We reported previously that the obesity hormone leptinis overexpressed in breast cancer biopsies. Here, we investigated molecular mechanisms involved in this process,focusing on conditions that are associated with obesity,that is, hyperinsulinemia and induction of hypoxia. Byusing quantitative real-time PCR, immunofluorescentdetection of proteins and enzyme-linked immunosorbentassays, we found that treatment of MCF-7 breast cancercells with high doses of insulin or the hypoxia-mimeticagent CoCl2, or culturing the cells under hypoxicconditions significantly increased the expression of leptinmRNA and protein. Notably, the greatest leptin mRNAand protein expression were observed under combinedhyperinsulinemia and hypoxia or hypoxia-mimetic treatments. Luciferase reporter assays suggested thatincreased leptin synthesis could be related to the activationof the leptin gene promoter. DNA affinity precipitationand chromatin immunoprecipitation experiments revealedthat insulin, CoCl2 and/or hypoxia treatments augmentednuclear accumulation of hypoxia-inducible factor-1a(HIF-1a) and increased its interaction with severalupstream leptin regulatory sequences, especially with theproximal promoter containing four hypoxia-responseelements and three GC-rich regions. By using reversechromatin precipitation, we determined that loading ofHIF-1a on the proximal leptin promoter concurred withthe recruitment of p300, the major HIF coactivator,suggesting that the HIF/p300 complex is involved in leptintranscription. The importance of HIF-1a in insulin- andCoCl2-activated leptin mRNA and protein expression wasconfirmed using RNA interference
|Numero di pagine||8|
|Stato di pubblicazione||Published - 2007|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cancer Research
Russo, A., Auriemma, A., Bartella, V., Johannes, Cascio, S., Giordano, A., Surmacz, E., & Cascio, S. (2007). Mechanism of leptin expression in breast cancer cells: role of hypoxia-inducible factor-1alpha. Oncogene, 2007, 1-8.