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Human T-cell leukemia virus type 2 Rex inhibits pre-mRNA splicing in vitro at an early stage of spliceosome formation
1Division of Hematology-Oncology, Department of Medicine, UCLA School of Medicine, California 90024-1678, USA.
Abstract:
The Rex protein is an essential regulator of RNA expression in human T-cell leukemia virus types 1 and 2 (HTLV-1 and HTLV-2) that promotes the accumulation of full-length and partially spliced viral transcripts in the cytoplasm. Rex-mediated regulation correlates with specific binding to a cognate RNA recognition element which overlaps the 5' splice site in the viral long terminal repeat. It has been unclear whether Rex directly affects splicing or only nuclear-to-cytoplasmic transport of viral mRNA. We demonstrate that HTLV-2 Rex is a potent inhibitor of splicing in vitro at an early step in spliceosome assembly. Inhibition requires phosphorylation of Rex and the ability of Rex to bind to the Rex response element. Direct inhibition of early spliceosome assembly by Rex may account for differential accumulation of unspliced transcripts and represents a novel mechanism of retroviral gene regulation.
Insights
Human T-cell leukemia virus Rex protein directly inhibits RNA splicing early in spliceosome assembly. This novel mechanism explains how Rex regulates viral gene expression and transcript accumulation.
Area of Science:
- Virology
- Molecular Biology
- Gene Regulation
Background:
- The Rex protein of human T-cell leukemia virus types 1 and 2 (HTLV-1 and HTLV-2) regulates viral RNA expression.
- Rex promotes the cytoplasmic accumulation of viral transcripts by binding to a specific RNA element.
- Its precise role in splicing versus nuclear-to-cytoplasmic transport has been unclear.
Purpose of the Study:
- To investigate the direct effect of HTLV-2 Rex on viral RNA splicing.
- To determine the mechanism by which Rex influences viral transcript accumulation.
Main Methods:
- In vitro splicing assays were performed using HTLV-2 Rex.
- Spliceosome assembly steps were analyzed.
- The role of Rex phosphorylation and binding to the Rex response element was assessed.
Main Results:
- HTLV-2 Rex was demonstrated to be a potent inhibitor of RNA splicing in vitro.
- Inhibition occurred at an early stage of spliceosome assembly.
- Rex-mediated splicing inhibition requires Rex phosphorylation and binding to its response element.
Conclusions:
- HTLV-2 Rex directly inhibits early spliceosome assembly, representing a novel mechanism for retroviral gene regulation.
- This direct inhibition explains the differential accumulation of unspliced viral transcripts.
- Rex's function extends beyond regulating nuclear-to-cytoplasmic transport to actively modulating splicing.