Related Experiment Videos
Proteasome inhibitors induce apoptosis in glucocorticoid-resistant chronic lymphocytic leukemic lymphocytes
J Chandra1, I Niemer, J Gilbreath
1Departments of Cell Biology and Hematology, The University of Texas, M.D. Anderson Cancer Center, Houston, TX, USA.
Abstract:
Our previous work showed that the nuclear scaffold (NS) protease is required for apoptosis of both thymocytes and chronic lymphocytic leukemic (CLL) lymphocytes. Because partial sequencing of one of the subunits of the NS protease revealed homology to the proteasome, we tested the effects of classical proteasome inhibitors on apoptosis in CLL cells. Here we report that proteasome inhibition caused high levels of DNA fragmentation in all patients analyzed, including those resistant to glucocorticoids or nucleoside analogs, in vitro. Proteasome inhibitor-induced DNA fragmentation was associated with activation of caspase/ICE family cysteine protease(s) and was blocked by the caspase antagonist, zVADfmk. Analysis of the biochemical mechanisms involved showed that proteasome inhibition resulted in mitochondrial dysregulation leading to the release of cytochrome c and a drop in mitochondrial transmembrane potential (triangle upPsi). These changes were associated with inhibition of NFkappaB, a proteasome-regulated transcription factor that has been implicated in the suppression of apoptosis in other systems. Together, our results suggest that drugs that target the proteasome might be capable of bypassing resistance to conventional chemotherapy in CLL.
Insights
Proteasome inhibitors induce DNA fragmentation and apoptosis in chronic lymphocytic leukemia (CLL) cells, even those resistant to standard therapies. This suggests proteasome-targeted drugs may overcome chemotherapy resistance in CLL.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Nuclear scaffold (NS) protease is crucial for apoptosis in thymocytes and chronic lymphocytic leukemia (CLL) cells.
- NS protease subunits show homology to proteasomes, prompting investigation into proteasome inhibitor effects.
Purpose of the Study:
- To evaluate the efficacy of proteasome inhibitors in inducing apoptosis in CLL cells.
- To elucidate the molecular mechanisms underlying proteasome inhibitor-induced apoptosis in CLL.
Main Methods:
- Treatment of CLL cells with classical proteasome inhibitors in vitro.
- Assessment of DNA fragmentation, caspase activation, and mitochondrial parameters (cytochrome c release, transmembrane potential).
- Analysis of Nuclear Factor-kappaB (NF-kappaB) inhibition.
Main Results:
- Proteasome inhibition led to significant DNA fragmentation in all analyzed CLL patients, including those resistant to glucocorticoids or nucleoside analogs.
- DNA fragmentation was linked to caspase activation and blocked by a caspase antagonist (zVADfmk).
- Mechanisms involved mitochondrial dysregulation, cytochrome c release, decreased mitochondrial transmembrane potential, and NF-kappaB inhibition.
Conclusions:
- Proteasome inhibition effectively induces apoptosis in CLL cells, irrespective of conventional chemotherapy resistance.
- Mitochondrial pathways and NF-kappaB inhibition are key mediators of proteasome inhibitor-induced apoptosis.
- Targeting the proteasome represents a promising therapeutic strategy to overcome chemoresistance in CLL.