Radiation-induced apoptosis in human myeloma cell line increases BCL-2/BAX dimer formation and does not result in BAX/BAX homodimerization

Abstract

A popular model of BCL‐2 and BAX involvement in apoptosis suggests that upon apoptosis induction cytosolic BAX translocates to the mitochondria, where it displays the pro‐apoptotic function, which involves its homodimerization. BCL‐2 exerts anti‐apoptotic function by forming heterodimers with BAX, thus neutralizing the pro‐apoptotic activity of the latter. We have shown that irradiation of the human myeloma cell line RPMI‐8226 induced apoptosis as determined by DNA degradation, cytochrome c release into cytoplasm and BCL‐2 caspase‐mediated cleavage. BCL‐2 protein was present only in the membrane fraction, whereas BAX was found both in cytosol and membranes isolated from non‐irradiated cells. Radiation induced moderate redistribution of BAX from cytosol to membranes with a concomitant increase in BCL‐2/BAX heterodimer formation. Rapid and transient BCL‐2 phosphorylation in membrane fractions of irradiated cells did not affect BCL‐2/BAX heterodimerization. We failed to detect any BAX/BAX homodimers in apoptotic cells. Our findings show that in irradiated RPMI‐8226 cells the formation of BCL‐2/BAX heterodimers correlates with apoptosis. We conclude that BCL‐2/BAX heterodimers are negative regulators of death protection, and our data agree with those who propose that BCL‐2 does not require BAX to exert its survival function. © 2001 Wiley‐Liss, Inc.

Lipopolysaccharide-induced dental pulp cell apoptosis and the expression of Bax and Bcl-2 in vitro

“…Our findings indicate that both proteins were up-regulated after stimulation with high LPS concentrations. This was consistent with a previous report that showed increased expression of Bcl-2 and Bax accompanying increased apoptosis (29). Several studies (29)(30)(31) have demonstrated that pro-and antiapoptotic members of the Bcl-2 family might interact with each other to form homodimers and heterodimers in regulating apoptosis.…”

Comparison of human lung cancer cell radiosensitivity after irradiations with therapeutic protons and carbon ions

“…The increase of Bax/Bcl-2 ratio is typical for apoptosis. 53 Zong and Thompson have showed that different doses of the same cell death stimulus can trigger different cell death pathways. Thus, lower doses can induce apoptosis, while higher doses can trigger necrosis or other cell death pathways.…”

Growth factors and antiapoptotic signaling pathways in multiple myeloma

“…66 Radiation-induced apoptosis is also associated with moderate changes in cytosol-to-mitochondria Bax redistribution. 91 Inhibition of NF-kB activity by the cell-permeable inhibitor SN50 resulted in a decrease in Bcl-2 and A1 and an upregulation of Bax protein levels, shifting the balance toward apoptosis. 46 Furthermore, IL-6-deprivation-induced apoptosis is associated with increased expression of Bax.…”

“…In myeloma cells, various apoptotic stimuli 89,91,93 result in the caspase-3-mediated cleavage of Bcl-2 into the 23 kDa proapoptotic Bcl-2 form, which localizes to mitochondria and stimulates the release of cytochrome c into the cytosol. 57 Therefore, cleavage of Bcl-2 in myeloma appears to promote further caspase activation as part of a positive feedback loop.…”