Long Isoform Of Leptin Receptor Research Articles

Expression of Leptin Receptors and Potential Effects of Leptin on the Cell Growth and Activation of Mitogen-Activated Protein Kinases in Ovarian Cancer Cells

Leptin, a secreted protein of the ob gene by white adipose tissue, plays an important role in the regulation of food intake and energy consumption in the brain and acts as a potential growth stimulator in normal and neoplastic breast cancer cells. However, a potential role of leptin as an endocrine regulator is unknown in ovarian cancer. In the present study, we investigated the expression of leptin receptors in immortalized ovarian surface epithelium (IOSE) and ovarian cancer cell lines, and potential effect of leptin on the cell growth and activation of mitogen-activated protein kinases (MAPKs) in the BG-1 ovarian cancer cell line. Both short and long isoforms of leptin receptors are expressed in IOSE-80PC (a post-crisis line), BG-1, OVCAR-3, and SKOV-3 cells. In addition, treatment with leptin resulted in the growth stimulation of BG-1 cells, an activation of ERK1/2 and inhibition of constitutive phosphorylation of p38 MAPK. These results suggest that further studies are necessary to validate whether leptin may be a potential regulator for ovarian cancer.

Transactivation of erbB2 by short and long isoforms of leptin receptors

Transactivation of erbB2 by short and long isoforms of leptin receptors

Transactivation of erbB2 by short and long isoforms of leptin receptors

We generated kinase-positive and kinase-negative erbB2 tagged with YFP and the long form of leptin receptor (LEPRb) tagged with CFP. Both were as active as their untagged analogs. Both short and long isoforms of leptin receptor phosphorylated and thereby activated erbB2 upon leptin binding and enhanced MAPK activity. Our results unveil a novel route by which leptin may provoke erbB2's phosphorylation and thus enhance its oncogenic potential independently of HER family ligands or its overexpression. Using FRET technology in living cells, we found no evidence of complex formation between erbB2 and prolactin or leptin receptors, indicating that the transactivation occurs through an indirect interaction.

Role of leptin deficiency in early acute renal failure during endotoxemia in ob/ob mice.

It is known that, among human patients with sepsis, acute renal failure (ARF) dramatically increases mortality rates to 50 to 80%. However, the pathogenesis of septic ARF is not fully understood. An increase in endotoxin-induced mortality rates for leptin-deficient ob/ob mice was recently demonstrated. In comparison with ob/ob mice, db/db mice, which are deficient in the long isoforms of leptin receptors (Ob/Rb), demonstrate lower mortality rates after exposure to the endotoxin LPS. In db/db mice, mRNA for the short isoforms of leptin receptors is constitutively expressed in the kidney, lung, liver, and macrophages. It is known that plasma leptin levels increase in rodents after exposure to LPS, and this was demonstrated for db/db mice. Because ob/ob and db/db mice are both obese, factors other than obesity must be involved in the increased mortality rates for ob/ob mice. In this study, the hypothesis that the short forms of leptin receptors might offer protection against endotoxin-induced lethality at least in part by providing protection against ARF was examined. Serum leptin levels were significantly increased with LPS treatment in wild-type and db/db mice but not ob/ob mice. GFR decreased significantly 16 h after the homozygous ob/ob mice received intraperitoneal injections of 0.3 mg/kg LPS (0.37 +/- 0.04 ml/min per g kidney versus 0.83 +/- 0.06 ml/min per g kidney, n = 6, P < 0.01); the mean arterial pressure (MAP) remained unchanged. For ob/ob littermates (+/?ob), there was no significant change in either MAP or GFR when the mice were challenged with the same time interval (16 h) and dose of LPS. In contrast to ob/ob mice, there was no significant change in GFR or MAP when homozygous db/db mice or their littermates received injections of an even higher dose of LPS (0.4 mg/kg). Mouse recombinant leptin had no effect on GFR when ob/ob mice received 0.3 mg/kg LPS injections. However, renal function (serum creatinine levels, 0.4 +/- 0.1 mg/dl versus 0.9 +/- 0.1 mg/dl, P < 0.01) and MAP (68 +/- 4 mmHg versus 51 +/- 2 mmHg, n = 6, P < 0.01) were significantly improved with leptin replacement when the ob/ob mice developed hypotensive ARF with a higher dose of LPS (0.5 mg/kg). In summary, the previously reported increased susceptibility to LPS of ob/ob mice, compared with db/db mice, may be attributable at least in part to increased susceptibility to ARF.

