View Program - 63rd Annual Drosophila Research Conference

The EGFR/ErbB family of receptor tyrosine kinases function in numerous developmental contexts and their dysregulation has been linked to various types of cancers. With receptor activation underlying their roles in cancer, molecules that inhibit EGFR/ErbB activity provide potential therapeutic avenues. One such inhibitory molecule is Kekkon1 (Kek1), a member of the Drosophila family of leucine-rich repeats (LRR) and immunoglobulin domain (Ig) containing transmembrane molecules. Kek1’s extracellular LRRs, along with Domain V of the Drosophila receptor, are critical for binding. It has also been reported that Kek1 is able bind in a cross-species fashion the mammalian ErbB receptors. However, while the extracellular regions of both mammalian and Drosophila receptors contain Domains I-IV, mammalian receptors lack Domain V. Therefore, to clarify the interaction of Kek1 with the receptors and elucidate the role of Domain V, we sought to further define the mechanism of binding and inhibition. Using an ELISA-based assay, a battery of wild-type, chimeras, and variants of the Drosophila and human receptors were assessed for interactions with Kek1. Our results demonstrate that Kek1 binds the Drosophila and not the human receptors, and that specificity occurs principally through Domain V, which is absent in the human receptors. Our results also implicate differences between Domain IV in the Drosophila and human receptors in further restricting Kek1’s interaction to the Drosophila receptor. Mechanistically, our results support a model in which Kek1 binds to Domain V on the dimerization and not the ligand-binding interface of the Drosophila receptor, thereby inhibiting receptor dimerization and consequent activation. Our work provides deeper insight to the structural requirements underlying Kek1’s interaction with dEGFR and has clear implications for the proposed use of Kek1 as a therapeutic.

Kek1 inhibition of EGFR signaling: a Domain V mediated event