Leptin-induced Cell Proliferation Research Articles

Leptin Enhances Hepatic Fibrosis and Inflammation in a Mouse Model of Cholestasis

Leptin is an adipokine with roles in food intake and energy metabolism through its actions on neurons in the hypothalamus. The role of leptin in obesity and cardiovascular disorders is well documented. However, its influence on liver conditions such as cholestasis is poorly understood. The effects of exogenous leptin and leptin-neutralizing antibody on biliary hyperplasia, hepatic fibrosis, and inflammation in the multidrug resistance protein 2 knockout (Mdr2KO) mouse model of cholestasis were assessed by quantifying markers specific for cholangiocytes, activated hepatic stellate cells (HSCs), and cytokines. Serum and hepatic leptin were increased in Mdr2KO mice compared with FVB/NJ (FVBN) controls, and exogenous leptin enhanced biliary hyperplasia and liver fibrosis in Mdr2KO and FVBN mice. Leptin administration increased hepatic expression of C-C motif chemokine ligand 2 and IL-6 in Mdr2KO mice. In contrast, leptin-neutralizing antibody reduced intrahepatic bile duct mass and decreased HSC activation in Mdr2KO mice compared with FVBN controls. Sex-related differences were noted, with female Mdr2KO mice having more leptin than males. In cholangiocytes and LX2 cells invitro, leptin increased phosphorylated Akt and stimulated cell proliferation. Leptin receptor siRNA and inhibitors of Akt phosphorylation impaired leptin-induced cell proliferation and proinflammatory cytokines. The current data suggest that leptin is abnormally increased in cholestatic mice, and excess leptin increases ductular reaction, hepatic fibrosis, and inflammation via leptin receptor-mediated phosphorylation of Akt in cholangiocytes and HSCs.

Abstract 1940: Autophagy mediates leptin induced migration and erk activation in breast cancer cells

Abstract Autophagy is an intracellular recycling process active in eukaryotic cells which involves the formation of an autophagosome that delivers cytoplasmic components to the lysosome for degradation. This process occurs at low rates under basal conditions, but it can be induced by diverse stress conditions such as starvation, hypoxia or metabolic disorders. Autophagic flux can also be enhanced in response to hormones, including leptin. Leptin is considered a pro-tumorigenic protein whose circulating levels have been related to a bad prognosis in obese breast cancer patients. It has been recently demonstrated that leptin can induce autophagy in cancer cell lines from different tissues, suggesting that autophagy could modulate the pro-tumorigenic effects associated with leptin. In this study, the role of autophagy in leptin-induced proliferation, migration, apoptosis and ERK phosphorylation in breast cancer cell lines was evaluated. Methods: MCF7 estrogen receptor positive and MDA-MB-231 triple negative breast cancer cell lines were used. MCF7 and MDA-MB-231 cell lines were stimulated with 400 and 50 ng/ml of leptin, respectively. Autophagy was assessed by LC3-II and p62 protein levels by western blot, and autophagosome formation by fluorescence microscopy. Proliferation and migration were assessed by real-time microscopy in an IncuCyte analyzer; and cell death was evaluated by fluorescence analysis of caspase activity. Changes in ERK phosphorylation were measure by western blot. Results: Leptin increased autophagy in MCF7 cells but not in triple negative MDA-MB-231 cells. In MCF7 cells, autophagy inhibition reduced leptin-induced cell proliferation, changes associated to a mesenchymal morphology, cell migration, and ERK activation. In MDA-MB-231 cells, autophagy inhibition reduced proliferation and increased apoptosis independently of leptin treatment. In both cell lines, leptin-induced migration and ERK phosphorylation were reduced by the inhibition of autophagy. Conclusion: Autophagy was important for increased cancer cell migration induced by leptin and for the maintenance of ERK phosphorylation. Our data suggest a potential use for the inhibition of autophagy in breast cancer associated with obesity. Citation Format: Alin García Miranda, Karen A. Solano Alcalá, José B. Montes Alvarado, Julio Reyes Leyva, Paola Maycotte, Eduardo Castañeda Saucedo. Autophagy mediates leptin induced migration and erk activation in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1940.

