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Amino acid analogs inhibit murine xenotropic retrovirus expression and cell cycle progression
Abstract:
Certain functional analogs of amino acids were examined for their capacity to inhibit chemically induced expression of endogenous xenotropic retrovirus from Kirsten sarcoma virus transformed BALB/c (K-BALB) mouse cells. Partially synchronized cells cultured with aminoethylcysteine (AEC), parafluorophenylalanine (PFA), or valinol, and subsequently induced with either 5-iododeoxyuridine (IUdR), cycloheximide, or histidinol, showed inhibition of virus activation. Inhibition was concentration- and time-dependent (1 to 4 h) and not a consequence of cytotoxicity. Inhibition was competed out by the analogous amino acid and was specific to the induction process. After a 4 h analog treatment, heteronuclear RNA synthesis was reduced 24, 38, and 35% by PFA, AEC, and valinol, respectively, whereas cycloheximide or actinomycin D reduced synthesis by 60 and 90%, respectively; therefore, the analogs did not seem to inhibit induction through a general transcriptional block. Culture of cells in the presence of the analogs resulted in an abrupt reduction (70 to 90%) in DNA synthesis. Using synchronized cells, it was found that 0.1 mM AEC added in G1 phase and followed by IUdR induction almost totally inhibited virus expression. No inhibition was observed when AEC was added during S phase concomitantly with the inducer. AEC added to synchronous cells in G1 phase inhibited the progression of cells into S phase and the onset of DNA synthesis. The results show that K-BALB cells have an AEC-sensitive restriction point in G1 phase that might relate to the effects amino acid analogs have on cell replication and S phase dependent gene expression, as well as subsequent differentiation.
Insights
Amino acid analogs like AEC, PFA, and valinol inhibit retrovirus activation in K-BALB cells. AEC specifically blocks virus expression by halting cell cycle progression in the G1 phase.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Endogenous retroviruses can be activated by chemical inducers.
- Kirsten sarcoma virus transformed BALB/c (K-BALB) mouse cells express xenotropic retrovirus.
- Amino acid analogs are investigated for their potential to modulate cellular processes.
Purpose of the Study:
- To investigate the inhibitory effects of functional amino acid analogs on chemically induced xenotropic retrovirus expression in K-BALB cells.
- To determine the mechanism and specificity of this inhibition.
Main Methods:
- K-BALB cells were treated with amino acid analogs (AEC, PFA, valinol) and subsequently induced with chemical agents (IUdR, cycloheximide, histidinol).
- Inhibition of virus activation, cytotoxicity, heteronuclear RNA synthesis, and DNA synthesis were measured.
- Synchronized cells were used to assess the effect of analog addition at different cell cycle phases (G1 vs. S).
Main Results:
- AEC, PFA, and valinol inhibited virus activation in a concentration- and time-dependent manner without significant cytotoxicity.
- The inhibition was specific to the induction process and could be competed by the analogous amino acid.
- Heteronuclear RNA synthesis was reduced, but not through a general transcriptional block.
- DNA synthesis was significantly reduced, and AEC addition in the G1 phase, but not S phase, almost totally inhibited virus expression.
- AEC in G1 phase inhibited cell progression into S phase and DNA synthesis onset.
Conclusions:
- Functional amino acid analogs, particularly AEC, can effectively inhibit chemically induced retrovirus expression in K-BALB cells.
- The inhibition is linked to the analogs' effect on cell cycle progression, specifically a restriction point in the G1 phase.
- These findings suggest a relationship between amino acid analog-induced cell cycle arrest and the regulation of S phase-dependent gene expression and differentiation.