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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2019)

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.

    Cover page: Oncogenic Fusion Protein FGFR2-PPHLN1 Functions through Ligand-independent Constitutive Kinase Activation, Membrane Trafficking and Membrane Localization
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2019)
    Considerable advances have been made in our understanding of the molecular basis of hematopoietic cancers. The discovery of the BCR-ABL fusion protein over 50 years ago has brought about a new era of therapeutic progress and overall improvement in patient care, mainly due to the development and use of personalized medicine and tyrosine kinase inhibitors (TKIs). However, since the detection of BCR-ABL, BCR has been identified as a commonly occurring fusion partner in hematopoietic disorders. BCR has been discovered fused to additional tyrosine kinases, including: Fibroblast Growth Factor Receptor 1 (FGFR1), Platelet-derived Growth Factor Receptor Alpha (PDGFRA), Ret Proto-Oncogene (RET), and Janus Kinase 2 (JAK2). While BCR translocations are infrequent in hematopoietic malignancies, clinical evidence suggests that patients who harbor these mutations benefit from TKIs and additional personalized therapies. The improvement of further methodologies for characterization of these fusions is crucial to determine a patient's treatment regimen, and optimal outcome. However, potential relapse and drug resistance among patients' highlights the need for additional treatment options and further understanding of these oncogenic fusion proteins. This review explores the mechanisms behind cancer progression of these BCR oncogenic fusion proteins, comparing their similarities and differences, examining the significance of BCR as a partner gene, and discussing current treatment options for these translocation-induced hematopoietic malignancies.
      Cover page: BCR: a promiscuous fusion partner in hematopoietic disorders
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2020)

      Aim of study

      Chromosomal translocations such as t(10;12)(q26,q12) are associated with intrahepatic cholangiocarcinoma, a universally fatal category of liver cancer. This translocation creates the oncogenic fusion protein of Fibroblast Growth Factor Receptor 2 joined to Periphilin 1. The aims of this study were to identify significant features required for biological activation, analyze the activation of downstream signaling pathways, and examine the efficacy of the TKIs BGJ398 and TAS-120, and of the MEK inhibitor Trametinib.

      Methods

      These studies examined FGFR2-PPHLN1 proteins containing a kinase-dead, kinase-activated, or WT kinase domain in comparison with analogous FGFR2 proteins. Biological activity was assayed using soft agar colony formation in epithelial RIE-1 cells and focus assays in NIH3T3 cells. The MAPK/ERK, JAK/STAT3 and PI3K/AKT signaling pathways were examined for activation. Membrane association was analyzed by indirect immunofluorescence comparing proteins altered by deletion of the signal peptide, or by addition of a myristylation signal.

      Results

      Biological activity of FGFR2-PPHLN1 required an active FGFR2-derived tyrosine kinase domain, and a dimerization domain contributed by PPHLN1. Strong activation of canonical MAPK/ERK, JAK/STAT3 and PI3K/AKT signaling pathways was observed. The efficacy of the tyrosine kinase inhibitors BGJ398 and TAS-120 was examined individually and combinatorially with the MEK inhibitor Trametinib; heterogeneous responses were observed in a mutation-specific manner. A requirement for membrane localization of the fusion protein was also demonstrated.

      Concluding statement

      Our study collectively demonstrates the potent transforming potential of FGFR2-PPHLN1 in driving cellular proliferation. We discuss the importance of sequencing-based, mutation-specific personalized therapeutics in treating FGFR2 fusion-positive intrahepatic cholangiocarcinoma.
        Cover page: Oncogenic fusion protein FGFR2-PPHLN1: Requirements for biological activation, and efficacy of inhibitors
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