Virion-associated spermidine transmits with Rift Valley fever virus particles to maintain infectivity

Abstract

24Viruses require host cell metabolites to productively infect, and the mechanisms by which 25 viruses usurp these molecules is diverse. One group of cellular metabolites important in virus 26 infection is the polyamines, small positively-charged molecules involved in cell cycle, translation, 27 and nucleic acid synthesis, among other cellular functions. Polyamines also support replication 28 of diverse viruses, and they are important for processes such as transcription, translation, and 29 viral protein enzymatic activity. Rift Valley fever virus (RVFV) is a negative-sense RNA virus that 30 requires polyamines to produce infectious particles. In polyamine depleted conditions, 31 noninfectious particles are produced that interfere with virus replication and stimulate immune 32 signaling. Here, we find that RVFV relies on virion-associated polyamines to maintain infectivity. 33Mastrodomenico et al. 2We show that RVFV replication is facilitated by any of the three biogenic polyamines; however, 34 we specifically find spermidine associated with purified virions. Using a panel of polyamine 35 homologs, we observe that virions can also associate with (R)-3-methylspermidine and 36 norspermidine, though not with other less homologous molecules. Using polyamine reporter 37 cells, we demonstrate that virion-associated polyamines transmit from one infected cell to 38 another. Finally, we find that virions devoid of polyamines are unstable and cannot be 39 supplemented with exogenous polyamines to regain stability or infectivity. These data highlight 40 a unique role for polyamines, and spermidine in particular, in maintaining virus infectivity, a 41 function not previously appreciated. Further, these studies are the first to identify polyamines 42 associated with RVFV virions. Targeting polyamines represents a promising antiviral strategy, 43 and this work highlights a new mechanism by which we can inhibit virus replication through 44 FDA-approved polyamine depleting pharmaceuticals. 45 46 the virus continues to present itself in frequent outbreaks 9-11 , infecting hundreds and severely 56 impacting local economies. Thus, the development of improved vaccines or the identification of 57 novel antiviral targets is essential to the treatment and prevention of RVFV. 58 59As obligate intracellular pathogens, viruses rely on their host cells for the building blocks of 60 replication. These building blocks include a variety of metabolites produced by the host cell. 61One set of these metabolites crucial to virus replication is the family of polyamines. Eukaryotic 62 cells synthesize polyamines to support transcription, translation, and cell cycling 12-14 . The 63 biogenic polyamines include putrescine, spermidine, and spermine, which are maintained at 64 millimolar level within cells 15 and readily interconvert within cells 16 . These molecules are carbon 65 chains of increasing length with primary and secondary amine groups. At physiological pH, 85% of polyamines are bound to nucleic acids (primarily RNA), proteins, or lipids t...

Targeting Polyamines Inhibits Coronavirus Infection by Reducing Cellular Attachment and Entry

“…We observed that the polyamines significantly reduced cellular viability at approximately 5 μM, reflecting prior descriptions of high polyamine concentrations leading to apoptosis. , Despite this reduction in viability, we observed modestly reduced viral titers (Figure B). We measured polyamines in supplemented cells and observed that supplementation with any of the three polyamines resulted in only modest changes in cell-associated polyamines (Figure B, lower), as we previously described . The reduced signal with high concentrations of spermidine and spermine likely was an artifact of reduced cellular viability at these doses.…”

“…We measured polyamines in supplemented cells and observed that supplementation with any of the three polyamines resulted in only modest changes in cell-associated polyamines (Figure 2B, lower), as we previously described. 27 The reduced signal with high concentrations of spermidine and spermine likely was an artifact of reduced cellular viability at these doses.…”