Cyclin-dependent kinase subunit (Cks) 1 or Cks2 overexpression overrides the DNA damage response barrier triggered by activated oncoproteins.

Cyclin-dependent kinase subunit (Cks) proteins are small cyclin-dependent kinase-interacting proteins that are frequently overexpressed in breast cancer, as well as in a broad spectrum of other human malignancies. However, the mechanistic link between Cks protein overexpression and oncogenesis is still unknown. In this work, we show that overexpression of Cks1 or Cks2 in human mammary epithelial and breast cancer-derived cells, as well as in other cell types, leads to override of the intra-S-phase checkpoint that blocks DNA replication in response to replication stress.

Cyclin-dependent kinase-associated proteins Cks1 and Cks2 are essential during early embryogenesis and for cell cycle progression in somatic cells.

Cks proteins associate with cyclin-dependent kinases and have therefore been assumed to play a direct role in cell cycle regulation. Mammals have two paralogs, Cks1 and Cks2, and individually deleting the gene encoding either in the mouse has previously been shown not to impact viability. In this study we show that simultaneously disrupting CKS1 and CKS2 leads to embryonic lethality, with embryos dying at or before the morula stage after only two to four cell division cycles.

Cyclin E dysregulation and chromosomal instability in endometrial cancer.

Deregulation of cyclin E, an activator of cyclin-dependent kinase 2 (Cdk2), has been associated with a broad spectrum of human malignancies. Yet the mechanism linking abnormal cyclin E expression to carcinogenesis is largely unknown. The gene encoding the F-box protein hCdc4, a key component of the molecular machinery that targets cyclin E for degradation, is frequently mutated in endometrial cancer, leading to deregulation of cyclin E expression.

Mutation of hCDC4 leads to cell cycle deregulation of cyclin E in cancer.

hCDC4, the gene that encodes the F-box protein responsible for targeting cyclin E for ubiquitin-mediated proteolysis, has been found to be mutated in a number of primary cancers and cancer-derived cell lines. We have observed that functional inactivation of hCDC4 does not necessarily correlate with elevated levels of cyclin E in tumors. Here we show, however, that hCDC4 mutation in primary tumors correlates strongly with loss of cell cycle regulation of cyclin E.

Requirement of Cks2 for the first metaphase/anaphase transition of mammalian meiosis.

We generated mice lacking Cks2, one of two mammalian homologs of the yeast Cdk1-binding proteins, Suc1 and Cks1, and found them to be viable but sterile in both sexes. Sterility is due to failure of both male and female germ cells to progress past the first meiotic metaphase. The chromosomal events up through the end of prophase I are normal in both CKS2-/- males and females, suggesting that the phenotype is due directly to failure to enter anaphase and not a consequence of a checkpoint-mediated metaphase I arrest.

Seek and destroy: SCF ubiquitin ligases in mammalian cell cycle control.

The eukaryotic cell cycle consists of a series of sequential phases, the order of which is highly regulated to ensure the faithful transmission of intact genome equivalents to daughter cells. Progression through the cell cycle depends on the activity of cyclin-dependent kinases (Cdks), which drive the transitions between phases by targeting numerous, but largely unknown, substrates for phosphorylation. The activity of Cdks is subject to both positive and negative regulation by their temporal association with cyclins and Cdk inhibitors, respectively.

hCDC4 gene mutations in endometrial cancer.

Cyclin-dependent kinase 2 activated by cyclin E is involved in the initiation of DNA replication and other S phase functions. Consistent with this role, cyclin E protein accumulates at the G1-S phase transition and declines during early S phase. This profile of expression is the result of periodic transcription and ubiquitin-mediated proteolysis directed by SCF(hCdc4).