Role of IKKα in skin squamous cell carcinomas

Nuclear versus cytoplasmic IKKα signaling in keratinocytes leads to opposite skin phenotypes and inflammatory responses, and a different predisposition to cancer

IKKα is known as an essential protein for skin homeostasis. However, the lack of suitable models to investigate its functions in the skin has led to IKKα being mistakenly considered as a suppressor of non-melanoma skin cancer (NMSC) development. In this study, using our previously generated transgenic mouse models expressing exogenous IKKα in the cytoplasm (C-IKKα mice) or in the nucleus (N-IKKα mice) of basal keratinocytes, we demonstrate that at each subcellular localization, IKKα differently regulates signaling pathways important for maintaining the balance between keratinocyte proliferation and differentiation, and for the cutaneous inflammatory response. In addition, each type of IKKα-transgenic mice shows different predisposition to the development of spontaneous NMSC. Specifically, N-IKKα mice display an atrophic epidermis with exacerbated terminal differentiation, signs of premature skin aging, premalignant lesions, and develop squamous cell carcinomas (SCCs). Conversely, C-IKKα mice, whose keratinocytes are nearly devoid of endogenous nuclear IKKα, do not develop skin SCCs, although they exhibit hyperplastic skin with deficiencies in terminal epidermal differentiation, chronic cutaneous inflammation, and constitutive activation of STAT-3 and NF-κB signaling pathways. Altogether, our data demonstrate that alterations in the localization of IKKα in the nucleus or cytoplasm of keratinocytes cause opposite skin changes and differentially predispose to the growth of skin SCCs.

Regulation of epidermal differentiation through KDF1-mediated deubiquitination of IKKα

Progenitor cells at the basal layer of skin epidermis play an essential role in maintaining tissue homeostasis and enhancing wound repair in skin. The proliferation, differentiation, and cell death of epidermal progenitor cells have to be delicately regulated, as deregulation of this process can lead to many skin diseases, including skin cancers. However, the underlying molecular mechanisms involved in skin homeostasis remain poorly defined. In this study, with quantitative proteomics approach, we identified an important interaction between KDF1 (keratinocyte differentiation factor 1) and IKKα (IκB kinase α) in differentiating skin keratinocytes. Ablation of either KDF1 or IKKα in mice leads to similar but striking abnormalities in skin development, particularly in skin epidermal differentiation. With biochemical and mouse genetics approach, we further demonstrate that the interaction of IKKα and KDF1 is essential for epidermal differentiation. To probe deeper into the mechanisms, we find that KDF1 associates with a deubiquitinating protease USP7 (ubiquitin-specific peptidase 7), and KDF1 can regulate skin differentiation through deubiquitination and stabilization of IKKα. Taken together, our study unravels an important molecular mechanism underlying epidermal differentiation and skin tissue homeostasis.

IκB kinase α: an independent prognostic factor that promotes the migration and invasion of oral squamous cell carcinoma

IκB kinase α (IKKα) is associated with tumourigenesis, metastasis, and poor prognosis. However, its expression and function in oral squamous cell carcinoma (SCC) remain unknown. The aim of this study was to elucidate the clinicopathological associations and functions of IKKα in oral squamous cell carcinoma (SCC). We made an immunohistochemical analysis of IKKα in 94 tissue microarrays of specimens of oral SCC. We also examined IKKα expression in the patients' samples by quantitative real-time polymerase chain reaction (qRT-PCR), as well as the migration, invasion, and matrix metalloproteinase (MMP) activity of the cells under IKKα knockdown treatment. In oral SCC, immunostaining for IKKα was found in 60 of the 94 patients, and it correlated with lymph node status and poor prognosis. Univariate and multivariate analysis using Cox's proportional hazards model identified that IKKα expression was an independent predictor of distant- disease-free survival (p<0.05) and overall survival in oral SCC (p<0.05). Knocking down IKKα suppressed cell migration and invasion in oral SCC cells. Our results indicate that IKKα has an important role in promoting oral SCC, and it may be a useful biomarker and therapeutic target for diagnosis and treatment.

