Axitinib or bevacizumab plus FOLFIRI or modified FOLFOX-6 after failure of first-line therapy for metastatic colorectal cancer: a randomized phase II study.

Objective: Axitinib, a potent and selective second-generation inhibitor of vascular endothelial growth factor receptors 1, 2, and 3, shows activity in multiple tumor types, including those refractory to previous antiangiogenic therapy. This randomized, multicenter, parallel-group, open-label phase II trial compared axitinib with bevacizumab each in combination with 5-fluorouracil/leucovorin/oxaliplatin (FOLFOX) or 5-fluorouracil/leucovorin/irinotecan (FOLFIRI) for second-line treatment of metastatic colorectal cancer.

Methods: Patients were randomized 1:1 to axitinib 5 mg twice daily or bevacizumab 5 mg/kg every 2 weeks plus modified FOLFOX-6 (if previously treated with irinotecan) or FOLFIRI (if previously treated with oxaliplatin) and were stratified by performance status and prior bevacizumab therapy.

Five-year survival in patients with cytokine-refractory metastatic renal cell carcinoma treated with axitinib.

Background: In a phase II study of axitinib for cytokine-refractory metastatic renal cell carcinoma, median overall survival (OS) was 29.9 months (95% CI, 20.3 to not estimable months).

Global analysis of Cdc14 phosphatase reveals diverse roles in mitotic processes.

Cdc14 phosphatase regulates multiple events during anaphase and is essential for mitotic exit in budding yeast. Cdc14 is regulated in both a spatial and temporal manner. It is sequestered in the nucleolus for most of the cell cycle by the nucleolar protein Net1 and is released into the nucleus and cytoplasm during anaphase.

Multiple levels of cyclin specificity in cell-cycle control.

Cyclins regulate the cell cycle by binding to and activating cyclin-dependent kinases (Cdks). Phosphorylation of specific targets by cyclin-Cdk complexes sets in motion different processes that drive the cell cycle in a timely manner. In budding yeast, a single Cdk is activated by multiple cyclins.

Novel role for Cdc14 sequestration: Cdc14 dephosphorylates factors that promote DNA replication.

The phosphatase Cdc14 is required for mitotic exit in budding yeast. Cdc14 promotes Cdk1 inactivation by targeting proteins that, when dephosphorylated, trigger degradation of mitotic cyclins and accumulation of the Cdk1 inhibitor, Sic1. Cdc14 is sequestered in the nucleolus during most of the cell cycle but is released into the nucleus and cytoplasm during anaphase.

Modification of Cul1 regulates its association with proteasomal subunits.

Background: Ubiquitylation targets proteins for degradation by the 26S proteasome. Some yeast and plant ubiquitin ligases, including the highly conserved SCF (Skp1/Cul1/F-box protein) complex, have been shown to associate with proteasomes. We sought to characterize interactions between SCF complexes and proteasomes in mammalian cells.

Experimental tests to definitively determine ubiquitylation of a substrate.

Ubiquitin-mediated proteolysis is a major pathway of protein degradation that regulates numerous cellular processes. An understanding of the circumstances that contribute to the ubiquitylation of a specific protein can yield vast insight into its regulation. This article examines multiple procedures that explain whether a protein is ubiquitylated and suggests methods to investigate the factors that specifically target the substrate for ubiquitylation, as well as the site of ubiquitin conjugation.

The acidic tail domain of human Cdc34 is required for p27Kip1 ubiquitination and complementation of a cdc34 temperature sensitive yeast strain.

Human Cdc34 is an ubiquitin conjugating enzyme or E2 that ubiquitinates substrates including p27(Kip1), IkappaBalpha, Wee1, and MyoD. Cdc34 possesses a core catalytic domain encoding the active site cysteine and an acidic tail domain within the carboxyl terminal 36 amino acids. Studies suggest that Cdc34 is phosphorylated in mammalian cells at 5 potential residues within the tail domain.

An Rb-Skp2-p27 pathway mediates acute cell cycle inhibition by Rb and is retained in a partial-penetrance Rb mutant.

It is believed that Rb blocks G1-S transition by inhibiting expression of E2F regulated genes. Here, we report that the effects of E2F repression lag behind the onset of G1 cell cycle arrest in timed Rb reexpression experiments. In comparison, kinase inhibitor p27Kip1 protein accumulates with a faster kinetics.

To be or not to be ubiquitinated?

Levels of p21, a cyclin-dependent kinase (CDK) inhibitor, are controlled in part at the post-translational level by protein degradation. Although the signaling pathways leading to p21 degradation have not yet been fully elucidated, it is evident that p21 ubiquitination is an essential factor in its degradation. We discuss that, with the only notable exception of ornithine decarboxylase, ubiquitination appears to be a prerequisite for proteasomal degradation rather than an unnecessary byproduct of such proteolysis.

Proteasome-mediated degradation of p21 via N-terminal ubiquitinylation.

We examined the mechanism responsible for the degradation of p21, a negative regulator of the cell division cycle. We found that p21 proteolysis requires functional ubiquitin and Nedd8 systems. Ubiquitinylated forms of p21 and p21(K0), a p21 mutant missing all lysines, are detected in vivo and in vitro, showing that the presence of lysines is dispensable for p21 ubiquitinylation.

Role of the SCFSkp2 ubiquitin ligase in the degradation of p21Cip1 in S phase.

The cyclin-dependent kinase inhibitor p21Cip1 has important roles in the control of cell proliferation, differentiation, senescence, and apoptosis. It has been observed that p21 is a highly unstable protein, but the mechanisms of its degradation remained unknown. We show here that p21 is a good substrate for an SCF (Skp1-Cullin1-F-box protein) ubiquitin ligase complex, which contains the F-box protein Skp2 (S phase kinase-associated protein 2) and the accessory protein Cks1 (cyclin kinase subunit 1).

Deregulated degradation of the cdk inhibitor p27 and malignant transformation.

p27 acts as a critical negative regulator of the cell cycle by inhibiting the activity of cyclin/cdk complexes during G0 and G1. Degradation of p27 is a critical event for the G1/S transition and occurs through ubiquitination by SCF(Skp2) and subsequent degradation by the 26S-proteasome. A tumor suppressing function of p27 has been demonstrated in mouse models and studies of human tumors.