p110 sEGFR, a 110-kD isoform of epidermal growth factor receptor, interacts with ErbB-2 in the presence of EGF

4505 The 110 kD isoform of epidermal growth factor receptor (p110 sEGFR) is an alternative-spliced variant of the 170 kD full-length epidermal growth factor receptor (EGFR/ErbB-1). This isoform has the same primary structure of the full-length receptor up to residue 603, thus having the same extracellular domain. The extracellular domain common to both proteins includes the ligand binding domain as well as residues involved in receptor dimerization with other members of the ErbB family: ErbB-2, ErbB-3 and ErbB-4. However, p110 sEGFR lacks the signal transduction capabilities of EGFR because the transmembrane, tyrosine kinase and regulatory domains are substituted by 78 unique amino acids in its c-terminal. Given that EGFR and p110 sEGFR have the same extracellular primary structure, we hypothesize that p110 sEGFR will interact with the same ligands and receptors as EGFR. To examine if p110 sEGFR interacts with ErbB-2, a co-immunoprecipitation assay was performed in the presence of the ligand of EGFR, epidermal growth factor (EGF). Equal amount of proteins in cell lysates from chinese hamster ovary (CHO) cells expressing p110 sEGFR or p170 EGFR, and SK-BR-3 cells were combined in the presence of EGF. After equilibration, the reactions were immunoprecipitated with either a monoclonal antibody against the extracellular domain of EGFR or with a polyclonal antibody against the intracellular domain of ErbB-2. The immunoprecipitated proteins were separated by SDS-PAGE and analyzed by immunoblot analysis. A band corresponding to ErbB-2 was observed by immunoblot analysis when p110 sEGFR was immunoprecipitated. Similarly, a band corresponding to p110 sEGFR was observed by immunoblot analysis when ErbB-2 was immunopreciptated. Together, these results suggest that p110 sEGFR interacts with ErbB-2. Future studies are directed to determine if this interaction is transduced to a cellular response. Supported by: NIH/NCI (CA73859 and CA8513), UPR-MSC MBRS RISE Program, NIH (COBRE P200RR016439).