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Stressing the ubiquitin-proteasome system without 20S proteolytic inhibition selectively kills cervical cancer cells
Ravi K Anchoori1, Saeed R Khan, Thanasak Sueblinvong
1Department of Pathology, Johns Hopkins University, Baltimore, Maryland, United States of America.
Abstract:
Cervical cancer cells exhibit an increased requirement for ubiquitin-dependent protein degradation associated with an elevated metabolic turnover rate, and for specific signaling pathways, notably HPV E6-targeted degradation of p53 and PDZ proteins. Natural compounds with antioxidant properties including flavonoids and triterpenoids hold promise as anticancer agents by interfering with ubiquitin-dependent protein degradation. An increasing body of evidence indicates that their α-β unsaturated carbonyl system is the molecular determinant for inhibition of ubiquitin-mediated protein degradation up-stream of the catalytic sites of the 20S proteasome. Herein we report the identification and characterization of a new class of chalcone-based, potent and cell permeable chemical inhibitors of ubiquitin-dependent protein degradation, and a lead compound RAMB1. RAMB1 inhibits ubiquitin-dependent protein degradation without compromising the catalytic activities of the 20S proteasome, a mechanism distinct from that of Bortezomib. Treatment of cervical cancer cells with RAMB1 triggers unfolded protein responses, including aggresome formation and Hsp90 stabilization, and increases p53 steady state levels. RAMB1 treatment results in activation of lysosomal-dependent degradation pathways as a mechanism to compensate for increasing levels of poly-ubiquitin enriched toxic aggregates. Importantly, RAMB1 synergistically triggers cell death of cervical cancer cells when combined with the lysosome inhibitor Chloroquine.
Insights
New chalcone-based compounds, like RAMB1, effectively inhibit protein degradation in cervical cancer cells. This novel approach triggers cell death pathways, offering a promising new therapeutic strategy distinct from existing treatments.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Cervical cancer cells rely on ubiquitin-dependent protein degradation and specific signaling pathways, such as HPV E6-mediated degradation of p53.
- Natural compounds like flavonoids and triterpenoids show potential by inhibiting protein degradation, with their α-β unsaturated carbonyl system being key.
- The 20S proteasome is a target for inhibiting ubiquitin-mediated protein degradation.
Purpose of the Study:
- To identify and characterize novel chemical inhibitors of ubiquitin-dependent protein degradation.
- To investigate the mechanism of action of a lead compound, RAMB1, in cervical cancer cells.
- To explore the synergistic effects of RAMB1 with other therapeutic agents.
Main Methods:
- Identification and characterization of chalcone-based inhibitors.
- Assessment of RAMB1's effect on ubiquitin-dependent protein degradation and 20S proteasome activity.
- Analysis of cellular responses to RAMB1, including unfolded protein responses and protein aggregate formation.
- Evaluation of RAMB1's efficacy in combination with the lysosome inhibitor Chloroquine.
Main Results:
- A new class of potent, cell-permeable chalcone-based inhibitors of ubiquitin-dependent protein degradation was identified, with RAMB1 as the lead compound.
- RAMB1 inhibits protein degradation independently of the 20S proteasome's catalytic activities, differentiating it from Bortezomib.
- RAMB1 treatment induced unfolded protein responses (aggresome formation, Hsp90 stabilization) and increased p53 levels in cervical cancer cells.
- RAMB1 activated lysosomal degradation pathways to manage toxic protein aggregates and synergistically enhanced cell death when combined with Chloroquine.
Conclusions:
- RAMB1 represents a novel therapeutic agent targeting ubiquitin-dependent protein degradation in cervical cancer.
- RAMB1's distinct mechanism of action, inducing unfolded protein responses and activating lysosomal pathways, offers a new strategy for cancer therapy.
- The synergistic effect of RAMB1 with Chloroquine highlights a potential combination therapy for cervical cancer treatment.
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