LGR5 expression is controled by IKKα in basal cell carcinoma through activating STAT3 signaling pathway

Basal cell carcinomas (BCC) of the skin are the most common of human cancers. The noncanonical NF-κB pathway is dependent on IKKα. However, the role of IKKα in BCC has not been elucidated. We show here that IKKα is expressed in the nucleus in BCC and non-malignant diseases. Nuclear IKKα could directly bind to the promoters of inflammation factors and LGR5, a stem cell marker, in turn, upregulating LGR5 expression through activation of STAT3 signaling pathway during cancer progression. Activation of STAT3 signaling pathway contributes LGR5 expression in dependent of IKKα after the interplay between STAT3 and IKKα. Meanwhile knockdown of IKKα inhibits tumor growth and transition of epithelial stage to mescheme stage. Taken together, we demonstrate that IKKα functions as a bone fide chromatin regulator in BCC, whose promoted expression contributes to oncogenic transformation via promoting expression stemness- and inflammatory- related genes. Our finding reveals a novel viewpoint for how IKKα may involve in BCCs tumor progression in the inflammatory microenvironment.

Systematical analysis of cutaneous squamous cell carcinoma network of microRNAs, transcription factors, and target and host genes

BACKGROUND

MicroRNAs (miRNAs) are small non-coding RNA molecules found in multicellular eukaryotes which are implicated in development of cancer, including cutaneous squamous cell carcinoma (cSCC). Expression is controlled by transcription factors (TFs) that bind to specific DNA sequences, thereby controlling the flow (or transcription) of genetic information from DNA to messenger RNA. Interactions result in biological signal control networks.

MATERIALS AND METHODS

Molecular components involved in cSCC were here assembled at abnormally expressed, related and global levels. Networks at these three levels were constructed with corresponding biological factors in term of interactions between miRNAs and target genes, TFs and miRNAs, and host genes and miRNAs. Up/down regulation or mutation of the factors were considered in the context of the regulation and significant patterns were extracted.

RESULTS

Participants of the networks were evaluated based on their expression and regulation of other factors. Sub-networks with two core TFs, TP53 and EIF2C2, as the centers are identified. These share self-adapt feedback regulation in which a mutual restraint exists. Up or down regulation of certain genes and miRNAs are discussed. Some, for example the expression of MMP13, were in line with expectation while others, including FGFR3, need further investigation of their unexpected behavior.

CONCLUSIONS

The present research suggests that dozens of components, miRNAs, TFs, target genes and host genes included, unite as networks through their regulation to function systematically in human cSCC. Networks built under the currently available sources provide critical signal controlling pathways and frequent patterns. Inappropriate controlling signal flow from abnormal expression of key TFs may push the system into an incontrollable situation and therefore contributes to cSCC development.

Ikappa B kinase alpha involvement in the development of nasopharyngeal carcinoma through a NF-κB-independent and ERK-dependent pathway

OBJECTIVES

Ikappa B kinase alpha (IKKα) plays an inhibitory role in the development of epithelial-derived tumors. However, its specific function in the development of nasopharyngeal carcinoma (NPC) remains unknown. In this study we identify the role and mechanism of IKKα in IKKα-mediated NPC development.

MATERIAL AND METHODS

The effect of IKKα on migration, invasion and tumorigenesis of NPC cell lines was determined using in vitro and in vivo studies. SUNE-1-5-8F cells transfected to overexpress IKKα, SUNE-1-6-10B cells with shRNA-mediated knockdown of IKKα, and three NPC cell lines were studied using Western blotting techniques to compare the major molecules in NF-κB pathways. Additionally, the extracellular signal-regulated kinase (ERK) pathway and matrix metalloproteinases (MMPs) in IKKα-regulated NPC and the effect of Epstein-Barr Nuclear Antigen 1 (EBNA1) on IKKα were examined.

