Polyamine depletion inhibits norovirus infection and blocks virus-induced apoptosis

Stefan Taube, University of Lübeck

Maryna Chaika1, Heike Laschin1, Marina Pekelis1, Alexander Müller1, Carmen Mirabelli1,3, Sandra Niendorf2, Christiane Wobus3, Stefan Taube1 1Institute of Virology and Cell Biology, University of Lübeck, Germany 2Unit for Gastroenteritis and Hepatitis Pathogens and Enteroviruses, Robert Koch Institute, Berlin, Germany 3Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, USA

Prevention & Control (antivirals)

Noroviruses, non-enveloped single-stranded RNA viruses of the Caliciviridae family, include murine norovirus (MNV) and human norovirus (HNoV). While HNoVs are a major cause of acute gastroenteritis globally, they are difficult to cultivate. MNV, which infects mice and shares key biological features with HNoV, serves as a useful surrogate model.

Polyamines (PAs)—small, positively charged molecules such as spermine and spermidine—are essential for cellular functions including growth and differentiation. Recent evidence suggests that PAs also influence infections by enteric viruses. An untargeted metabolomic screen examining Enterobacter cloacae–HNoV interactions revealed downregulation of spermine and spermidine, prompting investigation into PA roles in norovirus infections. Pre-treatment of cells with α-difluoromethylornithine (aka eflornithine or DFMO, a PA synthesis inhibitor) or Denspm (a spermine analog promoting degradation) depletes intracellular polyamine concentration.

We examined the effect of PA depletion on MNV and HNoV infections. MNV infections were carried out in susceptible murine cell lines and HNoV infections were performed in 3D stem cell-derived human intestinal enteroids (HIEs) using patient-derived stool isolates. Cells were treated depleted for polyamines prior to infected with MNV of HNoV. Viral replication was measured by plaque assay and RT-qPCR respectively.

PA depletion blocked MNV infection and abolished HNoV replication. Supplementing cultures with spermidine and spermine restored MNV and partially rescued HNoV infection. In MNV, depletion did not affect attachment or genome replication but impaired virus-induced apoptosis and release. PI3-kinase inhibition rescued MNV infection and apoptosis markers in polyamine depleted cells.

These findings show that intracellular PAs are essential for norovirus infection. In MNV, this is linked to virus-induced apoptosis via PI3-kinase signaling. Similar requirements in HNoV suggest a broadly conserved mechanism and the potential use of PAs depletion as a therapeutic target, especially since DFMO is a well-tolerated FDA-approved drug used to treat human African trypanosomiasis (HAT).