Ruifeng Yang

Repression of P66Shc Expression by SIRT1 Contributes to the Prevention of Hyperglycemia-Induced Endothelial Dysfunction

Rationale: Inactivation of the p66Shc adaptor protein confers resistance to oxidative stress and protects mice from aging-associated vascular diseases. However, there is limited information about the negative regulating mechanisms of p66Shc expression in the vascular system. Objective: In this study, we investigated the role of SIRT1, a class III histone deacetylase, in the regulation of p66Shc expression and hyperglycemia-induced endothelial dysfunction. Methods and Results: Expressions of p66Shc gene transcript and protein were significantly increased by different kinds of class III histone deacetylase (sirtuin) inhibitors in human umbilical vein endothelial cells and 293A cells. Adenoviral overexpression of SIRT1 inhibited high-glucose–induced p66Shc upregulation in human umbilical vein endothelial cells. Knockdown of SIRT1 increased p66Shc expression and also increased the expression levels of plasminogen activator inhibitor-1 expression, but decreased manganese superoxide dismutase expression in high-glucose conditions. However, knockdown of p66Shc significantly reversed the effects of SIRT1 knockdown. In addition, p66Shc overexpression significantly decreased manganese superoxide dismutase expression and increased plasminogen activator inhibitor-1 expression in high-glucose conditions, which were recovered by SIRT1 overexpression. Moreover, compared to streptozotocin-induced wild-type diabetic mice, endothelium-specific SIRT1 transgenic diabetic mice had decreased p66Shc expression at both the mRNA and the protein levels, improved endothelial function, and reduced accumulation of nitrotyrosine and 8-OHdG (markers of oxidative stress). We further found that SIRT1 was able to bind to the p66Shc promoter (−508 bp to −250 bp), resulting in a decrease in the acetylation of histone H3 bound to the p66Shc promoter region. Conclusion: Our findings indicate that repression of p66Shc expression by SIRT1 contributes to the protection of hyperglycemia-induced endothelial dysfunction.

SIRT1 Suppresses Activator Protein-1 Transcriptional Activity and Cyclooxygenase-2 Expression in Macrophages

SIRT1 (Sirtuin type 1), a mammalian orthologue of yeast SIR2 (silent information regulator 2), has been shown to mediate a variety of calorie restriction (CR)-induced physiological events, such as cell fate regulation via deacetylation of the substrate proteins. However, whether SIRT1 deacetylates activator protein-1 (AP-1) to influence its transcriptional activity and target gene expression is still unknown. Here we demonstrate that SIRT1 directly interacts with the basic leucine zipper domains of c-Fos and c-Jun, the major components of AP-1, by which SIRT1 suppressed the transcriptional activity of AP-1. This process requires the deacetylase activity of SIRT1. Notably, SIRT1 reduced the expression of COX-2, a typical AP-1 target gene, and decreased prostaglandin E2 (PGE2) production of peritoneal macrophages (pMΦs). pMΦs with SIRT1 overexpression displayed improved phagocytosis and tumoricidal functions, which are associated with depressed PGE2. Furthermore, SIRT1 protein level was up-regulated in CR mouse pMΦs, whereas elevated SIRT1 decreased COX-2 expression and improved PGE2-related macrophage functions that were reversed following inhibition of SIRT1 deacetylase activity. Thus, our results indicate that SIRT1 may be a mediator of CR-induced macrophage regulation, and its deacetylase activity contributes to the inhibition of AP-1 transcriptional activity and COX-2 expression leading to amelioration of macrophage function.

MicroRNA‐9 up‐regulates E‐cadherin through inhibition of NF‐κB1–Snail1 pathway in melanoma

MicroRNAs (miRNAs) are short non‐coding RNAs that post‐transcriptionally regulate gene expression. Hsa‐miR‐9 has been shown to have opposite functions in different tumour types; however, the underlying mechanism is unclear. Here we show that hsa‐miR‐9 is down‐regulated in metastatic melanomas compared to primary melanomas. Overexpression of miR‐9 in melanoma cells resulted in significantly decreased cell proliferation and migratory capacity with decreased F‐actin polymerization and down‐regulation of multiple GTPases involved in cytoskeleton remodelling. miR‐9 overexpression induced significant down‐regulation of Snail1 with a concomitant increase in E‐cadherin expression. In contrast, knockdown of miR‐9 increased Snail1 expression as well as melanoma cell proliferation and migration capacity. Mechanistically, miR‐9 expression down‐regulated NF‐κB1 in melanoma and the effect was abolished by mutations in the putative miR‐9 binding sites within the 3′‐untranslated region (UTR) of NF‐κB1. Anti‐miR‐9 miRNA inhibitor also increased the expression of NF‐κB1. The effects of miR‐9 on Snail1 expression and melanoma cell proliferation and migration were rescued by overexpression of NF‐κB1 in these cells. Furthermore, miR‐9 overexpression resulted in significantly decreased melanoma growth and metastasis in vivo. In summary, miR‐9 inhibits melanoma proliferation and metastasis through down‐regulation of the NF‐κB1‐Snail1 pathway. This study finds a new mechanism that miR‐9 utilizes to decrease E‐cadherin expression and inhibit melanoma progression. The results suggest that function of microRNAs is context and tumour type‐specific. Copyright

