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Hydroxyurea (HU) is a specific inhibitor of ribonucleotide reductase and thus impairs dNTP synthesis and DNA replication. The long-term transcriptional response of yeast cells to hydroxyurea was investigated using DNA microarrays containing all yeast coding sequences. We show that the redox-responsive Yap regulon and the iron-mobilization Aft regulon are activated in yeast cells treated with HU. Yap1 accumulates in the nucleus in response to HU, but HU activation of the Yap regulon was only partially dependent on Yap1 and yap1Delta mutants were not hypersensitive to HU. In contrast, deletion of the AFT1 and AFT2 transcription factor genes blocked the HU activation of a subset of the Aft regulon and the aft1Delta aft2Delta double mutant was hypersensitive to HU in an iron-suppressible manner. These results highlight the importance of the redox and iron mobilization regulons in the cellular response to HU.

The knowledge of the mechanism of keratinocyte differentiation in culture is still uncompleted. The emergence of new technologies, such as cDNA microarrays or 2D electrophoresis followed by mass spectrometry analysis, has allowed the identification of genes and proteins expressed in biological processes in keratinocytes. Here, we report a genome wide analysis of proliferating versus differentiated human HaCaT keratinocytes. We found that genes and proteins which take part in the cell cycle control, carbohydrate metabolism, cell auto-immunity, adhesion and cytokine signal transduction pathways were regulated in differentiated HaCaT keratinocytes. In addition, we identified seven proteins and 33 transcripts that had not been previously described as differentially expressed in proliferating versus differentiated HaCaT cells. Furthermore, some of these transcripts or proteins were similarly regulated in human primary keratinocytes and in human epidermis. The present study opens new areas of investigation in the comprehension of keratinocyte differentiation. (C) 2004 Wiley-Liss, Inc.

International audience; Purpose: To identify transcriptional gene-networks involved in the early in vivo response of liver cells to radiation exposure and improve our understanding of the molecular processes responsible for tissue radiosensitivity.Materials and methods: Transcriptome variations of liver RNA samples were measured 3 hours post-irradiation using microarray technology. The results were confirmed and extended using real-time polymerase-chain-reaction (RT-PCR).Results: We identified quantitative changes in the expression of 126 genes, most of which were observed for the first time. We show that some modifications, such as the upregulation of the cyclin-dependent kinase inhibitor 1A (Cdkn1A) gene, persisted for at least two months after the initial exposure. Other genes regulated by the transformation-related protein 53 (Trp53/p53) such as Bcl2-associated X protein (Bax) or etoposide-induced-2.4 (Ei24/PIG8) were not upregulated. Grouping differentially expressed genes into functional categories revealed that the primary response of liver cells to radiation exposure was the enhancement of oxidoreductase activity and inhibition of cell proliferation, involving cell cycle progression and apoptosis-related genes.Conclusions: The data provides evidence of gene expression modifications associated with the hepatic response to radiation exposure. One of the main differences observed with radiation-sensitive tissues such as the spleen was cell proliferation. The comparison of our data with transcriptome modifications in different biological models enabled the identification of networks of genes that might be co-regulated. Overall, our expression data revealed genes and cellular pathways that might help to improve our understanding of the molecular basis underlying tissue radiosensitivity and to identify possible targets for novel therapeutic strategies.

The knowledge of the mechanism of keratinocyte differentiation in culture is still uncompleted. The emergence of new technologies, such as cDNA microarrays or 2D electrophoresis followed by mass spectrometry analysis, has allowed the identification of genes and proteins expressed in biological processes in keratinocytes. Here, we report a genome wide analysis of proliferating versus differentiated human HaCaT keratinocytes. We found that genes and proteins which take part in the cell cycle control, carbohydrate metabolism, cell auto-immunity, adhesion and cytokine signal transduction pathways were regulated in differentiated HaCaT keratinocytes. In addition, we identified seven proteins and 33 transcripts that had not been previously described as differentially expressed in proliferating versus differentiated HaCaT cells. Furthermore, some of these transcripts or proteins were similarly regulated in human primary keratinocytes and in human epidermis. The present study opens new areas of investigation in the comprehension of keratinocyte differentiation.