Overexpression of Essential Splicing Factor ASF/SF2 Blocks the Temporal Shift in Adenovirus Pre-mRNA Splicing and Reduces Virus Progeny Formation

Abstract

Expression of cytoplasmic mRNA from most adenovirus transcription units is subjected to a temporal regulation at the level of alternative pre-mRNA splicing. The general tendency is that splice site selection changes from proximal to distal late after infection. Interestingly, ASF/SF2, which is a prototypical member of the SR family of splicing factors, has the opposite effect on splice site selection, inducing an increase in proximal splice site usage. We have previously shown that SR proteins late during an adenovirus infection become partially inactivated as splicing regulatory proteins. A prediction from these results is that overexpression of an SR protein, such as ASF/SF2, during virus growth will interfere with virus replication by disturbing the balance of functional and nonfunctional ASF/SF2 in the infected cell. To test this hypothesis, we reconstructed a recombinant adenovirus expressing ASF/SF2 under the transcriptional control of a regulated promoter. The results show that, as predicted, induction of ASF/SF2 during lytic virus growth prevents the early to late shift in mRNA expression from both early (E1A and E1B) and late (L1) transcription units. Furthermore, ASF/SF2 overexpression blocks viral DNA replication and reduces selectively cytoplasmic accumulation of major late mRNA, resulting in a lower virus yield. Collectively, our results provide additional support for the hypothesis that viral control of SR protein function is important for the proper expression of viral proteins during lytic virus growth.Adenovirus gene expression is to a large extent regulated at the level of pre-mRNA alternative splicing (reviewed in reference 21). Thus, the majority of adenovirus transcription units produce multiple differently spliced cytoplasmic mRNAs. The production of several mRNAs from each viral transcription unit increases the coding potential of the viral genome and, furthermore, enables the virus to control viral gene expression by regulating the specificity of RNA splicing. Importantly, the accumulation of alternatively spliced mRNAs is subjected to a temporal regulation, with distinct mRNA species accumulating at different time points of infection (reviewed in reference 21).Although the mechanism(s) responsible for this shift in RNA splice site choice is far from clear, a number of studies have suggested that the cellular SR family of splicing factors plays a critical role in this regulation. SR proteins constitute a family of splicing factors that are essential for generic premRNA splicing (reviewed in references 12 and 28). They contain one or two amino-terminal RNA binding domains and a characteristic carboxy-terminal RS domain consisting of repeats of serine/arginine dipeptides of variable length, hence the name SR proteins. The RNA recognition motif determines the RNA binding specificity, whereas the RS domain functions as an effector domain mediating interaction with other splicing factors (reviewed in references 12 and 28). SR proteins participate at multiple steps during the initial stages of ...

Precursor of human adenovirus core polypeptide Mu targets the nucleolus and modulates the expression of E2 proteins

“…A recombinant adenovirus that expressed ASF/SF2 under the control of an inducible promoter has been described (Molin & Akusjarvi, 2000). This report noted that when induced, ASF/SF2 blocked late gene expression but expression of DBP was evident.…”

“…This report noted that when induced, ASF/SF2 blocked late gene expression but expression of DBP was evident. We have previously noted unpublished evidence that overexpression of ASF/SF2 inhibited preTP expression (Molin & Akusjarvi, 2000). The lack of preTP expression would account for the lack of DNA replication and the loss of late protein expression.…”

Differential Effects of the SR Proteins 9G8, SC35, ASF/SF2, and SRp40 on the Utilization of the A1 to A5 Splicing Sites of HIV-1 RNA

“…SR proteins activate the production of the early mRNAs, but a limitation of their activity is required for the late phase of infection (34). This limitation results from titration of the SR proteins by the major late transcripts (35) and/or a virus-induced dephosphorylation (36).…”

Transcriptional Blocks Limit Adenoviral Replication in Primary Ovarian Tumor

“…Of note, previous studies have indicated that factors present in the infected cells can influence this process and thus affect the ability of the virus to replicate effectively in the host cell. For example, serine-rich proteins within the cell have been shown to suppress viral infection by blocking the obligate splicing of adenoviral pre-mRNA (15). Furthermore, the decrease in adenoviral replication may be due to ineffective or absent cleavage of polyadenylated RNA (16).…”