PCAF plays a role in transcriptional activation, cell-cycle arrest, and cell differentiation in cultured cells. PCAF contributes to transcriptional activation by acetylating chromatin and transcription factors through its intrinsic histone acetylase activity. In this report, we present evidence for the in vivo function of PCAF and the closely related PCAF-B͞GCN5. Mice lacking PCAF are developmentally normal without a distinct phenotype. In PCAF null-zygous mice, protein levels of PCAF-B͞GCN5 are drastically elevated in lung and liver, where PCAF is abundantly expressed in wild-type mice, suggesting that PCAF-B͞GCN5 functionally compensates for PCAF. In contrast, animals lacking PCAF-B͞GCN5 die between days 9.5 and 11.5 of gestation. Normally, PCAF-B͞GCN5 mRNA is expressed at high levels already by day 8, whereas PCAF mRNA is first detected on day 12.5, which may explain, in part, the distinct knockout phenotypes. These results provide evidence that PCAF and PCAF-B͞GCN5 play distinct but functionally overlapping roles in embryogenesis.H uman (h)PCAF (p300͞CBP associated factor; ref. 1) is a transcriptional coactivator with intrinsic histone acetylase activity, which contributes to transcriptional activation by modifying chromatin and transcriptional factors (for reviews, see refs. 2-5). Although an exact mechanism of how acetylation of histones contribute to transcriptional activation has not been clarified, it has been thought that acetylation of nucleosomal histones leads to relaxation of chromatin structure such that various transcription factors can gain access and function onto chromatin DNA. Although histones are physiologically relevant substrates for PCAF, PCAF also acetylates transcriptional activators p53 (6, 7) and MyoD (8), as originally demonstrated by p300 acetylase (9), and stimulates DNA binding.PCAF is present in a stable multisubunit complex consisting of more than 20 distinct polypeptides, whose molecular masses range from 10 to 400 kDa (10). Although recombinant PCAF per se cannot efficiently acetylate histones in nucleosomal contexts, the PCAF complex that we purified can, strongly suggesting that subunits in the PCAF complex could stimulate acetylation of relevant substrates (10). Moreover, characterization of subunits of the PCAF complex has revealed that they are TATA boxbinding protein-associated factors (TAFs), which were originally found in TFIID; TAF-related PAF65␣ and ␤; human homologs of yeast transcriptional cofactors ADA2, ADA3, and Spt3 as well as PAF400, which exhibits sequence similarity to members of the ATM superfamily (10, 11). Importantly, TAF80, TAF-like PAF65␣, and TAF20͞15 bear sequence similarities to core histones (10) and thus may form a histone octamer-like structure in the PCAF complex, as has been proposed for TFIID (12)(13)(14). Furthermore, TAF-like PAF65␤ has WD40-repeats, motifs often found in factors that target chromatin (10).The second family member is hPCAF-B͞GCN5 (5, 15). PCAF and PCAF-B͞GCN5 are well conserved over their entire sequence, and both exhibit p...

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PCAF histone acetylase is found in a complex with more than 20 associated polypeptides. Here we report cloning and characterization of the 400 kDa PCAF-associated factor referred to as PAF400. PAF400 is almost identical to TRRAP, which binds to c-Myc and E2F, and has significant sequence similarities to the ATM superfamily including FRAP, ATM, ATR, and the catalytic subunit of DNA-PK. Remarkably, PAF400 and FRAP share sequence similarity in broad regions that cover 80% of the entire PAF400 sequence. However, unlike the other members of the ATM superfamily, PAF400 is not a protein kinase as judged from the lack of kinase motif and autophosphorylation activity. We discuss the possibility that PAF400 may play a role in signaling of DNA damage to p53 by stimulation of p53 acetylation.

Background: Hypertriglyceridemia is the most common lipid disorder with incompletely understood mechanisms. Results: ATF4 deficiency attenuates lipogenesis in the liver and protects against high fructose-induced hypertriglyceridemia in mice. Conclusion: ATF4 plays a pivotal role in regulating hepatic lipid metabolism. Significance: ATF4 is a contributing factor for the pathogenesis of hypertriglyceridemia.

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Alpha-galactosylceramide (αGC), a lipid antigen present on CD1d molecules, is predicted to have clinical applications as a new class of adjuvant, because αGC strongly activates natural killer T (NKT) cells which produce large amounts of IFN-γ. Here, we incorporated αGC into stearylated octaarginine-modified liposomes (R8-Lip), our original delivery system developed for vaccines, and investigated the effect of nanoparticulation. Unexpectedly, the systemic administered R8-Lip incorporating αGC (αGC/R8-Lip) failed to improve the immune responses mediated by αGC compared with soluble αGC in vivo, although αGC/R8-Lip drastically enhanced αGC presentation on CD1d in antigen presenting cells in vitro. Thus, we optimized the αGC/R8-Lip in vivo to overcome this inverse correlation. In optimization in vivo, we found that size control of liposome and R8-modification were critical for enhancing the production of IFN-γ. The optimization led to the accumulation of αGC/R8-Lip in the spleen and a positive therapeutic effect against highly malignant B16 melanoma cells. The optimized αGC/R8-Lip also enhanced αGC presentation on CD1d in antigen presenting cells and resulted in an expansion in the population of NKT cells. Herein, we show that R8-Lip is a potent delivery system, and size control and R8-modification in liposomal construction are promising techniques for achieving systemic αGC therapy.

β-Cell compensation is an essential mechanism by which β-cells increase insulin secretion for overcoming insulin resistance to maintain euglycemia in obesity. Failure of β-cells to compensate for insulin resistance contributes to insulin insufficiency and overt diabetes. To understand the mechanism of β-cell compensation, we characterized the role of forkhead box O1 (FoxO1) in β-cell compensation in mice under physiological and pathological conditions. FoxO1 is a key transcription factor that serves as a nutrient sensor for integrating insulin signaling to cell metabolism, growth, and proliferation. We showed that FoxO1 improved β-cell compensation via 3 distinct mechanisms by increasing β-cell mass, enhancing β-cell glucose sensing, and augmenting β-cell antioxidative function. These effects accounted for increased glucose-stimulated insulin secretion and enhanced glucose tolerance in β-cell-specific FoxO1-transgenic mice. When fed a high-fat diet, β-cell-specific FoxO1-transgenic mice were protected from developing fat-induced glucose disorder. This effect was attributable to increased β-cell mass and function. Furthermore, we showed that FoxO1 activity was up-regulated in islets, correlating with the induction of physiological β-cell compensation in high-fat-induced obese C57BL/6J mice. These data characterize FoxO1 as a pivotal factor for orchestrating physiological adaptation of β-cell mass and function to overnutrition and obesity.