title: Mammalian target of rapamycin (mTOR) and S6 kinase down-regulate phospholipase D2 basal expression and function.
abstract: The mammalian target of rapamycin (mTOR) and S6 kinase (S6K) pathway is essential for cell differentiation, growth, and survival. Phospholipase D2 (PLD2) plays a key role in mTOR/S6K mitogenic signaling. However, the impact of PLD on mTOR/S6K gene expression is not known. Here we show that interleukin-8 (IL-8) increases mRNA expression levels for PLD2, mTOR, and S6K, with PLD2 preceding mTOR/S6K in time. Silencing of PLD2 gene expression abrogated IL-8-induced mTOR/S6K mRNA expression, whereas silencing of mTOR or S6K gene expression resulted in large (>3-fold and >5-fold, respectively) increased levels of PLD2 RNA, which was paralleled by increases in protein expression and lipase activity. Treatment of cells with 0.5 nm rapamycin induced a similar trend. These results suggest that, under basal conditions, PLD2 expression and concomitant activity is negatively regulated by the mTOR/S6K signaling pathway. Down-regulation of PLD2 was confirmed in differentiated HL-60 leukocytes overexpressing an mTOR-wild type, but not an mTOR kinase-dead construct. At the cellular level, overexpression of mTOR-wild type resulted in lower basal cell migration, which was reversed by treatment with IL-8. We propose that IL-8 reverses an mTOR/S6K-led down-regulation of PLD2 expression and enables PLD2 to fully function as a facilitator for cell migration.
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University School of Medicine, Dayton, Ohio 45435, USA.
authors.forename: Farnaz
authors.initials: F
authors.lastname: Tabatabaian
authors.forename: Kevin
authors.initials: K
authors.lastname: Dougherty
authors.forename: Mauricio
authors.initials: M
authors.lastname: Di Fulvio
authors.forename: Julian
authors.initials: J
authors.lastname: Gomez-Cambronero
mesh_terms: D000818:Animals; D019556:COS Cells; D002454:Cell Differentiation; D002522:Chlorocebus aethiops; D015971:Gene Expression Regulation, Enzymologic; D020868:Gene Silencing; D018922:HL-60 Cells; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008049:Lipase / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism; D010739:Phospholipase D / Q000096:biosynthesis*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000096:biosynthesis*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
chemical_list: D016209:Interleukin-8; D047908:Intracellular Signaling Peptides and Proteins; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D008049:Lipase; C105606:phospholipase D2; D010739:Phospholipase D; D020123:Sirolimus
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