ABSTRACT
Despite the progress made in targeted anticancer therapies in recent years, challenges remain. The identification of new potential targets will ensure that the arsenal of cancer therapies continues to expand. FAM83B was recently discovered in a forward genetic screen for novel oncogenes that drive human mammary epithelial cell (HMEC) transformation. We report here that elevated FAM83B expression increases Phospholipase D (PLD) activity, and that suppression of PLD1 activity prevents FAM83B-mediated transformation. The increased PLD activity is engaged by hyperactivation of epidermal growth factor receptor (EGFR), which is regulated by an interaction involving FAM83B and EGFR. Preventing the FAM83B/EGFR interaction by site-directed mutation of lysine 230 of FAM83B suppressed PLD activity and MAPK signaling. Furthermore, ablation of FAM83B expression from breast cancer cells inhibited EGFR phosphorylation and suppressed cell proliferation. We propose that understanding the mechanism of FAM83B-mediated transformation will provide a foundation for future therapies aimed at targeting its function as an intermediary in EGFR, MAPK and mTOR activation.
Subject(s)
ErbB Receptors/metabolism , Neoplasm Proteins/metabolism , Oncogenes/genetics , Phospholipase D/metabolism , Breast Neoplasms/enzymology , Breast Neoplasms/genetics , Breast Neoplasms/metabolism , Cell Growth Processes/physiology , Cell Line , Cell Transformation, Neoplastic/genetics , Cell Transformation, Neoplastic/metabolism , Enzyme Activation , Epithelial Cells/metabolism , ErbB Receptors/genetics , Female , Humans , Mitogen-Activated Protein Kinases/genetics , Mitogen-Activated Protein Kinases/metabolism , Neoplasm Proteins/genetics , Phospholipase D/genetics , Phosphorylation , Signal TransductionABSTRACT
Signal transducer and activator of transcription-5 (STAT5) is a critical transcription factor for normal hematopoiesis and its sustained activation is associated with hematologic malignancy. A persistently active mutant of STAT5 (STAT5a(S711F)) associates with Grb2-associated binding protein 2 (Gab2) in myeloid leukemias and promotes growth in vitro through AKT activation. Here we have retrovirally transduced wild-type or Gab2(-/-) mouse bone marrow cells expressing STAT5a(S711F) and transplanted into irradiated recipient mice to test an in vivo myeloproliferative disease model. To target Gab2-independent AKT/mTOR activation, we treated wild-type mice separately with rapamycin. In either case, mice lacking Gab2 or treated with rapamycin showed attenuated myeloid hyperplasia and modestly improved survival, but the effects were not cytotoxic and were reversible. To improve on this approach, we combined in vitro targeting of STAT5-mediated AKT/mTOR using rapamycin with inhibition of the STAT5 direct target genes bcl-2 and bcl-X(L) using ABT-737. Striking synergy with both drugs was observed in mouse BaF3 cells expressing STAT5a(S711F), TEL-JAK2 or BCR-ABL and in the relatively single agent-resistant human BCR-ABL-positive K562 cell line. Therefore, targeting distinct STAT5-mediated survival signals, for example, bcl-2/bcl-X(L) and AKT/mTOR may be an effective therapeutic approach for human myeloproliferative neoplasms.
