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Identification of the monomeric G-protein, Rhes, as an efaroxan-regulated protein in the pancreatic beta-cell.

ABSTRACT: Efaroxan induces membrane depolarization by interaction with the pore forming subunit of the ATP-sensitive potassium channel, Kir6.2. However, this effect is not responsible for its full secretory activity. In this study we have used an anti-idiotypic approach to generate antibodies that recognize additional proteins that may be regulated by efaroxan in pancreatic beta-cells. Using these antisera in an expression cloning strategy we have identified a monomeric GTP-binding protein, Rhes, as a potential target for regulation by imidazoline ligands. Rhes is shown to be expressed in beta-cells and its expression is regulated by efaroxan under conditions when a structurally related molecule, KU14R, is ineffective. The results reveal that beta-cells express Rhes and suggest that changes in the expression of this molecule may regulate the sensitivity of beta-cells to imidazoline secretagogues.

SUBMITTER: Chan SL

PROVIDER: S-EPMC1762110 | biostudies-literature | 2002 May

REPOSITORIES: biostudies-literature

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Identification of the monomeric G-protein, Rhes, as an efaroxan-regulated protein in the pancreatic beta-cell.

Chan Sue L F SL Monks Lara K LK Gao Hongwei H Deaville Pamela P Morgan Noel G NG

British journal of pharmacology 20020501 1

Efaroxan induces membrane depolarization by interaction with the pore forming subunit of the ATP-sensitive potassium channel, Kir6.2. However, this effect is not responsible for its full secretory activity. In this study we have used an anti-idiotypic approach to generate antibodies that recognize additional proteins that may be regulated by efaroxan in pancreatic beta-cells. Using these antisera in an expression cloning strategy we have identified a monomeric GTP-binding protein, Rhes, as a pot ...[more]

PMID: 11976265

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Project description:BackgroundPancreatic beta-cells are the target of an autoimmune attack in type 1 diabetes mellitus (T1DM). This is mediated in part by cytokines, such as interleukin (IL)-1beta and interferon (IFN)-gamma. These cytokines modify the expression of hundreds of genes, leading to beta-cell dysfunction and death by apoptosis. Several of these cytokine-induced genes are potentially regulated by the IL-1beta-activated transcription factor (TF) nuclear factor (NF)-kappaB, and previous studies by our group have shown that cytokine-induced NF-kappaB activation is pro-apoptotic in beta-cells. To identify NF-kappaB-regulated gene networks in beta-cells we presently used a discriminant analysis-based approach to predict NF-kappaB responding genes on the basis of putative regulatory elements.ResultsThe performance of linear and quadratic discriminant analysis (LDA, QDA) in identifying NF-kappaB-responding genes was examined on a dataset of 240 positive and negative examples of NF-kappaB regulation, using stratified cross-validation with an internal leave-one-out cross-validation (LOOCV) loop for automated feature selection and noise reduction. LDA performed slightly better than QDA, achieving 61% sensitivity, 91% specificity and 87% positive predictive value, and allowing the identification of 231, 251 and 580 NF-kappaB putative target genes in insulin-producing INS-1E cells, primary rat beta-cells and human pancreatic islets, respectively. Predicted NF-kappaB targets had a significant enrichment in genes regulated by cytokines (IL-1beta or IL-1beta + IFN-gamma) and double stranded RNA (dsRNA), as compared to genes not regulated by these NF-kappaB-dependent stimuli. We increased the confidence of the predictions by selecting only evolutionary stable genes, i.e. genes with homologs predicted as NF-kappaB targets in rat, mouse, human and chimpanzee.ConclusionThe present in silico analysis allowed us to identify novel regulatory targets of NF-kappaB using a supervised classification method based on putative binding motifs. This provides new insights into the gene networks regulating cytokine-induced beta-cell dysfunction and death.

Project description:Dendritic cells (DC) arise from a diverse group of hematopoietic progenitors and have marked phenotypic and functional heterogeneity. We have found previously that activation of protein kinase C beta 2 (PRKCB2) by cytokines or phorbol esters drives normal human CD34(+) hematopoietic progenitors and myeloid leukemic blasts (KG1, K562 cell lines, and primary patient blasts) to differentiate into DC, but the genetic program triggered by PRKCB2 activation that results in DC differentiation is only beginning to be characterized. Of the cPKC isoforms, only PRKCB2 was consistently activated by DC differentiation-inducing stimuli in normal and leukemic progenitors. To examine early changes in gene expression following PRKCB2 activation, we employed the following cell lines: (1) the CD34(+) human acute myeloid leukemia derived cell line KG1, which undergoes DC differentiation following phorbol ester treatment; (2) KG1a, a spontaneously arising differentiation-resistant daughter cell line of KG1 that has lost PRKCB2 expression; (3) clones established from KG1a that stably express exogenous PRKCB2-GFP fusion proteins and are once again able to undergo DC differentiation (KG1a-PRKCB2-GFP Clone E9 and Clone E11). We examined changes in gene expression in these cells following treatment with the phorbol ester PMA (phorbol 12-myristate 13-acetate) for 2 hours. Since KG1 and KG1a differ in PRKCB2 expression but have similar expression of the other protein kinase C isoforms, this protocol will allow for the identification of genes regulated by PRKCB2 activation. KG1, KG1a, E9, and E11 were cultured for 2 hours in normal media +/- PMA (10 ng/ml). RNA was then isolated using RNeasy mini-columns (Qiagen) following the standard protocol. Samples were then sent to Expression Analysis, who carried out quality control, sample processing/labeling, hybridization to Affymetrix GeneChip arrays (Human U133 2.0 Plus), imaging, and analysis according to their standard protocols. Gene expression profiles were generated for each cell line in the presence and absence of phorbol ester stimulation, for a total of 12 samples (E9 +/- PMA and E11 +/- PMA were run in duplicate).

Dataset Information

Identification of the monomeric G-protein, Rhes, as an efaroxan-regulated protein in the pancreatic beta-cell.

Publications

Identification of the monomeric G-protein, Rhes, as an efaroxan-regulated protein in the pancreatic beta-cell.

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