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- Christensen, Anna, et al.
(författare)
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Functional characterization of Arabidopsis calreticulin1a : a key alleviator of endoplasmic reticulum stress
- 2008
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Ingår i: Plant and Cell Physiology. - : Oxford University Press. - 0032-0781 .- 1471-9053. ; 49:6, s. 912-924
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Tidskriftsartikel (refereegranskat)abstract
- The chaperone calreticulin plays important roles in a variety of processes in the endoplasmic reticulum (ER) of animal cells, such as Ca2+ signaling and protein folding. Although the functions of calreticulin are well characterized in animals, only indirect evidence is available for plants. To increase our understanding of plant calreticulins we introduced one of the Arabidopsis isoforms, AtCRT1a, into calreticulin-deficient (crt–/–) mouse embryonic fibroblasts. As a result of calreticulin deficiency, the mouse crt–/– fibroblasts have decreased levels of Ca2+ in the ER and impaired protein folding abilities. Expression of the AtCRT1a in mouse crt–/– fibroblasts rescued these phenotypes, i.e. AtCRT1a restored the Ca2+-holding capacity and chaperone functions in the ER of the mouse crt–/– fibroblasts, demonstrating that the animal sorting machinery was also functional for a plant protein, and that basic calreticulin functions are conserved across the Kingdoms. Expression analyses using a β-glucuronidase (GUS)–AtCRT1a promoter construct revealed high expression of CRT1a in root tips, floral tissues and in association with vascular bundles. To assess the impact of AtCRT1a in planta, we generated Atcrt1a mutant plants. The Atcrt1a mutants exhibited increased sensitivity to the drug tunicamycin, an inducer of the unfolded protein response. We therefore conclude that AtCRT1a is an alleviator of the tunicamycin-induced unfolded protein response, and propose that the use of the mouse crt–/– fibroblasts as a calreticulin expression system may prove useful to assess functionalities of calreticulins from different species.
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- Christensen, Anna, et al.
(författare)
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Overexpression of the Ca2+-binding protein calreticulin in the endoplasmic reticulum improves growth of tobacco cell suspensions (Nicotiana tabacum) in high-Ca2+ medium
- 2005
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 123:1, s. 92-99
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Tidskriftsartikel (refereegranskat)abstract
- Calreticulin (CRT) is a eukaryotic, highly conserved, Ca2+-binding protein predominantly located in the endoplasmic reticulum (ER) lumen. In addition to being involved in the regulation of cellular Ca2+, calreticulin is a key quality control element during protein folding in the ER lumen. Tobacco (Nicotiana tabacum L.) suspension cells overexpressing a maize CRT (CRT1a) were used here to examine the properties of CRT in growing plant cells with respect to stress exposure. The endogenous CRT gene was induced rapidly after subculturing of the cells to new medium. In accordance, the CRT protein levels increased, peaking at days 3-4. At day 5, when the CRT transcript levels had levelled off, a further increase in endogenous CRT expression was obtained when the cells were treated with excess Ca2+ or the N-linked glycosylation inhibitor tunicamycin. Whereas the response to Ca2+ occurred within 30 min, the induction by tunicamycin took several hours to be established. Transforming tobacco cells with maize CRT1a, under a constitutive mannopine synthase promoter, resulted in a stable level of expressed CRT1a during the growth cycle compared with endogenous CRT. The CRTs showed differences in attached glycans, but both contained the high mannose-rich-type glycans characteristic of ER proteins. In agreement with an ER location, both tobacco CRT and the transgene product CRT1a codistributed with the ER marker NADH cytochrome c reductase after density gradient centrifugation of microsomal fractions from tobacco cells. Increased production of CRT, as was obtained in the transgenic tobacco cell lines, made cells more tolerant than wild-type cells to high Ca2+ during growth. These data suggest that overexpression of CRT1a in plant cells results in a more efficient calcium buffering capacity in the ER.
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- Conaway, H Herschel, et al.
(författare)
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Retinoids inhibit differentiation of hematopoietic osteoclast progenitors.
- 2009
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Ingår i: The FASEB journal. - Bethesda, Md. : Wiley. - 1530-6860 .- 0892-6638. ; 23:10, s. 3526-38
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Tidskriftsartikel (refereegranskat)abstract
- Whether vitamin A promotes skeletal fragility, has no effect on fracture rate, or protects against bone loss is unclear. In the present study, effects of retinoids on osteoclast differentiation in cultured mouse bone marrow cells (BMCs), bone marrow macrophages (BMMs), spleen cells, and RAW264.7 cells were evaluated by analyzing osteoclast formation and expression of genes important in signal transduction and osteoclast function. All-trans-retinoic acid (ATRA) did not stimulate osteoclastogenesis in BMCs, but inhibited hormone and RANKL-induced gene expression and formation of osteoclasts. In BMMs, spleen cells, and RAW264.7 cells, osteoclast differentiation and formation stimulated by M-CSF/RANKL were inhibited (IC(50) = 0.3 nM) by ATRA. The effect was exerted at an early step of RANKL-induced differentiation. ATRA also abolished increases of the transcription factors c-Fos and NFAT2 stimulated by RANKL and suppressed down-regulation of the antiosteoclastogenic transcription factor MafB. By comparing effects of several compounds structurally related to ATRA, as well as by using receptor antagonists, evaluation pointed to inhibition being mediated by RARalpha, with no involvement of PPARbeta/delta. The results suggest that activation of RARalpha by retinoids in myeloid hematopoietic precursor cells decreases osteoclast formation by altering expression of the transcription factors c-Fos, NFAT2, and MafB.
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- Mohlin, Camilla, et al.
(författare)
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Studies of the extracellular ATP-adenosine pathway in human urinary tract epithelial cells
- 2009
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Ingår i: Pharmacology. - : S. Karger AG. - 0031-7012 .- 1423-0313. ; 84:4, s. 196-202
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Tidskriftsartikel (refereegranskat)abstract
- The data demonstrate that adenosine formation from extracellular ATP is negligible in urinary tract epithelial cells due to low CD39 expression in this cell type. However, the epithelial cells express CD73 and are able to convert extracellular AMP to adenosine.
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- Nilholm, Claes, et al.
(författare)
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Kommuners arbete med elever i behov av särskilt stöd
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Skolans arbete med elever i behov av särskilt stöd är betydelsefullt. Inte minst är situationen för dessa elever en bra värdemätare på hur väl demokratin i samhället fungerar. Samtidigt har kunskap saknats när det gäller hur kommunernas arbete med denna grupp elever ser ut. I rapporten redovisas en enkätundersökning av kommunernas arbete med elever i behov av särskilt stöd som besvarats av 90 % av landets kommuner. Resultaten rör ett brett spektrum av detta arbete, t.ex. resursfördelningssystem, identifiering av eleverna, organisatoriska/personella lösningar, frågor om inflytande m.m.
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