Subversion of CtBP1-controlled macropinocytosis by human adenovirus serotype 3

Abstract

Endocytosis supports cell communication, growth, and pathogen infection. The species B human adenovirus serotype 3 (Ad3) is associated with epidemic conjunctivitis, and fatal respiratory and systemic disease. Here we show that Ad3 uses dynamin‐independent endocytosis for rapid infectious entry into epithelial and haematopoietic cells. Unlike Ad5, which uses dynamin‐dependent endocytosis, Ad3 endocytosis spatially and temporally coincided with enhanced fluid‐phase uptake. It was sensitive to macropinocytosis inhibitors targeting F‐actin, protein kinase C, the sodium–proton exchanger, and Rac1 but not Cdc42. Infectious Ad3 macropinocytosis required viral activation of p21‐activated kinase 1 (PAK1) and the C‐terminal binding protein 1 of E1A (CtBP1), recruited to macropinosomes. These macropinosomes also contained the Ad3 receptors CD46 and αv integrins. CtBP1 is a phosphorylation target of PAK1, and is bifunctionally involved in membrane traffic and transcriptional repression of cell cycle, cancer, and innate immunity pathways. Phosphorylation‐defective S147A‐CtBP1 blocked Ad3 but not Ad5 infection, providing a direct link between PAK1 and CtBP1. The data show that viruses induce macropinocytosis for infectious entry, a pathway used in antigen presentation and cell migration.