Functional analysis of the ‐2548G/A leptin gene polymorphism in breast cancer cells

• Published in: International journal of cancer Vol. 125; no. 5; pp. 1038 - 1044
• Main Authors: Terrasi, Marianna, Fiorio, Elena, Mercanti, Anna, Koda, Mariusz, Moncada, Camilo A., Sulkowski, Stanislaw, Merali, Salim, Russo, Antonio, Surmacz, Eva
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-09-2009; Wiley-Blackwell
• Subjects: Biological and medical sciences; Blotting, Western; Body Mass Index; breast cancer; Breast Neoplasms - complications; Breast Neoplasms - genetics; Chromatin Immunoprecipitation; Genotype; Gynecology. Andrology. Obstetrics; Humans; Hypoglycemic Agents - pharmacology; insulin; Insulin - pharmacology; leptin; Leptin - genetics; Mammary gland diseases; Medical sciences; Nucleolin; Obesity - genetics; Phosphoproteins - genetics; polymorphism; Polymorphism, Genetic - genetics; Promoter Regions, Genetic - genetics; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA-Binding Proteins - genetics; Sp1; Sp1 Transcription Factor - metabolism; Tumor Cells, Cultured; Tumors; Pancreatic hormone; Breast disease; Genetic variability; Genotype; Functional analysis; Breast cancer; Malignant tumor; Adipokine; Insulin; Nucleolin; Spl; Mammary gland diseases; Cancerology; Leptin; Tumor cell; Cancer; Polymorphism
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.24372

Leptin is overexpressed in human breast tumors and is produced by breast cancer cells in response to obesity‐related stimuli. The leptin promoter polymorphism Lep‐2548G/A can be associated with increased leptin secretion by adipocytes and elevated cancer risk. However, molecular mechanisms underlying the link between Lep‐2548G/A and breast cancer have never been addressed. Lep‐2548G/A is proximal to a binding site for the transcriptional factor Sp1. Furthermore nucleolin, a transcriptional repressor, can bind Sp1 or its consensus site. Consequently, we focused on the impact of Lep‐2548G/A on Sp1‐ and nucleolin‐dependent leptin transcription in breast cancer cells. The Lep‐2548G/A was identified in a homozygous conformation in BT‐474 and SK‐BR‐3 breast cancer cells, in a heterozygous conformation in MDA‐MB‐231 cells, and a wild‐type Lep‐2548G/G sequence was present in MCF‐7 and ZR‐75‐1 cells. The occurrence of Lep‐2548A/A and Lep‐2548G/A coincided with high and intermediate leptin mRNA expression, respectively, while cells containing Lep‐2548G/G expressed low leptin mRNA levels. We demonstrated that the existence of Lep‐2548G/A improved efficient recruitment of Sp1 to DNA under insulin treatment, while Sp1 loading on DNA containing Lep‐2548G/G was not insulin‐dependent. In contrast, nucleolin binding to Lep‐2548G/A was downregulated in response to insulin, while it was not regulated on Lep‐2548G/G. The presence of Lep‐2548G/A was studied in breast cancer epithelial cells by IHC and LCM. Interestingly, all 14 tumors expressing high leptin levels contained Lep‐2548A/A. In conclusion, the occurrence of Lep‐2548G/A can enhance leptin expression in breast cancer cells via Sp1‐ and nucleolin‐dependent mechanisms and possibly contribute to intratumoral leptin overexpression. © 2009 UICC