Generation of folliculogenic human epithelial stem cells from induced pluripotent stem cells

Epithelial stem cells (EpSCs) in the hair follicle bulge are required for hair follicle growth and cycling. The isolation and propagation of human EpSCs for tissue engineering purposes remains a challenge. Here we develop a strategy to differentiate human iPSCs (hiPSCs) into CD200+/ITGA6+ EpSCs that can reconstitute the epithelial components of the hair follicle and interfollicular epidermis. The hiPSC-derived CD200+/ITGA6+ cells show a similar gene expression signature as EpSCs directly isolated from human hair follicles. Human iPSC-derived CD200+/ITGA6+ cells are capable of generating all hair follicle lineages including the hair shaft, and the inner and outer root sheaths in skin reconstitution assays. The regenerated hair follicles possess a KRT15+ stem cell population and produce hair shafts expressing hair specific keratins. These results suggest an approach for generating large numbers of human EpSCs for tissue engineering and new treatments for hair loss, wound healing and other degenerative skin disorders.

Direct conversion of mouse and human fibroblasts to functional melanocytes by defined factors

Direct reprogramming provides a fundamentally new approach for the generation of patient-specific cells. Here, by screening a pool of candidate transcription factors, we identify that a combination of three factors, MITF, SOX10 and PAX3, directly converts mouse and human fibroblasts to functional melanocytes. Induced melanocytes (iMels) activate melanocyte-specific networks, express components of pigment production and delivery system, and produce melanosomes. Human iMels properly integrate into the dermal-epidermal junction, and produce and deliver melanin pigment to surrounding keratinocytes in a 3D organotypic skin reconstruct. Human iMels generate pigmented epidermis and hair follicles in skin reconstitution assays in vivo. The generation of iMels has important implications for studies of melanocyte lineage commitment, pigmentation disorders and cell replacement therapies.

Large-scale Analysis of PDGFRA Mutations in Melanomas and Evaluation of Their Sensitivity to Tyrosine Kinase Inhibitors Imatinib and Crenolanib

Purpose: Platelet-derived growth factor receptor α (PDGFRA) is a target for tyrosine kinase inhibitor (TKI)-based targeted therapy. Dysregulation of PDGFRA has been reported in many cancers. However, PDGFRA mutations in melanomas have not been well studied. We analyzed the genetic mutations of PDGFRA in Chinese patients with melanoma and determined the inhibitory potency of TKIs, such as imatinib and crenolanib, on mutant PDGFRA. Experimental Design: Of note, 351 melanoma tissue samples were examined for genetic mutations in exons 12, 14, and 18 of PDGFRA. Activities of mutations in response to imatinib and crenolanib were analyzed by Western blotting of tyrosine-phosphorylated PDGFRA and cell proliferation assays. Results: PDGFRA mutations were observed in 4.6% (16 of 351) of melanomas, and these mutations were mainly detected in acral and mucosal melanomas. PDGFRA mutations seem to be mutually exclusive with KIT mutations, but may coexist with BRAF and NRAS mutations. The genetic mutations of PDGFRA were unrelated to the age, thickness, and ulceration status of primary melanomas. Thirteen mutations were not reported before, and five (P577S, V658A, R841K, H845Y, and G853D) of them resulted in strong autophosphorylation of PDGFRA. Crenolanib showed higher potency than imatinib in inhibiting the kinase activity of PDGFRA. Except that V658A mutation was imatinib-resistant, all the other mutations were sensitive to both imatinib and crenolanib. Conclusions: PDGFRA mutations are detected in a small population of melanoma patients. Our study suggests that patients with melanoma harboring certain PDGFRA mutations may benefit from imatinib and crenolanib treatment. Clin Cancer Res; 19(24); 6935–42. ©2013 AACR.

