Inhibition of 6-formylindolo[3,2-b]carbazole metabolism sensitizes keratinocytes to UVA-induced apoptosis: Implications for vemurafenib-induced phototoxicity

Characterization of two melanoma cell lines resistant to BRAF/MEK inhibitors (vemurafenib and cobimetinib)

BACKGROUND

BRAF (v-raf murine sarcoma viral oncogene homolog B1)/MEK (mitogen-activated protein kinase kinase) inhibitors are used for melanoma treatment. Unfortunately, patients treated with this combined therapy develop resistance to treatment quite quickly, but the mechanisms underlying this phenomenon are not yet fully understood. Here, we report and characterize two melanoma cell lines (WM9 and Hs294T) resistant to BRAF (vemurafenib) and MEK (cobimetinib) inhibitors.

METHODS

Cell viability was assessed via the XTT test. The level of selected proteins as well as activation of signaling pathways were evaluated using Western blotting. The expression of the chosen genes was assessed by RT-PCR. The distribution of cell cycle phases was analyzed by flow cytometry, and confocal microscopy was used to take photos of spheroids. The composition of cytokines secreted by cells was determined using a human cytokine array.

RESULTS

The resistant cells had increased survival and activation of ERK kinase in the presence of BRAF/MEK inhibitors. The IC50 values for these cells were over 1000 times higher than for controls. Resistant cells also exhibited elevated activation of AKT, p38, and JNK signaling pathways with increased expression of EGFR, ErbB2, MET, and PDGFRβ receptors as well as reduced expression of ErbB3 receptor. Furthermore, these cells demonstrated increased expression of genes encoding proteins involved in drug transport and metabolism. Resistant cells also exhibited features of epithelial-mesenchymal transition and cancer stem cells as well as reduced proliferation rate and elevated cytokine secretion.

CONCLUSIONS

In summary, this work describes BRAF/MEK-inhibitor-resistant melanoma cells, allowing for better understanding the underlying mechanisms of resistance. The results may thus contribute to the development of new, more effective therapeutic strategies.

Targeting the aryl hydrocarbon receptor with FICZ regulates IL-2 and immune infiltration to alleviate Hashimoto's thyroiditis in mice

Hashimoto's thyroiditis (HT) is the most frequent autoimmune disorder. Growing work points to the involvement of aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, in the regulation of immune homeostasis. However, the roles of AhR and its ligands in HT remains unclear. In this study, we leveraged public human database analyses to postulate that the AhR expression was predominantly in thyroid follicular cells, correlating significantly with the thyroid infiltration levels of multiple immune cells in HT patients. Using a thyroglobulin-induced HT mouse model and in vitro thyroid follicular epithelial cell cultures, we found a significant downregulation of AhR expression in thyrocytes both in vivo and in vitro. Conversely, activating AhR by FICZ, a natural AhR ligand, mitigated inflammation and apoptosis in thyrocytes in vitro and conferred protection against HT in mice. RNA sequencing (RNA-seq) of thyroid tissues indicated that AhR activation moderated HT-associated immune or inflammatory signatures. Further, immunoinfiltration analysis indicated that AhR activation regulated immune cell infiltration in the thyroid of HT mice, such as suppressing cytotoxic CD8+ T cell infiltration and promoting anti-inflammatory M2 macrophage polarization. Concomitantly, the expression levels of interleukin-2 (IL-2), a lymphokine that downregulates immune responses, were typically decreased in HT but restored upon AhR activation. In silico validation substantiated the binding interaction between AhR and IL-2. In conclusion, targeting the AhR with FICZ regulates IL-2 and immune infiltration to alleviate experimental HT, shedding new light on the therapeutic intervention of this prevalent disease.

Targeting aryl hydrocarbon receptor to prevent cancer in barrier organs

The skin, lung, and gut are important barrier organs that control how the body reacts to environmental stressors such as ultraviolet (UV) radiation, air pollutants, dietary components, and microorganisms. The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that plays an important role in maintaining homeostasis of barrier organs. AhR was initially discovered as a receptor for environmental chemical carcinogens such as polycyclic aromatic hydrocarbons (PAHs). Activation of AhR pathways by PAHs leads to increased DNA damage and mutations which ultimately lead to carcinogenesis. Ongoing evidence reveals an ever-expanding role of AhR. Recently, AhR has been linked to immune systems by the interaction with the development of natural killer (NK) cells, regulatory T (Treg) cells, and T helper 17 (Th17) cells, as well as the production of immunosuppressive cytokines. However, the role of AhR in carcinogenesis is not as straightforward as we initially thought. Although AhR activation has been shown to promote carcinogenesis in some studies, others suggest that it may act as a tumor suppressor. In this review, we aim to explore the role of AhR in the development of cancer that originates from barrier organs. We also examined the preclinical efficacy data of AhR agonists and antagonists on carcinogenesis to determine whether AhR modulation can be a viable option for cancer chemoprevention.

