3952

LEP

Perturbations in the adipocytokine profile, especially higher levels of leptin, are a major cause of breast tumor progression and metastasis; the underlying mechanisms, however, are not well understood. In particular, it remains elusive whether leptin is involved in epithelial-mesenchymal transition (EMT). Here, we provide molecular evidence that leptin induces breast cancer cells to undergo a transition from epithelial to spindle-like mesenchymal morphology. Investigating the downstream mediator(s) that may direct leptin-induced EMT, we found functional interactions between leptin, metastasis-associated protein 1 (MTA1), and Wnt1 signaling components. Leptin increases accumulation and nuclear translocation of beta-catenin leading to increased promoter recruitment. Silencing of beta-catenin or treatment with the small molecule inhibitor, ICG-001, inhibits leptin-induced EMT, invasion, and tumorsphere formation. Mechanistically, leptin stimulates phosphorylation of glycogen synthase kinase 3beta (GSK3beta) via Akt activation resulting in a substantial decrease in the formation of the GSK3beta-LKB1-Axin complex that leads to increased accumulation of beta-catenin. Leptin treatment also increases Wnt1 expression that contributes to GSK3beta phosphorylation. Inhibition of Wnt1 abrogates leptin-stimulated GSK3beta phosphorylation. We also discovered that leptin increases the expression of an important modifier of Wnt1 signaling, MTA1, which is integral to leptin-mediated regulation of the Wnt/beta-catenin pathway as silencing of MTA1 inhibits leptin-induced Wnt1 expression, GSK3beta phosphorylation, and beta-catenin activation. Furthermore, analysis of leptin-treated breast tumors shows increased expression of Wnt1, pGSK3beta, and vimentin along with higher nuclear accumulation of beta-catenin and reduced E-cadherin expression providing in vivo evidence for a previously unrecognized cross-talk between leptin and MTA1/Wnt signaling in epithelial-mesenchymal transition of breast cancer cells.

BACKGROUND INFORMATION: Previous studies have revealed that leptin may be involved in epithelial-mesenchymal transition (EMT), a crucial initiator of cancer progression to facilitate metastatic cascade, increase tumor recurrence, and ultimately cause poor prognosis. However, the underlying mechanism remains unclear. The aim of our present study was to investigate the effect of leptin on EMT of breast cancer cells and the underlying mechanism. RESULTS: Our data demonstrated that leptin significantly increased the phosphorylation of STAT3, Akt, and ERK1/2, elevated the expression of IL-8, and induced breast cancer cells to undergo EMT. The effect of leptin on IL-8 could visibly abolished by the inhibitor of PI3K LY294002. In addition, leptin-induced EMT of breast cancer cells was blocked by anti-IL-8 antibodies. Examination of the expression of ObR, leptin, IL-8 and EMT-related biomarkers in patient specimens demonstrated that malignant breast carcinoma with lymph node metastases (LNM), which represents poor prognosis, expressed higher levels of ObR, leptin, IL-8 than other types of breast cancer, and displayed more obvious EMT transversion. In vivo xenograft experiment revealed that leptin signally promoted tumor growth and metastasis and increased the expressions of IL-8 and EMT-related biomarkers. CONCLUSIONS: Our results support that leptin-induced EMT in breast cancer cells requires IL-8 activation via the PI3K/Akt signal pathway.

BACKGROUND: Accumulating researches have shown that epithelial-mesenchymal transition (EMT) contributes to tumor metastasis. Leptin, a key adipokine secreted from adipocytes, shapes the tumor microenvironment, potentiates the migration of breast cancer cells and angiogenesis, and is also involved in EMT. However, the potential mechanism remains unknown. This study aims to explore the effect of leptin on EMT in breast cancer cells and the underlying mechanism. METHODS: With the assessment of EMT-associated marker expression in MCF-7, SK-BR-3, and MDA-MB-468 cells, the effect of leptin on breast cancer cells was analyzed. Besides, an array of pathway inhibitors as well as RNA interference targeting pyruvate kinase M2 (PKM2) were used to clarify the underlying mechanism of leptin-mediated EMT in vitro and in vivo. RESULTS: The results demonstrated that leptin promoted breast cancer cells EMT, visibly activated the PI3K/AKT signaling pathway, and upregulated PKM2 expression. An antibody against the leptin receptor (anti-ObR) and the PI3K/AKT signaling pathway inhibitor LY294002 significantly abolished leptin-induced PKM2 expression and EMT-associated marker expression. SiRNA targeting PKM2 partially abolished leptin-induced migration, invasion, and EMT-associated marker expression. In vivo xenograft experiments indicated that RNA interference against PKM2 suppressed breast cancer growth and metastasis. CONCLUSIONS: Our data suggest that leptin promotes EMT in breast cancer cells via the upregulation of PKM2 expression as well as activation of PI3K/AKT signaling pathway, and PKM2 might be one of the key points and potential targets for breast cancer therapy.

Leptin, a protein-related product of the obesity gene, plays an important role in the pathogenesis of fibrotic diseases including pulmonary fibrosis. As a highly conservative process, autophagy regulates various biological functions. Otherwise, insufficient autophagy has been described in alveolar epithelial cells (AEC) to cope with the progression of pulmonary fibrosis. Hence, this study is to investigate the effects of leptin on fibrosis in TGF-beta1 induced epithelial mesenchymal transition (EMT) and the potential roles of autophagy in this processes. Our results showed that the elevated leptin level in serum correlated with the severity of lung fibrosis and leptin significantly promoted the EMT in A549cells as evidenced by promoting collagen I and alpha-SMA production. Additionally, treatment with leptin decreased autophagosome formation, inhibited the lipidation of LC3I to LC3II, and up-regulated the expression of p62 via activating PI3K/Akt/mTOR pathway, which is indicative of inhibition of autophagy by leptin. Finally, rapmycin pretreatment reversed the pro-fibrogenic effects of leptin. Taken together, our study suggested that leptin accelerated the EMT of A549cells through inhibiting autophagy via PI3K/Akt/mTOR pathway.CI - Copyright (c) 2018 Elsevier Inc. All rights reserved.