Generation of melanocytes from Induced pluripotent stem cells

Epidermal melanocytes play an important role in protecting skin from ultraviolet (UV) rays, and are implicated in a variety of skin diseases. Here, we developed an efficient method for differentiating induced pluripotent stem cells (iPSCs) into melanocytes. We first generated iPSCs from adult mouse tail-tip fibroblasts (TTFs) using retroviral vectors or virus-free piggyBac transposon vectors carrying murine Sox2, Oct3/4, cMyc and Klf4. The TTF-derived iPSC clones exhibited similar morphology and growth properties as mouse embryonic stem (ES) cells. The iPSCs expressed ES cell markers, displayed characteristic epigenetic changes and formed teratomas with all three germ layers. The iPSCs were used to generate embryoid bodies (EBs) and were then successfully differentiated into melanocytes by treatment with growth factors. The iPSC-derived melanocytes expressed characteristic melanocyte markers and produced melanin pigment. Electron microscopy showed that the melanocytes contained mature melanosomes. We manipulated the conditions used to differentiate iPSCs to melanocytes and discovered that Wnt3a is not required for mouse melanocyte differentiation. This report shows that melanocytes can be readily generated from iPSCs, providing a powerful resource for the in vitro study of melanocyte developmental biology and diseases. By inducing iPSCs without viruses, the possibility of integration mutagenesis is alleviated, providing iPSCs are more compatible for cell replacement therapies.

Mitofilin regulates cytochrome c release during apoptosis by controlling mitochondrial cristae remodeling.

Mitochondria amplify caspase-dependent apoptosis by releasing proapoptotic proteins, especially cytochrome c. This process is accompanied by mitochondrial cristae remodeling. Our studies demonstrated that mitofilin, a mitochondrial inner membrane protein, acted as a cristae controller to regulate cytochrome c release during apoptosis. Knockdown of mitofilin in HeLa cells with RNAi led to fragmentation of the mitochondrial network and disorganization of the cristae. Mitofilin-deficient cells showed cytochrome c redistribution between mitochondrial cristae and the intermembrane space (IMS) upon intrinsic apoptotic stimuli. In vitro cytochrome c release experiments further confirmed that, compared with the control group, tBid treatment led to an increase in cytochrome c release from mitofilin-deficient mitochondria. Furthermore, the cells with mitofilin knockdown were more prone to apoptosis by accelerating cytochrome c release upon the intrinsic apoptotic stimuli than controls. Moreover, mitofilin deficiency did not interfere with the activation of proapoptotic member Bax upon intrinsic apoptotic stimuli. Thus, mitofilin distinctly functions in cristae remodeling and controls cytochrome c release during apoptosis.

Snail1 Mediates Hypoxia-Induced Melanoma Progression

Tumor hypoxia is a known adverse prognostic factor, and the hypoxic dermal microenvironment participates in melanomagenesis. High levels of hypoxia inducible factor (HIF) expression in melanoma cells, particularly HIF-2α, is associated with poor prognosis. The mechanism underlying the effect of hypoxia on melanoma progression, however, is not fully understood. We report evidence that the effects of hypoxia on melanoma cells are mediated through activation of Snail1. Hypoxia increased melanoma cell migration and drug resistance, and these changes were accompanied by increased Snail1 and decreased E-cadherin expression. Snail1 expression was regulated by HIF-2α in melanoma. Snail1 overexpression led to more aggressive tumor phenotypes and features associated with stem-like melanoma cells in vitro and increased metastatic capacity in vivo. In addition, we found that knockdown of endogenous Snail1 reduced melanoma proliferation and migratory capacity. Snail1 knockdown also prevented melanoma metastasis in vivo. In summary, hypoxia up-regulates Snail1 expression and leads to increased metastatic capacity and drug resistance in melanoma cells. Our findings support that the effects of hypoxia on melanoma are mediated through Snail1 gene activation and suggest that Snail1 is a potential therapeutic target for the treatment of melanoma.

Circulating Melanoma Cells as a Predictive Biomarker

The prognosis of patients with metastatic melanoma has improved significantly with targeted therapeutic agents and immunotherapies. Detection of early melanoma recurrence after treatment will be beneficial to switch patients who fail on one therapy to different modalities. Circulating tumor cells (CTCs) are cancer cells released by a tumor into the peripheral blood. These cells hold potential as prognostic, predictive, and pharmacodynamic biomarkers for treatment. In this issue, Khoja et al. report that melanoma CTCs can be detected using Melcam and high molecular weight melanoma-associated antibody. They found that in 101 stage IV melanoma patients, CTC numbers ranged between 0 and 36/7.5 ml blood; 26% of the patients had ≥ 2 CTCs at baseline. The CTC number (≥ 2 CTCs) at baseline was significantly prognostic for median overall survival (OS) in univariate and multivariate analysis. Patients receiving treatment where CTC numbers remained ≥ 2 CTCs during their treatment had shorter median OS than those who maintained <2 CTCs (7 vs. 10 months, hazard ratio 0.34, 95% confidence interval 0.14-0.81, log-rank test P=0.015). The implications of this work are substantial in counseling patients about their prognosis and in helping to assess responses to systemic therapies.