The autonomous growth of human papillomavirus type 16-immortalized keratinocytes is related to the endothelin-1 autocrine loop

Identification of Keratinocyte Mitogens: Implications for Hyperproliferation in Psoriasis and Atopic Dermatitis

Psoriasis and atopic dermatitis are chronic inflammatory skin diseases characterized by keratinocyte (KC) hyperproliferation and epidermal acanthosis (hyperplasia). The milieu of disease-associated cytokines and soluble factors is considered a mitogenic factor; however, pinpointing the exact mitogens in this complex microenvironment is challenging. We employed organotypic human epidermal equivalents, faithfully mimicking native epidermal proliferation and stratification, to evaluate the proliferative effects of a broad panel of (literature-based) potential mitogens. The KC GF molecule, the T-helper 2 cytokines IL-4 and IL-13, and the psoriasis-associated cytokine IL-17A caused acanthosis by hyperplasia through a doubling in the number of proliferating KCs. In contrast, IFN-γ lowered proliferation, whereas IL-6, IL-20, IL-22, and oncostatin M induced acanthosis not by hyperproliferation but by hypertrophy. The T-helper 2‒cytokine‒mediated hyperproliferation was Jak/signal transducer and activator of transcription 3 dependent, whereas IL-17A and KC GF induced MAPK/extracellular signal‒regulated kinase kinase/extracellular signal‒regulated kinase‒dependent proliferation. This discovery that key regulators in atopic dermatitis and psoriasis are direct KC mitogens not only adds evidence to their crucial role in the pathophysiological processes but also highlights an additional therapeutic pillar for the mode of action of targeting biologicals (e.g., dupilumab) or small-molecule drugs (e.g., tofacitinib) by the normalization of KC turnover within the epidermal compartment.

The endothelin axis in urologic tumors: mechanisms of tumor biology and therapeutic implications

Endothelin (ET)-1 and its receptors ET-A and ET-B, referred to commonly as the endothelin axis, have been identified in various human cancers, especially gynecologic tumors, such as breast cancer or ovarian cancer, but also including urologic tumor entities. They play a key role in tumor growth and progression by influencing critical cancer pathways, such as apoptosis, angiogenesis and proliferation. In prostate cancer, overexpression of the ET-A receptor increases with tumor progression, and clinical trials with selective ET-A receptor antagonists, such as atrasentan (ABT-627), have shown promising early results. In preclinical models of bladder cancer, overexpression of the ET axis has been demonstrated and ET-targeting agents are under investigation. This paper reviews the role of the ET axis in human cancers and focuses on preclinical and clinical studies in urologic tumor entities to further define the role of ET-targeting agents as targeted molecular therapy.

Endothelin in pulmonary fibrosis

The endothelin receptor-ligand system includes a family of polypeptides and G-protein-coupled receptors, which, in addition to their classic activity in the regulation of vascular tone (both directly and through the control of nitric oxide), were implicated in a wide variety of other key biological processes. In this regard, the endothelins are potent mitogens and motogens for mesenchymal cells, and can induce cell differentiation, increasing both the synthesis and deposition of extracellular matrix components and contractile ability. The endothelins are produced as inactive pre-pro-polypeptides, with gene transcription (as well as the proteolytic processing to mature active forms) under the influence of many factors, including cytokines, hypoxia, biomechanical and shear stress, pathogen products, and many growth factors. These complex regulatory events underlie the association and potential role of endothelins in a number of human diseases affecting many different target organs, including the vasculature (atherosclerosis and hypertension), kidney (renal crisis and chronic kidney disease), heart (coronary heart disease), and lungs (pulmonary fibrosis and pulmonary hypertension). This review focuses on the biochemistry of endothelin and the pathobiology of endothelin in lung fibrosis, with particular emphasis on idiopathic pulmonary fibrosis, and examines the antifibrotic potential of endothelin receptor antagonism.

UVB irradiation down-regulates HPV-16 RNA expression: implications for malignant progression of transformed cells

A new cell line obtained from normal human epithelial keratinocytes transfected with the whole HPV-16 genome has been extensively characterised. This cell line, named HK-168, has a basal/para-basal keratinocyte phenotype, requires the use of serum-free chemically defined media and maintains the ability to differentiate toward pluri-stratified epithelia. Although immortalised it is not capable of anchorage independent growth and is not tumorigenic. HK-168 has a distinctive kariotype, with a complete, transcriptionally active HPV-16 genome integrated at an almost 1:1 ratio into the host haploid genome thus providing a convenient experimental model for viral transformed pre-neoplastic cell phenotype. The oxidative stress, induced by mild UVB irradiation, caused in HK-168 a general suppression of viral transcription, accompanied by a moderate growth arrest, an appropriated response of cellular antioxidant enzymes, the activation of cell repair mechanisms and a mild induction of apoptosis. This response is similar to the one observed in the highly resistant diploid keratinocytes. Conversely, transformed cells devoid of HPV sequences (HaCaT), appeared extremely susceptible to apoptosis. We propose that reported suppression of viral oncogenes, restoring the cell control on growth and repair mechanisms, allows the damage repair, ultimately resulting in a surviving response.

