Proteasome Inhibitors Suppress ErbB Family Expression through HSP90-Mediated Lysosomal Degradation

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Lapatinib, a dual EGFR/HER2 tyrosine kinase inhibitor, is effective for HER2-positive breast cancer.
• Acquired resistance to lapatinib is a significant clinical challenge, necessitating alternative therapies.
• Proteasome inhibitors demonstrate potent anti-tumor activity in breast cancer cells.

Purpose of the Study:

• To investigate the efficacy of proteasome inhibitor bortezomib in overcoming lapatinib resistance in HER2-positive breast cancer.
• To elucidate the underlying molecular mechanisms by which proteasome inhibitors affect lapatinib-resistant cells.

Main Methods:

• Treatment of HER2-positive breast cancer cell lines and their lapatinib-resistant clones with various proteasome inhibitors (Bortezomib, MG132, PSI).
• Assessment of cell viability and proliferation following proteasome inhibitor treatment.
• Analysis of ErbB family expression at both transcriptional and translational levels.
• Investigation of the degradation pathway (lysosomal vs. proteasomal) and the role of heat shock protein 90 (HSP90).

Main Results:

• Proteasome inhibitors significantly inhibited the viability of both HER2-positive breast cancer cell lines and their lapatinib-resistant counterparts.
• Expression of the ErbB family (including EGFR and HER2) was downregulated at both transcriptional and translational levels by proteasome inhibitors.
• The downregulation of ErbB family members was mediated through lysosomal degradation in a manner dependent on heat shock protein 90 (HSP90).

Conclusions:

• Proteasome inhibitors represent a promising therapeutic strategy to overcome acquired lapatinib resistance in HER2-overexpressing breast cancer.
• Targeting the proteasome pathway can re-sensitize resistant cancer cells by reducing critical signaling proteins like ErbB family members.
• The HSP90-dependent lysosomal degradation pathway offers a novel mechanistic insight into overcoming drug resistance in breast cancer.