The regulation of sterol metabolism by cell interactions

Total and free cholesterol levels in C6 glial cells are regulated by a cell interaction-dependent mechanism that operates independently of exogenous cholesterol and serum lipoproteins. This mechanism, which is activated by changes in culture density, coordinately regulates the activities of HMG-CoA reductase and acyl-CoA:cholesterol acyltransferase (ACAT). Both enzyme activities are low in sparse density cultures, rise as density increases from sparse to moderate, and decrease with further density increases. When culture density is abruptly elevated, both enzyme activities decay rapidly and with biphasic kinetics. Neither enzyme phosphorylation nor diffusible cytosolic factors appear to be directly involved in density suppression of HMG-CoA reductase. Studies with human fibroblasts that are defective in LDL receptor function demonstrate that density regulation does not require a functional LDL receptor. Extracellular matrix and soluble factors have also been ruled out as intercellular mediators. The specific growth rate of C6 cultures changes with density in the same manner as sterol metabolism. The possibility that growth and sterol metabolism are regulated by a common cell interaction-dependent mechanism is discussed.     

Cell cycle control during the contact mediated growth inhibition of rat C6 glioma cells

Two separate control processes govern the cell cycle of rat C6 glioma cells. In subconfluent cultures growth inhibition is caused by cell contact interactions and the cell cycle is regulated primarily by changes in the duration of S phase. During advanced multilayering, medium depletion becomes the primary mechanism of growth inhibition and causes a pronounced G1 accumulation. Contact modulation acts by altering the velocity with which cells progress through the cell cycle, while depletion causes cycle arrest.     

Quantitative phosphoproteomic analysis of the PI3K‐regulated signaling network

The PI3K pathway is commonly activated in cancer. Only a few studies have attempted to explore the spectrum of phosphorylation signaling downstream of the PI3K cascade. Such insight, however, is imperative to understand the mechanisms responsible for oncogenic phenotypes. By applying MS‐based phosphoproteomics, we mapped 2509 phosphorylation sites on 1096 proteins, and quantified their responses to activation or inhibition of PIK3CA using isogenic knock‐in derivatives and a series of targeted inhibitors. We uncovered phosphorylation changes in a wide variety of proteins involved in cell growth and proliferation, many of which have not been previously associated with PI3K signaling. A significant update of the posttranslational modification database PHOSIDA ( http://www.phosida.com ) allows efficient use of the data. All MS data have been deposited in the ProteomeXchange with identifier PXD003899 ( http://proteomecentral.proteomexchange.org/dataset/PXD003899 ).     

Binding of complement component C3b to glycoprotein C is modulated by sialic acid on herpes simplex virus type 1-infected cells.

Neuraminidase treatment of cells infected with herpes simplex virus type 1 (HSV-1) markedly enhanced the binding of complement component C3b to HSV 1 glycoprotein C (gC). When HSV-1 was grown in BHK RicR14 cells in which glycoproteins had reduced amounts of N-linked complex oligosaccharides, including sialic acid, the binding of C3b to gC was markedly enhanced. We used neuraminidase treatment to demonstrate that cloning the gC gene from the HSV-1 F strain into an HSV-1 mutant which fails to express gC converted the mutant virus from C3b receptor negative to receptor positive. These results further support a role for gC as a C3b receptor and indicate that sialic acid modifies receptor activity.     

Comparison of a set of allelic QTL-NILs for chromosome 4 of tomato: Deductions about natural variation and implications for germplasm utilization

Quantitative Trait Locus (QTL) allelic variation was studied by analyzing near-isogenic lines (NILs) carrying homologous introgressions on chromosome 4 from three green-fruited wild tomato species. The NILs affect agronomic (yield, brix, fruit weight) and fruit (fruit shape, color, epidermal reticulation) traits in a similar manner. However, significant differences were detected in the magnitudes of the effects, the dominance deviations and epistatic interactions, indicating that those species carry different alleles for the QTL. As the QTL did not show any interaction across environments, gene-tic backgrounds or other QTLs, it can be used to introduce novel genetic variation into a broad range of cultivars. Analysis of new recombinant NILs showed that fruit traits are controlled by several linked genetic loci, whereas multiple genetic loci control the agronomic traits within the original introgression. The hypothesis that QTLs may be composed of multiple linked genes can not be rejected prior to implement projects for QTL isolation and cloning. Loci involved in color enhancement could not be related to any known gene involved in the carotenoid biosynthesis pathway, therefore it is hypothesized that the function of those loci must be related to the genetic regulation of the carotenoid biosynthetic pathway. Received: 14 April 2000 / Accepted: 12 May 2000     

Disintegrins: a family of integrin inhibitory proteins from viper venoms

Disintegrins represent a new class of low molecular weight, RGD-containing, cysteine-rich peptides isolated from the venom of various snakes. They interact with the beta 1 and beta 3 families of integrins and their potency is at least 500-2000 times higher than short RGDX peptides. Analysis of the amino acid sequences of 14 different disintegrins suggests that the RGD sequence, in the spatial configuration determined by the appropriate pairing of the cysteine residues, functions as a cell recognition site. However, certain nonconserved amino acids appear to modify the activity of disintegrins, their specificity for various receptors, and their ability to compete specifically with various ligands.     

Human and porcine early kidney precursors as a new source for transplantation

Kidney transplantation has been one of the major medical advances of the past 30 years. However, tissue availability remains a major obstacle. This can potentially be overcome by the use of undifferentiated or partially developed kidney precursor cells derived from early embryos and fetal tissue. Here, transplantation in mice reveals the earliest gestational time point at which kidney precursor cells, of both human and pig origin, differentiate into functional nephrons and not into other, non-renal professional cell types. Moreover, successful organogenesis is achieved when using the early kidney precursors, but not later-gestation kidneys. The formed, miniature kidneys are functional as evidenced by the dilute urine they produce. In addition, decreased immunogenicity of the transplants of early human and pig kidney precursors compared with adult kidney transplants is demonstrated in vivo. Our data pinpoint a window of human and pig kidney organogenesis that may be optimal for transplantation in humans.