LYTIC REACTIVATION OF KSHV IS ASSOCIATED WITH MAJOR NUCLEOLAR ALTERATIONS

The nucleolus is a subnuclear compartment whose primary function is biogenesis of ribosomal subunits. Previous studies have shown that certain viral infections affect the morphology and the composition of the nucleolar compartment and influence rRNA transcription and maturation. However, no description of the nucleolar morphology and function during KSHV infection is available to date.

By using immunofluorescence microscopy, we have documented an extensive destruction of the nuclear and nucleolar architecture during lytic reactivation of KSHV. Redistribution of key nucleolar proteins including UBF, Fibrillarin and Nucleophosmin was shown. Fluorescent in situ hybridization, combined with immunofluorescence, revealed a complete overlap between Fibrillarin and ITS-1, which represents the primary product of rDNA, whereas ITS-1 and UBF only partially overlapped. A complete co-localization of UBF and the RNA polymerase subunit RPA194 was observed, while UBF and Fibrillarin did not co-localized. No accumulation of pre-rRNA intermediates was evident by Northern blot analysis, suggesting that the processing of pre-rRNA proceeds properly.

Taken together, our results suggest that rRNA transcription and processing persist during lytic reactivation of KSHV, yet they appear to be uncoupled. Whether the observed nucleolar alterations favor productive infection or signify cellular anti-viral responses remain to be determined.