RESULTS

IKKα was underexpressed in highly invasive SUNE-1-5-8F cells compared with non-invasive cells (SUNE-1 and SUNE-6-10B). Overexpression of IKKα in SUNE-1-5-8F cells was achieved through transfection and resulted in inhibited migration and invasion in vitro. Furthermore, IKKα inhibited tumorigenesis in mice inoculated with IKKα-transfected NPC cells in vivo. These processes were independent of the conventional effect of IKKα on Nuclear factor κB (NF-κB) pathways. The ERK pathway was involved in IKKα-related NPC inhibition. Phosphorylation of ERK1/2 and subsequent secretion of MMP-9 were inhibited by the ERK inhibitor U0126 and not regulated by overexpressed IKKα. EBNA1 knockdown using small interfering RNA (siRNA) did not alter the expression of IKKα.

CONCLUSION

Increase in IKKα expression suppresses the progression of NPC through a NF-κB-independent and ERK-dependent pathway.

Aberrant IKKα and IKKβ cooperatively activate NF-κB and induce EGFR/AP1 signaling to promote survival and migration of head and neck cancer

The Inhibitor-κB Kinase-Nuclear Factor-κB (IKK-NF-κB) and Epidermal Growth Factor Receptor-Activator Protein-1 (EGFR-AP-1) pathways are often co-activated and promote malignant behavior, but the underlying basis for this relationship is unclear. Resistance to inhibitors of IKKβ or EGFR is observed in head and neck squamous cell carcinomas (HNSCC). Here, we reveal that both IKKα and β contribute to nuclear activation of canonical and alternate NF-κB/REL family transcription factors, and overexpression of signal components enhancing co-activation of the EGFR-AP1 pathway. We observed that IKKα and IKKβ exhibit increased protein expression, nuclear localization and phosphorylation in HNSCC tissues and cell lines. Individually, IKK activity varied amongst different cell lines, but overexpression of both IKKs induced the strongest NF-κB activation. Conversely, siRNA knockdown of both IKKs significantly decreased nuclear localization and phosphorylation of canonical RELA and IκBα, and alternative p52 and RELB subunits. Knockdown of both IKKs more effectively inhibited NF-κB activation, broadly modulated gene expression, and suppressed cell proliferation and migration. Global expression profiling revealed that NF-κB, cytokine, inflammatory response, and growth factor signaling are among the top pathways and networks regulated by IKKs. Importantly, IKKα and IKKβ together promoted the expression and activity of TGFα, EGFR, and AP1 transcription factors cJun, JunB, and Fra1. Knockdown of AP1 subunits individually decreased 8/15 (53%) of IKK-targeted genes sampled, and similarly inhibited cell proliferation and migration. Mutations of NF-κB and AP1 binding sites abolished or decreased IKK-induced IL-8 promoter activity. Compounds such as wedelactone with dual IKK inhibitory activity, and geldanomycins that block IKKα/β and EGFR pathways were more active than IKKβ-specific inhibitors in suppressing NF-κB activation and proliferation, and inducing cell death. We conclude that IKKα and IKKβ cooperatively activate NF-κB and EGFR/AP1 networks of signaling pathways, and contribute to the malignant phenotype and the intrinsic or acquired therapeutic resistance of HNSCC.

The pivotal role of TBK1 in inflammatory responses mediated by macrophages

Inflammation is a complex biological response of tissues to harmful stimuli such as pathogens, cell damage, or irritants. Inflammation is considered to be a major cause of most chronic diseases, especially in more than 100 types of inflammatory diseases which include Alzheimer's disease, rheumatoid arthritis, asthma, atherosclerosis, Crohn's disease, colitis, dermatitis, hepatitis, and Parkinson's disease. Recently, an increasing number of studies have focused on inflammatory diseases. TBK1 is a serine/threonine-protein kinase which regulates antiviral defense, host-virus interaction, and immunity. It is ubiquitously expressed in mouse stomach, colon, thymus, and liver. Interestingly, high levels of active TBK1 have also been found to be associated with inflammatory diseases, indicating that TBK1 is closely related to inflammatory responses. Even though relatively few studies have addressed the functional roles of TBK1 relating to inflammation, this paper discusses some recent findings that support the critical role of TBK1 in inflammatory diseases and underlie the necessity of trials to develop useful remedies or therapeutics that target TBK1 for the treatment of inflammatory diseases.