Endothelin-3 growth factor levels decreased in cervical cancer compared with normal cervical epithelial cells

We used cDNA microarray analysis of RNA extracted from normal, dysplastic, and cancerous cervical tissues to identify the changes in gene expression during the procession from normal to cancerous cervical epithelial cells. We found the expression of 5 genes in cancerous cervical epithelial cells that were not found in normal cervical epithelial cells, among which were lymphoid-restricted membrane protein, protease serine 2, WD repeat domain 59, thyrotropin-releasing hormone degrading enzyme, and the endothelin-3 growth factor. We then analyzed the expression levels of endothelin growth factors 1, 2, and 3 (ET-1, ET-2, and ET-3) and their receptors A and B (ETR-A and ETR-B) by reverse transcriptase-polymerase chain reaction in 3 cervical cancer cell lines and by immunohistochemical staining in cervical normal, dysplastic, and cancer tissues. ET-1, ET-2, and ET-3 growth factor levels were detectable in the maturing layer of cervical epithelium but not in the germinal layer. All 3 growth factors (ET-1, ET-2, and ET-3) were detected in the cytoplasm of the maturing normal cervical epithelial cells. In addition, there were decreased levels of ET-3 and increased levels of ET-1, ET-2, ETR-A, and ETR-B in cancerous cervical epithelial cells compared with normal cervical epithelial cells. These results suggest that the reduction of ET-3 growth factor levels may be important in the transition from normal to cancerous cervical epithelium.

Expression of endothelin 1 and endothelin A receptor in HPV-associated cervical carcinoma: new potential targets for anticancer therapy

Human papillomaviruses (HPV) are associated with cervical cancer and interact with growth factors that may enhance malignant transformation of cervical carcinoma cells. Endothelin-1 (ET-1) is released from HPV transfected keratinocytes and induces increased growth response in these cell lines in comparison with normal cells. In the present study several cervical carcinoma cell lines have been analyzed to investigate the expression of ET-1 and its receptors as well as their involvement in tumor growth. All HPV-positive cancer cells secreted ET-1 and expressed mRNA for ET-1 and its receptors, whereas a HPV-negative carcinoma cell line expressed only the ETBR mRNA and didn't secrete ET-1. Binding studies showed that HPV-associated cells expressed an increased number of functional ETAR. ET-1 stimulated a marked dose-dependent increase in [3H]-thymidine incorporation with respect to the normal cells whereas ET-3 and ETBR agonists had no effect. In HPV-positive cancer cells, a specific antagonist of ETAR inhibited the proliferation induced by ET-1 and substantially reduced the basal growth rate of unstimulated cervical tumor cells, whereas the ETBR antagonist had no effect. These results demonstrate that ET-1 participates in the progression of neoplastic growth in HPV-associated carcinoma, in which ETAR are increased and could be targeted for antitumor therapy.

Loss of IL-6 receptor expression in cervical carcinoma cells inhibits autocrine IL-6 stimulation: abrogation of constitutive monocyte chemoattractant protein-1 production

IL-6 is synthesized in human papilloma virus (HPV)-transformed cervical carcinoma cell lines and is supposed to stimulate these cells in an autocrine manner. We studied IL-6 production and responsiveness in nonmalignant HPV-transformed keratinocytes and cervical carcinoma cells in detail. IL-6 was detected in cervical carcinomas in situ. Correspondingly, HPV-positive carcinoma cell lines expressed high IL-6 levels. However, these carcinoma cell lines showed low responsiveness to IL-6 as revealed by low constitutive STAT3 binding activity, which was not further enhanced by exogenous IL-6. In contrast, in vitro-transformed nonmalignant keratinocytes without endogenous IL-6 production strongly responded to exogenous IL-6 with activation of STAT3. STAT3 protein expression levels were comparable in both responsive and nonresponsive cell lines. Also, gp130, the upstream signal-transducing receptor subunit conveying IL-6 signals into the cell, was expressed in all tested cell lines. However, the IL-6 binding subunit gp80 was lost in the malignant cells. Addition of soluble gp80 was sufficient to restore IL-6 responsiveness in carcinoma cells as shown by enhanced activation of STAT3 binding activity. As a consequence of the restored IL-6 responsiveness, carcinoma cells strongly produced the chemokine monocyte chemoattractant protein-1 (MCP-1). Our data demonstrate that cervical carcinoma cells producing high amounts of IL-6 only weakly respond to IL-6 in an autocrine manner due to limited gp80 expression. While production of IL-6 might contribute to a local immunosuppressive effect, silencing an autocrine IL-6 response prevents constitutive production of the mononuclear cell-attracting chemokine MCP-1. Both mechanisms might help the tumor to escape the immune system.