ABSTRACT
Obese breast cancer patients exhibit a higher risk for larger tumor burden and an increased likelyhood of metastasis. The molecular effects of obesity on carcinogenesis are mediated by the autocrine and paracrine effects of the adipocytokine leptin. Leptin participates in the tumor progression and metastasis of human breast. We show that leptin induces clonogenicity and increases the migration potential of breast cancer cells. We found that survivin expression is induced in response to leptin. In this study, we examine the role and leptin-mediated regulation of survivin. Leptin treatment leads to survivin upregulation, due in part to the activation of Notch1 and the release of a transcriptionally active Notch1 intracellular domain (NICD). Chromatin immunoprecipitation analysis shows that NICD gets recruited to the survivin promoter at the CSL (CBF1/RBP-Jk, Su(H), Lag-1) binding site in response to leptin treatment. Inhibition of Notch1 activity inhibits leptin-induced survivin upregulation. Leptin-induced transactivation of epidermal growth factor receptor (EGFR) is involved in leptin-mediated Notch1 and survivin upregulation, demonstrating a novel upstream role of leptin-EGFR-Notch1 axis. We further show that leptin-induced migration of breast cancer cells requires survivin, as overexpression of survivin further increases, whereas silencing survivin abrogates leptin-induced migration. Using a pharmacological approach to inhibit survivin, we show that 3-hydroxy-3-methylglutaryl-coenzyme-A-reductase inhibitors, such as lovastatin, can effectively inhibit leptin-induced survivin expression and migration. Importantly, leptin increased breast tumor growth in nude mice. These data show a novel role for survivin in leptin-induced migration and put forth pharmacological survivin inhibition as a potential novel therapeutic strategy. This conclusion is supported by in vivo data showing the overexpression of leptin and survivin in epithelial cells of high-grade ductal carcinomas in situ and in high-grade invasive carcinomas.
Subject(s)
Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Cell Movement , ErbB Receptors/metabolism , Inhibitor of Apoptosis Proteins/metabolism , Leptin/metabolism , Receptor, Notch1/metabolism , Animals , Blotting, Western , Breast Neoplasms/genetics , Cell Adhesion , Cell Line, Tumor , Chromatin Immunoprecipitation , ErbB Receptors/genetics , Female , Fluorescent Antibody Technique , Humans , Immunoenzyme Techniques , Immunoprecipitation , Inhibitor of Apoptosis Proteins/antagonists & inhibitors , Inhibitor of Apoptosis Proteins/genetics , Mice , Mice, Nude , RNA, Messenger/genetics , Receptor, Notch1/genetics , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction , Survivin , Up-Regulation , Wound HealingABSTRACT
Obesity is an independent risk factor for breast cancer, and obese breast cancer patients exhibit a higher risk for larger tumor burden and increased metastasis. Obesity, as associated with metabolic syndrome, results in an increase in circulating insulin-like growth factor (IGF), which acts as a mitogen. In addition, higher plasma level of adipocytokine leptin is associated with obesity. In the present study, we show that cotreatment with leptin and IGF-I significantly increases proliferation as well as invasion and migration of breast cancer cells. We found a novel bidirectional crosstalk between leptin and IGF-I signaling; IGF-I induced phosphorylation of leptin receptor (Ob-Rb) and leptin induced phosphorylation of IGF-I receptor (IGF-IR), whereas cotreatment induced synergistic phosphorylation and association of Ob-Rb and IGF-IR along with activation of downstream effectors, Akt and extracellular signal-regulated kinase. Leptin increased phosphorylation of IGF signaling molecules insulin-receptor substrate (IRS)-1 and IRS-2. Interestingly, we found that leptin and IGF-I cotreatment synergistically transactivated epidermal growth factor receptor (EGFR), depending on the proteolytic release of EGFR ligands, as the broad-spectrum matrix metalloproteinase inhibitor GM6001 could inhibit this effect. Using clinically relevant EGFR inhibitors, erlotinib and lapatinib, we found that inhibition of EGFR activation effectively inhibited leptin- and IGF-I-induced invasion and migration of breast cancer cells. Taken together, these data suggest a novel bidirectional crosstalk between leptin and IGF-I signaling that transactivates EGFR and promotes the metastatic properties as well as invasion and migration of breast cancer cells. Our findings indicate the possibility of using EGFR inhibitors erlotinib and lapatinib to counter the procancerous effects of leptin and IGF-I in breast cancers.