Clustering and a conformational switch drive activation of the mammalian receptor tyrosine kinase ROS1

Area of Science:

• Molecular Biology
• Structural Biology
• Oncology

Background:

• Receptor tyrosine kinases (RTKs) regulate cellular signaling and are frequently dysregulated in cancer.
• ROS1, an orphan RTK, is implicated in various tumors, but its activation mechanism and targeted therapies are lacking.

Purpose of the Study:

• To elucidate the activation mechanism of the mammalian ROS1 receptor.
• To characterize the structural basis of ROS1 activation by its ligand NELL2.
• To develop novel therapeutic strategies targeting ROS1 in cancer.

Main Methods:

• Cryo-electron microscopy (Cryo-EM) to determine structures of ROS1 in different states.
• Biochemical assays to characterize receptor activation and ligand binding.
• Development and testing of monoclonal antibodies targeting ROS1.

Main Results:

• Cryo-EM structures revealed that trimeric NELL2 binding induces ROS1 clustering and a conformational switch relieving autoinhibition.
• ROS1 activation requires both receptor clustering and the conformational switch induced by NELL2.
• Evolutionary comparison with dROS1 highlights divergent regulatory mechanisms in conserved RTKs.
• Monoclonal antibodies were developed that block NELL2 binding or trap ROS1 in an inactive state, potently suppressing ROS1 signaling.

Conclusions:

• NELL2 activates ROS1 through a unique mechanism involving receptor clustering and conformational changes.
• These findings reveal a novel mode of RTK regulation.
• The developed antibodies represent distinct therapeutic classes for ROS1-driven cancers, establishing a framework for targeted treatment.