Intact sphingomyelin biosynthetic pathway is essential for intracellular transport of influenza virus glycoproteins

Cells genetically deficient in sphingomyelin synthase-1 (SGMS1) or blocked in their synthesis pharmacologically through exposure to a serine palmitoyltransferase inhibitor (myriocin) show strongly reduced surface display of influenza virus glycoproteins hemag-glutinin (HA) and neuraminidase (NA). The transport of HA to the cell surface was assessed by accessibility of HA on intact cells to exogenously added trypsin and to HA-specific antibodies. Rates of de novo synthesis of viral proteins in wild-type and SGMS1-deficient cells were equivalent, and HA negotiated the intracellular trafficking pathway through the Golgi normally. We engineered a strain of influenza virus to allow site-specific labeling of HA and NA using sortase. Accessibility of both HA and NA to sortase was blocked in SGMS1-deficient cells and in cells exposed to myriocin, with a corresponding inhibition of the release of virus particles from infected cells. Generation of influenza virus particles thus critically relies on a functional sphingomyelin biosynthetic pathway, required to drive influenza viral glycoproteins into lipid domains of a composition compatible with virus budding and release.