TASOR epigenetic repressor cooperates with a CNOT1 RNA degradation pathway to repress HIV

Area of Science:

• Epigenetics and Gene Regulation
• Molecular Virology
• RNA Metabolism

Background:

• The Human Silencing Hub (HUSH) complex mediates heterochromatin formation via SETDB1 and H3K9me3 marks.
• HUSH's role in gene silencing, particularly for viral elements like HIV, is not fully elucidated.
• Understanding HUSH's mechanism is crucial for controlling proviral expression.

Purpose of the Study:

• To investigate the molecular mechanisms by which the HUSH complex represses gene expression.
• To identify novel HUSH complex interactors involved in RNA metabolism.
• To determine the role of HUSH in regulating HIV-1 proviral expression.

Main Methods:

• Yeast two-hybrid screening to identify protein interactors.
• Analysis of HIV-1 LTR-driven transcript accumulation upon TASOR manipulation.
• Co-immunoprecipitation and cellular localization studies to assess protein interactions and localization.
• Assays to detect RNA degradation protein association with RNA Polymerase II.

Main Results:

• TASOR silencing or degradation increases HIV-1 LTR transcript accumulation post-transcriptionally.
• CNOT1, a component of the CCR4-NOT complex, was identified as a novel TASOR interactor.
• TASOR and CNOT1 synergistically repress HIV-1 LTR expression.
• TASOR interacts with the RNA exosome and elongating RNA Polymerase II.
• TASOR facilitates RNA degradation protein recruitment to RNA Polymerase II at transcriptional centers.

Conclusions:

• The HUSH complex functions at both transcriptional and post-transcriptional levels to repress HIV-1 proviral expression.
• TASOR plays a key role in recruiting RNA degradation machinery to nascent transcripts.
• HUSH acts as a crucial regulator of viral gene silencing, integrating epigenetic and RNA decay pathways.