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The CCAAT/enhancer-binding protein alpha (C/EBP alpha) is essential for maintaining the differentiated state of hepatocytes in vivo. C/EBP alpha activates albumin transcription and coordinates the expression of multiple ornithine cycle enzymes involved in urea production. We have examined the effects of the C/EBP alpha knock-in gene on the mRNA and protein expression of genes involved in liver-specific functions, such as albumin and urea production. Albumin mRNA and protein levels are higher in knock-in hepatocytes compared with wild-type hepatocytes. mRNA levels for the ornithine cycle enzymes, namely arginase, carbamylphosphate synthetase 1, and ornithine transcarbamylase, also increase. Albumin secretion and urea production are sustained at higher levels in culture in knock-in hepatocytes. We have previously established that C/EBP alpha induces early liver glycogen storage in C/EBP alpha knock-in mice. Our present observations underline the importance of C/EBP alpha in liver metabolism and suggest that the induction of C/EBP alpha expression enhances hepatocyte function.

Hypoxia-inducible factor 1 (HIF-1) is the central mediator of cellular responses to low oxygen and has recently become an important therapeutic target for solid tumor therapy. Inhibition of HIF-1 is expected to result in the attenuation of hypoxia-inducible genes, which are vital to many aspects of tumor biology, including adaptative responses for survival under anaerobic conditions. To identify small molecules inhibiting the HIF-1 pathway, we did a biological screen on a 10,000-membered natural product-like combinatorial library. The compounds of the library, which share a 2,2-dimethylbenzopyran structural motif, were tested for their ability to inhibit the hypoxic activation of an alkaline phosphatase reporter gene under the control of hypoxiaresponsive elements in human glioma cells. This effort led to the discovery of 103D5R, a novel small-molecule inhibitor of HIF-1a. 103D5R markedly decreased HIF-1a protein levels induced by hypoxia or cobaltous ions in a dose- and timedependent manner, whereas minimally affecting global cellular protein expression levels, including that of control proteins such as HIF-1h ,I nBaa, and hh-actin. The inhibitory activity of 103D5R against HIF-1a was clearly shown under normoxia and hypoxia in cells derived from different cancer types, including glioma, prostate, and breast cancers. This inhibition prevented the activation of HIF-1 target genes under hypoxia such as vascular endothelial growth factor (VEGF) and glucose transporter-1 (Glut-1). Investigations into the molecular mechanism showed that 103D5R strongly reduced HIF-1a protein synthesis, whereas HIF-1a mRNA levels and HIF-1a degradation were not affected. 103D5R inhibited the phosphorylation of Akt, Erk1/2, and stressactivated protein kinase/c-jun-NH2-kinase, without changing the total levels of these proteins. Further studies on the mechanism of action of 103D5R will likely provide new insights into its validity/applicability for the pharmacologic targeting of HIF-1aa for therapeutic purposes. (Cancer Res 2005; 65(2): 605-12)

Transcription factors are master regulatory switches of differentiation, including the development of specific hematopoietic lineages from stem cells. Here we show that mice with targeted disruption of the CCAAT enhancer binding protein α gene (C/EBPα) demonstrate a selective block in differentiation of neutrophils. Mature neutrophils and eosinophils are not observed in the blood or fetal liver of mutant animals, while other hematopoietic lineages, including monocytes, are not affected. Instead, most of the white cells in the peripheral blood of mutant mice had the appearance of myeloid blasts. We also observed a selective loss of expression of a critical gene target of CCAAT enhancer binding protein α, the granulocyte colony-stimulating factor receptor. As a result, multipotential myeloid progenitors from the mutant fetal liver are unable to respond to granulocyte colony-stimulating factor signaling, although they are capable of forming granulocyte–macrophage and macrophage colonies in methylcellulose in response to other growth factors. Finally, we demonstrate that the lack of granulocyte development results from a defect intrinsic to the hematopoietic system; transplanted fetal liver from mutant mice can reconstitute lymphoid but not neutrophilic cells in irradiated recipients. These studies suggest a model by which transcription factors can direct the differentiation of multipotential precursors through activation of expression of a specific growth factor receptor, allowing proliferation and differentiation in response to a specific extracellular signal. In addition, thec/ebpα−/−mice may be useful in understanding the mechanisms involved in acute myelogenous leukemia, in which a block in differentiation of myeloid precursors is a key feature of the disease.

Mice homozygous for the targeted deletion of the c/ebp alpha gene, which expresses the CCAAT/enhancer-binding protein alpha (C/EBP alpha), did not store hepatic glycogen and died from hypoglycemia within 8 hours after birth. In these mutant mice, the amounts of glycogen synthase messenger RNA were 50 to 70 percent of normal and the transcriptional induction of the genes for two gluconeogenic enzymes, phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, was delayed. The hepatocytes and adipocytes of the mutant mice failed to accumulate lipid and the expression of the gene for uncoupling protein, the defining marker of brown adipose tissue, was reduced. This study demonstrates that C/EBP alpha is critical for the establishment and maintenance of energy homeostasis in neonates.

FAM-labeled oligo dT (FAMdT) was utilized as a means to gauge efficient transfection of small nucleic acids into mouse embryonic stem cell (mESC) colonies. Using colonies grown overnight, transfection was restricted largely to the periphery of the colonies with only a 40% decrease in Oct-3/4 RNA transcript levels following cognate Oct-3/4, small interfering RNA (siRNA) delivery. However, transfection of mESC 4 h after seeding gave greater than 90% cells being successfully transfected based on quantitative real-time PCR detection of approximately 90% Oct-3/4 RNA transcript knockdown. This method provides an economical and efficient means by which to determine effective transfection conditions, and establish efficient siRNA knockdown of reportedly difficult to transfect cell lines such as mESC.

Gene amplification is frequently present in human tumors, although specific target genes relevant to many amplified loci remain unidentified. An expression cloning assay enabled identification of a candidate oncogene derived from human chromosome 3p14.1. The cDNA retrieved from morphologically transformed cells contained the full-length protein coding region and detected an abundant transcript in the same cells. Sequence analysis revealed identity with the wild-type sequence of p44S10, a highly conserved subunit of the 26S proteasome that exhibits similarity to the Arabidopsis fus6/cop11 family of signaling molecules. p44S10 gene copy number and mRNA expression were increased in association with segmental 1.8 - 11-fold chromosomal gains in cutaneous malignant melanoma cell lines (5/13; 40%) and tumors (2/40; 5%), and in breast cancer MCF-7 cells. Likewise, malignant progression of human radial growth phase WM35 melanoma cells was associated with amplification and increased expression of endogenous p44S10, and increased expression of p44S10 was sufficient to induce proliferation of WM35 cells in vivo. The results demonstrate segmental copy number gains within chromosome 3p in cutaneous malignant melanoma and suggest that deregulation of a proteasome regulatory particle subunit may contribute to the malignant phenotype.