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Phorbol ester-mediated inhibition of IFN-alpha/beta gene transcription in blood mononuclear leukocytes
K Sandberg1, M L Eloranta, A E Gobl
1Department of Veterinary Microbiology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Abstract:
The phorbol ester PMA efficiently inhibits the in vitro IFN-alpha and -beta responses in human blood monocytes induced by Sendai virus and in natural IFN-producing cells induced by glutaraldehyde-fixed herpes simplex virus-infected human amnion (WISH) cells. This PMA-mediated inhibition of IFN-alpha/beta secretion is correlated with considerably reduced levels of IFN-alpha/beta mRNA, as determined by Northern blot analysis. Nuclear run-on assays further show that, at least in monocytes, PMA inhibits transcription of the IFN-alpha and -beta genes. The synthetic diacylglycerol 1-oleoyl-2-acetylglycerol has the same effects as PMA, and the protein kinase inhibitor staurosporine prevents the PMA-mediated inhibition of IFN-alpha/beta expression. These results suggest a role for protein kinase C in the inhibition of IFN-alpha/beta responses. The PMA does not inhibit the accumulation of IFN-beta mRNA in monocytes stimulated by Sendai virus in the presence of cycloheximide, indicating that the inhibitory action of the phorbol ester requires de novo protein synthesis.
Insights
Phorbol ester PMA inhibits interferon (IFN)-alpha/beta production and gene transcription in human monocytes. This inhibition requires new protein synthesis and suggests protein kinase C plays a role in regulating IFN responses.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Interferons (IFNs) are crucial cytokines for antiviral defense.
- Phorbol esters like PMA are known to modulate cellular responses.
- Understanding IFN regulation is key to developing antiviral therapies.
Purpose of the Study:
- To investigate the effect of PMA on IFN-alpha and IFN-beta production in human monocytes.
- To elucidate the molecular mechanisms underlying PMA-mediated inhibition of IFN responses.
- To determine the role of protein kinase C (PKC) in this inhibitory pathway.
Main Methods:
- Human blood monocytes and WISH cells were stimulated with Sendai virus or infected WISH cells.
- Interferon (IFN)-alpha/beta secretion was measured.
- IFN-alpha/beta mRNA levels were analyzed using Northern blot.
- Gene transcription was assessed via nuclear run-on assays.
- The effects of synthetic diacylglycerol and staurosporine were evaluated.
Main Results:
- PMA significantly inhibited IFN-alpha and IFN-beta responses in monocytes and WISH cells.
- PMA reduced IFN-alpha/beta mRNA levels and inhibited gene transcription.
- Synthetic diacylglycerol mimicked PMA's inhibitory effects.
- Staurosporine blocked PMA-mediated inhibition, implicating PKC.
- Inhibition by PMA required de novo protein synthesis.
Conclusions:
- Protein kinase C activation by PMA inhibits IFN-alpha/beta production and gene transcription.
- The inhibitory effect of PMA on IFN responses is dependent on new protein synthesis.
- These findings highlight PKC as a key regulator of antiviral interferon pathways.