DDB1, a component of the Cul4 ubiquitin ligase complex, promotes protein ubiquitination in diverse cellular functions, including nuclear excision repair, regulation of the cell cycle, and DNA replication. To investigate its physiological significance, we generated mice with null and floxed alleles of the DDB1 gene. Here we report that null mutation of DDB1 caused early embryonic lethality, while conditional inactivation of the gene in brain and lens led to neuronal and lens degeneration, brain hemorrhages, and neonatal death. These defects stemmed from a selective elimination of nearly all proliferating neuronal progenitor cells and lens epithelial cells by apoptosis. The cell death was preceded by aberrant accumulation of cell cycle regulators and increased genomic instability and could be partially rescued by removal of the tumor suppressor protein p53. Our results indicate that DDB1 plays an essential role in maintaining viability and genomic integrity of dividing cells.

SUMMARY Hepatocyte Nuclear Factor (HNF)4α is a central regulator of gene expression in cell types that play a critical role in metabolic homeostasis, including hepatocytes, enterocytes, and pancreatic β-cells. Although fatty acids were found to occupy the HNF4α ligand-binding pocket and proposed to act as ligands, there is controversy about both the nature of HNF4α ligands as well as the physiological role of the binding. Here, we report the discovery of potent synthetic HNF4α antagonists through a high-throughput screen for effectors of the human insulin promoter. These molecules bound to HNF4α with high affinity and modulated the expression of known HNF4α target genes. Notably, they were found to be selectively cytotoxic to cancer cell lines in vitro and in vivo, although in vivo potency was limited by suboptimal pharmacokinetic properties. The discovery of bioactive modulators for HNF4α raises the possibility that diseases involving HNF4α, such as diabetes and cancer, might be amenable to pharmacologic intervention by modulation of HNF4α activity.

The duration of a woman's reproductive period is determined by the size and persistence of a dormant oocyte pool. Specific oocyte genes are essential for follicle maintenance and female fertility. The mechanisms that regulate the expression of these genes are poorly understood. We found that a cullin-ring finger ligase-4 (CRL4) complex was crucial in this process. Oocyte-specific deletion of the CRL4 linker protein DDB1 or its substrate adaptor VPRBP (also known as DCAF1) caused rapid oocyte loss, premature ovarian insufficiency, and silencing of fertility maintaining genes. CRL4(VPRBP) activates the TET methylcytosine dioxygenases, which are involved in female germ cell development and zygote genome reprogramming. Hence, CRL4(VPRBP) ubiquitin ligase is a guardian of female reproductive life in germ cells and a maternal reprogramming factor after fertilization.

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) in the liver removes toxic aldehydes including acetaldehyde, an intermediate of ethanol metabolism. Nearly 40% of East Asians inherit an inactive ALDH2*2 variant, which has a lysine-for-glutamate substitution at position 487 (E487K), and show a characteristic alcohol flush reaction after drinking and a higher risk for gastrointestinal cancers. Here we report the characterization of knockin mice in which the ALDH2(E487K) mutation is inserted into the endogenous murine Aldh2 locus. These mutants recapitulate essentially all human phenotypes including impaired clearance of acetaldehyde, increased sensitivity to acute or chronic alcohol-induced toxicity, and reduced ALDH2 expression due to a dominant-negative effect of the mutation. When treated with a chemical carcinogen, these mutants exhibit increased DNA damage response in hepatocytes, pronounced liver injury, and accelerated development of hepatocellular carcinoma (HCC). Importantly, ALDH2 protein levels are also significantly lower in patient HCC than in peritumor or normal liver tissues. Our results reveal that ALDH2 functions as a tumor suppressor by maintaining genomic stability in the liver, and the common human ALDH2 variant would present a significant risk factor for hepatocarcinogenesis. Our study suggests that the ALDH2*2 allele-alcohol interaction may be an even greater human public health hazard than previously appreciated. ALDH2*2 polymorphism | Asian flush | alcohol metabolism | mouse model | liver cancer M itochondrial aldehyde dehydrogenase 2 (ALDH2) is essential for alcohol detoxification. It is the second enzyme in the major oxidative pathway of alcohol metabolism, removing acetaldehyde (ACE), a toxic intermediate product from ethanol metabolism (1). More than 500 million people worldwide, mostly in East Asia, have a G-to-A point mutation in their ALDH2 gene (2, 3). This mutation results in a glutamic acid-to-lysine substitution at residue 487 (E487K) of the human ALDH2 protein (designated ALDH2*2). ALDH2*2 has significantly reduced ability to metabolize ACE (4, 5). Importantly, its activity is partially dominant-negative over that of the wild-type ALDH2*1, due to the structural alterations introduced by the mutation to the ALDH2 homotetramer complex (6). As a result, individuals with a heterozygous ALDH2*2/2*1 genotype have less than half the wild-type activity, and ALDH2*2/2*2 homozygotes have very low residual activity (7). Accumulated ACE can cause an alcohol flush reaction, commonly found in Asians with this variant after alcohol consumption (also called "Asian glow").ACE binds to cellular proteins and DNA, leading to DNA damage and organ injury (8). Specifically, endogenous aldehydes are detrimental to hematopoietic stem cells that are defective in Fanconi anemia DNA repair (9, 10). As a result, Fanconi anemia patients with the ALDH2*2 allele exhibit accelerated disease progression (11). ALDH2*2 can also increase the risk for gastrointestinal cancers, such as gastric carcinoma (12), esophagea...