Infectious hematopoietic necrosis virus matrix protein inhibits host-directed gene expression and induces...

Area of Science:

• Virology
• Cell Biology
• Fish Immunology

Background:

• Infectious hematopoietic necrosis virus (IHNV) causes significant mortality in fish populations.
• IHNV infection leads to host protein synthesis shutdown, cell rounding, and death.
• The specific roles of IHNV viral proteins in cytopathogenicity are not fully understood.

Purpose of the Study:

• To investigate the cytopathic effects of IHNV phosphoprotein (P), matrix (M), and nonvirion (NV) proteins in cultured fish cells.
• To elucidate the functions of M protein in IHNV infection, specifically regarding host transcription and cell death.
• To identify the cellular effects associated with NV protein expression.

Main Methods:

• Transfection of cultured fish cells with plasmids expressing IHNV P, M, or NV proteins.
• Reporter gene assays to assess promoter activity and mRNA levels via Northern blot.
• Immunofluorescence confocal microscopy to observe nuclear morphology.
• Electron microscopy to identify apoptotic changes.
• DNA laddering assays to detect programmed cell death.

Main Results:

• M protein expression potently inhibited reporter gene expression from viral and IFN-inducible promoters.
• M protein cotransfection reduced reporter mRNA levels but not M mRNA.
• Cells expressing M protein showed fragmented nuclei and morphological changes indicative of apoptosis.
• IHNV infection induced DNA laddering, confirming apoptosis.
• NV protein expression was associated with cell rounding.

Conclusions:

• IHNV M protein down-regulates host transcription and induces programmed cell death (apoptosis).
• IHNV NV protein is responsible for cell rounding, an early cytopathic effect.
• These findings provide insights into the mechanisms of IHNV pathogenesis and viral protein functions.