Autophagy Mediates Leptin-Induced Migration and ERK Activation in Breast Cancer Cells.

Autophagy is an intracellular recycling process active in eukaryotic cells that involves the formation of an autophagosome which delivers cytoplasmic components to the lysosome for degradation. This process occurs at low rates under basal conditions, but it can be induced by diverse types of stress such as starvation, hypoxia, metabolic disorders or in response to hormones, including leptin. Leptin is considered a pro-tumorigenic protein whose circulating levels have been related to bad prognosis in obese breast cancer patients. It has been recently demonstrated that leptin can induce autophagy in cancer cell lines from different tissues, suggesting that autophagy could modulate the pro-tumorigenic effects associated with leptin. In this study, the role of autophagy in leptin-induced proliferation, migration, apoptosis and ERK phosphorylation in breast cancer cell lines was evaluated. Although leptin differentially induced autophagy in the breast cancer cell lines tested, autophagy inhibition reduced leptin-induced cell proliferation in MCF7 cells and decreased cell migration, ERK activation, and impaired morphological changes in both cell lines. Our data demonstrates an important role for basal autophagy or leptin-induced autophagy in leptin-induced migration and ERK phosphorylation in breast cancer cell lines, suggesting a potential use for the inhibition of autophagy in breast cancer associated with obesity.

Leptin-derived peptides block leptin-induced proliferation by reducing expression of pro-inflammatory genes in hepatocellular carcinoma cells

The obesity-regulated gene, leptin, is essential for diet. Leptin resistance causes obesity and related diseases. Certain types of diet are able to decrease leptin resistance. However, leptin has been shown to be correlated with inflammation and stimulate proliferation of various cancers. Two synthetic leptin derivatives (mimetics), OB3 and [D-Leu-4]-OB3, show more effective than leptin in reducing obesity and diabetes in mouse models. OB3 inhibits leptin-induced proliferation in ovarian cancer cells. However, effects of these mimetics in hepatocellular carcinoma (HCC) have not been investigated. In the present study, we examined the effects of OB3 and [D-Leu-4]-OB3 on cell proliferation and gene expressions in human HCC cell cultures. In contrast to what was reported for leptin, OB3 and [D-Leu-4]-OB3 reduced cell proliferation in hepatomas. Both OB3 and [D-Leu-4]-OB3 stimulated expression of pro-apoptotic genes. Both compounds also inhibited expressions of pro-inflammatory, proliferative and metastatic genes and PD-L1 expression. In combination with leptin, OB3 inhibited leptin-induced cell proliferation and expressions of pro-inflammation-, and proliferation-related genes. Furthermore, the OB3 peptide inhibited phosphoinositide 3-kinase (PI3K) activation which is essential for leptin-induced proliferation in HCC. These results indicate that OB3 and [D-Leu-4]-OB3 may have the potential to reduce leptin-related inflammation and proliferation in HCC cells.

Gallic acid modulates phenotypic behavior and gene expression in oral squamous cell carcinoma cells by interfering with leptin pathway

Gallic acid is a polyphenolic compost appointed to interfere with neoplastic cells behavior. Evidence suggests an important role of leptin in carcinogenesis pathways, inducing a proliferative phenotype. We investigated the potential of gallic acid to modulate leptin-induced cell proliferation and migration of oral squamous cell carcinoma cell lines. The gallic acid effect on leptin secretion by oral squamous cell carcinoma cells, as well as the underlying molecular mechanisms, was also assessed. For this, we performed proliferation, migration, immunocytochemical and qPCR assays. The expression levels of cell migration-related genes (MMP2, MMP9, Col1A1, and E-cadherin), angiogenesis (HIF-1α, mir210), leptin signaling (LepR, p44/42 MAPK), apoptosis (casp-3), and secreted leptin levels by oral squamous cell carcinoma cells were also measured. Gallic acid decreased proliferation and migration of leptin-treated oral squamous cell carcinoma cells, and reduced mRNA expression of MMP2, MMP9, Col1A1, mir210, but did not change HIF-1α. Gallic acid decreased levels of leptin secreted by oral squamous cell carcinoma cells, accordingly with downregulation of p44/42 MAPK expression. Thus, gallic acid appears to break down neoplastic phenotype of oral squamous cell carcinoma cells by interfering with leptin pathway.

