Genome replication and postencapsidation functions mapping to the nonstructural gene restrict the host range of a murine parvovirus in human cells

The infection outcome of the Parvoviridae largely relies on poorly characte rized intracellular factors modulated by proliferation, differentiation, an d transformation of host cells. We have studied the interactions displayed by the highly homologous p and i strains of the murine parvovirus minute vi rus of mice (MVM), with a series of transformed cells of rat (C6) and human (U373, U87, SW1088, SK-N-SH) nervous system origin, seeking for molecular mechanisms governing parvovirus host range. The MVMp infection of C6 and U3 73 cells was cytotoxic and productive, whereas the other nervous cells beha ved essentially as resistant to this virus. In contrast, MVMi did not compl ete its life cycle in any of the human nervous cells, though it efficiently killed the astrocytic tumor cells by two types of nonproductive infections : (i) normal synthesis of all viral macromolecules with a late defect in in fectious virion maturation and release to the medium in U373; and (ii) high levels of accumulation of the full set of viral messenger RNAs and of both nonstructural (NS-1) and structural (VP-1 and VP-2) proteins, under a very low viral DNA amplification, in U87 and SW1088 cells. Further analyses sho wed that U87 was permissive for nuclear transport of MVMi proteins, leading to efficient assembly of empty viral capsids with a normal phosphorylation and VP1-to-VP2 ratio. The DNA amplification blockade in U87 occurred after conversion of the incoming MVMi genome to the monomeric replicative form, and it operated independently of the delivery pathway used by the viral par ticle, since it could not be overcome by transfection with cloned infectiou s viral DNA. Significantly, a chimeric NVMi virus harboring the coding regi on of the nonstructural (NS) gene replaced with that of MVMp showed a simil ar pattern of restriction in U87 cells as the parental MVMi virus, and it a ttained in U373 cultures an infectious titer above 100-fold higher under eq ual levels of DNA amplification and genome encapsidation. The results sugge st that the activity of complexes formed by the NS polypeptides and recruit ed cellular factors restrict parvovirus DNA amplification in a cell type-de pendent manner and that NS functions may in addition determine MVM host ran ge acting at postencapsidation steps of viral maturation. These data are re levant for understanding the increased multiplication of autonomous parvovi rus in some transformed cells and the transduction efficacy of nonreplicati ve parvoviral vectors, as well as a general remark on the mechanisms by whi ch NS genes may regulate viral tropism and pathogenesis.