title: PI 3-K signaling pathway suppresses PMA-induced expression of p21WAF1/Cip1 in human leukemia cells.
abstract: Despite the understanding of the importance of phosphoinositide 3-kinase (PI 3-K) signaling pathway in the regulation of cellular proliferation, little is known about its role during phorbol 12-myristate 13-acetate (PMA)-induced differentiation in human leukemia cells. Here, we report a novel finding that PI 3-K inhibition by LY294002 significantly increases p21WAF1/Cip1 expression in PMA-stimulated human leukemia cells NB4 and THP1. LY294002 potentiated expression of p21WAF1/Cip1 via a p53-independent mechanism and did not affect mitogen activated protein kinase (MAPK) activation. Electrophoretic mobility shift (EMSA) experiments revealed that blocking of PI 3-K was associated with increased binding of transcription factor Sp1 to the PMA-responsive sites on the p21WAF1/Cip1 promoter. Pretreatment with rapamycin, an inhibitor of mTOR kinase, decreased the expression of p21WAF1/Cip1 protein in PMA-stimulated NB4 cells. The level of PMA-induced p21WAF1/Cip1 protein expression was lower in NB4 cells overexpressing wild type protein kinase C zeta (PKC zeta) compared to those transfected with empty vector or with kinase inactive PKC zeta. Sp1 binding to the p21WAF1/Cip1 promoter was completely lost in a wild type PKC zeta overexpressing and PMA-stimulated NB4 cells. We demonstrate that PI 3-K signaling pathway suppresses PMA-induced expression of p21WAF1/Cip1 in human leukemia cells, and that this effect is partly mediated by PKC zeta.
authors.affiliation: Department of Experimental Research, Institute of Experimental and Clinical Medicine, Zygimantu 9, 01102, Vilnius, Lithuania. augustas.pivoriunas@ekmi.vu.lt
authors.forename: Augustas
authors.initials: A
authors.lastname: Pivoriūnas
authors.forename: Jūrate
authors.initials: J
authors.lastname: Savickiene
authors.forename: Grazina
authors.initials: G
authors.lastname: Treigyte
authors.forename: Virginijus
authors.initials: V
authors.lastname: Tunaitis
authors.forename: Rūta
authors.initials: R
authors.lastname: Navakauskiene
authors.forename: Karl-Eric
authors.initials: KE
authors.lastname: Magnusson
mesh_terms: D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007938:Leukemia / Q000201:enzymology* / Q000473:pathology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D016329:Sp1 Transcription Factor / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000099221:Protein Kinase C zeta
chemical_list: D002867:Chromones; D050759:Cyclin-Dependent Kinase Inhibitor p21; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D011494:Protein Kinases; D020123:Sirolimus; D016329:Sp1 Transcription Factor; D058570:TOR Serine-Threonine Kinases; D013755:Tetradecanoylphorbol Acetate; D016159:Tumor Suppressor Protein p53; D000099221:Protein Kinase C zeta; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C546842:MTOR protein, human