Regulatory role of endoplasmic reticulum resident chaperone protein ERp29 in anti-murine β-coronavirus host cell response

Gap junctional intercellular communication (GJIC) involving astrocytes is important for proper CNS homeostasis. As determined in our previous studies, trafficking of the pre-dominant astrocyte GJ protein, Connexin43 (Cx43), is dis-rupted in response to infection with a neurotropic murine beta-coronavirus (MHV-A59). However, how host factors are involved in Cx43 trafficking and the infection response is not clear. Here, we show that Cx43 retention due to MHV-A59 infection was associated with increased ER stress and reduced expression of chaperone protein ERp29. Treatment of MHV-A59-infected astrocytes with the chemical chaperone 4-sodium phenylbutyrate increased ERp29 expression, rescued Cx43 transport to the cell surface, increased GJIC, and reduced ER stress. We obtained similar results using an astrocytoma cell line (delayed brain tumor) upon MHV-A59 infection. Critically, delayed brain tumor cells transfected to express exogenous ERp29 were less susceptible to MHV-A59 infection and showed increased Cx43-mediated GJIC. Treatment with Cx43 mimetic peptides inhibited GJIC and increased viral susceptibility, demonstrating a role for intercellular communication in reducing MHV-A59 infectivity. Taken together, these results support a therapeutically targetable ERp29-dependent mecha-nism where beta-coronavirus infectivity is modulated by reducing ER stress and rescuing Cx43 trafficking and function.

Automated summary

Gap junctional intercellular communication involving astrocytes is essential for CNS homeostasis. Infection with MHV-A59 disrupts the trafficking of Cx43, the main GJ protein in astrocytes, but the underlying mechanism is not clear. In this study, we found that retention of Cx43 due to MHV-A59 infection is associated with increased ER stress and reduced expression of chaperone protein ERp29. Treatment with a chemical chaperone rescues Cx43 transport, increases GJIC, and reduces ER stress. These findings provide insights into a therapeutically targetable mechanism where ERp29 modulates beta-coronavirus infectivity by alleviating ER stress and restoring Cx43 trafficking.