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Proteasome inhibitors differentially affect heat shock protein response in cancer cells
B T Ashok1, E Kim, A Mittelman
1Department of Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA.
Abstract:
The heat shock proteins (HSPs) are molecular chaperones that are emerging as biochemical regulators of cell growth, apoptosis, protein homeostasis and intracellular targeting of peptides. The immunological function of the HSPs are imparted by tissue specific peptides associated with the HSPs and as such autologous cancer derived HSP-peptide complexes are unique therapeutic agents. Since a majority of the intracellular peptides are generated by the proteasome, we examined the consequence of abrogation of proteasome function by proteasome inhibitors (PIs) such as Lactacystin, MG-132 and LLM on the growth and induction profile of HSP70 and gp96 using hematopoietic, lymphoid, and epithelial derived cancer cell lines. The effect on growth was measured by the XTT assay and induction of the heat shock proteins by western blot analyses using HSP70 and gp96 specific antibodies. Of the PIs tested, cancer cells, were most sensitive to MG-132 and least sensitive to LLM. MG-132 also showed a 10-fold differential sensitivity between estrogen receptor positive, (ER+) MCF-7 cells and negative cells, (ER-) MDA-MB-231. Induction of heat shock proteins, gp96 and HSP70 was, however, noted in response to LLM. Since LLM exhibited minimal cytotoxic effect, metabolic stress that results in induction of HSPs may not be translated in cell growth inhibition and that there may exist a cell-type specific phenomenon in the HSP response to PI mediated metabolic stress.
Insights
Proteasome inhibitors (PIs) affect cancer cell growth and heat shock protein (HSP) induction. MG-132 strongly inhibited growth, while LLM induced HSP70 and gp96 with minimal cytotoxicity, suggesting cell-type specific responses.
Area of Science:
- Molecular Biology
- Cancer Research
- Immunology
Background:
- Heat shock proteins (HSPs) are crucial molecular chaperones regulating cell growth, apoptosis, and protein homeostasis.
- Autologous cancer-derived HSP-peptide complexes show therapeutic potential due to their immunological functions.
- The proteasome generates intracellular peptides, making its function critical for HSP regulation.
Purpose of the Study:
- To investigate the impact of proteasome inhibitors (PIs) on cancer cell growth and heat shock protein (HSP70, gp96) induction.
- To compare the efficacy of different PIs (Lactacystin, MG-132, LLM) across various cancer cell types.
- To explore the relationship between proteasome inhibition, HSP induction, and cell growth inhibition.
Main Methods:
- Utilized XTT assay to measure the effect of PIs on cancer cell growth.
- Employed western blot analysis with specific antibodies to detect HSP70 and gp96 induction.
- Tested PIs on hematopoietic, lymphoid, and epithelial-derived cancer cell lines.
Main Results:
- MG-132 demonstrated the highest sensitivity in cancer cells, while LLM showed the least.
- MG-132 exhibited a 10-fold differential sensitivity between estrogen receptor-positive (ER+) and negative (ER-) breast cancer cells.
- LLM induced HSP70 and gp96 expression without significant cytotoxic effects, indicating a dissociation between HSP induction and growth inhibition.
Conclusions:
- Proteasome inhibition by PIs has varied effects on cancer cell growth and HSP induction.
- LLM's ability to induce HSPs with minimal cytotoxicity suggests a potential therapeutic window, but its efficacy may be cell-type specific.
- Metabolic stress induced by PIs does not always translate to cell growth inhibition, highlighting a complex, cell-type specific HSP response.