Induction of transcription factor Egr-1 gene expression in astrocytoma cells by Murine coronavirus infection

Abstract

Mouse hepatitis virus (MHV) causes encephalitis and demyelination in the central nervous system (CNS) of susceptible rodents. Astrocytes are one of the major targets for MHV infection in the CNS, and respond to MHV infection by expressing diverse molecules that may contribute to CNS pathogenesis. Here we characterized the activation of an immediate-early transcription factor Egr-1 by MHV infection in an astrocytoma cell line. We found that the expression of Egr-1 was dramatically increased following virus infection. Using various inhibitors of mitogen-activated protein kinases, we identified that the extracellular signal-regulated kinases 1/2 were involved in the activation of Egr-1 transcription by MHV infection. Experiments with ultraviolet light-inactivated virus revealed that the induction of Egr-1 did not require virus replication and was likely mediated during cell entry. We further found that over-expression of Egr-1 suppressed the expression of BNip3, a pro-apoptotic member of the Bcl-2 family. This finding may provide an explanation for our previously observed down-regulation of BNip3 by MHV infection in astrocytoma cells (Cai, Liu, Yu, and Zhang, Virology 316:104-115, 2003). Furthermore, knockdown of Egr-1 by an siRNA inhibited MHV propagation, suggesting the biological relevance of Egr-1 induction to virus replication. In addition, the persistence/demylinating-positive strains (JHM and A59) induced Egr-1 expression, whereas the persistence/demylinating-negative strain (MHV-2) did not. These results indicate a correlation between the ability of MHVs to induce Egr-1 expression and their ability to cause demyelination in the CNS, which may suggest a potential role for the induction of Egr-1 in viral pathogenesis.

Regulation of Cellular MicroRNA Expression in Oligodendrocytes during Acute and Persistent Coronavirus Infection

“…While the number of miRNAs tested in the current experiments is rather limited, the results appear to suggest that miRNAs play a role in coronavirus replication. However, it is not known whether the net outcome of the altered miRNA expression contributes to restricting MHV replication as does the antiviral type I interferon response to MHV infection in N20.1 cells [32][33][34][35]. Nevertheless, our studies show that cellular miRNAs are potential regulators of viral replication and host gene expression during acute and persistent coronaviral infection that might contribute to the pathogenesis of coronavirus infection in oligodendrocytes in vitro and in vivo.…”

“…We have shown previously that 125 genes are up-regulated while 124 genes are downregulated in a mouse astrocytoma cell line infected by MHV in a genome-wide DNA microarray analysis [31]. Interestingly, many transcription factors such as extracellular regulatory kinase (Erk)-1/2, c-Jun, early growth regulator (Egr)-1, interferon regulatory factor (IRF)-3, nuclear factor (NF)-kB are activated in various types of cells by MHV infection [32][33][34][35]. As expression of many cellular genes is regulated by transcription factors, it is possible that expression of cellular miRNAs can be regulated by coronavirus infection through activation or suppression of the transcription factors.…”

Μελέτη της τροποποίησης της σηματοδότησης των MAPKs - ERKs παρουσία των HCV δομικών πρωτεϊνών

“…Οι καθεψίνες υπάρχουν και στα όψιμα ενδοσώματα και λυσοσώματα λόγο του χαμηλού pH (88). Η ομάδα των κυστεϊνών που μελετήθηκε στην παρούσα εργασία περιλαμβάνει δυο πολύ γνωστά μέλη, τις καθεψίνες B και L. Οι πρωτεΐνες αυτές συντίθενται στο ενδοπλασματικό δίκτυο με την μορφή προ-καθεψινών και ενεργοποιούνται μετά από υδρόλυση λόγω του χαμηλού όξινου περιβάλλοντος των ενδοσωμάτων (89,90). Οι συγκεκριμένες καθεψίνες έχουν σημαντικό ρόλο στην ενδοκύτωση διαφόρων ουσιών, συμπλόκων μορίων-υποδοχέων καθώς και ιών.…”

“…Στην παρούσα μελέτη παρουσιάστηκαν στοιχεία που υποδηλώνουν ότι στην μετακίνηση των core καψιδίων στο εσωτερικό των κυττάρων εμπλέκονται γνωστές υδρολάσες που βρίσκονται στα πρώιμα ενδοσώματα, και συγκεκριμένα οι καθεψίνες B και L. Πρόκειται για πρωτεΐνες που ενεργοποιούνται από το χαμηλό pH και είναι ιδιαίτερα ενεργές σε περιπτώσεις καρκίνων (89). Η εμπλοκή τους αποδείχτηκε με την χρήση των ειδικών χημικών αναστολέων E64 και πεπστατίνη A (pepstatin A), και επιβεβαιώθηκε με έναν άλλο αναστολέα την χλωροκίνη (chloroquine) που ουσιαστικά διατηρεί υψηλό το pH στα ενδοσώματα εμποδίζοντας έτσι τη σωστή λειτουργία των συγκεκριμένων ενζύμων (90).…”

“…Even though to a lower extent, a sustained transcriptional activation was observed. Egr-1 upregulation has been described in murine hepatitis virus entry and infection and correlates with the establishment of viral persistence (89). It has also been involved in human polyoma JC, rabies and borna disease viruses life cycles (90,91).…”