Department of Molecular Carcinogenesis, Lankenau Institute for Medical Research, Wynnewood, PA, USA.
Carcinogenesis. 2019 Aug 22;40(8):1042-1051. doi: 10.1093/carcin/bgz115.
Tumor promotion is strongly associated with inflammation and increased polyamine levels. Our understanding of relevant mechanisms responsible for arsenic-induced cancer remains limited. Previous studies suggest that arsenic targets and dysregulates stem cell populations that remain dormant in the skin until promoted to be recruited out of the bulge stem cell region, thus giving rise to skin tumors. In this study, we explored a possible mechanism by which increased keratinocyte polyamine biosynthesis promotes tumorsphere formation and invasiveness of arsenic-transformed HaCaT keratinocytes (As-HaCaT). Unlike parental HaCaT cells, As-HaCaT cells were tumorigenic in athymic nude mice, and the CD45negative epithelial tumor cells had enriched expression of Toll-Like Receptor 4 (TLR4), CD34 and CXCR4 as did As-HaCaT tumorsphere cultures compared to As-HaCaT monolayer cultures. Ornithine decarboxylase (ODC) overexpressing keratinocytes (Ker/ODC) release increased levels of the alarmin high mobility group box 1 (HMGB1). Ker/ODC conditioned medium (CM) stimulated As-HaCaT but not parental HaCaT tumorsphere formation, and this was inhibited by glycyrrhizin, an inhibitor of HMGB1, and by TAK242, an inhibitor of the HMGB1 receptor TLR4. Compared to parental HaCaT cells, As-HaCaT cells demonstrated greater invasiveness across a Matrigel-coated filter using either fibroblast CM or SDF-1α as chemoattractants. Addition of Ker/ODC CM or HMGB1 dramatically increased As-HaCaT invasiveness. Glycyrrhizin and TAK242 inhibited this Ker/ODC CM-stimulated invasion of As-HaCaT cells but not HaCaT cells. These results show that polyamine-dependent release of HMGB1 promotes the expansion of stem cell-like subpopulations in arsenic-transformed keratinocytes while also increasing their invasiveness, suggesting that polyamines may be a potential therapeutic target for the prevention and treatment of arsenic-initiated skin cancers.
肿瘤促进与炎症和多胺水平升高密切相关。我们对砷诱导癌症相关机制的理解仍然有限。先前的研究表明，砷的靶标是失调的干细胞群体，这些细胞在皮肤中处于休眠状态，直到被募集到毛囊干细胞区域之外，从而导致皮肤肿瘤。在这项研究中，我们探索了一种可能的机制，即角质细胞多胺生物合成的增加促进了砷转化的 HaCaT 角质细胞（As-HaCaT）肿瘤球的形成和侵袭性。与亲本 HaCaT 细胞不同，As-HaCaT 细胞在无胸腺裸鼠中具有致瘤性，而 CD45 阴性上皮肿瘤细胞的 Toll 样受体 4 (TLR4)、CD34 和 CXCR4 的表达丰富，与 As-HaCaT 肿瘤球培养物相比，As-HaCaT 单层培养物也是如此。精氨酸脱羧酶（ODC）过表达的角质细胞（Ker/ODC）释放高水平的警报素高迁移率族蛋白 1（HMGB1）。Ker/ODC 条件培养基（CM）刺激 As-HaCaT 但不刺激亲本 HaCaT 肿瘤球的形成，而这种作用被 HMGB1 的抑制剂甘氨酸和 HMGB1 受体 TLR4 的抑制剂 TAK242 所抑制。与亲本 HaCaT 细胞相比，As-HaCaT 细胞在使用成纤维细胞 CM 或 SDF-1α 作为趋化剂穿过 Matrigel 涂层过滤器时表现出更强的侵袭性。添加 Ker/ODC CM 或 HMGB1 可显著增加 As-HaCaT 的侵袭性。甘氨酸和 TAK242 抑制了 Ker/ODC CM 刺激的 As-HaCaT 细胞的侵袭，但不抑制 HaCaT 细胞。这些结果表明，多胺依赖性 HMGB1 的释放促进了砷转化的角质细胞中干细胞样亚群的扩增，同时也增加了它们的侵袭性，这表明多胺可能是预防和治疗砷引发的皮肤癌的潜在治疗靶点。