Leptin induces CREB-dependent aromatase activation through COX-2 expression in breast cancer cells

Leptin plays a key role in the control of adipocyte formation, as well as in the associated regulation of energy intake and expenditure. The goal of this study was to determine if leptin-induced aromatase enhances estrogen production and induces tumor cell growth stimulation. To this end, breast cancer cells were incubated with leptin in the absence or presence of inhibitor pretreatment, and changes in aromatase and cyclooxygenase-2 (COX-2) expression were evaluated at the mRNA and protein levels. Transient transfection assays were performed to examine the aromatase and COX-2 gene promoter activities and immunoblot analysis was used to examine protein expression. Leptin induced aromatase expression, estradiol production, and promoter activity in breast cancer cells. Protein levels of phospho-STAT3, PKA, Akt, ERK, and JNK were increased by leptin. Leptin also significantly increased cAMP levels, cAMP response element (CRE) activation, and CREB phosphorylation. In addition, leptin induced COX-2 expression, promoter activity, and increased the production of prostaglandin E2. Finally, a COX-2 inhibitor and aromatase inhibitor suppressed leptin-induced cell proliferation in MCF-7 breast cancer cells. Together, our data show that leptin increased aromatase expression in breast cancer cells, which was correlated with COX-2 upregulation, mediated through CRE activation and cooperation among multiple signaling pathways.

Ursolic acid suppresses leptin-induced cell proliferation in rat vascular smooth muscle cells.

Accumulating lines of evidence indicate that high leptin levels are associated with adverse cardiovascular health in obese individuals. Proatherogenic effects of leptin include endothelial cell activation and vascular smooth muscle cell proliferation and migration. Ursolic acid (UA) has been reported to exhibit multiple biological effects including antioxidant and anti-inflammatory properties. In this study, we investigated the effect of UA on leptin-induced biological responses in rat vascular smooth muscle cells (VSMCs). A-10 VSMCs were treated with leptin in the presence or absence of UA. Intracellular reactive oxygen species (ROS) was probed by 2',7'-dichlorofluorescein diacetate. The expression of extracellular signal-regulated kinase (ERK)1/2, phospho-(ERK)1/2, nuclear factor-kappa B (NF-κB) p65 and p50, and matrix metalloproteinase-2 (MMP2) was determined by Western blotting. Immunocytochemistry and confocal laser scanning microscopy were also used for the detection of NF-κB. The secretion of MMP2 was detected by gelatin zymography. UA exhibited antioxidant activities in vitro. In rat VSMCs, UA effectively inhibited cell growth and the activity of MMP2 induced by leptin. These suppressive effects appeared by decreasing the activation of (ERK)1/2, the nuclear expression and translocation of NF-κB, and the production of ROS. UA appeared to inhibit leptin-induced atherosclerosis, which may prevent the development of obesity-induced cardiovascular diseases.

Suberoylanilide hydroxamic acid-induced specific epigenetic regulation controls Leptin-induced proliferation of breast cancer cell lines.

