Redistribution of the delta antigens in cells replicating the genome of hepatitis delta virus.
When the small form of the delta antigen (deltaAg-S) was expressed from a cDNA expression plasmid and subsequently detected by immunofluorescence, it was found localized to the nucleoli. However, if the cDNA was cotransfected with a cDNA expressing a mutated hepatitis delta virus (HDV) genome that could only replicate by using the deltaAg-S provided by the first plasmid, then most of the deltaAg-S was redistributed to the nucleoplasm, largely to specific discrete nucleoplasmic sites or speckles; this pattern was stable for at least 50 days after transfection. These speckles coincided with those detected with an antibody to SC35, an essential non-small nuclear ribonucleoprotein splicing factor. Others have shown that SC35 speckles correspond to active sites of DNA-directed transcription by RNA polymerase II and also of RNA processing. We also found, in contrast to the cotransfections with the mutant HDV and the deltaAg-S provided in trans, that cells transfected with wild-type HDV showed a variable pattern of staining. The SC35-like speckle pattern of accumulation of delta antigen deltaAg was maintained for only 6 days, after which the pattern began to change. By 18 days posttransfection, a variety of different deltaAg staining patterns were observed. This pattern of change occurs at a time when the large form of the delta antigen deltaAg-L appears and HDV RNA synthesis begins to shut down. Our studies therefore support the interpretation that HDV RNA and deltaAg-S accumulate at SC35 speckle sites in the nucleoplasm. We speculate that these may be the sites at which HDV RNA is transcribed by RNA polymerase II and/or sites of HDV RNA processing. Furthermore, when deltaAg-L, as well as other mutant deltaAg accumulate, the speckle association is disrupted, thereby stopping HDV RNA replication.
Bichko
V V
VV
Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111-2497, USA.
Taylor
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D018963:Hepatitis Antigens / Q000235:genetics / Q000378:metabolism*; D003698:Hepatitis Delta Virus / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D035923:Hepatitis delta Antigens; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011817:Rabbits; D014407:Tumor Cells, Cultured; D014779:Virus Replication
D018963:Hepatitis Antigens; D035923:Hepatitis delta Antigens; C442244:hepatitis delta virus large antigen