scholarly journals The selective recruitment of mRNA to the ER and an increase in initiation are important for glucose-stimulated proinsulin synthesis in pancreatic β-cells

2005 ◽  
Vol 391 (2) ◽  
pp. 291-300 ◽  
Author(s):  
Isabel C. Greenman ◽  
Edith Gomez ◽  
Claire E. J. Moore ◽  
Terence P. Herbert

Glucose acutely stimulates proinsulin synthesis in pancreatic β-cells through a poorly understood post-transcriptional mechanism. In the present study, we demonstrate in pancreatic β-cells that glucose stimulates the recruitment of ribosome-associated proinsulin mRNA, located in the cytoplasm, to the ER (endoplasmic reticulum), the site of proinsulin synthesis, and that this plays an important role in glucose-stimulated proinsulin synthesis. Interestingly, glucose has greater stimulatory effect on the recruitment of proinsulin mRNA to the ER compared with other mRNAs encoding secretory proteins. This, as far as we are aware, is the first example whereby mRNAs encoding secretory proteins are selectively recruited to the ER and provides a novel regulatory mechanism for secretory protein synthesis. Contrary to previous reports, and importantly in understanding the mechanism by which glucose stimulates proinsulin synthesis, we demonstrate that there is no large pool of ‘free’ proinsulin mRNA in the cytoplasm and that glucose does not increase the rate of de novo initiation on the proinsulin mRNA. However, we show that glucose does stimulate the rate of ribosome recruitment on to ribosome-associated proinsulin mRNA. In conclusion, our results provide evidence that the selective recruitment of proinsulin mRNA to the ER, together with increases in the rate of initiation are important mediators of glucose-stimulated proinsulin synthesis in pancreatic β-cells.

2008 ◽  
Vol 410 (3) ◽  
pp. 485-493 ◽  
Author(s):  
Edith Gomez ◽  
Mike L. Powell ◽  
Alan Bevington ◽  
Terence P. Herbert

In the present study, we demonstrate that, in pancreatic β-cells, eIF2α (eukaryotic initiation factor 2α) phosphorylation in response to a decrease in glucose concentration is primarily mediated by the activation of PERK [PKR (protein kinase RNA activated)-like endoplasmic reticulum kinase]. We provide evidence that this increase in PERK activity is evoked by a decrease in the energy status of the cell via a potentially novel mechanism that is independent of IRE1 (inositol requiring enzyme 1) activation and the accumulation of unfolded nascent proteins within the endoplasmic reticulum. The inhibition of eIF2α phosphorylation in glucose-deprived cells by the overexpression of dominant-negative PERK or an N-terminal truncation mutant of GADD34 (growth-arrest and DNA-damage-inducible protein 34) leads to a 53% increase in the rate of total protein synthesis. Polysome analysis revealed that this coincides with an increase in the amplitude but not the number of ribosomes per mRNA, indicating that eIF2α dephosphorylation mobilizes hitherto untranslated mRNAs on to polysomes. In summary, we show that PERK is activated at low glucose concentrations in response to a decrease in energy status and that this plays an important role in glucose-regulated protein synthesis in pancreatic β-cells.


Contact ◽  
2019 ◽  
Vol 2 ◽  
pp. 251525641986122 ◽  
Author(s):  
Corina T. Madreiter-Sokolowski ◽  
Roland M. Malli ◽  
Wolfgang F. Graier

This article comments recent publications that highlight an intriguing importance of specific settings in the interaction between the mitochondria and the endoplasmic reticulum to ensure cell-specific functions like the responsiveness to elevated glucose in pancreatic β-cells. Hence, alterations of the mitochondria–endoplasmic reticulum communications under various pathological conditions like aging or cancer often come with enhanced Ca2+ transfer that, in turn, yields stimulation of basal mitochondrial activity to meet the increasing adenosine triphosphate demand of the very cell. Such observations identify mitochondria-associated membranes as potential target for new therapeutic strategies against aging or cancer.


Diabetes ◽  
2009 ◽  
Vol 58 (12) ◽  
pp. 2851-2862 ◽  
Author(s):  
Daniel A. Cunha ◽  
Laurence Ladrière ◽  
Fernanda Ortis ◽  
Mariana Igoillo-Esteve ◽  
Esteban N. Gurzov ◽  
...  

2016 ◽  
Vol 420 (1-2) ◽  
pp. 95-106 ◽  
Author(s):  
Hao-Hao Zhang ◽  
Xiao-Jun Ma ◽  
Li-Na Wu ◽  
Yan-Yan Zhao ◽  
Peng-Yu Zhang ◽  
...  

2018 ◽  
Vol 33 (1) ◽  
pp. 105 ◽  
Author(s):  
Seok-Woo Hong ◽  
Jinmi Lee ◽  
Jung Hwan Cho ◽  
Hyemi Kwon ◽  
Se Eun Park ◽  
...  

1982 ◽  
Vol 204 (3) ◽  
pp. 639-645 ◽  
Author(s):  
E M Danielsen

The biogenesis of two microvillar enzymes, aminopeptidase N (EC 3.4.11.2) and sucrase (EC 3.2.1.48)-isomaltase (EC 3.2.1.10), was studied by pulse-chase labelling of pig small-intestinal explants kept in organ culture. Both enzymes became inserted into the membrane during or immediately after polypeptide synthesis, indicating that translation takes place on ribosomes attached to the rough endoplasmic reticulum. The earliest detectable forms of aminopeptidase and sucrase-isomaltase were polypeptides of Mr 140 000 and 240 000 respectively. These polypeptides were susceptible to treatment with endo-β-N-acetylglucosaminidiase H (EC 3.2.1.96), suggesting that the microvillar enzymes during or immediately after completion of protein synthesis become glycosylated with a ‘high-mannose’ oligosaccharide structure similarly to other plasma-membrane and secretory proteins. After 20-40 min or 60-90 min of chase, respectively, aminopeptidase N and sucrase-isomaltase were reglycosylated to give the polypeptides of Mr 166 000 (aminopeptidase N) and 265 000 (sucrase-isomaltase). These were expressed at the microvillar membrane after 60-90 min. During the entire process of synthesis and transport to the microvillar membrane the enzymes were bound to membranes, indicating that the biogenesis of aminopeptidase N and sucrase-isomaltase occurs in accordance with the membrane flow hypothesis.


Sign in / Sign up

Export Citation Format

Share Document