title: Loss of PTEN expression does not contribute to PDK-1 activity and PKC activation-loop phosphorylation in Jurkat leukaemic T cells.
abstract: Unopposed PI3-kinase activity and 3'-phosphoinositide production in Jurkat T cells, due to a mutation in the PTEN tumour suppressor protein, results in deregulation of PH domain-containing proteins including the serine/threonine kinase PKB/Akt. In Jurkat cells, PKB/Akt is constitutively active and phosphorylated at the activation-loop residue (Thr308). 3'-phosphoinositide-dependent protein kinase-1 (PDK-1), an enzyme that also contains a PH domain, is thought to catalyse Thr308 phosphorylation of PKB/Akt in addition to other kinase families such as PKC isoforms. It is unknown however if the loss of PTEN in Jurkat cells also results in unregulated PDK-1 activity and whether such loss impacts on activation-loop phosphorylation of other putative PDK-1 substrates such as PKC. In this study we have addressed if loss of PTEN in Jurkat T cells affects PDK-1 catalytic activity and intracellular localisation. We demonstrate that reducing the level of 3'-phosphoinositides in Jurkat cells with pharmacological inhibitors of PI3-kinase or expression of PTEN does not affect PDK-1 activity, Ser241 phosphorylation or intracellular localisation. In support of this finding, we show that the levels of PKC activation-loop phosphorylation are unaffected by reductions in the levels of 3'-phosphoinositides. Instead, the dephosphorylation that occurs on PKB/Akt at Thr308 following reductions in 3'-phosphoinositides is dependent on PP2A-like phosphatase activity. Our finding that PDK-1 functions independently of 3'-phosphoinositides in T cells is also confirmed by studies in HuT-78 T cells, a PTEN-expressing cell line with undetectable levels of 3'-phosphoinositides. We conclude therefore that loss of PTEN expression in Jurkat T cells does not impact on the PDK-1/PKC pathway and that only a subset of kinases, such as PKB/Akt, are perturbed as a consequence PTEN loss.
authors.affiliation: Department of Clinical Medicine, Institute of Molecular Medicine, Trinity College, Dublin, Ireland. freeleym@tcd.ie
authors.forename: Michael
authors.initials: M
authors.lastname: Freeley
authors.forename: Jongsun
authors.initials: J
authors.lastname: Park
authors.forename: Keum-Jin
authors.initials: KJ
authors.lastname: Yang
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Wange
authors.forename: Yuri
authors.initials: Y
authors.lastname: Volkov
authors.forename: Dermot
authors.initials: D
authors.lastname: Kelleher
authors.forename: Aideen
authors.initials: A
authors.lastname: Long
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D015536:Down-Regulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D015458:Leukemia, T-Cell / Q000201:enzymology / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D019319:Okadaic Acid / Q000494:pharmacology; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D000077191:Wortmannin