Breast cancer is one of the most common malignancies among women in the world, investigating the characteristics and special transduction pathways is important for better understanding breast development and tumorigenesis. Leptin, a peptide hormone secreted from white adipocytes, may be an independent risk factor for breast cancer.Here, we treated suberoylanilide hydroxamic acid (SAHA) on Leptin-induced cell proliferation and invasion in the estrogen-receptor-positive breast cancer cell line MCF-7 and triple-negative breast cancer cell line MDA-MB-231. Low concentrations of Leptin (0.625 nM) significantly stimulated breast cancer cell growth, enhanced cell viability, minimized apoptosis, and increased cell cycle transition. In contrast, SAHA (5 μM) treatment had reverse effects. Wound healing assay showed that, in MCF-7 and MDA-MB-231 cell line, cell migrating stimulated by Leptin was significantly repressed with SAHA treatment. Moreover, cell cycle real-time PCR array and proteome profiler antibody array confirmed that Leptin and SAHA treatment significantly changed the expressions of factors associated with cell cycle regulation and apoptosis including p53 and p21WAF1/CIP1.In DNA-ChIP analysis, we found that acetylation levels binding with p21WAF1/CIP1 promoters are regulated in a manner specific to histone type, lysine residue and selective promoter regions. SAHA significantly up-regulated the acetylation levels of AcH3-k14 and AcH3-k27 in MCF-7 cells, whereas Leptin repressed the modification. In addition, SAHA or Leptin had no significant effects on the AcH4 acetylation binding with any regions of p21WAF1/CIP1 promoter. In MDA-MB-231 cells, SAHA alone or in combination with Leptin significantly increased acetylation levels of Ach3-k27, Ach3-k18 and Ach4-k5 residues. However, no clear change was found with Leptin alone at all. Overall, our data will inform future studies to elucidate the mechanisms of p21WAF1/CIP1 transcriptional regulation, and the functional roles of p21WAF1/CIP1 in breast cancer tumorigenesis.

The effect of ferulic acid ethyl ester on leptin-induced proliferation and migration of aortic smooth muscle cells.

Leptin is a peptide hormone, which has a central role in the regulation of body weight; it also exerts many potentially atherogenic effects. Ferulic acid ethyl ester (FAEE) has been approved for antioxidant properties. The aim of this study was to investigate whether FAEE can inhibit the atherogenic effects of leptin and the possible molecular mechanism of its action. Both of cell proliferation and migration were measured when the aortic smooth muscle cell (A10 cell) treated with leptin and/or FAEE. Phosphorylated p44/42MAPK, cell cycle-regulatory protein (for example, cyclin D1, p21, p27), β-catenin and matrix metalloproteinase-9 (MMP-9) proteins levels were also measured. Results demonstrated that leptin (10, 100 ng ml−1) significantly increased the proliferation of cells and the phosphorylation of p44/42MAPK in A10 cells. The proliferative effect of leptin was significantly reduced by the pretreatment of U0126 (0.5 μM), a MEK inhibitor, in A10 cells. Meanwhile, leptin significantly increased the protein expression of cyclin D1, p21, β-catenin and decreased the expression of p27 in A10 cells. In addition, leptin (10 ng ml−1) significantly increased the migration of A10 cells and the expression of MMP-9 protein. Above effects of leptin were significantly reduced by the pretreatment of FAEE (1 and 10 μM) in A10 cells. In conclusion, FAEE exerts multiple effects on leptin-induced cell proliferation and migration, including the inhibition of p44/42MAPK phosphorylation, cell cycle-regulatory proteins and MMP-9, thereby suggesting that FAEE may be a possible therapeutic approach to the inhibition of obese vascular disease.

The antiproliferative effects of pterostilbene on breast cancer in vitro are via inhibition of constitutive and leptin-induced Janus kinase/signal transducer and activator of transcription activation

Background The hormone leptin is implicated in breast carcinogenesis in obese women. One mechanism is through its activation of Janus kinase/signal transducer and activator of transcription (JAK/STAT3) and apoptosis dysregulation. We have shown that the antioxidant pterostilbene inhibits proliferation and induces apoptosis in breast cancer. Therefore, the goal of this study was to evaluate the effect of pterostilbene on cell proliferation and JAK/STAT3 signaling in leptin-stimulated breast cancer. Methods Breast cancer cells were treated with leptin alone or in combination with pterostilbene. Detection of cell proliferation and JAK/STAT3 signaling were performed using enzyme-linked immunosorbent assay protocols. Statistical analysis was performed with analysis of variance and Tukey post hoc analysis. Results Pterostilbene suppresses constitutive as well as leptin-induced JAK/STAT3 activation. Pterostilbene treatment also inhibited leptin-induced cell proliferation. Conclusions Pterostilbene has an inhibitory effect on leptin-stimulated breast cancer in vitro through reduction of cell proliferation and JAK/STAT3 signaling, a critical regulatory component of tumorigenesis in obesity-related breast cancer.

