Direct stimulation of ERBB2 highlights a novel cytostatic signaling pathway driven by the receptor Thr⁷⁰¹...

Area of Science:

• Oncology
• Molecular Biology
• Cell Signaling

Background:

• ERBB2 (Epidermal Growth Factor Receptor 2) is a tyrosine kinase receptor implicated in various carcinomas when overexpressed.
• ERBB2 signaling is crucial in cancer, often partnering with other ERBB family members to enhance oncogenic signals via ERK and AKT activation.
• Studying ERBB2 signaling is challenging due to its ligand-less nature and the lack of selective activation methods.

Purpose of the Study:

• To investigate the signaling pathways activated by antibodies targeting the ERBB2 extracellular domain.
• To explore the role of ERBB2 dimerization status in its pro- or anti-oncogenic functions.

Main Methods:

• Utilized antibodies targeting different epitopes on the ERBB2 extracellular domain.
• Analyzed ERBB2 homodimer activation and downstream signaling events, including phosphorylation and de-phosphorylation.
• Investigated the involvement of PP2A Ser/Thr phosphatases and Cyclophilin A in the observed signaling cascade.

Main Results:

• Antibodies targeting ERBB2 extracellular domain induced ERBB2 homodimer activation.
• This activation triggered a unique cytostatic signaling cascade involving ERK-dependent ERBB2 Thr701 phosphorylation and AKT de-phosphorylation via PP2A phosphatases.
• Cyclophilin A was identified as a negative modulator of AKT de-phosphorylation, potentially competing with phosphatases for AKT binding.

Conclusions:

• Antibodies against ERBB2 extracellular domain act as agonists, promoting homodimerization and initiating anti-proliferative signaling.
• ERBB2's ultimate role (pro-oncogenic vs. anti-oncogenic) depends on its dimerization status: heterodimeric form is pro-oncogenic, while homodimeric form is anti-oncogenic.
• These findings offer new insights into ERBB2 signaling and potential therapeutic strategies targeting ERBB2 dimerization.