Complex pattern of HTLV-2 temporal expression in infected cell lines and patient PBMCs and identification of a novel splicing acceptor site

Background: Similarly to other retroviruses, HTLV-2 expresses multiple gene products from the same coding region by means of different strategies, including a complex pattern of alternative splicing. Methods: Our investigation has been focused on the analysis of the levels of expression of different HTLV-2 transcripts, to highlight the kinetics of transcription at different stages of virus gene expression and their quantitation, by real time RT-PCR, in infected cell lines and in short term cultures of PBMCs from infected patients. Results: Results obtained show an early transcription of tax/rex regulatory mRNA, followed by a gradual and steady increase of gag/pol and env structural transcripts and of other accessory mRNAs.Data demostrate that the expression of different HTLV-2 genes follows a distinct timing, both in chronically infected cells and in PBMCs isolated from infected patients. The regulatory transcript tax/rex is the first one to be expressed whereas the structural and accessory mRNAs are expressed at a later time point. Further studies aimed at better understanding the complex pattern of splicing, allowed us to identify a novel 3’ acceptor site of splicing for the second exon of HTLV-2. This new 3’ acceptor site is capable of expressing an isoform of the singly spliced env mRNA. In addition, it could also be used as an alternative splicing system within the X region for the tax/rex, p10/p11 and p? transcripts. Conclusions: This study demostrated that the expression of HTLV-2 transcripts is presenting distinct patterns, indicating that the control of viral gene expression is highly regulated both in its kinetics and expression level. Moreover, the use of multiple acceptor sites is likely to play an important role for the preferential expression of specific proteins at different phases of the viral cycle.