Cdc45 is a critical effector of myc-dependent DNA replication stress.

c-Myc oncogenic activity is thought to be mediated in part by its ability to generate DNA replication stress and subsequent genomic instability when deregulated. Previous studies have demonstrated a nontranscriptional role for c-Myc in regulating DNA replication. Here, we analyze the mechanisms by which c-Myc deregulation generates DNA replication stress.

Study of cell cycle checkpoints using Xenopus cell-free extracts.

Cell cycle checkpoints are involved in the coordinated response to DNA damage and thus play a key role in maintaining genome integrity. Several model systems have been developed to study the mechanisms and complexity of checkpoint function. Here we describe the application of cell-free extracts derived from Xenopus eggs as a model system to investigate DNA replication, damage, and checkpoint activation.

RB loss abrogates cell cycle control and genome integrity to promote liver tumorigenesis.

Background & Aims: The retinoblastoma (RB) tumor suppressor is functionally inactivated in most hepatocellular carcinomas (HCC), although the mechanisms by which RB suppresses liver tumorigenesis are poorly defined. We investigated the impact of RB loss on carcinogen-induced liver tumorigenesis.

Methods: Mice harboring liver-specific RB ablation and normal littermates were exposed to the hepatocarcinogen diethylnitrosamine (DEN).

RB loss promotes aberrant ploidy by deregulating levels and activity of DNA replication factors.

The retinoblastoma tumor suppressor (RB) is functionally inactivated in many human cancers. Classically, RB functions to repress E2F-mediated transcription and inhibit cell cycle progression. Consequently, RB ablation leads to loss of cell cycle control and aberrant expression of E2F target genes.

The KLF2 transcription factor does not affect the formation of preadipocytes but inhibits their differentiation into adipocytes.

Kruppel-like transcription factor 2 (KLF2), a critical gene for mouse embryogenesis, was recently identified as an inhibitor of adipogenesis. However, it is still unknown whether KLF2 is a natural repressor of adipocyte differentiation and if KLF2 affects the formation of preadipocytes. It may also be important for preadipocyte formation, as KLF2 is crucial for lung development and blood vessel formation.

Induction of KLF2 by fluid shear stress requires a novel promoter element activated by a phosphatidylinositol 3-kinase-dependent chromatin-remodeling pathway.

Fluid shear stress maintains vascular homeostasis by influencing endothelial gene expression. One mechanism by which shear stress achieves this is through the induction of transcription factors including Krüppel-like factor 2(KLF2). We have previously reported that a 62-bp region of the KLF2 promoter is responsible for its shear stress-induced expression via the binding of nuclear factors.

Fluid shear stress induces endothelial KLF2 gene expression through a defined promoter region.

Fluid shear stress is crucial for maintenance of a properly functioning endothelium. In this study we demonstrate that the KLF2 transcription factor is greatly induced by pulsatile shear stress in murine microvascular endothelial cells. The promoter elements responsible for the induction were studied by transfection with luciferase-reporter plasmids including the 5' flanking region of the murine KLF2 gene.

WWP1-dependent ubiquitination and degradation of the lung Krüppel-like factor, KLF2.

The zinc-finger transcription factor Krüppel-like factor-2 plays an important role in pulmonary development, inhibition of adipocyte differentiation, and maintaining quiescence in single-positive T cells. KLF2 levels rapidly decrease during adipogenesis and activation of T cells, but the pathways involved remain unclear. Previously, we identified WWP1, a HECT-domain E3-ubiquitin ligase, as an interacting partner of KLF2.

Human papillomavirus oncoprotein E6 inactivates the transcriptional coactivator human ADA3.

High-risk human papillomaviruses (HPVs) are associated with carcinomas of the cervix and other genital tumors. The HPV oncoprotein E6 is essential for oncogenic transformation. We identify here hADA3, human homologue of the yeast transcriptional coactivator yADA3, as a novel E6-interacting protein and a target of E6-induced degradation.

Human papillomavirus E6-induced degradation of E6TP1 is mediated by E6AP ubiquitin ligase.

High-risk human papilloma viruses are known to be associated with cervical cancers. We have reported previously that the high-risk human papillomavirus (HPV) E6 oncoprotein interacts with E6TP1, a novel Rap GTPase-activating protein (RapGAP). Similar to p53 tumor suppressor protein, the high-risk HPV E6 oncoproteins target E6TP1 for degradation.