Pathogenic HER3 dimerization domain mutations create a structural bias towards un-conventional EGFR-HER3 signalling axis in breast cancer

Among the EGFR family of receptors, HER3 is considered as a pseudo-kinase which primarily interacts with HER2 in presence of heregulin-1 beta. We identified two hotspot mutations i.e. G284R and D297Y and one double mutant HER2-S310F/HER3-G284R in breast cancer patients. Long term MDS (7.5 mu s) revealed that HER3-D297Y and HER2-S310F:HER3-G284R do not allow the interaction with HER2 as these mutations cause dramatic conformational changes in its flanking regions. This results in formation of an unstable HER2-WT:HER3-D297Y heterodimer, thereby abrogating the downstream signalling by AKT. We found that His228 and Ser300 of HER3-D297Y form stable interactions with Glu245 and Tyr270 of EGFR-WT, in the presence of either EGF or heregulin-1 beta. Applying TRIM-ing mediated direct knockdown of endogenous EGFR protein, specificity of the unconven-tional EGFR:HER3-D297Y interaction was validated. Due to this unusual ligand mediated interaction, cancer cells were found susceptible to EGFR targeted therapeutics i.e. Gefitinib and Erlotinib. Further, in TCGA analysis, BC patients harbouring HER3-D297Y mutation showed increased p-EGFR levels as compared to the patients harbouring HER3-WT and HER3-G284R mutations. For the first time, this comprehensive study showed the importance of specific hotspot mutations in HER3 dimerization domain can defy the Trastuzumab therapy, rather cells become susceptible to the EGFR inhibitors.

Automated summary

Among the EGFR family, HER3 acts as a pseudo-kinase and primarily interacts with HER2 in the presence of heregulin-1 beta. The hotspot mutations G284R and D297Y, as well as the double mutant HER2-S310F/HER3-G284R, were identified in breast cancer patients. These mutations cause conformational changes in the flanking regions of HER2, resulting in an unstable heterodimer and abrogating downstream signalling. The HER3-D297Y mutation forms stable interactions with EGFR-WT in the presence of EGF or heregulin-1 beta, making cancer cells susceptible to EGFR-targeted drugs.