Leptin-regulated gene expression in MCF-7 breast cancer cells: mechanistic insights into leptin-regulated mammary tumor growth and progression

Abstract

Obesity is a recently established risk factor for breast cancer incidence and mortality. A characteristic of obesity is elevated circulating levels of adipocyte-derived hormone leptin. Evidence indicates that leptin plays an important role in mammary tumor formation; however, the mechanisms involved are poorly understood. Toward better defining the role of leptin in breast cancer, we describe the identification of leptin-regulated genes in hormone-responsive Michigan Cancer Foundation-7 (MCF-7) human breast cancer cells using a microarray system. More than 64 leptin-regulated genes were identified including those for growth factors, cell cycle regulators, extracellular matrix (ECM) proteins, and genes associated with metastasis. Cell cycle genes up-regulated by leptin include cyclins D and G, cyclin-dependent kinase 2, p21, p27, and p16. Leptin suppressed the expression of transforming growth factor-b , a cell cycle suppressor. Determining the significance of this effect, treatment of MCF-7 cells with TGFB1 abrogated leptin-stimulated proliferation. Leptin up-regulated the expression of connective tissue growth factor, villin 2, and basigin, factors that are associated with ECM and are known to impact tumor growth. Finally, leptin induced the expression of anti-apoptotic genes BCL2 and survivin, and reduced the expression of apoptotic genes. The effect of leptin on MCF-7 survival was evaluated via TUNEL assay and demonstrated a sixfold reduction in apoptosis in leptin-treated cells, compared with controls. These data suggest leptin promotes mammary tumor growth through multiple mechanisms, including regulating the cell cycle, apoptosis, and by modulating the extracellular environment. The identification of leptinregulated genes begins to provide mechanistic links into the relationship between obesity and breast cancer incidence and morbidity.

Autophagy induction by leptin contributes to suppression of apoptosis in cancer cells and xenograft model: Involvement of p53/FoxO3A axis

“…Many previous studies have used leptin concentration ranging from 10-200 nM, which is equivalent to 160-3200 ng/ml. In fact, these concentrations are higher than that seen in normal subjects, but commonly observed in obese subjects [3, 7, 9, 34, 57]. The leptin concentration used in our study would be relevant to the obese people and was within the range used by many previous studies.…”

“…Autophagy also targets apoptosis-related proteins such as Bax for degradation, and cleaves caspases, thereby inhibiting apoptosis [33]. Leptin has been shown to induce proliferation of hepatocellular [7], esophageal [3], breast [34], prostate [9], colon [35], and gastric cancer cell lines [36] and suppresses apoptosis in hepatocellular carcinoma cell lines [7] and esophageal adenocarcinoma cells [3] etc. Although previous studies have demonstrated mutual negative relationship between autophagy and apoptosis, the role of leptin-induced autophagy in the suppression of apoptosis in cancer cells has not been reported.…”

The cellular and molecular mechanisms by which insulin influences breast cancer risk and progression

“…Plasma leptin levels are elevated in type 2 diabetes and exhibit a positive correlation with the degree of insulin resistance that is independent of the BMI and body fat mass (Fischer et al 2002, Wauters et al 2003. Insulin regulates leptin availability by stimulating both new leptin synthesis and the release of leptin from pre-existing intracellular pools; this elevation in leptin levels involves interaction between insulin and glucocorticoids and is dependent on the Breast cancer cells possess leptin receptors, and leptin stimulates mitogenesis and also functions as an anti-apoptotic (survival) factor (Perera et al 2008). In consequence, when hyperinsulinemia is present to provide an endocrine stimulus for leptin production by tumor-associated adipocytes, all the elements are in place for the establishment of an insulin-mediated, growth-promoting, paracrine loop between adipocytesecreted leptin and the leptin receptor-expressing breast cancer cell (Fig.…”

Obesity and renal cancer

“…Thus, the progeny of LEP-signaling (ob/ob or db/db) mice crossed with MTTV-TGFα mice (the latter or which are prone to undergo spontaneous mammary carcinogenesis) do not develop mammary tumors 15 , 16 . Several carcinogenic actions have been attributed to LEP, including the modulation of cell cycle-regulatory proteins as cyclin D1 and G, cyclin-dependent kinase 2 (CDK2), cyclin-dependent kinase inhibitor 1A (CDKN1A, best known as p21 CIP1 ), CDKN1B (best known as p27 KIP1 ), and CDKN2A (best known as p16 INK4A ) and transforming growth factor β1 (TGFβ1), resulting in the acceleration of cancer cell growth 17 , 18 . LEP also sustains angiogenesis.…”

“…For instance, human MCF7 and MDA-MB-231 breast carcinoma cells exposed to LEP secrete increased levels of vascular endothelial growth factor (VEGF) and are more invasive than their untreated counterparts 19 . Finally, LEP signaling not only induces the expression of the anti-apoptotic proteins BCL-2 and survivin, 17 but also limits the reduces the activity of caspases 20 …”