Polyamine-stimulation of arsenic-transformed keratinocytes

Dysregulation of mRNA expression by hsa-miR-186 overexpression in arsenic-induced skin carcinogenesis

Dysregulated miRNA expression contributes to development of arsenic-induced cutaneous squamous cell carcinoma (cSCC). hsa-miR-186 (miR-186) is overexpressed in arsenical cSCC tissues as well as in preclinical cell line model of arsenical cSCC. Simultaneous miR-186 overexpression and chronic inorganic trivalent arsenite (iAs; 100 nM) exposure transformed human HaCaT cell line preferentially over miR-186 overexpression or iAs exposure alone. Both iAs and miR-186 regulate the expression of wide range of mRNA targets. However, how their interaction impacts the transcriptome-wide mRNA expression landscape ushering in cancer is unknown. We performed longitudinal RNA-seq analysis in passage-matched HaCaT cell clones (±miR-186 overexpression) with simultaneous chronic iAs exposure (0/100 nM) at 12 and 29 weeks. We determined the impact of each factor and their interaction towards differential gene expression and pathway dysregulation employing two different statistical approaches (t-statistic and 2-factor ANOVA). We show that a core set of pathways are dysregulated deterministically irrespective of the statistical approach chosen, possibly representing necessary changes for transformation. The data suggest that each clonal line could take a unique route to dysregulate this core set of pathways necessary for transformation, highlighting the possible role of stochasticity in cancer development. Evidence is presented to sift the strengths and weaknesses of each statistical methodology in providing biological understanding of events that play crucial roles in carcinogenesis in large datasets with multiple contributing variables.

Ectoine Globally Hypomethylates DNA in Skin Cells and Suppresses Cancer Proliferation

Epigenetic modifications, mainly aberrant DNA methylation, have been shown to silence the expression of genes involved in epigenetic diseases, including cancer suppression genes. Almost all conventional cancer therapeutic agents, such as the DNA hypomethylation drug 5-aza-2-deoxycytidine, have insurmountable side effects. To investigate the role of the well-known DNA protectant (ectoine) in skin cell DNA methylation and cancer cell proliferation, comprehensive methylome sequence analysis, 5-methyl cytosine (5mC) analysis, proliferation and tumorigenicity assays, and DNA epigenetic modifications-related gene analysis were performed. The results showed that extended ectoine treatment globally hypomethylated DNA in skin cells, especially in the CpG island (CGIs) element, and 5mC percentage was significantly reduced. Moreover, ectoine mildly inhibited skin cell proliferation and did not induce tumorigenicity in HaCaT cells injected into athymic nude mice. HaCaT cells treated with ectoine for 24 weeks modulated the mRNA expression levels of Dnmt1, Dnmt3a, Dnmt3b, Dnmt3l, Hdac1, Hdac2, Kdm3a, Mettl3, Mettl14, Snrpn, and Mest. Overall, ectoine mildly demethylates DNA in skin cells, modulates the expression of epigenetic modification-related genes, and reduces cell proliferation. This evidence suggests that ectoine is a potential anti-aging agent that prevents DNA hypermethylation and subsequently activates cancer-suppressing genes.

Delineating the Effects of Passaging and Exposure in a Longitudinal Study of Arsenic-Induced Squamous Cell Carcinoma in a HaCaT Cell Line Model

Cutaneous squamous cell carcinoma (cSCC) is a major deleterious health effect of chronic arsenic (iAs) exposure. The molecular mechanism of arsenic-induced cSCC remains poorly understood. We recently demonstrated that chronic iAs exposure leads to temporally regulated genome-wide changes in profiles of differentially expressed mRNAs and miRNAs at each stage of carcinogenesis (7, 19 and 28 weeks) employing a well-established passage-matched HaCaT cell line model of arsenic-induced cSCC. Here, we performed longitudinal differential expression analysis (miRNA and mRNA) between the different time points (7 vs. 19 weeks and 19 vs. 28 weeks) within unexposed and exposed groups, coupled to expression pairing and pathway analyses to differentiate the relative effects of long-term passaging and chronic iAs exposure. Data showed that 66-105 miRNA [p < 0.05; log2(Fold Change)>I1I] and 2826-4079 mRNA [p < 0.001; log2(Fold Change)>I1I] molecules were differentially expressed depending on the longitudinal comparison. Several mRNA molecules differentially expressed as a function of time, independent of iAs exposure were being targeted by miRNA molecules which were also differentially expressed in a time dependent manner. Distinct pathways were predicted to be modulated as a function of time or iAs exposure. Some pathways were also modulated both by time and exposure. Thus, the HaCaT model can distinguish between the effects of passaging and chronic iAs exposure individually and corroborate our previously published data on effects of iAs exposure compared to unexposed passage matched HaCaT cells. In addition, this work provides a template for cell line based longitudinal chronic exposure studies to follow for optimal efficacy.

Ornithine decarboxylase inhibition downregulates multiple pathways involved in the formation of precancerous lesions of esophageal squamous cell cancer

The high incidence and mortality of esophageal squamous cell cancer (ESCC) is a major health problem worldwide. Precancerous lesions of ESCC may either progress to cancer or revert to normal epithelium with appropriate interventions; the bidirectional instability of the precancerous lesions of ESCC provides opportunities for intervention. Reports suggest that the upregulation of ornithine decarboxylase (ODC) is closely related to carcinogenesis. In this study, we investigated whether ODC may act as a target for chemoprevention in ESCC. Immunohistochemistry (IHC) assays indicate that ODC expression is higher in esophageal precancerous lesions compared with normal tissue controls. Its overexpression promotes cell proliferation and transformation of normal esophageal epithelial cells, and its activity is increased after N-nitrosomethylbenzylamine (NMBA) induction in Shantou human embryonic esophageal cell line (SHEE) and human immortalized cells (Het1A) cells. In addition, p38 α, extracellular regulated kinase (ERK1/2) in the mitogen-activated protein kinase pathway and protein kinase B (AKT)/mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (p70S6K) pathways are activated in response to NMBA treatment. Difluoromethylornithine (DFMO) is an ODC inhibitor, which inhibits NMBA-induced activation of p38 α, ERK1/2 and AKT/mTOR/p70S6K pathways; this has been verified by Western blotting. DFMO was also found to suppress the development of esophageal precancerous lesions in an NMBA-induced rat model; IHC demonstrated p38 α, ERK1/2, and AKT/mTOR/p70S6K pathways to be downregulated in these rats. These findings indicate the mechanisms by which ODC inhibition suppresses the development of esophageal precancerous lesions by downregulating p38 α, ERK1/2, and AKT/mTOR/p70S6k signaling pathways, ODC may be a potential target for chemoprevention in ESCC.