抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Rab GTPases control intracellular vesicle traffic by acting as regulatable switches that recruit effector molecules when in their GTP-bound form. The functional coupling between multiple Rab GTPases ensures the spatiotemporally coordinated regulation of vesicle traffic. Membrane trafficking between organelles by vesiculotubular carriers is fundamental to the existence of eukaryotic cells. Central in ensuring that cargoes are delivered to their correct destinations are the Rab GTPases, a large family of small GTPases that control membrane identity and vesicle budding, uncoating, motility and fusion through the recruitment of effector proteins, such as sorting adaptors, tethering factors, kinases, phosphatases and motors. Crosstalk between multiple Rab GTPases through shared effectors, or through effectors that recruit selective Rab activators, ensures the spatiotemporal regulation of vesicle traffic. Functional impairments of Rab pathways are associated with diseases, such as immunodeficiencies, cancer and neurological disorders.

Rab GTPases as coordinators of vesicle traffic.

AMP-activated protein kinase: Ancient energy gauge provides clues to modern understanding of metabolism

Glucagon-like peptide 1 (GLP-1) is a 30-amino acid peptide hormone produced in the intestinal epithelial endocrine L-cells by differential processing of proglucagon, the gene which is expressed in ...

The Physiology of Glucagon-like Peptide 1

MicroRNAs (miRNAs) constitute a growing class of non-coding RNAs that are thought to regulate gene expression by translational repression Several miRNAs in animals exhibit tissue-specific or developmental-stage-specific expression, indicating that they could play important roles in many biological processes To study the role of miRNAs in pancreatic endocrine cells we cloned and identified a novel, evolutionarily conserved and islet-specific miRNA (miR-375) Here we show that overexpression of miR-375 suppressed glucose-induced insulin secretion, and conversely, inhibition of endogenous miR-375 function enhanced insulin secretion The mechanism by which secretion is modified by miR-375 is independent of changes in glucose metabolism or intracellular Ca2+-signalling but correlated with a direct effect on insulin exocytosis Myotrophin (Mtpn) was predicted to be and validated as a target of miR-375 Inhibition of Mtpn by small interfering (si)RNA mimicked the effects of miR-375 on glucose-stimulated insulin secretion and exocytosis Thus, miR-375 is a regulator of insulin secretion and may thereby constitute a novel pharmacological target for the treatment of diabetes

A pancreatic islet-specific microRNA regulates insulin secretion

AMP-activated protein kinase (AMPK) has recently been implicated in the control of preproinsulin gene expression in pancreatic islet beta-cells [da Silva Xavier, Leclerc, Salt, Doiron, Hardie, Kahn and Rutter (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 4023-4028]. Using pharmacological and molecular strategies to regulate AMPK activity in rat islets and clonal MIN6 beta-cells, we show here that the effects of AMPK are exerted largely upstream of insulin release. Thus forced increases in AMPK activity achieved pharmacologically with 5-amino-4-imidazolecarboxamide riboside (AICAR), or by adenoviral overexpression of a truncated, constitutively active form of the enzyme (AMPK alpha 1.T(172)D), blocked glucose-stimulated insulin secretion. In MIN6 cells, activation of AMPK suppressed glucose metabolism, as assessed by changes in total, cytosolic or mitochondrial [ATP] and NAD(P)H, and reduced increases in intracellular [Ca(2+)] caused by either glucose or tolbutamide. By contrast, inactivation of AMPK by expression of a dominant-negative form of the enzyme mutated in the catalytic site (AMPK alpha 1.D(157)A) did not affect glucose-stimulated increases in [ATP], NAD(P)H or intracellular [Ca(2+)], but led to the unregulated release of insulin. These results indicate that inhibition of AMPK by glucose is essential for the activation of insulin secretion by the sugar, and may contribute to the transcriptional stimulation of the preproinsulin gene. Modulation of AMPK activity in the beta-cell may thus represent a novel therapeutic strategy for the treatment of type 2 diabetes mellitus.

/pdf/role-for-amp-activated-protein-kinase-in-glucose-stimulated-334j33m714.pdf

Role for AMP-activated protein kinase in glucose-stimulated insulin secretion and preproinsulin gene expression

https://www.cell.com/current-biology/pdf/S0960-9822(03)00176-3.pdf

Multiple Forms of “Kiss-and-Run” Exocytosis Revealed by Evanescent Wave Microscopy

http://www2.mrc-lmb.cam.ac.uk/groups/hmm/publica/Insulin_Tsuboi_JBC2004/Insulin_TsuboiJBC2004.pdf

Mechanisms of dense core vesicle recapture following "kiss and run" ("cavicapture") exocytosis in insulin-secreting cells.

