The unfolded protein response in nutrient sensing and differentiation

Tang

Molecular Genetics and Metabolism

et al. 2007

Inherited deficiency of galactose-1-phosphate uridyltransferase (GALT) activity in humans leads to a potentially lethal disorder called Classic Galactosemia. It is well known that patients often accumulate high levels of galactose metabolites such as galactose-1-phosphate (gal-1-p) in their tissues. However, specific targets of gal-1-p and other accumulated metabolites remain uncertain. In this study, we developed a new model system to study this toxicity using primary fibroblasts derived from galactosemic patients. GALT activity was reconstituted in these primary cells through lentivirus-mediated gene transfer. Gene expression profiling showed that GALT-deficient cells, but not normal cells, responded to galactose challenge by activating a set of genes characteristic of endoplasmic reticulum (ER) stress. Western Blot analysis showed that the master regulator of ER stress, BiP, was up-regulated at least three-fold in these-cells upon galactose challenge. We also found that treatment of these cells with galactose, but not glucose or hexose-free media reduced Ca 2+ mobilization in response to activation of Gq-coupled receptors. To explore whether the muted Ca 2+ mobilization is related to reduced inositol turnover, we discovered that gal-1-p competitively inhibited human inositol monophosphatase (hIMPase1). We hypothesize that galactose intoxication under GALT deficiency resulted from accumulation of toxic galactose metabolite products, which led to the accumulation of unfolded proteins, altered calcium homeostasis, and subsequently ER stress.

Section: Discussionmentioning

confidence: 99%

Section: Galactose Challenge Of Galt-deficient Fibroblasts Triggers Ementioning

confidence: 99%

Involvement of endoplasmic reticulum stress in a novel Classic Galactosemia model

Tang

Molecular Genetics and Metabolism

et al. 2007

“…In mice genetically inactivated for the PERK-eIF2a pathway and in humans lacking PERK, revealed b-cells are the most susceptible to ER stress. 17,[74][75][76] PERK À/À mice develop progressive apoptosis in their b-cells and show marked hyperglycemia from 4 weeks of age. 67,68 Mutations in the PERK gene were identified, in patients with Wolcott-Rallison syndrome, as an autosomal recessive disease with severe infant diabetes due to pancreatic hypoplasia and a reduced number of b-cells.…”

Section: Diabetesmentioning

confidence: 99%

Roles of CHOP/GADD153 in endoplasmic reticulum stress

2003

Endoplasmic reticulum (ER) is the site of synthesis and folding of secretory proteins. Perturbations of ER homeostasis affect protein folding and cause ER stress. ER can sense the stress and respond to it through translational attenuation, upregulation of the genes for ER chaperones and related proteins, and degradation of unfolded proteins by a quality-control system. However, when the ER function is severely impaired, the organelle elicits apoptotic signals. ER stress has been implicated in a variety of common diseases such as diabetes, ischemia and neurodegenerative disorders. One of the components of the ER stress-mediated apoptosis pathway is C/EBP homologous protein (CHOP), also known as growth arrestand DNA damage-inducible gene 153 (GADD153). Here, we summarize the current understanding of the roles of CHOP/ GADD153 in ER stress-mediated apoptosis and in diseases including diabetes, brain ischemia and neurodegenerative disease.

“…In combination with the results for the ER it seems that, although the ER is upregulated for high protein cargo, in the high producing subclones this is not happening under stress response. Rather, due to the upregulation of proteins that support folding and secretion as well as the upregulation of some components of the UPR, cells are able to handle high protein loads, and less protein needs to be degraded and is lost due to misfolding and lack of proper assembly [63,64].…”

Section: Proteasomementioning

confidence: 99%

Microarray profiling of preselected CHO host cell subclones identifies gene expression patterns associated with in‐creased production capacity

Harreither

Hackl

Pichler

et al. 2015

Biotechnology Journal

Over the last three decades, product yields from CHO cells have increased dramatically, yet specific productivity (qP) remains a limiting factor. In a previous study, using repeated cell-sorting, we have established different host cell subclones that show superior transient qP over their respective parental cell lines (CHO-K1, CHO-S). The transcriptome of the resulting six cell lines in different biological states (untransfected, mock transfected, plasmid transfected) was first explored by hierarchical clustering and indicated that gene activity associated with increased qP did not stem from a certain cellular state but seemed to be inherent for a high qP host line. We then performed a novel gene regression analysis identifying drivers for an increase in qP. Genes significantly implicated were first systematically tested for enrichment of GO terms using a Bayesian approach incorporating the hierarchical structure of the GO term tree. Results indicated that specific cellular components such as nucleus, ER, and Golgi are relevant for cellular productivity. This was complemented by targeted GSA that tested functionally homogeneous, manually curated subsets of KEGG pathways known to be involved in transcription, translation, and protein processing. Significantly implicated pathways included mRNA surveillance, proteasome, protein processing in the ER and SNARE interactions in vesicular transport.