Abstract
ABSTRACTSimian virus 40 (SV40), a polyomavirus that has served as an important model to understand many aspects of biology, induces dramatic cytoplasmic vacuolization late during productive infection of monkey host cells. Although this activity led to the discovery of the virus in 1960, the mechanism of vacuolization is still not known. Pentamers of the major SV40 capsid protein VP1 bind to the ganglioside GM1, which serves as the cellular receptor for the virus. In this report, we show that binding of VP1 to cell surface GM1 plays a key role in SV40 infection-induced vacuolization. We previously showed that SV40 VP1 mutants defective for GM1 binding fail to induce vacuolization, even though they replicate efficiently. Here, we show that interfering with GM1-VP1 binding by knockdown of GM1 after infection is established abrogates vacuolization by wild-type SV40. Vacuole formation during permissive infection requires efficient virus release, and conditioned medium harvested late during SV40 infection rapidly induces vacuoles in a VP1- and GM1-dependent fashion. Furthermore, vacuolization can also be induced by a nonreplicating SV40 pseudovirus in a GM1-dependent manner, and a mutation in BK pseudovirus VP1 that generates GM1 binding confers vacuole-inducing activity. Vacuolization can also be triggered by purified pentamers of wild-type SV40 VP1, but not by GM1 binding-defective pentamers or by intracellular expression of VP1. These results demonstrate that SV40 infection-induced vacuolization is caused by the binding of released progeny viruses to GM1, thereby identifying the molecular trigger for the activity that led to the discovery of SV40.
Highlights
In the late 1950s, Sweet and Hilleman observed that incubation of African green monkey kidney cells with poliovirus vaccine stocks caused dramatic cytoplasmic vacuolization [1]
Transient, early cellular vacuolization (ECV) occurs in primary African green monkey kidney cells infected at a high input multiplicity by infectious or UV-inactivated simian virus 40 (SV40), suggesting the capacity to induce early vacuolization resides in a structural component of the SV40 virion and does not require replication of SV40 DNA [13]
Helenius and coworkers showed that binding of SV40 capsids or isolated pentameric VP1 to cell surface GM1 induced dramatic membrane curvature that led to the formation of tight-fitting, virus-filled invaginations and tubules of the plasma membrane of monkey CV-1 cells [20]
Summary
In the late 1950s, Sweet and Hilleman observed that incubation of African green monkey kidney cells with poliovirus vaccine stocks caused dramatic cytoplasmic vacuolization [1]. Helenius and coworkers showed that binding of SV40 capsids or isolated pentameric VP1 to cell surface GM1 induced dramatic membrane curvature that led to the formation of tight-fitting, virus-filled invaginations and tubules of the plasma membrane of monkey CV-1 cells [20]. This process appears to provide a route of virus internalization during cellular uptake of SV40
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