Article

The use of calnexin and calreticulin by cellular and viral glycoproteins.

Institute for Research in Biomedicine, 6500 Bellinzona, Switzerland.
Journal of Biological Chemistry (impact factor: 4.77). 09/2005; 280(31):28265-71. DOI:10.1074/jbc.M501020200 pp.28265-71
Source: PubMed

ABSTRACT Calnexin and calreticulin are homologous lectin chaperones that assist maturation of cellular and viral glycoproteins in the mammalian endoplasmic reticulum. Calnexin and calreticulin share the same specificity for monoglucosylated protein-bound N-glycans but associate with a distinct set of newly synthesized polypeptides. We report here that most calnexin substrates do not associate with calreticulin even upon selective calnexin inactivation, while BiP associates more abundantly with nascent polypeptides under these conditions. Calreticulin associated more abundantly with orphan calnexin substrates only in infected cells and preferentially with polypeptides of viral origin, showing stronger dependence of model viral glycoproteins on endoplasmic reticulum lectins. This may explain why inactivation of the calnexin cycle affects viral replication and infectivity but not viability of mammalian cells.

0 0
 · 
0 Bookmarks
 · 
26 Views
  • Source
    Article: Calnexin is not essential for mammalian rod opsin biogenesis.
    Maria Kosmaoglou, Michael E Cheetham
    [show abstract] [hide abstract]
    ABSTRACT: Misfolding mutations in rod opsin are a major cause of the inherited blindness retinitis pigmentosa. Therefore, understanding the role of molecular chaperones in facilitating rod opsin biogenesis and the response to mutant rod opsin is important for retinal disease and fundamental retinal cell biology. A recent report has shown that Drosophila rhodopsin Rh1 requires calnexin (Cnx) for its maturation and correct localization to R1-6 rhabdomeres. In this report, we investigate the role of Cnx in the processing of wild-type and mutant mammalian rod opsin. Mouse embryonic fibroblasts (MEFs) from control mice (WT) and mice that express a truncated dysfunctional version of Cnx (sCnx) were used to assess the role of Cnx in the biogenesis, maturation, degradation, and aggregation of mutant and wild-type rod opsin. The mutant P23H rod opsin was used as a prototypical class II misfolding mutant as it is retained in the endoplasmic reticulum (ER) and is either degraded by ER associated degradation (ERAD) or forms aggregates that coalesce to form intracellular inclusions. Wild-type rod opsin protein translocated normally to the plasma membrane in both cell lines. In contrast, P23H rod opsin was retained in the ER in both cell lines. The only difference observed in rod opsin processing between the WT and sCnx MEFs was a small increase in the incidence of P23H intracellular inclusions in the sCnx cells. This did not appear to be specific for rod opsin, however, as non-rod opsin-expressing sCnx cells also had an increased incidence of ubiquitylated inclusions. Our data show that, unlike Drosophila Rh1, mammalian rod opsin biogenesis does not appear to have an absolute requirement for Cnx. Other chaperones are likely to be more important for mammalian rod opsin biogenesis and quality control.
    Molecular vision 02/2008; 14:2466-74. · 2.20 Impact Factor
  • Source
    Article: Viral subversion of immunogenic cell death.
    Oliver Kepp, Laura Senovilla, Lorenzo Galluzzi, Theocharis Panaretakis, Antoine Tesniere, Frederic Schlemmer, Frank Madeo, Laurence Zitvogel, Guido Kroemer
    [show abstract] [hide abstract]
    ABSTRACT: While physiological cell death is non-immunogenic, pathogen induced cell death can be immunogenic and hence stimulate an immune response against antigens that derive from dying cells and are presented by dendritic cells (DCs). The obligate immunogenic "eat-me" signal generated by dying cells consists in the exposure of calreticulin (CRT) at the cell surface. This particular "eat-me" signal, which facilitates engulfment by DCs, can only be found on cells that succumb to immunogenic apoptosis, while it is not present on cells dying in an immunologically silent fashion. CRT normally resides in the lumen of the endoplasmic reticulum (ER), yet can translocate to the plasma membrane surface through a complex pathway that involves elements of the ER stress response (e.g., the eIF2alpha-phosphorylating kinase PERK), the apoptotic machinery (e.g., caspase-8 and its substrate BAP31, Bax, Bak), the anterograde transport from the ER to the Golgi apparatus, and SNARE-dependent exocytosis. A large panoply of viruses encodes proteins that inhibit eIF2alpha kinases, catalyze the dephosphorylation of eIF2alpha, bind to caspase-8, Bap31, Bax or Bak, or perturb exocytosis. We therefore postulate that obligate intracellular pathogens have developed a variety of strategies to subvert CRT exposure, thereby avoiding immunogenic cell death.
    Cell cycle (Georgetown, Tex.) 04/2009; 8(6):860-9. · 5.36 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

assist maturation
 
BiP associates
 
Calnexin
 
calnexin cycle
 
calnexin substrates
 
Calreticulin
 
calreticulin share
 
distinct
 
endoplasmic reticulum lectins
 
infectivity
 
mammalian endoplasmic reticulum
 
monoglucosylated protein-bound N-glycans
 
nascent polypeptides
 
orphan calnexin substrates
 
polypeptides
 
preferentially
 
selective calnexin inactivation
 
specificity
 
stronger dependence
 
synthesized polypeptides