Cellular and early viral factors in the interaction of adenovirus type 12 with hamster cells: the abortive response

Abstract

The interaction of human adenovirus type 12 (Ad12) with Syrian hamster cells is remarkable in that there is a block of viral DNA replication and late gene transcription. We have screened several cellular factors known to play a role in adenovirus replication for their possible contributions to the interactions of Ad12 in the abortive BHK21 hamster cell system. (1) Western blot analyses of total protein extracts from Ad12- or Ad2-infected BHK21 cells do not reveal a significant difference in the accumulation of NFIII protein at different times after infection. Transcriptional levels of the NFIII gene in BHK21 cells are not altered upon the abortive infection with Ad12 or the productive infection with Ad2. The amount of NFIII protein is markedly reduced in nuclear extracts from BHK21 cells as compared with extracts from C131 hamster cells or human HeLa cells. A presumptive defect in NFIII transport to the nuclei rather than overall reduced NFIII gene transcription might explain the low abundance of NFIII in the nuclei of uninfected or Ad12-infected BHK21 cells. The productive infection of BHK21 or C131 cells with Ad2 leads to an increase in the NFIII concentration in the nuclei of infected cells, late after infection to a decrease; (2) NFI levels in the nuclei of mock-infected or Ad2- or Ad12-infected BHK21 cells are comparable with those in HeLa or in C131 cells. Thus, deficiencies in NFI may not play a role in the abortive system; (3) The absence of morphological alterations in PML protein domains from globular to track-like structures in the nuclei of Ad12-infected hamster cells correlates with the inability of Ad12 DNA to replicate in BHK21 cells. In BHK21 cells, the E4-ORF3 of Ad12 DNA is only weakly transcribed and only small amounts of the gene product are synthesized. In Ad12-infected C131 cells, which allow the replication of Ad12 DNA, the E4-ORF3 of Ad12 DNA is expressed, and track-like PML protein structures are observed. Transfection of the 12-E4-ORF3-EGFP construct leads to the expression of both the green fluorescent protein (GFP) and of the 12-E4-ORF3 gene product in 20–30% of the transfected BHK21 cells and elicits the morphological reorganization of the PML protein structures in the successfully transfected BHK21 cells. Similar results are obtained upon transfection of the 2-E4-ORF3 construct. Untransfected cells or cells transfected with the empty pIRES2-pEGFP vector carry the globular PML protein phenotype; (4) The expression of the 12-E4-ORF3-EGFP and/or of the NFIII-EGFP constructs upon transfection following Ad12-infection of BHK21 cells fails to promote Ad12 DNA replication. Hence, the formation of track-like PML protein structures in BHK21 cells by itself is not a sufficient precondition for Ad12 DNA replication in this abortive system. The data demonstrate that the expression of NFI, NFIII, and/or the conversion of the PML domains do not suffice to elicit Ad12 DNA replication in the abortive hamster cell system.