The adenovirus E1A proteins differentially regulate AP‐1‐responsive genes. Collagenase and stromelysin are repressed by E1A, whereas the expression of c‐jun is elevated. Inhibition of collagenase has been found to be exerted through the consensus AP‐1 binding site TGAGTCA. Here we show that the distal AP‐1 binding site in the c‐jun promoter, the jun2TRE (TTACCTCA), is the decisive element of this promoter in mediating the positive response to the 243 amino acid E1A product. In vitro binding studies revealed that, in contrast to the consensus AP‐1 site which is preferentially targeted by dimers composed of the Jun and Fos families, the jun2TRE binds heterodimers composed of cJun and ATF‐2(‐like) proteins. Since stimulation of c‐jun transcription is a function of the transforming domain of E1A encoded by conserved region 1, cJun‐‐ATF‐2 may be one of the effector factors involved in transformation. The data further suggest that E1A can distinguish between cJun‐‐cJun and cJun‐‐ATF‐2 in imposing opposite states of activity.

Many neurons in the developing nervous system undergo programmed cell death, or apoptosis. However, the molecular mechanism underlying this phenomenon is largely unknown. In the present report, we present evidence that the cell cycle regulator cyclin D1 is involved in the regulation of neuronal cell death. During neuronal apoptosis, cyclin D1‐dependent kinase activity is stimulated, due to an increase in cyclin D1 levels. Moreover, artificial elevation of cyclin D1 levels is sufficient to induce apoptosis, even in non‐neural cell types. Cyclin D1‐induced apoptosis, like neuronal apoptosis, can be inhibited by 21 kDa E1B, Bcl2 and pRb, but not by 55 kDa E1B. Most importantly, however, overexpression of the cyclin D‐dependent kinase inhibitor p16INK4 protects neurons from apoptotic cell death, demonstrating that activation of endogenous cyclin D1‐dependent kinases is essential during neuronal apoptosis. These data support a model in which neuronal apoptosis results from an aborted attempt to activate the cell cycle in terminally differentiated neurons.

The activity of transcription factor NFκB is regulated by its subcellular localization. In most cell types, NFκB is sequestered in the cytoplasm due to binding of the inhibitory protein IκBα. Stimulation of cells with a wide variety of agents results in degradation of IκBα, which allows translocation of NFκB to the nucleus. Degradation of IκBα is triggered by phosphorylation of two serine residues, i.e. Ser32 and Ser36, by as yet unknown kinases. Here we report that the mitogen‐activated 90 kDa ribosomal S6 kinase (p90rsk1) is an IκBα kinase. p90rsk1 phosphorylates IκBα at Ser32 and it physically associates with IκBα in vivo. Moreover, when the function of p90rsk1 is impaired by expression of a dominant‐negative mutant, IκBα degradation in response to mitogenic stimuli, e.g. 12‐O‐tetradecanoylphorbol 13‐acetate (TPA), is inhibited. Finally, NFκB cannot be activated by TPA in cell lines that have low levels of p90rsk1. We conclude that p90rsk1 is an essential kinase required for phosphorylation and subsequent degradation of IκBα in response to mitogens.

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Despite high levels of homology, transcription coactivators p300 and CREB binding protein (CBP) are both indispensable during embryogenesis. They are largely known to regulate the same genes. To identify genes preferentially regulated by p300 or CBP, we performed an extensive genome-wide survey using the ChIP-seq on cell-cycle synchronized cells. We found that 57% of the tags were within genes or proximal promoters, with an overall preference for binding to transcription start and end sites. The heterogeneous binding patterns possibly reflect the divergent roles of CBP and p300 in transcriptional regulation. Most of the 16 103 genes were bound by both CBP and p300. However, after stimulation 89 and 1944 genes were preferentially bound by CBP or p300, respectively. Target genes were found to be primarily involved in the regulation of metabolic and developmental processes, and transcription, with CBP showing a stronger preference than p300 for genes active in negative regulation of transcription. Analysis of transcription factor binding sites suggest that CBP and p300 have many partners in common, but AP-1 and Serum Response Factor (SRF) appear to be more prominent in CBP-specific sequences, whereas AP-2 and SP1 are enriched in p300-specific targets. Taken together, our findings further elucidate the distinct roles of coactivators p300 and CBP in transcriptional regulation.