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. Specifically, binding of Cks1 or Cks2 to cyclin-dependent kinase 2 confers partial resistance to the effects of inhibitory tyrosine phosphorylation mediated by the intra-S-phase checkpoint, allowing cells to continue replicating DNA even under conditions of replicative stress. Because many activated oncoproteins trigger a DNA damage checkpoint response, which serves as a barrier to proliferation and clonal expansion, Cks protein overexpression likely constitutes one mechanism whereby premalignant cells can circumvent this DNA damage response barrier, conferring a proliferative advantage under stress conditions, and therefore contributing to tumor development.

Performance Evaluation of a Dengue IgG Rapid Diagnostic Test Designed to Determine Dengue Serostatus as Part of Prevaccination Screening.

The World Health Organization has recommended prevaccination screening for prior dengue infection as the preferred approach prior to vaccination with the dengue vaccine CYD-TDV. These screening tests need to be highly specific and sensitive, and deliverable at the point-of-care. We evaluate here the sensitivity and specificity of the newly developed OnSite Dengue IgG rapid diagnostic test (RDT). A retrospective double-blind study of the sensitivity and specificity of the OnSite Dengue IgG RDT was performed using a sample panel consisting of archived serum specimens collected during CYD-TDV clinical trials in Latin American and Asia, with the reference serostatus for each sample determined by an algorithm using measured dengue PRNT90, PRNT50, and NS1 IgG ELISA. An additional panel of dengue seronegative samples positive for other flaviviruses and infections was used to assess cross-reactivity. Samples were included from 579 participants; 346 in the specificity panel and 233 in the sensitivity panel. The OnSite dengue IgG RDT exhibited a specificity of 98.0% (95% CI = 95.9 to 99.2) and sensitivity of 95.3% (95% CI = 91.7 to 97.6). The sensitivity for samples exhibiting a multitypic immune profile (PRNT90-positive to >1 dengue serotype) was 98.8% while for monotypic immune samples (PRNT90-positive to a single dengue serotype) it was 88.1%. The OnSite dengue IgG RDT showed minimal to no cross-reactivity to related flaviviruses. These findings support the use of the OnSite dengue IgG RDT to determine dengue serostatus in CYD-TDV prevaccination screening. IMPORTANCE Dengue remains a significant public health issue, with over 5.2 million cases reported to the World Health Organization (WHO) in 2019. The tetravalent dengue vaccine (CYD-TDV) is currently licensed for use in those aged ≥9 years; however, vaccinees with no previous exposure to dengue experience an increased risk of hospitalized and severe dengue upon subsequent heterotypic infection. Consequently, WHO recommends screening for prior dengue infection before vaccination. Screening tests for previous infection need to be highly specific and sensitive, and deliverable at the point-of-care. High sensitivity ensures that the largest number of individuals with previous infection can be identified and vaccinated, while high specificity prevents the inadvertent vaccination of those without previous infection. This study of the OnSite Dengue IgG Rapid Test, which was explicitly developed to meet this need, found that it had both high specificity (98.0% [95% CI = 95.9 to 99.2]) and sensitivity (95.3% [95% CI = 91.7 to 97.6]).

Reduced spermatogonial proliferation and decreased fertility in mice overexpressing cyclin E in spermatogonia.

Cyclin E is a key component of the cell cycle regulatory machinery, contributing to the activation of Cdk2 and the control of cell cycle progression at several stages. Cyclin E expression is tightly regulated, by periodic transcription and ubiquitin-mediated degradation. Overexpression of cyclin E has been associated with tumor development and poor prognosis in several tumor types, including germ cell tumors and both cyclin E and its partner Cdk2 are required for normal spermatogenesis. Here we have generated and characterized transgenic mice overexpressing a cyclin E mutant protein, resistant to ubiquitin-mediated proteolysis, in testicular germ cells, under the control of the human EF-1alpha promoter. The transgenic mice develop normally and live a normal life span, with no signs of testicular tumor development. The transgenic mice display however reduced fertility and testicular atrophy, due to reduced spermatogonial proliferation as a consequence of deregulated cyclin E levels. Overall our results show that deregulation of cyclin E expression contribute to infertility, due to inability of the spermatogonial cells to start the mitotic cycles prior to entering meiosis.

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. RNA interference (RNAi)-mediated silencing of CKS genes in mouse embryonic fibroblasts (MEFs) or HeLa cells causes cessation of proliferation. In MEFs CKS silencing leads to cell cycle arrest in G(2), followed by rereplication and polyploidy. This phenotype can be attributed to impaired transcription of the CCNB1, CCNA2, and CDK1 genes, encoding cyclin B1, cyclin A, and Cdk1, respectively. Restoration of cyclin B1 expression rescues the cell cycle arrest phenotype conferred by RNAi-mediated Cks protein depletion. Consistent with a direct role in transcription, Cks2 is recruited to chromatin in general and to the promoter regions and open reading frames of genes requiring Cks function with a cell cycle periodicity that correlates with their transcription.

Mad2 phosphorylation regulates its association with Mad1 and the APC/C.

Improper attachment of the mitotic spindle to the kinetochores of paired sister chromatids in mitosis is monitored by a checkpoint that leads to an arrest in early metaphase. This arrest requires the inhibitory association of Mad2 with the anaphase promoting complex/cyclosome (APC/C). It is not known how the association of Mad2 with the kinetochore and the APC/C is regulated in mitosis. Here, we demonstrate that human Mad2 is modified through phosphorylation on multiple serine residues in vivo in a cell cycle dependent manner and that only unphosphorylated Mad2 interacts with Mad1 or the APC/C in vivo. A Mad2 mutant containing serine to aspartic acid mutations mimicking the C-terminal phosphorylation events fails to interact with Mad1 or the APC/C and acts as a dominant-negative antagonist of wild-type Mad2. These data suggest that the phosphorylation state of Mad2 regulates its checkpoint activity by modulating its association with Mad1 and the APC/C.