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: Augustas Pivoriūnas, Jūrate Savickiene, Grazina Treigyte, Virginijus Tunaitis, Rūta Navakauskiene, Karl-Eric Magnusson
• Journal: Molecular and cellular biochemistry (Mol Cell Biochem) Vol. 302 Issue 1-2 Pg. 9-18 (Aug 2007) ISSN: 0300-8177 [Print] Netherlands
• PMID: 17286201 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Chromones
• Cyclin-Dependent Kinase Inhibitor p21
• Morpholines
• Phosphoinositide-3 Kinase Inhibitors
• Sp1 Transcription Factor
• Tumor Suppressor Protein p53
• 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
• Protein Kinases
• MTOR protein, human
• TOR Serine-Threonine Kinases
• protein kinase C zeta
• Protein Kinase C
• Mitogen-Activated Protein Kinases
• Tetradecanoylphorbol Acetate
• Sirolimus

Topics

• Cell Line, Tumor
• Chromones (pharmacology)
• Cyclin-Dependent Kinase Inhibitor p21 (metabolism)
• Enzyme Activation (drug effects)
• Humans
• Leukemia (enzymology, pathology)
• Mitogen-Activated Protein Kinases (metabolism)
• Morpholines (pharmacology)
• Phosphatidylinositol 3-Kinases (metabolism)
• Phosphoinositide-3 Kinase Inhibitors
• Promoter Regions, Genetic (genetics)
• Protein Binding (drug effects)
• Protein Kinase C (metabolism)
• Protein Kinases (metabolism)
• Signal Transduction (drug effects)
• Sirolimus (pharmacology)
• Sp1 Transcription Factor (metabolism)
• TOR Serine-Threonine Kinases
• Tetradecanoylphorbol Acetate (pharmacology)
• Tumor Suppressor Protein p53 (metabolism)