Antisense transcription (transcription from the opposite strand to a protein-coding or sense strand) has been ascribed roles in gene regulation involving degradation of the corresponding sense transcripts (RNA interference), as well as gene silencing at the chromatin level. Global transcriptome analysis provides evidence that a large proportion of the genome can produce transcripts from both strands, and that antisense transcripts commonly link neighboring "genes" in complex loci into chains of linked transcriptional units. Expression profiling reveals frequent concordant regulation of sense/antisense pairs. We present experimental evidence that perturbation of an antisense RNA can alter the expression of sense messenger RNAs, suggesting that antisense transcription contributes to control of transcriptional outputs in mammals.

Store-operated Ca2+ entry mediated by STIM1 and ORAI1 constitutes one of the major Ca2+ entry routes in mammalian cells. The molecular choreography of STIM1-ORAI1 coupling is initiated by endoplasmic reticulum (ER) Ca2+ store depletion with subsequent oligomerization of the STIM1 ER-luminal domain, followed by its redistribution toward the plasma membrane to gate ORAI1 channels. The mechanistic underpinnings of this inside-out Ca2+ signaling were largely undefined. By taking advantage of a unique gain-of-function mutation within the STIM1 transmembrane domain (STIM1-TM), here we show that local rearrangement, rather than alteration in the oligomeric state of STIM1-TM, prompts conformational changes in the cytosolic juxtamembrane coiled coil region. Importantly, we further identify critical residues within the cytoplasmic domain of STIM1 (STIM1-CT) that entail autoinhibition. Based on these findings we propose a model in which STIM1-TM reorganization switches STIM1-CT into an extended conformation, thereby projecting the ORAI-activating domain to gate ORAI1 channels.

Animals, including humans, express two isoforms of acetyl-CoA carboxylase (EC 6.4.1.2), ACC1 (Mr ‫؍‬ 265 kDa) and ACC2 (Mr ‫؍‬ 280 kDa). The predicted amino acid sequence of ACC2 contains an additional 136 aa relative to ACC1, 114 of which constitute the unique N-terminal sequence of ACC2. The hydropathic profiles of the two ACC isoforms generally are comparable, except for the unique N-terminal sequence in ACC2. The sequence of amino acid residues 1-20 of ACC2 is highly hydrophobic, suggesting that it is a leader sequence that targets ACC2 for insertion into membranes. The subcellular localization of ACC2 in mammalian cells was determined by performing immunofluorescence microscopic analysis using affinity-purified anti-ACC2-specific antibodies and transient expression of the green fluorescent protein fused to the C terminus of the N-terminal sequences of ACC1 and ACC2. These analyses demonstrated that ACC1 is a cytosolic protein and that ACC2 was associated with the mitochondria, a finding that was confirmed further by the immunocolocalization of a known human mitochondria-specific protein and the carnitine palmitoyltransferase 1. Based on analyses of the fusion proteins of ACC-green fluorescent protein, we concluded that the N-terminal sequences of ACC2 are responsible for mitochondrial targeting of ACC2. The association of ACC2 with the mitochondria is consistent with the hypothesis that ACC2 is involved in the regulation of mitochondrial fatty acid oxidation through the inhibition of carnitine palmitoyltransferase 1 by its product malonyl-CoA.A cetyl-CoA carboxylase (ACC) catalyzes the carboxylation of acetyl-CoA to form malonyl-CoA, an intermediate substrate that plays a pivotal role in the regulation of fatty acid metabolism. Besides its role in the biosynthesis of long-chain fatty acids (1-3), malonyl-CoA has been implicated in the regulation of the carnitine palmitoyl-CoA shuttle system that is involved in the mitochondrial ␤-oxidation of long-chain fatty acids. In animals, two isoforms of the carboxylase have been identified, ACC1 (M r ϭ 265,000) and ACC2 (M r ϭ 280,000) (4, 5). The two enzymes are encoded by separate genes and display distinct tissue distribution and regulation (6-9). The ACC1 carboxylases are highly expressed in lipogenic tissues, such as liver and adipose, and their levels are regulated transcriptionally while their activities are regulated posttranslationally by phosphorylation͞dephosphorylation of selected serine residues and by allosteric regulation through the action of citrate and palmitoyl-CoA (10-18). Dietary and hormonal states of the animal affect the level and activities of the ACC1 enzymes. A carbohydrate-rich, low-fat diet stimulates the expression and activities of ACC1, whereas starvation and diabetes reduce the ACC1 activities by repressing the expression of the ACC1 gene or by increasing the phosphorylation levels of the ACC1 protein (or both). Treating diabetic animals with insulin increases the activity of the enzyme either by dephosphorylation of the protein or by...

Hepatic gluconeogenesis is a main source of blood glucose during prolonged fasting and is orchestrated by endocrine and neural pathways. Here we show that the hepatocytesecreted hormone fibroblast growth factor 21 (FGF21) induces fasting gluconeogenesis via the brain-liver axis. Prolonged fasting induces activation of the transcription factor peroxisome proliferator-activated receptor a (PPARa) in the liver and subsequent hepatic production of FGF21, which enters into the brain to activate the hypothalamic-pituitary-adrenal (HPA) axis for release of corticosterone, thereby stimulating hepatic gluconeogenesis. Fasted FGF21 knockout (KO) mice exhibit severe hypoglycemia and defective hepatic gluconeogenesis due to impaired activation of the HPA axis and blunted release of corticosterone, a phenotype similar to that observed in PPARa KO mice. By contrast, intracerebroventricular injection of FGF21 reverses fasting hypoglycemia and impairment in hepatic gluconeogenesis by restoring corticosterone production in both FGF21 KO and PPARa KO mice, whereas all these central effects of FGF21 were abrogated by blockage of hypothalamic FGF receptor-1. FGF21 acts directly on the hypothalamic neurons to activate the mitogen-activated protein kinase extracellular signalrelated kinase 1/2 (ERK1/2), thereby stimulating the expression of corticotropin-releasing hormone by activation of the transcription factor cAMP response element binding protein. Therefore, FGF21 maintains glucose homeostasis during prolonged fasting by fine tuning the interorgan cross talk between liver and brain.Hepatic gluconeogenesis is tightly controlled by counterregulatory hormones such as glucagon, cortisol, and insulin, via regulating the expression of key gluconeogenic enzymes, including glucose 6 phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Fibroblast growth factor 21 (FGF21), a metabolic regulator mainly secreted from the liver in response to fasting and starvation under the control of the nuclear receptor peroxisome proliferatoractivated receptor a (PPARa), plays a critical role in maintaining energy homeostasis and insulin sensitivity in both rodents and nonhuman primates (1-6). A therapeutic dose of FGF21 decreased blood glucose in diabetic animals without causing hypoglycemia (4). FGF21 has also been shown to act as a key downstream effector of PPARa, mediating several metabolic adaptation responses to starvation, including hepatic fatty acid oxidation, ketogenesis, and growth hormone resistance (1,2,7). In addition, FGF21 is implicated in hepatic gluconeogenesis, although it remains controversial whether hepatocytes are a direct action site of FGF21 (8,9). There is an obvious dichotomy between the effects of endogenous FGF21 and pharmacological actions of the recombinant peptide with respect to hepatic metabolism (4,6,9).FGF21 can cross the blood-brain barrier (10) and is detectable in both human and rodent cerebrospinal fluid (10,11). Continuous intracerebroventricular injection of FGF21 into obese rats increases energy e...