title: XB130, a tissue-specific adaptor protein that couples the RET/PTC oncogenic kinase to PI 3-kinase pathway.
abstract: XB130 is a recently cloned 130 kDa-adaptor protein and Src kinase substrate, structurally similar to actin-filament-associated protein. Here we show that XB130 is predominantly expressed in the thyroid. Given that XB130 is a thyroid-specific tyrosine kinase substrate, we asked whether it is targeted by RET/PTC, a genetically rearranged, constitutively active, thyroid-specific tyrosine kinase that plays a pathogenic role in papillary thyroid cancer. RET/PTC induced robust tyrosine phosphorylation of XB130, which promoted its subsequent association with the p85alpha subunit of phosphatidylinositol 3-kinase (PI 3-kinase). We identified tyrosine 54 of XB130 as the major target of RET/PTC-mediated phosphorylation and a critical binding site for the SH2 domains of p85alpha. Importantly, downregulation of XB130 in TPC1 papillary thyroid cancer cells, harboring the RET/PTC1 kinase, strongly reduced Akt activity without altering ERK1/2 phosphorylation, and concomitantly inhibited cell-cycle progression and survival in suspension. In conclusion, XB130 is a novel substrate of the RET/PTC kinase that links RET/PTC signaling to PI 3-kinase activation, and thereby plays an important role in sustaining proliferation and survival of thyroid tumor cells.
authors.affiliation: Division of Cellular and Molecular Biology, Toronto General Research Institute, University Health Network, Toronto, Ontario, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Lodyga
authors.forename: V
authors.initials: V
authors.lastname: De Falco
authors.forename: X-H
authors.initials: XH
authors.lastname: Bai
authors.forename: A
authors.initials: A
authors.lastname: Kapus
authors.forename: R M
authors.initials: RM
authors.lastname: Melillo
authors.forename: M
authors.initials: M
authors.lastname: Santoro
authors.forename: M
authors.initials: M
authors.lastname: Liu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis; D015152:Blotting, Northern; D001973:Bromodeoxyuridine; D002291:Carcinoma, Papillary / Q000378:metabolism / Q000473:pathology; D049109:Cell Proliferation; D005434:Flow Cytometry; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D015398:Signal Transduction; D013964:Thyroid Neoplasms / Q000378:metabolism* / Q000473:pathology; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
chemical_list: C521126:AFAP1L2 protein, human; D048868:Adaptor Proteins, Signal Transducing; D015514:Oncogene Proteins, Fusion; D034741:RNA, Small Interfering; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; C093573:ret-PTC fusion oncoproteins, human; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D001973:Bromodeoxyuridine