GRP78 promotes rabies virus entry through interacting with viral receptors.

The rabies virus (RABV) is known to have four potential receptors, including the nicotinic acetylcholine receptor (nAChR), neural cell adhesion molecule (NCAM), low-affinity nerve growth factor receptor (NGFR), and metabolic glutamate receptor 2 (mGluR2). However, the regulatory mechanism that maintains the stability of these receptors on the cell membrane remains unclear. In this study, we found that 78 kDa glucose-regulated protein (GRP78) is required for RABV infection in cells. Knockdown of GRP78 decreased the internalization of RABV. A GRP78 monoclonal antibody effectively blocked RABV infection. Mechanistically, GRP78 interacts with RABV candidate receptors directly through the 19 to 50 amino acids at the N-terminal of GRP78, which is crucial for RABV infection. GRP78 can form complexes with viral receptors and viral envelope glycoproteins on the cell membrane. Silencing GRP78 led to a decrease in the expression of RABV candidate receptors on the cell membrane. Our findings suggest that GRP78 plays a critical role in stabilizing the cell-surface expression of these receptors by directly interacting with them, which in turn facilitates the internalization of RABV. These findings provide new insights into the complex process of RABV invasion into cells and may contribute to the development of therapeutics against RABV. IMPORTANCE: Rabies virus (RABV) is a neglected but fatal zoonotic virus. Research has shown that the RABV glycoprotein binds to cell receptors and, with host factors' cooperation, invades cells to initiate its life cycle. Although several potential receptors and host factors for RABV have been identified, the process of virus invasion remains unclear. Here, we report that GRP78 has a significant inhibitory effect on RABV infection and plays a crucial role in its early stage, particularly during virus internalization. Furthermore, we found that GRP78 directly interacts with all candidate receptors of RABV, and this interaction is critical for virus internalization. Our study reveals how GRP78 mediates RABV invading cells and deepens our understanding of host-virus interaction mechanisms during RABV infection, providing a promising target for preventing and treating rabies.