title: Essential requirement for PP2A inhibition by the oncogenic receptor c-KIT suggests PP2A reactivation as a strategy to treat c-KIT+ cancers.
abstract: Oncogenic mutations of the receptor tyrosine kinase c-KIT play an important role in the pathogenesis of gastrointestinal stromal tumors, systemic mastocytosis, and some acute myeloid leukemias (AML). Although juxtamembrane mutations commonly detected in gastrointestinal stromal tumor are sensitive to tyrosine kinase inhibitors, the kinase domain mutations frequently encountered in systemic mastocytosis and AML confer resistance and are largely unresponsive to targeted inhibition by the existing agent imatinib. In this study, we show that myeloid cells expressing activated c-KIT mutants that are imatinib sensitive (V560G) or imatinib resistant (D816V) can inhibit the tumor suppressor activity of protein phosphatase 2A (PP2A). This effect was associated with the reduced expression of PP2A structural (A) and regulatory subunits (B55alpha, B56alpha, B56gamma, and B56delta). Overexpression of PP2A-Aalpha in D816V c-KIT cells induced apoptosis and inhibited proliferation. In addition, pharmacologic activation of PP2A by FTY720 reduced proliferation, inhibited clonogenic potential, and induced apoptosis of mutant c-KIT(+) cells, while having no effect on wild-type c-KIT cells or empty vector controls. FTY720 treatment caused the dephosphorylation of the D816V c-KIT receptor and its downstream signaling targets pAkt, pSTAT5, and pERK1/2. Additionally, in vivo administration of FTY720 delayed the growth of V560G and D816V c-KIT tumors, inhibited splenic and bone marrow infiltration, and prolonged survival. Our findings show that PP2A inhibition is essential for c-KIT-mediated tumorigenesis, and that reactivating PP2A may offer an attractive strategy to treat drug-resistant c-KIT(+) cancers.
authors.affiliation: School of Biomedical Sciences, University of Newcastle, Callaghan, New South Wales, Australia.
authors.forename: Kathryn G
authors.initials: KG
authors.lastname: Roberts
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Smith
authors.forename: Fiona
authors.initials: F
authors.lastname: McDougall
authors.forename: Helen
authors.initials: H
authors.lastname: Carpenter
authors.forename: Martin
authors.initials: M
authors.lastname: Horan
authors.forename: Paolo
authors.initials: P
authors.lastname: Neviani
authors.forename: Jason A
authors.initials: JA
authors.lastname: Powell
authors.forename: Daniel
authors.initials: D
authors.lastname: Thomas
authors.forename: Mark A
authors.initials: MA
authors.lastname: Guthridge
authors.forename: Danilo
authors.initials: D
authors.lastname: Perrotti
authors.forename: Alistair T R
authors.initials: AT
authors.lastname: Sim
authors.forename: Leonie K
authors.initials: LK
authors.lastname: Ashman
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Verrills
mesh_terms: D000368:Aged; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D005260:Female; D000068876:Fingolimod Hydrochloride; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000201:enzymology*; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D010766:Phosphorylation; D011409:Propylene Glycols / Q000494:pharmacology; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013110:Sphingosine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D011409:Propylene Glycols; D021122:Protein Subunits; D019009:Proto-Oncogene Proteins c-kit; D054648:Protein Phosphatase 2; D000068876:Fingolimod Hydrochloride; D013110:Sphingosine