Synergistic effects of hypoxia and insulin are regulated by different transcriptional elements of the human leptin promoter

Meißner, Udo; Östreicher, Iris; Allabauer, Ida; Rascher, Wolfgang; Dötsch, Jörg

doi:10.1016/s0006-291x(03)00401-7

Cited by 38 publications

(36 citation statements)

References 36 publications

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“…For instance, seven Sp1 sites, and 8 elements binding HIF. 22,35,36 Our previous study demonstrated that in MDA-MB-231 cells treated with insulin, Sp1 acts through two sites, one of which is in Lep-2548 region. On the other hand, functional insulin-regulated Sp1 sites in the leptin promoter have not been mapped in other cells lines.…”

Section: Discussionmentioning

confidence: 99%

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

Terrasi

Fiorio

Mercanti

et al. 2009

Intl Journal of Cancer

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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

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Section: Discussionmentioning

confidence: 99%

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

Terrasi

Fiorio

Mercanti

et al. 2009

Intl Journal of Cancer

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“…The same conditions and with similar dynamics appeared to stimulate the leptin gene promoter (from À2924 to þ 31; Figure 4). Although the same promoter has previously been shown to respond to glucocorticoids in 3T3-L1 cells (De Vos et al, 1998), and to insulin and hypoxia in BeWo cells (Grosfeld et al, 2002;Meissner et al, 2003), its activity in breast cancer cells has never been described.…”

Section: Hif-1a Controls Leptin Expression In Breast Cancer S Cascio mentioning

confidence: 99%

“…The human leptin gene promoter is B3000 long and contains several regulatory motifs, including AP2, SP-1, CREB, C/EBP, GRE, CRE elements (Mason et al, 1998;Ahima and Flier, 2000;Melzner et al, 2002;Meissner et al, 2003). Most importantly, the promoter contains eight hypoxia-responsive elements (HRE) with the minimal core sequence 5 0 -RCGTG-3 0 that can recruit hypoxia-inducible factor (HIF) (Grosfeld et al, 2002;Meissner et al, 2003). HIF is a master transcriptional factor in nutrient stress signaling and can induce an array of genes involved in energy metabolism, neovascularization, survival, cell migration and pH balance.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of leptin expression in breast cancer cells: role of hypoxia-inducible factor-1α

et al. 2007

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We reported previously that the obesity hormone leptin is 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. By using quantitative real-time PCR, immunofluorescent detection of proteins and enzyme-linked immunosorbent assays, we found that treatment of MCF-7 breast cancer cells with high doses of insulin or the hypoxia-mimetic agent CoCl 2 , or culturing the cells under hypoxic conditions significantly increased the expression of leptin mRNA and protein. Notably, the greatest leptin mRNA and protein expression were observed under combined hyperinsulinemia and hypoxia or hypoxia-mimetic treatments. Luciferase reporter assays suggested that increased leptin synthesis could be related to the activation of the leptin gene promoter. DNA affinity precipitation and chromatin immunoprecipitation experiments revealed that insulin, CoCl 2 and/or hypoxia treatments augmented nuclear accumulation of hypoxia-inducible factor-1a (HIF-1a) and increased its interaction with several upstream leptin regulatory sequences, especially with the proximal promoter containing four hypoxia-response elements and three GC-rich regions. By using reverse chromatin precipitation, we determined that loading of HIF-1a on the proximal leptin promoter concurred with the recruitment of p300, the major HIF coactivator, suggesting that the HIF/p300 complex is involved in leptin transcription. The importance of HIF-1a in insulin-and CoCl 2 -activated leptin mRNA and protein expression was confirmed using RNA interference.

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“…Comparing sera from women with preeclampsia with sera of mothers with uncomplicated pregnancies (44), elevated concentrations of this cytokine can be found in the preeclamptic mothers. This effect is mediated by the fact that leptin production could be enhanced by hypoxia (20,21,26,29). Conflicting results have been found regarding the ability of the ob-gene product, leptin, to interfere with apoptosis (11 -13).…”

Section: Discussionmentioning

confidence: 99%

“…For analyzing the gene expression (mRNA) of leptin and of the hypoxanthine-guanine phosphoribosyltransferase (HPRT), as well as of porphobilinogen deaminase (PBGD) as housekeeping genes, we used the primers as previously described (21). All assays were performed using a quantitative real-time polymerase chain reaction (TaqMan PCR, PerkinElmer Life Sciences Inc. Boston, MA, USA).…”

Section: Real-time Pcrmentioning

confidence: 99%

Hypoxia-induced leptin production in human trophoblasts does not protect from apoptosis

et al. 2005

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Objective: The ob-gene product, leptin, is an important regulator of placental and fetal development during pregnancy. Leptin, being induced by hypoxia in the placenta, is a known pro-apoptotic molecule in adipose tissue but is also known to inhibit apoptosis in other tissues like neuroblastoma cells. Based on these findings, we investigated if leptin has a pro-or anti-apoptotic effect on a trophoblastic cell line (JAr cells) in the presence or absence of oxygen. Methods and results: Measurement of leptin in the supernatant by using ELISA showed hypoxiainduced leptin production in JAr cells in vitro. This could be confirmed by a leptin-specific RT-PCR. By analyzing leptin and/or hypoxia exposed cells with FACS cytometry we found that JAr cells can cope with hypoxia down to oxygen tensions of 1%. At this level, only a small number of cells underwent apoptosis. Interestingly, leptin added to the culture medium in high concentrations was not able to interfere with the rate of proliferation or apoptosis in these cells independent of the oxygen tension. Finally, an anti-caspase-3 and anti-caspase-9 Western blot was performed. Again, no difference in the expression of caspase-3 and -9 under the conditions tested was seen. Conclusions: These results show that leptin, produced by placental cells after hypoxia in vitro, has no influence on the rate of proliferation of these cells. Furthermore, it does not influence apoptotic pathways in the trophoblastic cell line tested under hypoxic and non-hypoxic conditions. European Journal of Endocrinology 153 455-461

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Synergistic effects of hypoxia and insulin are regulated by different transcriptional elements of the human leptin promoter

Cited by 38 publications

References 36 publications

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

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

Mechanism of leptin expression in breast cancer cells: role of hypoxia-inducible factor-1α

Hypoxia-induced leptin production in human trophoblasts does not protect from apoptosis

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