Early events in polyoma virus infection: attachment, penetration, and nuclear entry

Abstract

The plaque-assay technique was used as a tool to determine the optimal conditions for adsorption of polyoma virions to host cells. Using these optimal conditions of adsorption, an electron microscopy study of the early events of infection was performed. By electron microscopy and autoradiography, it was demonstrated that both the viral coat proteins and DNA arrive simultaneously in the nucleus as early as 15 min postinfection. When horseradish peroxidaselabeled virions, pseudovirions, and capsids were used to infect cells, only the particles with nucleic acid or a factor(s) associated with the nucleic acid, i.e., histones, appeared to enter the nucleus. Moreover, when virions were used to infect either permissive or nonpermissive cells, identical early events of viral infection, i.e., adsorption, penetration, and nuclear transport, were observed, suggesting that these early events of infection are a property of the virion and not the host cell.

An Update on Non-clathrin-coated Endocytosis

“…EBV has been detected entering cells via large, non-coated macropinosomal vesicles 20 and uptake has been reported to be sensitive to cytochalasins. 21 Papovaviruses and SV40 are known to be internalised predominantly into non-coated vesicles which are very small, tight-fitting 22,23 and resemble caveolae morphologically. In the picornavirus family, polioviruses appear to enter cells via coated vesicles and by a clathrin-independent endocytic pathway, along with human rhinovirus type 2, 24 while others bind to GPIlinked receptors, molecules known to cluster in caveolae (see below).…”

Virus Entry into Animal Cells

“…Electron-microscopic evidence has, on the other hand, been presented suggesting that adenovirus particles, presumably released into the cytosol after lysis of endosomal membranes, may actually uncoat at nuclear pores and inject their genome into the nucleus (Dales, 1978). It cannot be ruled out that some (such as polyoma and SV40) may be delivered to the nucleus by membrane-bound vesicles (Mackay and Consigli, 1976;Maul et al, 1978;Nishimura et al, 1986) or enter the nucleus during mitosis when the nuclear membrane is dissociated. L 111.…”

“…Whereas poliovirus seems to enter mainly by coated pits, HRV-2 may infect cells via a coated vesicle-independent endocytic mechanism (Madshus et al, 1987). Papovaviruses are known to be internalized mainly in noncoated vesicles (Maul et al, 1978;Mackay and Consigli, 1976). They are so small and tight fitting that it almost looks like the viral particles would be budding from the extracellular space into the cell.…”

The Polyomaviridae: Contributions of virus structure to our understanding of virus receptors and infectious entry

“…The ability to plaque purify virus preparations allowed for an enrichment of infectious virions and for their separation from empty capsids by density gradient centrifugation. Detailed analyses of these individual populations by EM indicated that empty capsids and light populations of virions (pseudovirions) were endocytosed by two different pathways (Bolen and Consigli, 1979;Mackay and Consigli, 1976). Virions and pseudovirions were predominantly endocytosed as single membrane-bound particles that trafficked intact to the nucleus.…”

“…Some virions were found in large tubular structures that likely represent the pinching off of these structures from caveosomes described years later by Helenius (see text for detailed descriptions). Modified from information in Mackay andConsigli, 1976 andMaul et al, 1978. addition, the neuraminidase used for treating cells before challenge with SV40 does not cleave the sialic acid off GM1 so that it leaves the receptor intact (Miller-Podraza et al, 1982). It can even cleave sialic acid off higher order gangliosides to yield GM1.…”