Recently, there have been considerable efforts to search for naturally occurring substances for the intervention of carcinogenesis. Many components derived from dietary or medicinal plants have been found to possess substantial chemopreventive properties. Curcumin, a yellow coloring ingredient of turmeric (Curcuma longa L., Zingiberaceae), has been shown to inhibit experimental carcinogenesis and mutagenesis, but molecular mechanisms underlying its chemopreventive activities remain unclear. In the present work, we assessed the effects of curcumin on 12-O- tetradecanoylphorbol-13-acetate (TPA)-induced expression of cyclooxygenase-2 (COX-2) in female ICR mouse skin. Topical application of the dorsal skin of female ICR mice with 10 nmol TPA led to maximal induction of cox-2 mRNA and protein expression at approximately 1 and 4 h, respectively. When applied topically onto shaven backs of mice 30 min prior to TPA, curcumin inhibited the expression of COX-2 protein in a dose-related manner. Immunohistochemical analysis of TPA-treated mouse skin revealed enhanced expression of COX-2 localized primarily in epidermal layer, which was markedly suppressed by curcumin pre-treatment. Curcumin treatment attenuated TPA- stimulated NF-kappaB activation in mouse skin, which was associated with its blockade of degradation of the inhibitory protein IkappaBalpha and also of subsequent translocation of the p65 subunit to nucleus. TPA treatment resulted in rapid activation via phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein (MAP) kinases, which are upstream of NF-kappaB. The MEK1/2 inhibitor U0126 strongly inhibited NF-kappaB activation, while p38 inhibitor SB203580 failed to block TPA-induced NF-kappaB activation in mouse skin. Furthermore, U0126 blocked the IkappaBalpha phosphorylation by TPA, thereby blocking the nuclear translocation of NF-kappaB. Curcumin inhibited the catalytic activity of ERK1/2 in mouse skin. Taken together, suppression of COX-2 expression by inhibiting ERK activity and NF-kappaB activation may represent molecular mechanisms underlying previously reported antitumor promoting effects of this phytochemical in mouse skin tumorigenesis.

Abstract. Nuclear factor κB (NF-κB), a transcription factor, plays an important role in carcinogenesis as well as in the regulation of immune and inflammatory responses. NF-κB induces the expression of diverse target genes that promote cell proliferation, regulate apoptosis, facilitate angiogenesis and stimulate invasion and metastasis. Furthermore, many cancer cells show aberrant or constitutive NF-κB activation which mediates resistance to chemo-and radio-therapy. Therefore, the inhibition of NF-κB activation and its signaling pathway offers a potential cancer therapy strategy. In addition, recent studies have shown that NF-κB can also play a tumor suppressor role in certain settings. In this review, we focus on the role of NF-κB in carcinogenesis and the therapeutic potential of targeting NF-κB in cancer therapy.Keywords: NF-κB, NF-κB inhibitor, carcinogenesis, cancer therapy Structure, function and regulation of NF-κBNuclear factor-κB (NF-κB) was first identified in 1986 as a transcription factor that binds to a 10 bp DNA element in kappa immunoglobulin light-chain enhancer in B cells [128]. The mammalian NF-κB family consists of 5 members: NF-κB1 (p50/p105), NF-κB2 (p52/p100), c-Rel, RelA (p65) and RelB (Fig. 1). RelA, c-Rel and RelB are synthesized in their mature forms and contain a transactivation domain that interacts with the transcriptional apparatus. On the other hand, NF-κB1 (p50/p105) and NF-κB2 (p52/p100) are synthesized in precursor forms (p100 and p105) which contain C-terminal ankyrin repeats that are proteolysed by the proteasome resulting in the production of mature proteins (p50 and p52). Both p50 and p52 contain a DNA binding domain but lack a transactivation domain. NF-κB proteins exist in unstimulated cells as homo-or heterodimers bound to IκB proteins. Whereas RelB forms only heterodimers, all the other proteins can form both homo-and heterodimers. NF-κB proteins are characterized by the presence of a highly conserved 300 amino acid Rel homology domain that is located toward the N terminus of the protein, and which is responsible for DNA binding, dimerization, and interaction with specific inhibitory factors known as IκB proteins [7,36].

The human papillomavirus (HPV) E6 and E7 oncoproteins play important roles in cervical carcinogenesis through multiple mechanisms, including upregulation of cyclooxygenase-2 (COX-2), which has been shown to be involved in both carcinogenesis and cancer progression. To explore the role of E5 in cervical carcinogenesis, we herein investigated the effect of HPV 16 E5 on COX-2 expression. Our results revealed that E5 induced COX-2 expression through the epidermal growth factor receptor-signaling pathway, with nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1) acting as critical factors in E5-induced COX-2 expression. NF-kappaB inhibition blocked COX-2 expression more potently than inhibition of AP-1. Our findings collectively suggest that the HPV 16 E5 oncoprotein mediates cervical carcinogenesis at least in part via upregulation of COX-2 expression through NF-kappaB and AP-1, with NF-kappaB playing a larger role.

We previously identified the transcription factor ZNF217 (human) / Zfp217 (mouse) as an oncogene and prognostic indicator of reduced survival, increased metastasis, and reduced response to therapy in breast cancer patients. Here we investigated the role of Zfp217 in chemotherapy resistance. Preclinical animal models of Zfp217 overexpression were treated with a combination therapy of the microtubule inhibitor epothilone B, doxorubicin (Adriamycin), and cyclophosphamide (EAC). Tumors overexpressing Zfp217 increased their tumor burden compared to control tumors after treatment and accumulated a mammary gland progenitor cell population (K8 + K14 +). To overcome this chemoresistance after ZNF217 overexpression, we treated tumors ± Zfp217 overexpression with paclitaxel and triciribine, a nucleoside analog and AKT inhibitor that kills cells that overexpress ZNF217. Treatment order critically impacted the efficacy of the therapy. Combination treatment of triciribine followed by paclitaxel (TCN→PAC) inhibited tumor burden and increased survival in tumors that overexpressed Zfp217, whereas single agent or combination treatment in the reverse order (PAC→TCN) did not improve response. Analysis of these tumors and patient-derived tumor xenograft tumors treated with the same therapies suggested that Zfp217 overexpression in tumors contributes both to decreased microvessel density and vessel maturity, while TCN→PAC tumors overexpressing Zfp217 showed improved vessel maturity.

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