title: A critical role for the protein phosphatase 2A B'α regulatory subunit in dephosphorylation of sphingosine kinase 1.
abstract: Sphingosine kinase 1 (SK1) is an important regulator of cellular signalling that has gained recent attention as a potential target for anti-cancer therapies. SK1 activity, subcellular localization and oncogenic function are regulated by phosphorylation and dephosphorylation at Ser225. ERK1/2 have been identified as the protein kinases responsible for phosphorylation and activation of SK1. Conversely, dephosphorylation and deactivation of SK1 occurs by protein phosphatase 2A (PP2A). Active PP2A, however, is a heterotrimer, composed of tightly associated catalytic and structural subunits that can interact with an array of regulatory subunits, which are critical for determining holoenzyme substrate specificity and subcellular localization. Thus, PP2A represents a large family of holoenzyme complexes with different activities and diverse substrate specificities. To date the regulatory subunit essential for targeting PP2A to SK1 has remained undefined. Here, we demonstrate a critical role for the B'α (B56α/PR61α/PPP2R5A) regulatory subunit of PP2A in SK1 dephosphorylation. B'α was found to interact with the c-terminus of SK1, and reduce SK1 phosphorylation when overexpressed, while having no effect on upstream ERK1/2 activation. siRNA-mediated knockdown of B'α increased SK1 phosphorylation, activity and membrane localization of endogenous SK1. Furthermore, overexpression of B'α blocked agonist-induced translocation of SK1 to the plasma membrane and abrogated SK1-induced neoplastic transformation of NIH3T3 fibroblasts. Thus, the PP2A-B'α holoenzyme appears to function as an important endogenous regulator of SK1.
authors.affiliation: Molecular Signalling Laboratory, Centre for Cancer Biology, SA Pathology, Frome Road, Adelaide, South Australia 5000, Australia.
authors.forename: Melissa R
authors.initials: MR
authors.lastname: Pitman
authors.forename: Renae K
authors.initials: RK
authors.lastname: Barr
authors.forename: Briony L
authors.initials: BL
authors.lastname: Gliddon
authors.forename: Angus M
authors.initials: AM
authors.lastname: Magarey
authors.forename: Paul A B
authors.initials: PA
authors.lastname: Moretti
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Pitson
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology*; D002471:Cell Transformation, Neoplastic; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D021381:Protein Transport; D000099157:Sphingosine Kinase
chemical_list: D017853:Phosphotransferases (Alcohol Group Acceptor); D054648:Protein Phosphatase 2; D000099157:Sphingosine Kinase; C525690:PPP2R5A protein, human