Characterization of herpes simplex virus 2 primary microRNA Transcript regulation

Area of Science:

• Virology
• Molecular Biology
• Gene Regulation

Background:

• Herpes simplex virus 2 (HSV-2) latency is characterized by abundant viral transcripts, including latency-associated transcripts (LAT) and LAT-associated microRNAs (miRNAs).
• The balance between LAT-miRNA expression and lytic viral transcripts influences neuronal infection outcomes, potentially depending on primary miRNA gene regulation.

Purpose of the Study:

• To characterize promoter sequences driving miRNA expression in HSV-2 latency.
• To identify the 5' ends of primary miRNAs and evaluate the response to the viral protein ICP4.
• To elucidate the regulatory mechanisms controlling the switch between HSV-2 latency and productive reactivation.

Main Methods:

• Mapping transcription initiation sites of primary miRNA transcripts.
• Identifying ICP4-binding sequences within promoter regions.
• Assessing promoter activity and the effect of ICP4 on transcription through mutation analysis.

Main Results:

• Identified ICP4-binding sequences at the transcription initiation sites of HSV-2 LAT and L/ST promoters, but not for primary miR-H6.
• Confirmed activity of the L/ST promoter and demonstrated ICP4 trans-activation, suggesting a dual role in regulating miR-I and miR-II expression.
• LAT exon 1 and the LAT promoter region function as a bidirectional promoter for LAT-encoded miRNAs and miR-H6.

Conclusions:

• ICP4 plays a critical role in regulating HSV-2 latency and reactivation by influencing the expression of LAT-associated miRNAs.
• ICP4's ability to suppress miRNAs targeting ICP34.5 and activate lytic genes suggests a key mechanism for transitioning between latency and productive infection.
• Understanding these regulatory mechanisms provides insight into HSV-2's strategy for controlling viral gene expression during different infection phases.