Clinical insulin resistance is associated with decreased activation of phosphatidylinositol 3-kinase (PI3K) and its downstream substrate protein kinase B (PKB)/Akt. However, its physiological protein substrates remain poorly characterized. In the present study, the effect of in vivo insulin action on phosphorylation of the PKB/Akt substrate 40 (PRAS40) was examined. In rat and mice, insulin stimulated PRAS40-Thr246 phosphorylation in skeletal and cardiac muscle, the liver, and adipose tissue in vivo. Physiological hyperinsulinemia increased PRAS40-Thr246 phosphorylation in human skeletal muscle biopsies. In cultured cell lines, insulin-mediated PRAS40 phosphorylation was prevented by the PI3K inhibitors wortmannin and LY294002. Immunohistochemical and immunofluorescence studies showed that phosphorylated PRAS40 is predominantly localized to the nucleus. Finally, in rats fed a high-fat diet (HFD), phosphorylation of PRAS40 was markedly reduced compared with low-fat diet-fed animals in all tissues examined. In conclusion, the current study identifies PRAS40 as a physiological target of in vivo insulin action. Phosphorylation of PRAS40 is increased by insulin in human, rat, and mouse insulin target tissues. In rats, this response is reduced under conditions of HFD-induced insulin resistance. Diabetes 55:3221-3228, 2006 I nsulin resistance and type 2 diabetes are associated with impaired insulin action in peripheral tissues like skeletal muscle, adipose tissue, liver, and the heart (1). Insulin action is initiated by binding of insulin to its receptor, leading to activation and phosphorylation of the receptor tyrosine kinase, which in turn phosphorylates several endogenous substrates, including the insulin receptor substrate proteins (1). Tyrosine phosphorylation of the insulin receptor substrate proteins facilitates the binding and activation of phosphatidylinositol 3Ј-kinase (PI3K), thus catalyzing the formation of phosphatidylinositol 3,4,5-trisphosphate and providing a platform for the binding and activation of protein kinase B (PKB)/Akt (1). Numerous studies have linked PKB/Akt to the regulation of glucose metabolism, cell growth, and antiapoptosis (2,3). However, the endogenous substrates regulating these responses are only starting to become characterized (4).The PKB/Akt protein kinase phosphorylates proteins on serine (S/Ser) or threonine (T/Thr) residues within a RxRxxpS/pT motif (5). The use of phospho-specific antibodies recognizing this PKB/Akt consensus sequence led to the identification of multiple novel proteins, including proline-rich Akt substrate 40 (PRAS40; also known as Akt1 substrate 1 [Akt1S1]) (6,7). PRAS40 is ubiquitously expressed and appears to be localized to the nucleus (7,8). In response to growth factors, PRAS40 is phosphorylated on Thr246 via PI3K-and PKB/Akt-dependent signaling pathways (6,8). In vitro, phosphorylation of PRAS40 facilitates the binding of 14-3-3 proteins, and this protein complex has been implicated in nerve growth factor-mediated neuroprotection from ischemia (8). Al...

Rosekrans SL, Baan B, Muncan V, van den Brink GR. Esophageal development and epithelial homeostasis. Am J Physiol Gastrointest Liver Physiol 309: G216 -G228, 2015. First published July 2, 2015; doi:10.1152/ajpgi.00088.2015.-The esophagus is a relatively simple organ that evolved to transport food and liquids through the thoracic cavity. It is the only part of the gastrointestinal tract that lacks any metabolic, digestive, or absorptive function. The mucosa of the adult esophagus is covered by a multilayered squamous epithelium with a remarkable similarity to the epithelium of the skin despite the fact that these tissues originate from two different germ layers. Here we review the developmental pathways involved in the establishment of the esophagus and the way these pathways regulate gut-airway separation. We summarize current knowledge of the mechanisms that maintain homeostasis in esophageal epithelial renewal in the adult and the molecular mechanism of the development of Barrett's metaplasia, the precursor lesion to esophageal adenocarcinoma. Finally, we examine the ongoing debate on the hierarchy of esophageal epithelial precursor cells and on the presence or absence of a specific esophageal stem cell population. Together the recent insights into esophageal development and homeostasis suggest that the pathways that establish the esophagus during development also play a role in the maintenance of the adult epithelium. We are beginning to understand how reflux of gastric content and the resulting chronic inflammation can transform the squamous esophageal epithelium to columnar intestinal type metaplasia in Barrett's esophagus. esophagus; development; homeostasis; stem cell; endoderm THE WORD ESOPHAGUS IS DERIVED from the Greek words ε (oisein, to carry) and ␣␥ε (phagein, to eat). This description fits well with the functional role of the esophagus that mainly serves to "carry food" into the stomach. From the pharyngoesophageal junction, the esophagus passes through the mediastinum and diaphragm and connects to the cardia of the stomach at the gastroesophageal junction or Z-line. The pharyngoesophageal and gastroesophageal junctions anatomically overlap with the upper and lower esophageal sphincters. Both sphincters are closed except during swallowing to assure a unidirectional flow of esophageal content toward the stomach and to prevent reflux of gastric content into the esophagus. The relatively simple histology of the esophageal epithelium corresponds with the fact that the esophagus has no role other than to pass food through the thorax to the stomach. It does not play a known digestive, endocrine, or metabolic role and the epithelium consists of a simple stratified squamous epithelium, which provides a good protective layer against the unmodified food stream on its way to the stomach. Despite the perhaps somewhat prosaic functional role of the esophagus compared with other organs in the body, we feel that it is essential to gain a better understanding of the mechanisms that regulate normal esophageal homeo...

We show that the transcriptional repressor Tel plays an evolutionarily conserved role in angiogenesis: it is indispensable for the sprouting of human endothelial cells and for normal development of the Danio rerio blood circulatory system. Tel orchestrates endothelial sprouting by binding to the generic co-repressor, CtBP. The Tel-CtBP complex temporally restricts a VEGF (vascular endothelial growth factor)-mediated pulse of dll4 expression and thereby directly links VEGF receptor intracellular signalling and intercellular Notch-Dll4 signalling. It further controls branching by regulating expression of other factors that constrain angiogenesis such as sprouty family members and ve-cadherin. Thus, the Tel-CtBP complex conditions endothelial cells for angiogenesis by controlling the balance between stimulatory and antagonistic sprouting cues. Tel control of branching seems to be a refinement of invertebrate tracheae morphogenesis that requires Yan, the invertebrate orthologue of Tel. This work highlights Tel and its associated networks as potential targets for the development of therapeutic strategies to inhibit pathological angiogenesis.

5-ASA interferes with proliferation of colorectal cancer cells via inhibition of PLD-dependent generation of PA and loss of mTOR signalling.