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Transcriptional modulation of human IL-6 gene expression by verapamil
Abstract:
Calcium channel-blocking agents interfere with the initial increase of cytosolic calcium that follows mitogenic stimulation of T lymphocytes. In cultures of mitogen-stimulated PBMC, verapamil also blocked T cell accumulation of cytoplasmic IL-2-encoding mRNA. In sharp contrast, the addition of verapamil to PHA and PMA-stimulated PBMC augmented the mitogen-stimulated increases in nuclear transcription of IL-6-encoding mRNA, steady state levels of IL-6 encoding mRNA, and release of IL-6 bioactivity. These experiments indicated that an increased IL-6 transcriptional rate rather than stabilization of transcripts accounted for the increased cytoplasmic IL-6 mRNA levels and subsequent expression of IL-6 bioactivity. These effects were not produced by nicardipine, another potent calcium channel blocker, or EGTA. We suggest that a non-calcium-dependent, IL-6 regulatory factor, absent or inactive in verapamil-treated cultures, inhibits IL-6 gene activation in mitogen-stimulated PBMC. Failure to express this inhibitory factor would result in IL-6 gene superinduction at a transcriptional level.
Insights
Verapamil, a calcium channel blocker, inhibits IL-2 mRNA but unexpectedly boosts IL-6 gene activation in T lymphocytes. This suggests a non-calcium-dependent factor regulates IL-6 expression.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Calcium influx is crucial for T lymphocyte activation.
- Mitogenic stimulation triggers T cell responses, including cytokine production.
Purpose of the Study:
- To investigate the role of calcium channel blockers in T lymphocyte activation and cytokine gene expression.
- To elucidate the mechanisms regulating Interleukin-6 (IL-6) mRNA accumulation and bioactivity.
Main Methods:
- Peripheral blood mononuclear cells (PBMC) were stimulated with mitogens (PHA, PMA).
- Verapamil and other agents (nicardipine, EGTA) were added to assess their effects on T cell activation.
- Interleukin-2 (IL-2) and Interleukin-6 (IL-6) mRNA levels were quantified using molecular techniques.
- IL-6 bioactivity was measured in cell culture supernatants.
Main Results:
- Verapamil inhibited T cell accumulation of IL-2 mRNA.
- Verapamil significantly increased IL-6 mRNA transcription, steady-state levels, and IL-6 bioactivity release.
- These verapamil effects on IL-6 were not replicated by nicardipine or EGTA, indicating a non-calcium-dependent mechanism.
- The increase in IL-6 was attributed to enhanced gene transcription, not mRNA stabilization.
Conclusions:
- Calcium channel blockers can differentially affect cytokine gene expression in T lymphocytes.
- Verapamil's augmentation of IL-6 suggests the involvement of a non-calcium-dependent regulatory factor.
- This factor appears to inhibit IL-6 gene activation, and its absence or inactivation leads to IL-6 superinduction.