UC San Diego

Chromosomal translocations have been a focus in human cancer research. Since the exponential advancement in sequencing technology, a number of actionable fusion proteins have emerged as oncogenic drivers, serving as potential targets for personalized treatments. As the second most common form of liver cancer, Intrahepatic Cholangiocarcinoma (ICC) is as a universally fatal disease with limited treatment options. Recent studies have revealed that translocation of Fibroblast Growth Factor Receptor 2 (FGFR2) to Periphilin 1 (PPHLN1) occurs in 16% ICC cases and FGFR2-PPHLN1 alone is sufficient in driving carcinogenesis. The clinically discovered FGFR2-PPHLN1 preserves the N-terminal structure of FGFR2 containing the extracellular domain, transmembrane domain, as well as an intact kinase domain; joined at the C-terminus of FGFR2 is the PPHLN1 moiety that contains a coiled-coil domain. In this study, we demonstrate that functions of FGFR2-PPHLN1 are achieved through constitutive receptor phosphorylation, thereby activating the canonical MAPK/ERK, JAK/STAT3 and PI3K/AKT pathways. Furthermore, we show that the introduction of an activating mutation in the kinase domain N549/550K on the fusion showed an even higher activation of these pathways, while the kinase dead K517/518R mutation completely abolished the signaling activities. These findings collectively reinforce the essential function of the kinase activity of the FGFR2 moiety. We also show that the oncogenicity of FGFR2-PPHLN1 is dependent upon the coiled-coil PPHLN1 domain. Finally, we determine the localization of this fusion protein and its entrance into the secretory pathway on its transforming ability by engineering a myristylation (Myr) signal, introducing a Myr G2A mutation, as well as deletion of the delta signal.