Evolutionary analyses guide selection of model systems to investigate proto-oncogene function in ALK and LTK

Model systems to investigate oncogene-driven cancer have played an essential role in the development of therapies for cancer. However, not all systems are appropriate for all therapeutic targets. Knowing where and when proto-oncogenes and their interactors originated in evolutionary history is key to understanding which organisms can serve as models. Here we investigate two tyrosine kinase receptors that underlie tumorigenesis in cancer: anaplastic lymphoma kinase (ALK) and leukocyte tyrosine kinase (LTK). In Drosophila melanogaster, Caenorhabitis elegans , and Homo sapiens , the discovery of putative ligands Jeb, Hen-1, and AUG has the potential to accelerate the development of novel therapeutics. However, homology of these ligands and receptors is unclear. We performed an exhaustive search for their homologs spanning the metazoan tree of life. Jeb and Hen-1 were restricted to species that diverged prior to the origin of all vertebrates. No non-vertebrate species had ligands orthologous to AUG. Instead, an ancestral receptor tyrosine kinase and AUG gene were present in early vertebrates and are still solitary in lamprey; we demonstrate that the early embryonic expression of AUG in lamprey parallels its expression in model mammal systems. The presence of ALK and LTK in jawed vertebrates is an evolutionary innovation, as is a previously unrecognized functional convergence within ALK and LTK occurring between actinopterygians and sarcopterygians. Our results provide the phylogenetic context necessary for the selection of model organisms that will provide informative investigations of the biology of these critically important tyrosine kinase receptors, enabling successful therapeutic development. Significance The anaplastic lymphoma kinase ALK can be oncogenically altered to become a driver of several malignancies, including non-small-cell lung cancer and anaplastic large-cell lymphomas. The development of therapeutics targeting this gene depend on the discovery of its interacting partner ligands in relevant model organisms. ALK is found across most major animal groups including mammals, fishes, and invertebrates. Correspondly, several candidate ligands for ALK and its duplicate LTK have been advanced by research in model species. However their homology to the human ligands and therefore their potential to guide therapeutic development is unknown. Our comparative evolutionary analysis revealed which model organisms had functional receptor-ligand pairings that are informative regarding the role of these genes in human tumorigenesis.