Limits...
Morbillivirus glycoprotein expression induces ER stress, alters Ca2+ homeostasis and results in the release of vasostatin.

Brunner JM, Plattet P, Doucey MA, Rosso L, Curie T, Montagner A, Wittek R, Vandelvelde M, Zurbriggen A, Hirling H, Desvergne B - PLoS ONE (2012)

Bottom Line: Transient expression of recombinant CDV F and H surface glycoproteins in Vero cells and primary hippocampal neurons further confirmed a correlation between their accumulation in the ER, CRT upregulation, ER stress and disruption of ER Ca(2+) homeostasis.Furthermore, CDV infection induced CRT fragmentation with re-localisation of a CRT amino-terminal fragment, also known as vasostatin, on the surface of infected and neighbouring non-infected cells.Altogether, these results suggest that ER stress, CRT fragmentation and re-localization on the cell surface may contribute to cytotoxic effects and ensuing cell dysfunctions triggered by Morbillivirus, a mechanism that might potentially be relevant for other neurotropic viruses.

View Article: PubMed Central - PubMed

Affiliation: Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

ABSTRACT
Although the pathology of Morbillivirus in the central nervous system (CNS) is well described, the molecular basis of neurodegenerative events still remains poorly understood. As a model to explore Morbillivirus-mediated CNS dysfunctions, we used canine distemper virus (CDV) that we inoculated into two different cell systems: a monkey cell line (Vero) and rat primary hippocampal neurons. Importantly, the recombinant CDV used in these studies not only efficiently infects both cell types but recapitulates the uncommon, non-cytolytic cell-to-cell spread mediated by virulent CDVs in brain of dogs. Here, we demonstrated that both CDV surface glycoproteins (F and H) markedly accumulated in the endoplasmic reticulum (ER). This accumulation triggered an ER stress, characterized by increased expression of the ER resident chaperon calnexin and the proapoptotic transcription factor CHOP/GADD 153. The expression of calreticulin (CRT), another ER resident chaperon critically involved in the response to misfolded proteins and in Ca(2+) homeostasis, was also upregulated. Transient expression of recombinant CDV F and H surface glycoproteins in Vero cells and primary hippocampal neurons further confirmed a correlation between their accumulation in the ER, CRT upregulation, ER stress and disruption of ER Ca(2+) homeostasis. Furthermore, CDV infection induced CRT fragmentation with re-localisation of a CRT amino-terminal fragment, also known as vasostatin, on the surface of infected and neighbouring non-infected cells. Altogether, these results suggest that ER stress, CRT fragmentation and re-localization on the cell surface may contribute to cytotoxic effects and ensuing cell dysfunctions triggered by Morbillivirus, a mechanism that might potentially be relevant for other neurotropic viruses.

Show MeSH

Related in: MedlinePlus

Mechanistic model of neurodegenerative processes induced by CDV infection.The F and H CDV proteins are accumulating in the ER. This event induces an early ER stress event. In early ER stress, the quantities of CRT chaperon increase, the Ca2+ homeostasis is altered and Ca2+ is depleted from ER stores. Increase of cytosolic Ca2+ can have as consequence a glutamate release during CDV infection as previously described [3]. Glutamate release could induce, in the neighbouring neurons, Ca2+ entry followed by an ER stress induction [56]. During ER stress, the infected cells show enhance expression of the chaperons CRT, calnexin and GRP94 and relocalisation of the transcription factor ATF-6 in the nucleus followed by the expression of the proapoptotic factor CHOP/GADD 153. More importantly, infected cells show CRT fragmentation in a CDV-dependent manner. C-terminal fragments are retained in the ER by the KDEL signal whereas CRT N-terminal fragments are present after 24 hours at the cell surface. Cell surface exposition of CRT N-terminal fragment may contribute to CDV-mediated neurodegenerative auto-immunity. In grey italic are events described in previous publications.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3293893&req=5

pone-0032803-g006: Mechanistic model of neurodegenerative processes induced by CDV infection.The F and H CDV proteins are accumulating in the ER. This event induces an early ER stress event. In early ER stress, the quantities of CRT chaperon increase, the Ca2+ homeostasis is altered and Ca2+ is depleted from ER stores. Increase of cytosolic Ca2+ can have as consequence a glutamate release during CDV infection as previously described [3]. Glutamate release could induce, in the neighbouring neurons, Ca2+ entry followed by an ER stress induction [56]. During ER stress, the infected cells show enhance expression of the chaperons CRT, calnexin and GRP94 and relocalisation of the transcription factor ATF-6 in the nucleus followed by the expression of the proapoptotic factor CHOP/GADD 153. More importantly, infected cells show CRT fragmentation in a CDV-dependent manner. C-terminal fragments are retained in the ER by the KDEL signal whereas CRT N-terminal fragments are present after 24 hours at the cell surface. Cell surface exposition of CRT N-terminal fragment may contribute to CDV-mediated neurodegenerative auto-immunity. In grey italic are events described in previous publications.

