Insulin-stimulated MAP-2 kinase phosphorylates and activates ribosomal protein S6 kinase II

Ribosomal protein S6 is a component of the eukaryotic 40S ribosomal subunit that becomes phosphorylated on multiple serine residues in response to a variety of mitogens, including insulin, growth factors, and transforming proteins of many oncogenic viruses. Recently, an activated S6 kinase (S6 K II) has been purified to homogeneity from Xenopus eggs, and characterized immunologically and at the molecular level. Purified S6 K II can be deactivated in vitro by incubation with either protein phosphatase 1 or protein phosphatase 2A. Reactivation and phosphorylation of S6 K II occurs in vitro with an insulin-stimulated microtubule-associated protein-2 (MAP-2) protein kinase which is itself a phosphoprotein that can be deactivated by protein phosphatase 2A. These studies suggest that a step in insulin signalling involves sequential activation by phosphorylation of at least two serine/threonine protein kinases.     

Insulin stimulation of glucose uptake can be mediated by diacylglycerol in adipocytes

An early effect of insulin in adipocytes is to stimulate glucose uptake. The increased uptake appears to be due to mobilization of glucose transporters from an intracellular location to the plasma membrane and to enhanced intrinsic activity of the transporters. Little is known about the insulin-generated signals causing these changes. Phorbol esters have been shown to mimic the insulin effect, but phosphorylation of the transporter does not seem to be involved. A phospho-oligosaccharide was recently shown to mimic the effects of insulin on protein phosphorylation, suggesting that it could be a mediator for some intracellular metabolic effects of the hormone, but it did not affect glucose uptake. A diacyglycerol is produced in the plasma membrane in conjunction with the generation of the phospho-oligosaccharide. Here I show that added 1,2-diacylglycerols potently increase glucose transporter-mediated uptake of glucose in rat adipocytes, but without activation of protein kinase C.     

Type I phosphatidylinositol kinase makes a novel inositol phospholipid, phosphatidylinositol-3-phosphate

The generation of second messengers from the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdInsP2) by phosphoinositidase C has been implicated in the mediation of cellular responses to a variety of growth factors and oncogene products. The first step in the production of PtdInsP2 from phosphatidylinositol (PtdIns) is catalysed by PtdIns kinase. A PtdIns kinase activity has been found to associate specifically with several oncogene products, as well as with the platelet-derived growth factor (PDGF) receptor. We have previously identified two biochemically distinct PtdIns kinases in fibroblasts, and have found that only one of these, designated type I, specifically associates with activated tyrosine kinases. We have now characterized the site on the inositol ring phosphorylated by type I PtdIns kinase, and find that this kinase specifically phosphorylates the D-3 ring position to generate a novel phospholipid, phosphatidylinositol-3-phosphate (PtdIns(3)P). In contrast, the main PtdIns kinase in fibroblasts, designated type II, specifically phosphorylates the D-4 position to produce phosphatidylinositol-4-phosphate (PtdIns(4)P), previously considered to be the only form of PtdInsP. We have also tentatively identified PtdIns(3)P as a minor component of total PtdInsP in intact fibroblasts. We propose that type I PtdIns kinase is responsible for the generation of PtdIns(3)P in intact cells, and that this novel phosphoinositide could be important in the transduction of mitogenic and oncogenic signals.     

Novel anti-inflammatory peptides from the region of highest similarity between uteroglobin and lipocortin I

Significant future developments in the effective treatment of inflammatory diseases may arise from non-toxic dual inhibitors of both cyclooxygenase and lipoxygenase pathways in the arachidonate cascade. Inhibition of phospholipase A2(PLA2)(EC3.1.1.4), may provide such a dual action and recent research has concentrated on the role of PLA2-inhibitory proteins as possible anti-inflammatory agents. Blastokinin or uteroglobin is a steroid-induced rabbit secretory protein with PLA2-inhibitory activity. Its biochemical and biological properties have been extensively studied and its crystallographic structure has been resolved at 1.34 A (refs 15, 16). Lipocortins are a family of related proteins, which, it has been suggested, mediate the anti-inflammatory effects of glucocorticoids (for a review, see ref. 23). Some proteins of this group have been purified and the complementary DNA sequences of two human lipocortins are known. Lipocortins inhibit PLA2 in vitro, although their mechanism of action is still unclear. Recombinant lipocortin I inhibits eicosanoid synthesis in isolated perfused lungs from the guinea pig. Here, we report that synthetic oligopeptides corresponding to a region of high amino-acid sequence similarity between uteroglobin and lipocortin I have potent PLA2 inhibitory activity in vitro and striking anti-inflammatory effects in vivo.     

Inositol 1,4,5-trisphosphate activates a channel from smooth muscle sarcoplasmic reticulum

Inositol 1,4,5-trisphosphate (InsP3) can initiate calcium release into the cytoplasm in a variety of cells. From experiments using permeabilized cells, membrane vesicles, and patch-clamp techniques, it has been suggested that InsP3 acts by directly opening calcium channels. Here, we show that InsP3 induced openings of channels in planar lipid bilayers into which vesicles made from aortic muscle sarcoplasmic reticulum (SR) were incorporated. Activation of channels by InsP3 was not observed when vesicles made from SR of cardiac or skeletal muscle were incorporated into planar lipid bilayers. The present study demonstrates for the first time unique properties of an InsP3-gated calcium channel in sarcoplasmic reticulum vesicles from vascular smooth muscle. This InsP3-activated channel from aortic SR differs strikingly from the calcium-gated calcium channel of striated muscle SR in single-channel conductance and pharmacology.     

Self-tolerance eliminates T cells specific for Mls-modified products of the major histocompatibility complex

In mice the product of the Mlsa locus is an unusual antigen capable of interaction with certain products of the major histocompatibility locus (MHC) to form a ligand for a large portion of the T-cell alpha/beta receptor repertoire, including nearly all receptors that use V beta 8.1. The presence of Mlsa/MHC during T-cell development results in the deletion of T cells that express V beta 8.1, documenting the importance of clonal deletion in establishing tolerance to self antigens.     

Incubation periods for paediatric AIDS patients

A recent seroprevalence study of newborns indicates that one in 62 children born in New York City has antibodies to the human immunodeficiency virus (HIV). The distribution of incubation periods for paediatric patients is needed to estimate future AIDS case loads from these seroprevalence data. Current estimates of incubation periods for paediatric patients are based on limited data. We use parametric and non-parametric methods to analyse incubation periods for 215 paediatric patients with AIDS whose only known route of infection is maternal. We conclude that incubation periods are longer than previously reported; that there is a distinct knee in the incubation period distribution at seven months which suggests two risk populations; and that there is an increase in incidence which is consistent with exponential growth.