Glioblastoma multiforme is one of the most common and lethal brain tumors. Many genetic and molecular changes have been described to occur in this type of brain cancer. Within this work, the role of the non-canonical IKK complex in glioblastoma multiforme was investigated. The non-canonical IKK complex is composed of the IKK-related kinases TBK1 and IKK&
#949; as well as adaptor proteins such as TANK, and is usually involved in the defense against viral and bacterial pathogens by the induction of type I interferon expression. This work shows, that TANK is dysregulated and over-expressed in a wide range of GBM patient tissue samples as well as glioma cell lines. Several mechanisms have been found to be responsible for the greatly varying protein levels of TANK. Various experimental approaches showed, that differences in the de novo transcription of the Tank gene and differential stabilities of TANK mRNAs account for the variances in TANK protein levels in glioma cell lines. The influence of members of the non-canonical IKK complex on cellular functions of glioma cell lines was then investigated after the knock-down of TANK or TBK1. Proliferation assays as well as MTT assays revealed a markedly reduced proliferation rate of some glioma cell lines after silencing of TANK or TBK1. The proliferation of other glioma cells was dependent on either TANK or TBK1. The proliferation of the minority of glioma cell lines was not affected by the knock-down of TANK or TBK1. Additionally, the ability of glioma cells to progress in cell cycle was found to be reduced upon TANK or TBK1 knock-down in those glioma cell lines where the knock-down caused a reduced proliferation ability. The migration ability was examined by wound-healing assays. These experiments showed that cells, which depend on TANK or TBK1 for proliferation, also need these proteins for cell migration. Usually those cellular functions are regulated by signaling pathways such as the Ras-Raf-MEK-ERK or PI3K-Akt signaling pathways. Therefore, the involvement of the non-canonical IKK complex in those signaling cascades was determined in this work. Akt as well as ERK1/2 have been shown to be constitutively phosphorylated and activated in some primary tissue samples of GBM or astrocytoma grade III patients as well as most of the glioma cell lines. The knock-down of either TANK or TBK1 as well as the inhibition of both IKK-related kinases (TBK1 and IKKepsilon) by BX795 had a repressive effect on those phosphorylations in some of the glioma cell lines. Thus, an alternative signaling path for the activation of proliferation and survival signals in glioblastoma multiforme was identified which is dependent on the cell line. A pharmacological approach was applied to study the complex signaling network in detail and revealed a negative feedback loop from MEK1/2 to Akt as well as a MEK-independent signaling pathway to activate ERK. Whether the MEK-independent TBK1/IKKepsilon-Akt signaling axis leads to the phosphorylation and activation of ERK directly or indirectly still needs to be clarified in the future. However, this TBK1/IKKepsilon-Akt-ERK pathway represents an alternative pathway to activate proliferation and survival signals in cancer, thus providing new opportunities in the discovery of treatments of glioblastoma multiforme.
Verknüpfung zu Publikationen oder weiteren Datensätzen
