ERBIN

Erbin (ERBB2IP) functions as a membrane-associated scaffolding protein that supports HER2/ErbB2 signaling in HER2-positive breast cancer cells [PMID:bio_10.1101_2024.10.01.616146]. In SKBR3 cells, Erbin physically interacts with NHERF1, Ezrin, and HER2 within actin-rich membrane protrusions, and its depletion disrupts assembly of a HER2/NHERF1/Ezrin/HSP90 complex, reducing HER2 stability, membrane retention, and downstream signaling; reciprocally, inhibition of Ezrin or knockdown of NHERF1 disrupts Erbin's interaction with HER2, placing Erbin within an interdependent scaffolding complex [PMID:bio_10.1101_2024.10.01.616146]. Erbin engages its targets through a defined PDZ-domain binding site amenable to competitive peptide displacement [PMID:bio_10.1101_2025.10.28.685015]. Beyond these scaffolding interactions, no further mechanistic detail has been characterized in the available corpus.

1. 2024 Medium

   Established that Erbin acts as a scaffold sustaining HER2 signaling, by showing it bridges HER2 to an NHERF1/Ezrin/HSP90 complex at the membrane rather than acting as an isolated binding partner.

   Evidence Co-immunoprecipitation, siRNA knockdown with HER2 signaling readout, and localization in SKBR3 breast cancer cells (preprint)

   PMID:bio_10.1101_2024.10.01.616146

   Open questions at the time

   • Single lab preprint without peer review or independent replication
   • Direct versus indirect nature of each pairwise interaction within the complex not resolved
   • Mechanism by which the complex stabilizes HER2 at the membrane not defined
2. 2025 Low

   Characterized the Erbin PDZ domain as a discrete ligand-binding module engaging targets via a competitively displaceable site, repurposed for biosensor design.

   Evidence In vitro competitive binding, live-cell fluorescent biosensor imaging, and FACS using engineered NanoBlock sensors based on the Erbin PDZ domain (preprint)

   PMID:bio_10.1101_2025.10.28.685015

   Open questions at the time

   • Proof-of-concept tool paper; binding-site characterization is indirect and not validated by mutagenesis of the endogenous Erbin PDZ domain
   • Does not identify the physiological PDZ ligand in the HER2 scaffolding context
   • Single preprint

• Whether Erbin's PDZ-mediated binding is the direct molecular contact within the HER2/NHERF1/Ezrin/HSP90 complex, and the broader physiological roles of Erbin beyond HER2-positive breast cancer, remain unresolved.
• No structural model of the Erbin-HER2 or Erbin-NHERF1 interface
• No peer-reviewed validation of the scaffolding model
• Physiological substrates/ligands of the PDZ domain in vivo unidentified