title: Negative regulation of Pim-1 protein kinase levels by the B56beta subunit of PP2A.
abstract: The Pim protein kinases are serine threonine protein kinases that regulate important cellular signaling pathway molecules, and enhance the ability of c-Myc to induce lymphomas. We demonstrate that a cascade of events controls the cellular levels of Pim. We find that overexpression of the protein phosphatase (PP) 2A catalytic subunit decreases the activity and protein levels of Pim-1. This effect is reversed by the application of okadaic acid, an inhibitor of PP2A, and is blocked by SV40 small T antigen that is known to disrupt B subunit binding to PP2A A and C subunits. Pim-1 can coimmunoprecipitate with the PP2A regulatory B subunit, B56beta, but not B56alpha, gamma, delta, epsilon or B55alpha. Using short hairpin RNA targeted at B56beta, we demonstrate that decreasing the level of B56beta increases the half-life of Pim-1 from 0.7 to 2.8 h, and decreases the ubiquitinylation level of Pim-1. We also find that Pin1, a prolyl-isomerase, is capable of binding Pim-1 and leads to a decrease in the protein level of Pim-1. On the basis of these observations, we hypothesize that phosphorylated Pim-1 binds Pin1 allowing the interaction of PP2A through B56beta. Dephosphorylation of Pim-1 then allows for ubiquitinylation and protein degradation of Pim-1.
authors.affiliation: Hollings Cancer Center at the Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.forename: H K
authors.initials: HK
authors.lastname: Arnold
authors.forename: M B
authors.initials: MB
authors.lastname: Lilly
authors.forename: R C
authors.initials: RC
authors.lastname: Sears
authors.forename: A S
authors.initials: AS
authors.lastname: Kraft
mesh_terms: D000818:Animals; D002460:Cell Line; D015536:Down-Regulation; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D019696:Peptidylprolyl Isomerase / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051573:Proto-Oncogene Proteins c-pim-1 / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D021122:Protein Subunits; D034741:RNA, Small Interfering; D025801:Ubiquitin; D051573:Proto-Oncogene Proteins c-pim-1; D010749:Phosphoprotein Phosphatases; C000606846:PIN1 protein, human; D019696:Peptidylprolyl Isomerase; C000606850:Pin1 protein, mouse