CD44 mediates the internalization of foot-and-mouth disease virus through macropinocytosis

Foot-and-mouth disease virus (FMDV), a member of the Picornavirus family, poses a significant threat to global animal husbandry. While it is known that macropinocytosis plays a crucial role in the entry of FMDV into cells, the specific cellular proteins that regulate this process and the downstream signalling pathways associated with these proteins are not yet fully understood. In this study, we demonstrated that the membrane protein cluster of differentiation 44 (CD44) is essential for the internalization of FMDV in BHK-21 cells, while it is not involved in the attachment of the virus to the cell. In addition, we found that CD44 is internalized in response to FMDV entry. Interestingly, the use of a macropinocytosis inhibitor impaired both CD44 internalization and FMDV entry and infection, indicating a strong connection between these two processes. Further experiments revealed that CD44 facilitates FMDV internalization through macropinocytosis. Importantly, our study shows that CD44 interacts with FMDV capsid proteins VP2 and VP3 and becomes phosphorylated during the entry of the virus. The phosphorylation of CD44 subsequently promotes the phosphorylation of p21-activated kinase 1 (PAK1), which is a critical component in the macropinocytotic entry of FMDV. Overall, this study provides new insights into the role of CD44 in the invasion of pathogens into host cells and highlights potential strategies for improving FMDV vaccines.