxO forkhead transcription factors FoxO4 (AFX), FoxO3a (FKHR.L1), and FoxO1a (FKHR) represent important physiological targets of phosphatidylinositol-3 kinase (PI3K)/protein kinase B (PKB) signaling. Overexpression or conditional activation of FoxO factors is able to antagonize many responses to constitutive PI3K/PKB activation including its effect on cellular proliferation.

Inhibition of Polo-like kinase-1 by DNA damage occurs in an ATM- or ATR-dependent fashion.

Polo-like kinases play multiple roles in different phases of mitosis. We have recently shown that the mammalian polo-like kinase, Plk1, is inhibited in response to DNA damage and that this inhibition may lead to cell cycle arrests at multiple points in mitosis. Here we have investigated the role of the checkpoint kinases ATM (ataxia telangiectasia mutated) and ATR (ATM- and Rad3-related) in DNA damage-induced inhibition of Plk1.

Polo-like kinase-1 is a target of the DNA damage checkpoint.

Polo-like kinases (PLKs) have an important role in several stages of mitosis. They contribute to the activation of cyclin B/Cdc2 and are involved in centrosome maturation and bipolar spindle formation at the onset of mitosis. PLKs also control mitotic exit by regulating the anaphase-promoting complex (APC) and have been implicated in the temporal and spatial coordination of cytokinesis.

p21 inhibits Thr161 phosphorylation of Cdc2 to enforce the G2 DNA damage checkpoint.

The cyclin-dependent kinase inhibitor p21 is required for a sustained G(2) arrest after activation of the DNA damage checkpoint. Here we have addressed the mechanism by which p21 can contribute to this arrest in G(2). We show that p21 blocks the activating phosphorylation of Cdc2 on Thr(161).

Negative growth regulation of SK-N-MC cells by bFGF defines a growth factor-sensitive point in G2.

Basic fibroblast growth factor (bFGF) has been shown to induce growth inhibition of the neuroepithelioma cell line SK-N-MC. Here we show that this growth inhibition occurs in G(2). We show that bFGF is active on these cells during S and early G(2) phase.

Inhibition of cell proliferation by lithium is associated with interference in cdc2 activation.

Lithium can interfere with embryonal development in a variety of organisms. We investigated the effect of lithium on the proliferation of early embryonal cells. [3H]Thymidine incorporation of non-committed mouse P19 embryonal carcinoma cells was inhibited by lithium treatment.

p21waf1 can block cells at two points in the cell cycle, but does not interfere with processive DNA-replication or stress-activated kinases.

p21waf1 has been shown to mediate the p53-dependent growth arrest induced by DNA-damaging agents. Several functions have been ascribed to p21waf1 that could be involved in this growth arrest. For one, p21waf1 is an efficient inhibitor of cyclin-dependent kinases (CDKs).

CDK-independent activation of estrogen receptor by cyclin D1.

Both cyclin D1 and estrogens have an essential role in regulating proliferation of breast epithelial cells. We show here a novel role for cyclin D1 in growth regulation of estrogen-responsive tissues by potentiating transcription of estrogen receptor-regulated genes. Cyclin D1 mediates this activation independent of complex formation to a CDK partner.

Cyclin D1 triggers autonomous growth of breast cancer cells by governing cell cycle exit.

Cyclin D1 controls G1-associated processes, including G0-to-G1 and G1-to-S transitions. This study demonstrates a novel aspect of cyclin D1 as a regulator of the transition between G1 and G0. Overexpression of cyclin D1 in MCF7 breast tumor cells resulted in a continued proliferation under low-serum conditions, whereas nonoverexpressing cells ceased to grow.

A clinicopathological study on overexpression of cyclin D1 and of p53 in a series of 248 patients with operable breast cancer.

Overexpression of cyclin D1 is frequently found in various types of human tumours and results from clonal rearrangement and/or amplification involving chromosomal region 11q13. In order to evaluate the pathological relevance of cyclin D1 overexpression in human breast cancer, we generated a polyclonal antiserum against the carboxy-terminal part of the cyclin D1 protein. After affinity purification, the antiserum specifically detected overexpression of cyclin D1 in formalin-fixed, paraffin-embedded tumour material also.