|Genome-wide histone acetylation is altered in a transgenic mouse model of Huntington's disease.|
McFarland, KN; Das, S; Sun, TT; Leyfer, D; Xia, E; Sangrey, GR; Kuhn, A; Luthi-Carter, R; Clark, TW; Sadri-Vakili, G; Cha, JH
In Huntington's disease (HD; MIM ID #143100), a fatal neurodegenerative disorder, transcriptional dysregulation is a key pathogenic feature. Histone modifications are altered in multiple cellular and animal models of HD suggesting a potential mechanism for the observed changes in transcriptional levels. In particular, previous work has suggested an important link between decreased histone acetylation, particularly acetylated histone H3 (AcH3; H3K9K14ac), and downregulated gene expression. However, the question remains whether changes in histone modifications correlate with transcriptional abnormalities across the entire transcriptome. Using chromatin immunoprecipitation paired with microarray hybridization (ChIP-chip), we interrogated AcH3-gene interactions genome-wide in striata of 12-week old wild-type (WT) and transgenic (TG) R6/2 mice, an HD mouse model, and correlated these interactions with gene expression levels. At the level of the individual gene, we found decreases in the number of sites occupied by AcH3 in the TG striatum. In addition, the total number of genes bound by AcH3 was decreased. Surprisingly, the loss of AcH3 binding sites occurred within the coding regions of the genes rather than at the promoter region. We also found that the presence of AcH3 at any location within a gene strongly correlated with the presence of its transcript in both WT and TG striatum. In the TG striatum, treatment with histone deacetylase (HDAC) inhibitors increased global AcH3 levels with concomitant increases in transcript levels; however, AcH3 binding at select gene loci increased only slightly. This study demonstrates that histone H3 acetylation at lysine residues 9 and 14 and active gene expression are intimately tied in the rodent brain, and that this fundamental relationship remains unchanged in an HD mouse model despite genome-wide decreases in histone H3 acetylation.
|Effect of insulin levels on the phosphorylation of specific amino acid residues in IRS-1: implications for burn-induced insulin resistance.|
Lu, XM; Hamrahi, VF; Tompkins, RG; Fischman, AJ
International journal of molecular medicine
Alterations in the phosphorylation and/or degradation of insulin receptor substrate-1 (IRS-1) produced by burn injury may be responsible, at least in part, for burn-induced insulin resistance. In particular, following burn injury, reductions in glucose uptake by skeletal muscle may be secondary to altered abundance and/or phosphorylation of IRS-1. In this study, we performed in vitro experiments with 293 cells transfected with IRS-1. These studies demonstrated that there is a dramatic change in the phosphorylation pattern of Tyr, Ser and Thr residues in IRS-1 as a function of insulin levels. Specifically, Ser and Thr residues in the C-terminal region were phosphorylated only at high insulin levels. SILAC (stable isotope labeling with amino acids in cell culture) followed by sequencing of C-terminal IRS-1 fragments by tandem mass spectrometry demonstrated that there is significant protein cleavage at these sites. These findings suggest that one of the biological roles of the C-terminal region of IRS-1 may be negative modulation of the finely coordinated insulin signaling system. Clearly, this could represent an important factor in insulin resistance, and identification of kinase inhibitors that are responsible for the phosphorylation may foster new lines of research for the development of drugs for treating insulin resistance.
|Phosphoinositide 3-kinase p110beta activity: key role in metabolism and mammary gland cancer but not development.|
Ciraolo, E; Iezzi, M; Marone, R; Marengo, S; Curcio, C; Costa, C; Azzolino, O; Gonella, C; Rubinetto, C; Wu, H; Dastrù, W; Martin, EL; Silengo, L; Altruda, F; Turco, E; Lanzetti, L; Musiani, P; Rückle, T; Rommel, C; Backer, JM; Forni, G; Wymann, MP; Hirsch, E
The phosphoinositide 3-kinase (PI3K) pathway crucially controls metabolism and cell growth. Although different PI3K catalytic subunits are known to play distinct roles, the specific in vivo function of p110beta (the product of the PIK3CB gene) is not clear. Here, we show that mouse mutants expressing a catalytically inactive PIK3CB(K805R) mutant survived to adulthood but showed growth retardation and developed mild insulin resistance with age. Pharmacological and genetic analyses of p110beta function revealed that p110beta catalytic activity is required for PI3K signaling downstream of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors as well as to sustain long-term insulin signaling. In addition, PIK3CB(K805R) mice were protected in a model of ERBB2-driven tumor development. These findings indicate an unexpected role for p110beta catalytic activity in diabetes and cancer, opening potential avenues for therapeutic intervention.