Abstract
Bovine parainfluenza virus 3 (BPIV3) is an important respiratory pathogen of both young and adult cattle. The pathways of cell entry are highly related to viral transmission and pathogenicity. In previous studies, we demonstrated that macropinocytosis and clathrin-dependent endocytosis play critical roles in the entry of BPIV3 into MDBK cells. Macropinocytosis is special endocytic process which need to activate signaling pathways that remodle the actin cytoskeleton. Parainfluenza viruses (PIVs) initiate infection by binding to sialic acid receptors on cell surfaces. Nevertheless, sialic acids are not able to transmit signals across the plasma membrane, indicating the necessity for additional signaling receptors. Here, we have demonstrated that specific inhibitors and siRNAs targeting EGFR inhibit the entry of BPIV3 into MDBK cells. BPIV3 productive infection in MDBK cells led to activation of EGFR. Inactivation of EGFR suppressed BPIV3-induced rearrangement of the F-actin cytoskeleton. In addition, PI3K-Akt and ERK1/2 were activated in an EGFR-dependent manner during BPIV3 infection. Specific inhibitors targeting these canonical downstream effectors of EGFR could significantly reduce viral entry efficacy. Moreover, we also demonstrated that the important regulators of macropinocytosis, Rac1 and Pak1, are downstream mediators of EGFR during BPIV3 internalization. These results indicated that EGFR is a host-entry cofactor used by BPIV3 to enter MDBK cells.