Involvement of adiponectin and leptin in breast cancer: clinical and in vitro studies

Obesity is a risk factor for breast cancer development. A recent hypothesis suggests that the adipokines, adiponectin and leptin, are involved in breast cancer development. This prompted us to investigate the role of adiponectin and leptin in mammary carcinogenesis. Adiponectin receptors (AdipoR1 and AdipoR2) and leptin receptor (Ob-Rt, representing all the isoforms of Ob-R) proteins were detected by immunohistochemistry in in situ ductal carcinoma, invasive ductal malignancy, and healthy adjacent tissue. In addition, mRNA expression of adiponectin, AdipoR1, AdipoR2, leptin, Ob-Rt, and Ob-Rl (the long isoform of Ob-R) was observed in MCF-7 breast cancer cells. Interestingly, leptin mRNA expression was 34.7-fold higher than adiponectin mRNA expression in the MCF-7 cell line. Moreover, adiponectin (10 microg/ml) tended to decrease the mRNA expression of leptin (-36%) and Ob-Rl (-28%) and significantly decreased Ob-Rt mRNA level (-26%). In contrast, leptin treatment (1 microg/ml) significantly decreased AdipoR1 mRNA (-23%). Adiponectin treatment (10 microg/ml) inhibited the proliferation of MCF-7 cells, whereas leptin (1 microg/ml) stimulated the growth of cancer cells. In addition, adiponectin inhibited leptin-induced cell proliferation (both 1 microg/ml). Using microarray analysis, we found that adiponectin reduced the mRNA levels of genes involved in cell cycle regulation (mitogen-activated protein kinase 3 and ATM), apoptosis (BAG1, BAG3, and TP53), and potential diagnosis/prognosis markers (ACADS, CYP19A1, DEGS1, and EVL), whereas leptin induced progesterone receptor mRNA expression. In conclusion, the current study indicates an interaction of leptin- and adiponectin-signaling pathways in MCF-7 cancer cells whose proliferation is stimulated by leptin and suppressed by adiponectin.

Leptin Increases Adult Hippocampal Neurogenesis in Vivo and in Vitro

Leptin, an adipose-derived hormone, has been implicated in several physiological processes involving the hippocampus. However, the role of leptin in adult hippocampal neurogenesis remains unknown. Here we show that leptin regulates neurogenesis in the dentate gyrus of adult mice as well as in cultured adult hippocampal progenitor cells. Chronic administration of leptin to adult mice increased cell proliferation without significant effects on the differentiation and the survival of newly proliferated cells in the dentate gyrus. The expression of the long form leptin receptor, LepRb, was detected in hippocampal progenitor cells by reverse transcription-PCR and immunohistochemistry. Leptin treatment also increased proliferation of cultured adult hippocampal progenitor cells. Analysis of signal transduction pathways revealed that leptin stimulated phosphorylation of Akt and STAT3 but not ERK1/2. Furthermore, pre-treating the cells with specific inhibitors of Akt or STAT3 attenuated leptin-induced cell proliferation in a dose-dependent manner. Taken together, our results support a role for leptin in adult hippocampal neurogenesis and suggest the involvement of the Akt and STAT3 signaling pathways in mediating the actions of leptin on neurogenesis.

