Nuclear export and expression of human T-cell leukemia virus type 1 tax/rex mRNA are RxRE/Rex dependent

Area of Science:

• Virology
• Molecular Biology
• Cellular Biology

Background:

• Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy (TSP/HAM).
• Viral replication relies on trans-acting proteins Tax and Rex, with Tax regulating transcription and Rex controlling post-transcriptional RNA export.
• The Rex-responsive element (RxRE) is found in all HTLV-1 mRNAs, but nuclear export of the doubly spliced tax/rex RNA was thought to be Rex-independent.

Purpose of the Study:

• To investigate the role of the Rex protein in the nuclear export and expression of the tax/rex RNA in HTLV-1 replication.
• To elucidate the mechanism and dependencies of Rex-mediated tax/rex RNA export.

Main Methods:

• Utilized RNA immunoprecipitation (RNA-IP) to confirm Rex binding to tax/rex RNA.
• Employed molecular clones and HTLV-1-infected T cells for experiments.
• Investigated the effect of leptomycin B treatment to assess CRM1 dependency.

Main Results:

• Demonstrated that Rex stimulates Tax expression through the nuclear-cytoplasmic export of tax/rex RNA, mediated by the RxRE element and Rex's RNA-binding activity.
• Confirmed that Rex-mediated export of tax/rex RNA is CRM1-dependent and inhibited by leptomycin B.
• Showed that while a basal export mechanism exists, Rex significantly enhances tax/rex RNA export and subsequent Tax expression.

Conclusions:

• Rex plays a crucial role in regulating HTLV-1 replication by promoting the nuclear export of tax/rex RNA.
• The interaction between Rex and tax/rex RNA, along with potential interactions with p30, suggests a complex and dynamic regulatory network governing HTLV-1 replication.
• These findings offer new insights into the intricate mechanisms controlling HTLV-1 viral replication.