Independent activation of Akt and NF‐kappaB pathways and their role in resistance to TNF‐α mediated cytotoxicity in gliomas

Abstract

Tumor associated macrophages (TAMs) constitute a substantial mass in gliomas. The activated macrophages secrete various cytokines that affect diverse functions of tumors. The aim of this study was to elucidate the role of Akt and NF-kappaB pathways in resistance to TNF-alpha mediated cell death in human gliomas using monolayers and multicellular spheroids (MCS) as in vitro models. Akt and NF-kappaB are constitutively expressed and intimately involved in progression of gliomas. The activation of these pathways also renders the tumors resistant to conventional treatments including chemotherapy. While PI3K/Akt is shown to regulate the NF-kappaB activation in diverse systems, other studies place NF-kappaB upstream of Akt activation. Using a stable IkappaBalpha mutant LN-18 cell line and pharmacological inhibitors to PI3K/Akt (LY294002) and Akt (Akt2), we provide evidence that Akt and NF-kappaB are activated independently on stimulation with TNF-alpha and both the pathways contribute towards resistance to TNF-alpha mediated cell death. TNF-alpha-induced NF-kappaB activation independent of PI3K/Akt pathway was also confirmed in human glioma cell lines-LN-229 and U373MG. We also show that NF-kappaB and Akt are activated during spheroidogenesis and their expression is further enhanced on stimulation with TNF-alpha implicating their involvement in resistance to cell death. The findings thus underscore the relevance of spheroids as appropriate in vitro models for studying the signaling pathways in drug induced resistance.

NF‐kappa B is required for the development of tumor spheroids

“…Supporting our data, a previous report has shown that NF-kB is activated in glioma spheroids, becoming relatively resistant to TNF-a [Sudheerkumar et al, 2008]. Although not studied, IAPs could mediate this resistance, since it is well known that they can also repress apoptosis induced by TNF-a [Uren et al, 1996].…”

Genistein suppresses tumor necrosis factor α-induced inflammation via modulating reactive oxygen species/Akt/nuclear factor ΚB and adenosine monophosphate-activated protein kinase signal pathways in human synoviocyte MH7A cells

“…However, the involvement of the PI3K/Akt pathway in NF-κB activation is a cell- and tissue-specific event. It has been confirmed that TNF-α-induced NF-κB activation is independent of the PI3K/Akt pathway in human glioma cell lines 23. Shao et al suggested that radiation-induced NF-κB activation is independent of Akt activation in parental cancer cells 24.…”

Nicotine-induced survival signaling in lung cancer cells is dependent on their p53 status while its down-regulation by curcumin is independent

“…Despite studies reporting the interdependence and cross-talk between Akt and NF-κB [26], phosphorylation of Akt by PI3K pathway independent of NF-κB is also well evidenced [30-33]. Similarly, while several reports strongly correlate the involvement of NF-κB in Cyclin D1 regulation [30], there are reports which clearly demonstrate the transcription of Cyclin D1, independent of NF-κB, in cell lines including A549 [32,4]. The protein level expression of Cyclin D1 in A549 was low compared to that in H1299 cells at all the concentrations studied (Fig.…”