Adiponectin blocks multiple signaling cascades associated with leptin‐induced cell proliferation in ApcMin/+ colon epithelial cells

We previously demonstrated that leptin, an adipose-derived hormone, induces cell proliferation in a model of preneoplastic (IMCE (Apc(Min/+)), but not normal (YAMC (Apc(+/+)), colon epithelial cells by inducing autocrine IL-6 production and trans-IL-6 signaling. Low serum adiponectin is associated with colon, prostate and breast cancer. Adiponectin is secreted by white adipose tissue; the levels of adiponectin in the blood decrease as body mass index (and leptin) increases. In our study, we tested whether murine recombinant globular adiponectin (gArcp30) could modulate leptin-induced cell proliferation, autocrine IL-6 production, trans-IL-6 signaling and other leptin-induced cell signaling events previously observed in IMCE cells but not YAMC cells. Under serum-free conditions, adiponectin (1 mug/ml) inhibited leptin-induced autocrine IL-6 production, soluble IL-6 receptor shedding, trans-IL-6 signaling and subsequent STAT3 phosphorylation in IMCE cells. Adiponectin inhibited leptin-induced cell proliferation in the IMCE cells and this inhibition was associated with I kappa B-alpha phosphorylation, I kappa B-alpha degradation and decreased NF-kappaB p65 DNA activation and binding. These data indicate that adiponectin acts on preneoplastic colon epithelial cells to regulate cell growth via 2 distinct pathways inhibiting leptin-induced NF-kappaB-dependent autocrine IL-6 production and trans-IL-6 signaling. We hypothesize that adiponectin may be an important regulator of colon epithelial cell homeostasis by linking the observed reduced risk for cancer in populations with high serum adiponectin concentrations to specific mechanisms of cell number homeostasis in a model of preneoplastic colon epithelial cells. These data may have broad implications for diet and lifestyle strategies for the prevention and treatment of obesity-associated cancers.

Defining the mechanisms by which leptin stimulates proliferation of ovarian cancer cells

15017 Background: Ovarian cancer (OvCa) ranks fourth as the cause of death related to cancer in women in the U.S. The vast majority (>90%) of OvCa originates from the ovarian surface epithelium. There is sufficient evidence to suggest that hormones, especially estrogen, may be involved in the etiopathogenesis of epithelial OvCa. Recent studies indicate that leptin participates either directly or indirectly to promote carcinogenesis in both breast and endometrial cancers. Furthermore it has been proposed that leptin may elicit its action via an estrogen related pathway. Leptin can stimulate proliferation of some OvCa cell lines and has been implicated as a potential biomarker for OvCa. However the mechanism(s) by which leptin contributes to the growth of OvCa has yet to be defined. We hypothesize that leptin’s effect will be mediated in part by estrogen receptor (ER) pathways. Methods: Three epithelial OvCa cell lines (IGROV1, OVCAR5 and TOV21G) and one benign human ovarian surface epithelial cell line (HOSE) were evaluated. Enzyme linked immunosorbent assay (ELISA) and Western blotting were used to assess leptin and leptin receptor (ObR), respectively. Leptin (0.06 nM–6.25 nM) induced effects on cell proliferation were assessed in the presence or absence of an aromatase enzyme inhibitor (Anastrozole) or the ER antagonist (ICI182780). Further, we explored leptin-induced effects on ERα promoter activity as evidenced by change in fluorescence via a dual luciferase promoter reporter. All experiments were conducted in triplicate. All data were subjected to ANOVA followed by Tukey’s post hoc test (p < 0.05). Results: All ovarian cell lines expressed ObR; whereas, no measurable amounts of leptin were detected in conditioned media. Leptin stimulated cell proliferation in both the benign and malignant lines. Leptin-induced cell proliferation was inhibited by Anastrozole and ICI182780. Furthermore, leptin stimulated luciferase activity of the ERα promoter/reporter. Conclusions: Leptin promotes proliferation of benign and malignant ovarian epithelial cells and appears to be mediated, at least in part, via aromatase and ER which may have therapeutic implications. This work was supported by the Vincent Memorial Hospital, SG Komen Foundation and the Advanced Medical Research Foundation. No significant financial relationships to disclose.

