Alternative splicing and polyadenylation of human cytomegalovirus (HCMV) immediate-early (IE) pre-mRNAs are temporally regulated and rely on cellular RNA-processing factors. This study examined the location and abundance of essential RNA-processing factors, which affect alternative processing of UL37 IE pre-mRNAs, during HCMV
infection.
Serine/threonine protein kinase 1 (SRPK1) phosphorylates
serine/
arginine-rich
proteins, necessary for pre-spliceosome commitment. It was found that HCMV
infection progressively increased the abundance of cytoplasmic SRPK1, which is regulated by subcellular partitioning. The essential
polyadenylation factor CstF-64 was similarly increased in abundance, albeit in the nucleus, proximal to and within viral replication compartments (VRCs). In contrast, the location of
polypyrimidine tract-binding protein (PTB), known to adversely affect splicing of HCMV major IE RNAs, was temporally regulated during
infection. PTB co-localized with CstF-64 in the nucleus at IE times. By early times, PTB was detected in punctate cytoplasmic sites of some infected cells. At late times, PTB relocalized to the nucleus, where it was notably excluded from HCMV VRCs. Moreover, HCMV
infection induced the formation of nucleolar stress structures,
fibrillarin-containing caps, in close proximity to its VRCs. PTB exclusion from HCMV VRCs required HCMV
DNA synthesis and/or late gene expression, whereas the regulation of SRPK1 subcellular distribution did not. Taken together, these results indicated that HCMV increasingly regulates the subcellular distribution and abundance of essential RNA-processing factors, thereby altering their ability to affect the processing of viral pre-mRNAs. These results further suggest that HCMV
infection selectively induces sorting of nucleolar and nucleoplasmic components.