Epidermal growth factor activation of NF-κB is mediated through IκBα degradation and intracellular free calcium

Abstract

The transcription factor NF-kB is normally sequestered in the cytoplasm by its inhibitory subunit IkB. Most extracellular signals activate NF-kB through a mechanism involving the phosphorylation and proteasomedependent degradation of IkB. EGF activates NF-kB in A-431 carcinoma cells, which overexpress EGF receptors and in mouse embryo ®broblasts, which have a normal complement of receptors. Supershift experiments indicate that the NF-kB complexes induced by EGF are composed of p50/p50 homodimers and p65/p50 heterodimers, but not c-rel. EGF stimulation enhances the degradation of IkBa, but not IkBb nor an N-terminal deletion mutant of IkBa. Treatment of cells with a proteasome inhibitor, such as ALLN or MG132, blocks EGF-mediated NF-kB activation, indicating that EGFinduced NF-kB activation requires proteasome-dependent IkB degradation. Also, Bapta A/M (a cell-permeable chelator of intracellular calcium) blocks EGF-induced NF-kB activation and IkBa degradation, suggesting a requirement of intracellular free Ca 2+ for this growth factor response. Protein kinase C inhibition, in contrast, did not in¯uence EGF activation of NF-kB.

EGFR and NF-κB: partners in cancer

“…The family of NF-kB transcription factors are typically activated by proinflammatory cytokines such as tumor necrosis factor (TNF)-a or IL1b, as well as by Toll-like receptor (TLR) ligands through extremely well defined signaling cascades (Box 2) [29]. Early studies demonstrated that EGF triggers NF-kB activation through the proteasome-mediated degradation of the inhibitory molecule IkBa in estrogen receptor ERanegative breast cancer cells and in lung cancer-derived cells [30,31]. Heregulin also triggers NF-kB activation through the IKK complex in ERa-negative and ERBB2-positive breast cancer cells [32].…”

The nuclear factor kappa B (NF-κB): A potential therapeutic target for estrogen receptor negative breast cancers

“…This could be correlated with the increased level of epidermal growth factor family receptors (EGFR) in ERϪ cells (3,7,(8)(9)(10). Our previous results demonstrated that activation of NF-B is a downstream consequence of EGF-EGFR interaction (7).…”

ABINs inhibit EGF receptor-mediated NF-κB activation and growth of EGF receptor-overexpressing tumour cells

“…ABIN-mediated inhibition of constitutive NF-kB activity in EGFR-overexpressing A431 and DU145 tumour cells reduces their proliferation We next investigated whether ABINs also affect NF-kB activity in A431 epidermoid and DU145 prostate carcinoma cell lines, which rely on endogenous EGFR overexpression and signalling to sustain their growth and proliferation (Fan et al, 1993;Peng et al, 1996), and which already show high constitutive NF-kB activity (Sun and Carpenter, 1998;Gasparian et al, 2002;Meeran and Katiyar, 2008). As a result, stimulation with 1 ng/ml EGF, known to maximally induce the growth of these cell lines (Konger and Chan, 1993;El Sheikh et al, 2004), only marginally further increased the expression of an NF-kB-dependent luciferase gene (Figure 8a).…”

“…In carcinoma cells that overexpress EGFR family members, EGF has been shown to induce IkBa degradation and NF-kB DNA binding (Sun and Carpenter, 1998;Biswas et al, 2000). Likewise, it has been shown that heregulin induces the IKK-dependent and NF-kB-mediated proliferation of ErbB2-overexpressing breast cancer cells (Biswas et al, 2004), and potentiates ErbB3-and ErB4-mediated NF-kB activation (Bhat-Nakshatri et al, 2002;Yang et al, 2008).…”