Leptin Promotes Metastasis by Inducing an Epithelial‐Mesenchymal Transition in A549 Lung Cancer Cells

Abstract

Leptin, an adipocyte-derived cytokine associated with obesity, has been reported to participate in carcinogenesis. Epithelial-mesenchymal transition (EMT) is also considered as a key event in tumor metastasis. The aim of this study is to investigate the mechanism of leptin in the promotion of EMT leading to metastasis in A549 lung cancer cells. We investigated the effect of leptin on migration of A549 cells using wound healing and transwell assays. The incidence of EMT in A549 cells was examined by real-time PCR and immunofluorescence staining. The expression of TGF-β in A549 cells was detected by real-time PCR, and blocking of TGF-β in A549 cells was achieved by siRNA techniques. Additional work was performed using 100 patient samples, which included samples from 50 patients diagnosed with lung cancer and an additional 50 patients diagnosed with lung cancer with metastatic bone lesions. Leptin expression was measured using immunohistochemistry techniques. We demonstrated that leptin can effectively enhance the metastasis of human lung cancer A549 cell line using both wound healing and transwell assays. We also found the incidence of EMT in A549 cells after leptin exposure. Furthermore, we detected the expression of TGF-β in A549 cells, which had been reported to play an important role in inducing EMT. We showed that leptin can significantly upregulate TGF-β at both the mRNA and protein levels in A549 cells. Using siRNA to block the expression of TGF-β in A549 cells, we confirmed the role of TGF-β in the promotion of metastasis and induction of EMT. Furthermore, we found that in patient samples leptin was present at higher levels in samples associated with diagnosis of lung cancer bone metastases tissue than lung cancer tissue. Our results indicated that leptin promoted the metastasis of A549 human lung cancer cell lines by inducing EMT in a TGF-β-dependent manner.

Leptin induces epithelial-to-mesenchymal transition via activation of the ERK signaling pathway in lung cancer cells

“…Consistent with the results of the present study, a previous report regarding the mechanism of leptin in the promotion of EMT leading to metastasis in A549 lung cancer cells was studied (21). In the previous study, the incidence of EMT in A549 cells was examined by real-time PCR and immunofluorescence staining.…”

“…However, few studies have investigated the association between leptin and the metastasis of lung cancer. A previous study demonstrated that leptin is differentially expressed in lung cancer tissues that do not occur or metastasize, and the expression of leptin is increased in lung cancers with bone metastasis (21), indicating that the leptin pathway may be involved in the metastasis of lung cancer. However, the effect and mechanisms of leptin on metastasis of lung cancer have not yet been fully elucidated.…”

The potential role of leptin in tumor invasion and metastasis

“…This was demonstrated by an increased accumulation and nuclear translocation of β-catenin by leptin due to a decrease in the formation of glycogen synthase kinase 3β (GSK3β)-liver kinase B1 (LKB1)-axin complex in MCF-7, MDA-MB-468 and MDA-MB-231 breast cancer cells. In addition, using A549 human lung cancer cells, Feng and colleagues reported that leptin significantly upregulated TGF-β that may play an important role in inducing EMT [14]. Leptin-mediated activation of intracellular signaling molecules such as STAT3, AKT, and PI3K could contribute to EMT-linked mechanisms [15,16].…”

Vitamin D3 in cancer prevention and therapy: the nutritional issue

“…This suggestion comes from observations reporting leptin as a molecule associated with many autoimmune disorders [83][84][85], while reduced calcitriol availability has been recently considered a risk factor for several chronic inflammatory or autoimmune diseases [86]. The leptin molecule, which would modulate energy balance and cell cycle [87], can promote EMT mechanism [63], thus worsening the pro-cancerogenic role of tumor associated WAT. In this perspective, dietary supplementation with vitamin D might not result in any efficacy against tumors [15].…”

“…The apparent procancerogenic action of leptin should be inhibited by calcitriol but this active form of vitamin D 3 regulates cancer progression through VDR and the expression of vitamin D receptor is highly downregulated or dampened in cancer cells during metastasis, affecting both function of tumor associated macrophages (TAMs) and EMT [60]. Paradoxically, calcitriol up-regulates, in a VDR-dependent manner, the expression and release of leptin from white adipose tissue (WAT) [61], and in this sense, adipocytes may be considered as cells able to fuel and promote cancer development [62,63]. This circumstance appears to be worsened by the increasing inability of calcitriol to interact with cancer cells through a VDR-mediated mechanism.…”