IL-22 as a target for therapeutic intervention: Current knowledge on its role in various diseases

IL-22 has emerged as a crucial cytokine mediating protective response against pathogens and tissue regeneration. Dysregulated production of IL-22 has been shown to play a pivotal role in the pathogenesis of various diseases like malignant tumours, viral, cardiovascular, allergic and autoimmune disorders. Interleukin 22 belongs to IFN-IL-10 cytokine family. It is a major proinflammatory cytokine secreted by activated Th1 cells (Th22), though can also be secreted by many other immune cells like group 3 innate lymphocytes, γδ T cells, NK cells, NK T cells, and mucosal associated invariant T cells. Th22 cells exclusively release IL-22 but not IL-17 or IFN-γ (as Th1 cells releases IFN-γ along with IL-22 and Th17 cells releases IL-17 along with IL-22) and also express aryl hydrocarbon receptor as the key transcription factor. Th22 cells also exhibit expression of chemokine receptor CCR6 and skin-homing receptors CCR4 and CCR10 indicating the involvement of this subset in bolstering epithelial barrier immunity and promoting secretion of antimicrobial peptides (AMPs) from intestinal epithelial cells. The function of IL-22 is modulated by IL-22 binding protein (binds to IL-22 and inhibits it binding to its cell surface receptor); which serves as a competitor for IL-22R1 chain of IL-22 receptor. The pathogenic and protective nature of the Th22 cells is modulated both by the site of infected tissue and the type of disease pathology. This review aims to discuss key features of IL-22 biology, comparisons between IL and 22 and IFN-γ and its role as a potential immune therapy target in different maladies.

Functions of the aryl hydrocarbon receptor (AHR) beyond the canonical AHR/ARNT signaling pathway

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor regulating adaptive and maladaptive responses toward exogenous and endogenous signals. Research from various biomedical disciplines has provided compelling evidence that the AHR is critically involved in the pathogenesis of a variety of diseases and disorders, including autoimmunity, inflammatory diseases, endocrine disruption, premature aging and cancer. Accordingly, AHR is considered an attractive target for the development of novel preventive and therapeutic measures. However, the ligand-based targeting of AHR is considerably complicated by the fact that the receptor does not always follow the beaten track, i.e. the canonical AHR/ARNT signaling pathway. Instead, AHR might team up with other transcription factors and signaling molecules to shape gene expression patterns and associated physiological or pathophysiological functions in a ligand-, cell- and micromilieu-dependent manner. Herein, we provide an overview about some of the most important non-canonical functions of AHR, including crosstalk with major signaling pathways involved in controlling cell fate and function, immune responses, adaptation to low oxygen levels and oxidative stress, ubiquitination and proteasomal degradation. Further research on these diverse and exciting yet often ambivalent facets of AHR biology is urgently needed in order to exploit the full potential of AHR modulation for disease prevention and treatment.

The Role of T Helper 22 Cells in Dermatological Disorders

T helper 22 (Th22) cells are a newly identified subset of CD4+ T cells that secrete the effector cytokine interleukin 22 (IL-22) upon specific antigen stimulation, barely with IFN-γ or IL-17. Increasing studies have demonstrated that Th22 cells and IL-22 play essential roles in skin barrier defense and skin disease pathogenesis since the IL-22 receptor is widely expressed in the skin, especially in keratinocytes. Herein, we reviewed the characterization, differentiation, and biological activities of Th22 cells and elucidated their roles in skin health and disease. We mainly focused on the intricate crosstalk between Th22 cells and keratinocytes and provided potential therapeutic strategies targeting the Th22/IL-22 signaling pathway.

The Aryl Hydrocarbon Receptor in the Pathogenesis of Environmentally-Induced Squamous Cell Carcinomas of the Skin

Cutaneous squamous cell carcinoma (SCC) is one of the most frequent malignancies in humans and academia as well as public authorities expect a further increase of its incidence in the next years. The major risk factor for the development of SCC of the general population is the repeated and unprotected exposure to ultraviolet (UV) radiation. Another important risk factor, in particular with regards to occupational settings, is the chronic exposure to polycyclic aromatic hydrocarbons (PAH) which are formed during incomplete combustion of organic material and thus can be found in coal tar, creosote, bitumen and related working materials. Importantly, both exposomal factors unleash their carcinogenic potential, at least to some extent, by activating the aryl hydrocarbon receptor (AHR). The AHR is a ligand-dependent transcription factor and key regulator in xenobiotic metabolism and immunity. The AHR is expressed in all cutaneous cell-types investigated so far and maintains skin integrity. We and others have reported that in response to a chronic exposure to environmental stressors, in particular UV radiation and PAHs, an activation of AHR and downstream signaling pathways critically contributes to the development of SCC. Here, we summarize the current knowledge about AHR's role in skin carcinogenesis and focus on its impact on defense mechanisms, such as DNA repair, apoptosis and anti-tumor immune responses. In addition, we discuss the possible consequences of a simultaneous exposure to different AHR-stimulating environmental factors for the development of cutaneous SCC.