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.

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.