Measles Virus Ribonucleoprotein Complexes Rapidly Spread across Well-Differentiated Primary Human Airway Epithelial Cells along F-Actin Rings (original) (raw)

Measles virus (MeV) is a highly contagious human pathogen that continues to be a worldwide health burden. One of the challenges for the study of MeV spread is the identification of model systems that accurately reflect how MeV behaves in humans. For our studies, we use unpassaged, well-differentiated primary cultures of airway epithelial cells from human donor lungs to examine MeV infection and spread. Here, we show that the main components of the MeV ribonucleoprotein complex (RNP), the nucleocapsid and phosphoprotein, colocalize with the apical and circumapical F-actin networks. To better understand how MeV infections spread across the airway epithelium, we generated a recombinant virus incorporating chimeric fluorescent proteins in its RNP complex. By live cell imaging, we observed rapid movement of RNPs along the circumapical F-actin rings of newly infected cells. This strikingly rapid mechanism of horizontal trafficking across epithelia is consistent with the opening of pores between columnar cells by the viral membrane fusion apparatus. Our work provides mechanistic insights into how MeV rapidly spreads through airway epithelial cells, contributing to its extremely contagious nature. IMPORTANCE The ability of viral particles to directly spread cell to cell within the airways without particle release is considered to be highly advantageous to many respiratory viruses. Our previous studies in well-differentiated, primary human airway epithelial cells suggest that measles virus (MeV) spreads cell to cell by eliciting the formation of intercellular membrane pores. Based on a newly generated ribonucleoprotein complex (RNP) "tracker" virus, we document by live-cell microscopy that MeV RNPs move along F-actin rings before entering a new cell. Thus, rather than diffusing through the cytoplasm of a newly infected columnar cell, RNPs take advantage of the cytoskeletal infrastructure to rapidly spread laterally across the human airway epithelium. This results in rapid horizontal spread through the epithelium that does not require particle release. KEYWORDS actin, airways, lungs, measles, paramyxovirus M easles virus (MeV), a highly transmissible human pathogen (1, 2), is a nonsegmented negative-strand RNA virus of the genus Morbillivirus in the family Paramyxoviridae (3). Its genome is organized into six transcription units and is enclosed by the nucleocapsid (N) protein, forming a ribonucleoprotein (RNP). The RNAdependent RNA polymerase, constituted by a single L protein and minimally a homotetramer of the P protein, further contribute to the RNP complex (3). Viral particle assembly depends on the matrix (M) protein (4, 5), which also controls the activity of the membrane fusion apparatus that consists of the fusion (F) and hemagglutinin (H) Citation Singh BK, Pfaller CK, Cattaneo R, Sinn PL. 2019. Measles virus ribonucleoprotein complexes rapidly spread across welldifferentiated primary human airway epithelial cells along F-actin rings. mBio 10:e02434-19.