Leptin receptor expression and cell signaling in breast cancer

Obesity is considered a risk factor for many cancers, including breast cancer. Our laboratory has previously shown that leptin is mitogenic in many cancer cell lines, including breast. Information regarding the effects of high leptin levels on leptin receptor expression and signaling is lacking. The purpose of this study was to characterize leptin receptor expression in response to leptin in breast cancer cells. In addition, SOCS-3 expression (a leptin inducible inhibitor of leptin signaling), plus MAPK and PI3K signaling, were examined to determine their role in leptin-induced cell proliferation. Breast cancer cell lines, ZR75-1 and HTB-26, were treated with 0, 4, 40 or 80 ng/ml of leptin. Multiplex RT-PCR was performed to determine relative mRNA expression levels of the human short (huOB-Ra) or long (huOB-Rb) leptin receptor isoforms, or SOCS-3. MAPK and PI3K signaling was analyzed by phosphorylation of ERK and Akt, respectively, via Western blotting. Cell proliferation and inhibitor studies were analyzed by MTT assay. HTB-26 and ZR75-1 both expressed huOB-Ra, huOB-Rb and SOCS-3 mRNA; however, mRNA expression levels generally remained unchanged over time with leptin treatment. MAPK and PI3K pathways were activated in the presence of leptin over time. MAPK and PI3K inhibitors significantly blocked leptin-induced proliferation. Higher levels of circulating leptin contribute to breast cancer proliferation by activation of the MAPK and PI3K signaling pathways involved in cell growth and survival. The mitogenic effects of leptin are not a consequence of altered leptin receptor or SOCS-3 mRNA expression.

Molecular mechanisms involved in the growth stimulation of breast cancer cells by leptin.

Obesity is a risk factor for breast cancer in postmenopausal women. Leptin, an adipocyte-derived cytokine, elicits proliferative effects in some cell types and potentially stimulates the growth of mammary epithelium. Here we show that leptin induced time- and dose-dependent signal transducer and activator of transcription 3 (STAT3) phosphorylation and extracellular signal-regulated kinase (ERK) 1/2 kinase activation in breast carcinoma cells. Blocking STAT3 phosphorylation with a specific inhibitor, AG490, abolished leptin-induced proliferation of MCF-7 cells, whereas blocking ERK1/2 activation by a specific ERK1/2 kinase inhibitor, U0126, did not result in any significant changes in leptin-induced cell proliferation. Our experiments also showed that one member of the p160 family of steroid receptor coactivators, steroid receptor coactivator (SRC)-1, but not glucocorticoid receptor interacting protein 1 (GRIP1) or amplified in breast cancer 1 (AIB1), also functioned in gene transactivation in response to leptin treatment. Glutathione S-transferase pull-down experiments showed that SRC-1 physically interacted with the activation domain of STAT3 and that chromatin immunoprecipitation experiments detected the occupancy of SRC-1, but not GRIP1 or AIB1, on the promoter of STAT3 target genes. Our experiments collectively showed that SRC-1 is involved in STAT3 signaling pathway that is implicated in leptin-stimulated cell growth.

Leptin mediates a proliferative response in human gastric mucosa cells with functional receptor.

Recently, the rat stomach was reported as a source of leptin, a hormone mainly secreted by adipocytes. Also Helicobacter pylori-induced gastritis in humans was associated with locally elevated leptin levels. In addition, it was suggested that gastric leptin adjusts the function of the intestinal tract in parallel to the function of hypothalamic satiety centers. Here we examined the synthesis and potential physiologic role of leptin in the human stomach. RT-PCR was employed to detect leptin mRNA in the human stomach and the human gastric carcinoma cell line AGS while immunogold staining and electron microscopy were used to detect leptin protein. The in vitro effects of leptin on cell proliferation were examined in the AGS cell line. No leptin mRNA could be detected by RT-PCR, yet immunogold labeling and electron microscopy allowed visualization of leptin protein in the human gastric mucosa. At concentrations of 100 nM, leptin led to a significantly increased BrdU-uptake in AGS cells (+27%, p < 0.017). The MAP-kinase-1-specific inhibitor U0126 blocked the leptin-induced cell proliferation in a dose-dependent fashion. Leptin protein may not be produced but rather stored in human gastric cells. Leptin-induced increases in the proliferation of gastric mucosa cells suggests that leptin might contribute to mucosal integrity and gastroprotection.