Glucagon-like peptide-1 (GLP-1) is a potent regulator of glucose-stimulated insulin secretion whose mechanisms of action are only partly understood. In the present paper, we show that at low (3 mM) glucose concentrations, GLP-1 increases the free intramitochondrial concentrations of both Ca(2+) ([Ca(2+)](m)), and ATP ([ATP](m)) in clonal MIN6 beta-cells. Suggesting that cAMP-mediated release of Ca(2+) from intracellular stores is responsible for these effects, increases in [ATP](m) that were induced by GLP-1 were completely blocked by the Rp isomer of adenosine-3',5'-cyclic monophosphothioate (Rp-cAMPS), or by chelation of intracellular Ca(2+). Furthermore, inhibition of Ins(1,4,5) P (3) (IP(3)) receptors with xestospongin C, or application of ryanodine, partially inhibited GLP-1-induced [ATP](m) increases, and the simultaneous blockade of both IP(3) and ryanodine receptors (RyR) completely eliminated the rise in [ATP](m). GLP-1 appeared to prompt Ca(2+)-induced Ca(2+) release through IP(3) receptors via a protein kinase A (PKA)-mediated phosphorylation event, since ryanodine-insensitive [ATP](m) increases were abrogated with the PKA inhibitor, H89. In contrast, the effects of GLP-1 on RyR-mediated [ATP](m) increases were apparently mediated by the cAMP-regulated guanine nucleotide exchange factor cAMP-GEFII, since xestospongin C-insensitive [ATP](m) increases were blocked by a dominant-negative form of cAMP-GEFII (G114E,G422D). Taken together, these results demonstrate that GLP-1 potentiates glucose-stimulated insulin release in part via the mobilization of intracellular Ca(2+), and the stimulation of mitochondrial ATP synthesis.

/pdf/glucagon-like-peptide-1-mobilizes-intracellular-ca2-and-2pacxzrp1l.pdf

Glucagon-like peptide-1 mobilizes intracellular Ca2+ and stimulates mitochondrial ATP synthesis in pancreatic MIN6 beta-cells.

Recent studies have suggested that two small GTPases, Rab3A and Rab27A, play a key role in the late steps of dense-core vesicle exocytosis in endocrine cells; however, neither the precise mechanisms by which these two GTPases regulate dense-core vesicle exocytosis nor the functional relationship between them is clear. In this study, we expressed a number of different Rab proteins, from Rab1 to Rab41 in PC12 cells and systematically screened them for those that are specifically localized on dense-core vesicles. We found that four Rabs (Rab3A, Rab27A, Rab33A, Rab37) are predominantly targeted to dense-core vesicles in PC12 cells, and that three of them (Rab3A, Rab27A, Rab33A) are endogenously expressed on dense-core vesicles. We further investigated the effect of silencing each Rab with specific small interfering RNA on vesicle dynamics by total internal reflection fluorescence microscopy in a single PC12 cell. Silencing either Rab3A or Rab27A in PC12 cells significantly decreased the number of dense-core vesicles docked to the plasma membrane without altering the kinetics of individual exocytotic events, whereas silencing of Rab33A had no effect at all. Simultaneous silencing of Rab3A and Rab27A caused a significantly greater decrease in number of vesicles docked to the plasma membrane. Our findings indicate that Rab3A and Rab27A cooperatively regulate docking step(s) of dense-core vesicles to the plasma membrane.

/pdf/rab3a-and-rab27a-cooperatively-regulate-the-docking-step-of-32sokaiwnf.pdf

Takashi Tsuboi

Papers

Role for AMP-activated protein kinase in glucose-stimulated insulin secretion and preproinsulin gene expression

Multiple Forms of “Kiss-and-Run” Exocytosis Revealed by Evanescent Wave Microscopy

Mechanisms of dense core vesicle recapture following "kiss and run" ("cavicapture") exocytosis in insulin-secreting cells.

Glucagon-like peptide-1 mobilizes intracellular Ca2+ and stimulates mitochondrial ATP synthesis in pancreatic MIN6 beta-cells.

Rab3A and Rab27A cooperatively regulate the docking step of dense-core vesicle exocytosis in PC12 cells