IKK1/2 protect human cells from TNF-mediated RIPK1-dependent apoptosis in an NF-κB-independent manner

Abstract

TNF signaling is directly linked to cancer development and progression. A broad range of tumor cells is able to evade cell death induced by TNF impairing the potential anti-cancer value of TNF in therapy. Although sensitizing cells to TNF-induced death therefore has great clinical implications, detailed mechanistic insights into TNF-mediated human cell death still remain unknown. Here, we analyzed human cells by applying CRISPR/Cas9n to generate cells deficient of IKK1, IKK2, IKK1/2 and RELA. Despite stimulation with TNF resulted in impaired NF-κB activation in all genotypes compared to wildtype cells, increased cell death was observable only in IKK1/2-double-deficient cells. Cell death could be detected by Caspase-3 activation and binding of Annexin V. TNF-induced programmed cell death in IKK1/2 cells was further shown to be mediated via RIPK1 in a predominantly apoptotic manner. Our findings demonstrate the IKK complex to protect from TNF-induced cell death in human cells independently to NF-κB RelA suggesting IKK1/2 to be highly promising targets for cancer therapy.

Subunit-Specific Role of NF-κB in Cancer

“…Constitutive IKK2 activation in intestinal epithelial cells was further demonstrated to induce intestinal tumors in mice [ 43 ]. These findings are in accordance with the profound overexpression of IKK2 observed in cancers of the large intestine ( Table 2 ) [ 38 ]. On the functional level, IKK2 was shown to directly promote the development of lung cancer in an inflammation-dependent manner triggered by tobacco smoke, which was abrogated by ablation of IKK2 in myeloid cells [ 44 ].…”

“…To investigate the role of the upstream regulators of NF-κB-signaling IKK1 and IKK2 in human cancers, we applied database mining using COSMIC to determine their levels of overexpression ( Table 2 ) [ 37 , 38 ].…”

“…Interestingly, IKK-mediated phosphorylation of IκB was shown to mainly depend on the IKK2 catalytic subunit of the IKK complex in mice [ 40 ], particularly in terms of prevention of apoptosis [ 41 ]. On the contrary, we recently observed TNF-α-mediated cell death only in human cells lacking IKK1 and IKK2 and not in single CRISPR/Cas-mediated IKK knockouts, suggesting that both IKK1 and IKK2 are required for functional TNF-signaling [ 38 ] ( Figure 2 ). However, knockout of IKK2 was shown to be associated with about a one-third reduced number of tumors in a colitis-associated cancer model.…”

Targeting IKKβ in Cancer: Challenges and Opportunities for the Therapeutic Utilisation of IKKβ Inhibitors

“…However, this isoform-specific delineation of function has turned out to be overly simplistic. Increasingly, it appears that in certain human cell-types IKKα may play a substantial role, alongside IKKβ, in activation of canonical NF-κB signalling, both under physiological or pathological conditions [ 133 , 134 , 135 ] and as an adaptive response to inhibition of IKKβ [ 136 ]. The relative contribution of IKKα and IKKβ to disease-associated canonical NF-κB signalling should therefore be assessed prior to any decisions to apply IKKβ-, IKKα- or dual-selective inhibitors.…”

The RAS‐PI3K‐AKT‐NF‐κB pathway transcriptionally regulates the expression of BCL2 family and IAP family genes and inhibits apoptosis in fibrous epulis

“…32,33 Moreover, it has been found that the activation of NF-κB suppresses caspase-8 activation through the induction of cIAP1 and cIAP2. 34,35 At this point, the Ras signaling pathway is connected to the anti-apoptosis pathway, which might be the major mechanism of fibrous epulis.…”