Mentions: Under physiological conditions, full-length CRT [35] or N-terminal fragments [44] have been detected in small amounts at the cell surface. Importantly, the adaptive immune system is strongly activated by increasing amounts of full-length CRT [45], [46] or by vasostatin, the 27 kDa N-terminal CRT fragment [28] at the cell surface. Here, we reported that CDV can also trigger CRT fragmentation and relocation of the N-terminal vasostatin CRT fragment to the cell surface of both infected and non-infected cells (Figure 6). Though CRT cleavage appeared to be caused by CDV-induced ER stress, the fact that the well-known ER stress inducers thapsigargin and DTT do not cause CRT cleavage, suggest that the triggering of ER stress may not be equivalent in both conditions. Interestingly, cell surface localization or secretion of the vasostatin has been first described in Epstein-Barr-Virus (EBV)-infected cells [44], [47] although the precise molecular mechanism underlying this phenomenon remains undetermined. Pike and co-workers additionally demonstrated that vasostatin efficiently inhibited endothelial cell proliferation and could supressed angiogenesis in vivo[28]. In addition, vasostatin also significantly reduced tumor growth in mice [47]. While one possible explanation to explain CDV-induced CRT cleavage would implicate a direct role of F and/or H on CRT processing and subsequent secretion of the vasostatin from the cell, any other indirect effects cannot be rule out. Further works are hence warranted to illuminate the precise molecular mechanism leading to CRT cleavage in CDV-infected cells. Moreover, we speculate that secretion of the CDV-induced N-terminal vasostatin fragment may contribute to the establishment of the chronic phase of the disease over many months or years. Indeed, vasostatin may stimulate the adaptive immune system, which may generate auto-antibodies directed against it. This alteration might even be amplified by the fact that we detected the vasostatin on the surface of non-infected cells in infected cultures, suggestive of a molecular mechanism by which the released CRT fragments might bind to an unknown receptor on the surface of neighbouring cells [44], [46] (Figure 6). Increased CRT-specific auto-antibodies have been reported in autoimmune diseases such as Sjögrens's syndrome and systemic lupus erythematosus. In some cases these diseases show neurodegenerative progression [44], [48], [49]. It is interesting to note that early stages of multiple sclerosis and systemic lupus erythematosus share some clinical signs than those induced by CDV [50]. Alternatively, vasostatin-dependent inhibition of angiogenesis in the brain may also contribute to CDV-induced neurological disorders.


Morbillivirus glycoprotein expression induces ER stress, alters Ca2+ homeostasis and results in the release of vasostatin.

Brunner JM, Plattet P, Doucey MA, Rosso L, Curie T, Montagner A, Wittek R, Vandelvelde M, Zurbriggen A, Hirling H, Desvergne B - PLoS ONE (2012)

Mechanistic model of neurodegenerative processes induced by CDV infection.The F and H CDV proteins are accumulating in the ER. This event induces an early ER stress event. In early ER stress, the quantities of CRT chaperon increase, the Ca2+ homeostasis is altered and Ca2+ is depleted from ER stores. Increase of cytosolic Ca2+ can have as consequence a glutamate release during CDV infection as previously described [3]. Glutamate release could induce, in the neighbouring neurons, Ca2+ entry followed by an ER stress induction [56]. During ER stress, the infected cells show enhance expression of the chaperons CRT, calnexin and GRP94 and relocalisation of the transcription factor ATF-6 in the nucleus followed by the expression of the proapoptotic factor CHOP/GADD 153. More importantly, infected cells show CRT fragmentation in a CDV-dependent manner. C-terminal fragments are retained in the ER by the KDEL signal whereas CRT N-terminal fragments are present after 24 hours at the cell surface. Cell surface exposition of CRT N-terminal fragment may contribute to CDV-mediated neurodegenerative auto-immunity. In grey italic are events described in previous publications.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3293893&req=5

