The Regulation of Prototype Foamy Virus 5'Long Terminal Repeats and Internal Promoter by Endogenous Transcription Factors

BACKGROUND

For foamy virus, the transactivator of spumaretrovirus (Tas) could bind directly to target DNA sequences termed as Tas responsive elements and trigger the viral internal promoter (IP) and long terminal repeat (LTR) promoters. The cellular endogenous factors also play an important role in viral gene expressions. We hypothesized that except the viral transcription factor Tas, the cellular endogenous factors also affect the viral gene expression.

METHODS

The full length of the prototype foamy virus (PFV) genome (U21247) was used to predict the potential binding sites of the transcription factors by online software JASPAR (http://jaspar.genereg.net) and Softberry (http://linux1.softberry.com/berry.phtml?topic=index&group=programs&subgroup=promoter). The Dual-Luciferase® Reporter Assay System (Promega, USA) was used to confirm the relative luciferase activities of the test groups. The different representative activating agents or inhibitors of each canonical signal pathway were used to identify the impact of these pathways on PFV 5'LTR and IP promoters.

RESULTS

The results showed different cellular endogenous factors might have respective effects on PFV 5'LTR and IP. It is worth mentioning that activator protein-1 and BCL2-associated athanogene 3, 2 kinds of vital proteins associated with NF-κB and PKC pathways, could activate the basal activity of 5'LTR and IP promoters but inhibit the Tas-regulated activity of both promoters. Furthermore, PFV Tas was identified to trigger the transcription of the NF-κB promoter.

CONCLUSION

NF-κB had a negative effect on PFV 5'LTR and IP promoter activities, the PKC pathway might upregulate 5'LTR and IP promoter activities, and the JNK and NF-AT signal pathway could increase the Tas-regulated promoter activity of PFV 5'LTR. This study sheds light on the interaction between PFV and the host cell and may help utilize the viral promoters in retroviral vectors designed for gene transfer experiments.