Increase of cellular murine leukemia virus reverse transcriptase in interferon-treated cells

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Murine leukemia virus (MuLV) is a retrovirus that can cause leukemia in mice.
• Interferon (IFN) is a protein that plays a role in the immune system's response to viral infections.
• The precise mechanism by which IFN inhibits MuLV replication is not fully understood.

Purpose of the Study:

• To investigate the effect of mouse interferon (IFN) on murine leukemia virus (MuLV) production in NIH3T3 cells.
• To determine the specific stage of the MuLV life cycle at which IFN exerts its inhibitory effect.

Main Methods:

• AKR MuLV-producing NIH3T3 cells were treated with mouse IFN.
• Viral reverse transcriptase activity and infectious virus production were measured.
• Proviral DNA and viral RNA levels were assessed.
• Cellular extracts were analyzed using poly(G)-Sepharose chromatography to separate reverse transcriptase peaks.
• Reverse transcriptase from purified virions was also characterized.

Main Results:

• IFN treatment inhibited extracellular MuLV release but did not affect proviral DNA or viral RNA levels.
• IFN treatment increased the cellular reverse transcriptase activity eluting at 0.45 M NaCl (Peak I), which corresponds to the virion-associated reverse transcriptase.
• Peak II (0.65 M NaCl) and cellular DNA polymerase beta (0.3 M NaCl) were unaffected by IFN.
• IFN treatment prior to infection did not alter reverse transcriptase levels, indicating the effect is on chronically infected cells.

Conclusions:

• Mouse interferon primarily acts at the level of MuLV maturation and assembly.
• IFN treatment leads to an accumulation of the virion-associated form of reverse transcriptase within the cell.
• These findings provide further evidence for IFN's role in controlling retroviral replication through effects on virus particle formation.