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Interleukin-6 inhibits apoptosis of malignant plasma cells
1Department of Medicine, VA Wadsworth Hospital-UCLA Medical Center, USA.
Abstract:
Multiple myeloma (MM) is a slow-growing malignancy whose plasma cells express the BCL-2 antiapoptosis gene. It is also associated with high levels of interleukin-6 (IL-6), a cytokine that prevents programmed cell death (PCD) in other target cell types. We thus investigated the ability of MM cells to undergo PCD and the possible regulatory effects of IL-6. Four MM cell lines underwent PCD when exposed to serum starvation, doxorubicin (dox), etoposide (VP-16), or dexamethasone (dex). Apoptosis was confirmed by morphologic criteria and/or detection of endonucleosomal DNA fragmentation. The concentrations of dox, VP-16, and dex required for PCD were at least 10-fold greater than that required to inhibit proliferation. Addition of IL-6 (but not IL-1 beta, IL-4, IL-7, or IL-10) inhibited PCD of 8226 targets induced by serum starvation or dexamethasone in a concentration-dependent fashion. In contrast, it had no effect on PCD induced by dox or VP-16. Exposure of targets to IL-6 did not increase BCL-2 expression (it actually consistently decreased expression), suggesting IL-6's protection against apoptosis was not mediated by direct effects on BCL-2. Targets protected from PCD by IL-6 were still sensitive to serum starvation and dex-induced cytostasis, but, after reculturing in drug-free complete media, they reinitiated normal proliferation. These data suggest that high levels of IL-6 may contribute to expansion of myeloma clones by inhibiting apoptotic death.
Insights
Interleukin-6 (IL-6) inhibits programmed cell death (PCD) in multiple myeloma (MM) cells, potentially promoting cancer growth. This cytokine protects MM cells from certain death-inducing stimuli but not all, suggesting a complex role in MM pathogenesis.
Area of Science:
- Molecular Biology
- Cancer Research
- Immunology
Background:
- Multiple myeloma (MM) is a plasma cell malignancy characterized by slow growth.
- MM cells express the anti-apoptotic BCL-2 gene and high levels of interleukin-6 (IL-6).
- IL-6 is a cytokine known to prevent programmed cell death (PCD) in various cell types.
Purpose of the Study:
- To investigate the capacity of MM cells to undergo PCD.
- To determine the regulatory effects of IL-6 on MM cell PCD.
- To elucidate the mechanisms by which IL-6 influences apoptosis in MM.
Main Methods:
- Four MM cell lines were exposed to apoptosis-inducing agents (serum starvation, doxorubicin, etoposide, dexamethasone).
- Programmed cell death (PCD) was assessed using morphologic criteria and DNA fragmentation assays.
- The impact of IL-6 addition on PCD induction and BCL-2 expression was evaluated.
Main Results:
- MM cell lines underwent PCD when treated with serum starvation, doxorubicin, etoposide, or dexamethasone.
- IL-6 significantly inhibited PCD induced by serum starvation and dexamethasone in a concentration-dependent manner.
- IL-6 did not affect PCD induced by doxorubicin or etoposide and did not increase BCL-2 expression.
Conclusions:
- High levels of IL-6 may contribute to the expansion of multiple myeloma clones by inhibiting apoptotic cell death.
- IL-6's protective effect against apoptosis in MM cells is not mediated by direct upregulation of BCL-2.
- These findings highlight IL-6 as a potential therapeutic target in managing multiple myeloma.