Cell Type-specific Expression of the IκB Kinases Determines the Significance of Phosphatidylinositol 3-Kinase/Akt Signaling to NF-κB Activation

Jason A. Gustin, Osman N. Ozes, Hakan Akca, Roxana Pincheira, Lindsey D. Mayo, Qiutang Li, Javier Rivera Guzman, Chandrashekhar K. Korgaonkar, David B. Donner
2003 Journal of Biological Chemistry  
Phosphatidylinositol (PI) 3-kinase/Akt signaling activates NF-B through pleiotropic, cell type-specific mechanisms. This study investigated the significance of PI 3-kinase/Akt signaling to tumor necrosis factor (TNF)-induced NF-B activation in transformed, immortalized, and primary cells. Pharmacological inhibition of PI 3-kinase blocked TNF-induced NF-B DNA binding in the 293 line of embryonic kidney cells, partially affected binding in MCF-7 breast cancer cells, HeLa and ME-180 cervical
more » ... -180 cervical carcinoma cells, and NIH 3T3 cells but was without significant effect in H1299 and human umbilical vein endothelial cells, cell types in which TNF activated Akt. NF-B is retained in the cytoplasm by inhibitory proteins, IBs, which are phosphorylated and targeted for degradation by IB kinases (IKK␣ and IKK␤). Expression and the ratios of IKK␣ and IKK␤, which homo-and heterodimerize, varied among cell types. Cells with a high proportion of IKK␣ (the IKK kinase activated by Akt) to IKK␤ were most sensitive to PI 3-kinase inhibitors. Consequently, transient expression of IKK␤ diminished the capacity of the inhibitors to block NF-B DNA binding in 293 cells. Also, inhibitors of PI 3-kinase blocked NF-B DNA binding in Ikk␤؊/؊ but not Ikk␣؊/؊ or wild-type cells in which the ratio of IKK␣ to IKK␤ is low. Thus, noncoordinate expression of IB kinases plays a role in determining the cell type-specific role of Akt in NF-B activation. The NF-B family of transcription factors plays a fundamental role in development, maintenance of the immune system, and cell viability (1-3). NF-B is composed of heterodimers of DNA-binding subunits (p50 and p52) and subunits with transcriptional activity (p65 (RelA), RelB, or c-Rel). In unstimulated cells, binary complexes of these subunits are restricted to the cytoplasm by interaction with members of a family of inhibitory proteins, inhibitors of B (IBs) 1 (4, 5). In response to
doi:10.1074/jbc.m306976200 pmid:14585846 fatcat:47zx7cmvsngvfleppf552xm75m