pone-0032803-g006: Mechanistic model of neurodegenerative processes induced by CDV infection.The F and H CDV proteins are accumulating in the ER. This event induces an early ER stress event. In early ER stress, the quantities of CRT chaperon increase, the Ca2+ homeostasis is altered and Ca2+ is depleted from ER stores. Increase of cytosolic Ca2+ can have as consequence a glutamate release during CDV infection as previously described [3]. Glutamate release could induce, in the neighbouring neurons, Ca2+ entry followed by an ER stress induction [56]. During ER stress, the infected cells show enhance expression of the chaperons CRT, calnexin and GRP94 and relocalisation of the transcription factor ATF-6 in the nucleus followed by the expression of the proapoptotic factor CHOP/GADD 153. More importantly, infected cells show CRT fragmentation in a CDV-dependent manner. C-terminal fragments are retained in the ER by the KDEL signal whereas CRT N-terminal fragments are present after 24 hours at the cell surface. Cell surface exposition of CRT N-terminal fragment may contribute to CDV-mediated neurodegenerative auto-immunity. In grey italic are events described in previous publications.
Mentions: Under physiological conditions, full-length CRT [35] or N-terminal fragments [44] have been detected in small amounts at the cell surface. Importantly, the adaptive immune system is strongly activated by increasing amounts of full-length CRT [45], [46] or by vasostatin, the 27 kDa N-terminal CRT fragment [28] at the cell surface. Here, we reported that CDV can also trigger CRT fragmentation and relocation of the N-terminal vasostatin CRT fragment to the cell surface of both infected and non-infected cells (Figure 6). Though CRT cleavage appeared to be caused by CDV-induced ER stress, the fact that the well-known ER stress inducers thapsigargin and DTT do not cause CRT cleavage, suggest that the triggering of ER stress may not be equivalent in both conditions. Interestingly, cell surface localization or secretion of the vasostatin has been first described in Epstein-Barr-Virus (EBV)-infected cells [44], [47] although the precise molecular mechanism underlying this phenomenon remains undetermined. Pike and co-workers additionally demonstrated that vasostatin efficiently inhibited endothelial cell proliferation and could supressed angiogenesis in vivo[28]. In addition, vasostatin also significantly reduced tumor growth in mice [47]. While one possible explanation to explain CDV-induced CRT cleavage would implicate a direct role of F and/or H on CRT processing and subsequent secretion of the vasostatin from the cell, any other indirect effects cannot be rule out. Further works are hence warranted to illuminate the precise molecular mechanism leading to CRT cleavage in CDV-infected cells. Moreover, we speculate that secretion of the CDV-induced N-terminal vasostatin fragment may contribute to the establishment of the chronic phase of the disease over many months or years. Indeed, vasostatin may stimulate the adaptive immune system, which may generate auto-antibodies directed against it. This alteration might even be amplified by the fact that we detected the vasostatin on the surface of non-infected cells in infected cultures, suggestive of a molecular mechanism by which the released CRT fragments might bind to an unknown receptor on the surface of neighbouring cells [44], [46] (Figure 6). Increased CRT-specific auto-antibodies have been reported in autoimmune diseases such as Sjögrens's syndrome and systemic lupus erythematosus. In some cases these diseases show neurodegenerative progression [44], [48], [49]. It is interesting to note that early stages of multiple sclerosis and systemic lupus erythematosus share some clinical signs than those induced by CDV [50]. Alternatively, vasostatin-dependent inhibition of angiogenesis in the brain may also contribute to CDV-induced neurological disorders.

Bottom Line: Transient expression of recombinant CDV F and H surface glycoproteins in Vero cells and primary hippocampal neurons further confirmed a correlation between their accumulation in the ER, CRT upregulation, ER stress and disruption of ER Ca(2+) homeostasis.Furthermore, CDV infection induced CRT fragmentation with re-localisation of a CRT amino-terminal fragment, also known as vasostatin, on the surface of infected and neighbouring non-infected cells.Altogether, these results suggest that ER stress, CRT fragmentation and re-localization on the cell surface may contribute to cytotoxic effects and ensuing cell dysfunctions triggered by Morbillivirus, a mechanism that might potentially be relevant for other neurotropic viruses.

View Article: PubMed Central - PubMed

Affiliation: Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

ABSTRACT
Although the pathology of Morbillivirus in the central nervous system (CNS) is well described, the molecular basis of neurodegenerative events still remains poorly understood. As a model to explore Morbillivirus-mediated CNS dysfunctions, we used canine distemper virus (CDV) that we inoculated into two different cell systems: a monkey cell line (Vero) and rat primary hippocampal neurons. Importantly, the recombinant CDV used in these studies not only efficiently infects both cell types but recapitulates the uncommon, non-cytolytic cell-to-cell spread mediated by virulent CDVs in brain of dogs. Here, we demonstrated that both CDV surface glycoproteins (F and H) markedly accumulated in the endoplasmic reticulum (ER). This accumulation triggered an ER stress, characterized by increased expression of the ER resident chaperon calnexin and the proapoptotic transcription factor CHOP/GADD 153. The expression of calreticulin (CRT), another ER resident chaperon critically involved in the response to misfolded proteins and in Ca(2+) homeostasis, was also upregulated. Transient expression of recombinant CDV F and H surface glycoproteins in Vero cells and primary hippocampal neurons further confirmed a correlation between their accumulation in the ER, CRT upregulation, ER stress and disruption of ER Ca(2+) homeostasis. Furthermore, CDV infection induced CRT fragmentation with re-localisation of a CRT amino-terminal fragment, also known as vasostatin, on the surface of infected and neighbouring non-infected cells. Altogether, these results suggest that ER stress, CRT fragmentation and re-localization on the cell surface may contribute to cytotoxic effects and ensuing cell dysfunctions triggered by Morbillivirus, a mechanism that might potentially be relevant for other neurotropic viruses.

Show MeSH
Related in: MedlinePlus