Identifying opportunities for extracellular inhibition of ALK signaling

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Project Summary This proposal aims to resolve the molecular basis for activation of an atypical receptor tyrosine kinase (RTK) family – ALK. The ALK family consists of two receptors, ALK and LTK. ALKs are involved in neuronal development and, like other RTKs, are critically important in numerous cancers. In particular, ALK is the oncogenic driver in neuroblastoma – an aggressive and often lethal childhood cancer. Significantly, ALK receptors are distinct from the 19 other RTK families (56 receptors in total). Perhaps most prominent, they do not share the standard RTK architecture. Typically, RTKs are composed of multiple repeats of common domains (e.g. Ig, fibronectin, cysteine-rich) in their extracellular region. On the contrary, ALK’s extracellular ‘sensory’ region is highly enriched in glycines (termed the glycine rich domain, GRD). Only recently the ALK GRD has been shown to be a receiver for Augmentor (AUG) signals. Augmentors are small peptides with ~50 highly conserved amino acids that are sufficient for stimulating ALKs kinase activity. Given ALK’s remarkable molecular design, we expect ALK to have an equally distinguishable mechanism of receptor control – potentially broadening the paradigm for RTK regulation. Despite the importance of this receptor family in cancer, surprisingly little is known about how the receptor functions: 1) there are no reported structures for the GRD, AUG or their complex, and 2) it remains unknown how engagement of ligand translates into receptor kinase activity. The research proposed here focuses on understanding the molecular mechanism of ALK and LTK activation by AUG. With this foundation we hope to reveal how oncogenic dysregulation usurps the control mechanisms in place during normal development. Our goals over the next 10 years are: 1) To develop a complete mechanistic understanding of how ALK receptors perceive Augmentors and transmit their signals, 2) To understand how receptor mutations and matrix changes alter ALK signal transduction in cancer and 3) to determine if ALK’s unique structural and regulatory elements present novel targets for therapeutic interventions. We will study ligand-receptor complexes biochemically and with structural techniques, in order to understand in detail how AUG peptide binding leads to activation of ALKs in the signaling complex. In pursuing studies of ALK’s activation, we will investigate how preclinical monoclonal antibodies and discovered Fabs modulate and inhibit ALK function. In sum, our studies will provide necessary fundamental insight into signaling by this unique family of receptors that does not fit into the canonical RTK schema. Understanding the mechanism of receptor activation in this family will be crucial for designing and deploying effective inhibitors that will need to differ from those targeting other well-studied RTKs. In addition, our findings will reveal the signaling differences induced by common cancer mutations that will steer clinical strategies to approach ALK dependent diseases.