Leptin-induced transactivation of NPY gene promoter mediated by JAK1, JAK2 and STAT3 in the neural cell lines

Neuropeptide Y (NPY) plays an important role in the central and sympathetic regulation of food intake and blood pressure. Although the NPY gene expression is regulated by a number of agents such as leptin, the mechanism responsible for leptin-induced regulation of the transcription of the NPY gene remains to be explored. In this study, the NPY gene promoter was transactivated by leptin in N18TG2, NG108-15 and PC12 cells which expressed the functional leptin receptor. The long isoform of leptin receptor (OB-Rb) could induce the transactivation, but the C-terminal truncated form (OB-Ra) could not. When dominant negative type of STAT3, JAK1 or JAK2 and was co-expressed, the leptin-induced transactivation was suppressed almost completely. The leptin-response element which confers NPY gene transactivation by leptin was determined in the 221-bp region of rat NPY gene promoter (−553/−335), where two STAT3-binding site-like elements (TCCAGTA) exist. These results indicated that activation of JAK1, JAK2 and STAT3 is necessary for leptin-induced transactivation of NPY gene through the leptin-response element in these neural cells.

Effect of Leptin on the Expression of Chemokine Genes in THP-1 Cells

Background: Leptin is a 16-KDa non-glycosylated peptide hormone synthesized almost exclusively by adipocytes. The well-known function of leptin is regulation of food intake and energy expenditure. Leptin also plays a regulatory role in immune and inflammatory process including cytokine production. The purpose of this study was to investigate the effect of leptin on the expression of several chemokine genes(RANTES, IL-8, MCP-1, IP-10, Mig, MIP-, MIP-, and GRO-) in THP-1 cells. Materials and Methods: Total RNA of THP-1 cells were prepared by Trizol method, and then stimulated with the leptin(250 ng/) or LPS(100 ng/). We examined the expression patterns of various chemokine mRNAs in THP-1 cell lines by RT-PCR and Northern blot. Results: Leptin did not induce the expression of chemokine mRNAs in THP-1 cells. The expression patterns of RANTES, IL-8, MCP-1, IP-10, and Mig mRNAs in THP-1 cells stimulated with leptin and LPS simultaneously was almost same to the patterns of LPS alone-induced chemokine mRNAs. RANTES mRNA expression was independent on the concentrations of leptin. Although leptin did not have strong effect on the expression of RANTES, IL-8, MCP-1, IP-10, Mig, MIP-, MIP-, and GRO- mRNAs in THP-1 cells, leptin could induce the expression of long isoform of leptin receptor(OB-RL) mRNA, and its expression was elevated in simultaneous stimulation of leptin and LPS. Conclusion: These data suggest that leptin is able to induce OB-RL in THP-1 cells, however, leptin has little effect on the expression of pro-inflammatory chemokine genes.

Leptin regulates interleukin-1β expression in the brain via the STAT3-independent mechanisms

Leptin is known to be an important circulating signal for regulation of food intake and body weight. These effects were suggested to be mediated through the hypothalamic center via the Ob-Rb receptor (long isoform of leptin receptor). Although short isoforms of leptin receptor exist in many regions of the brain, there has been little in vivo functional study of these areas such as for leptin’s target site. We report here that peripherally applied leptin increased interleukin (IL)-1β transcripts in many regions of the brain such as the hypothalamus, the hippocampus, the cortex, the cerebellum and the brainstem. Although leptin did not induce STAT3 activation or suppressor of cytokine signaling3 (SOCS3) expression in the hypothalamus of the db/db mice, which lack a functional Ob-Rb receptor, leptin increased the IL-1β levels to similar extents as normal mice. Therefore, a novel function of leptin is suggested as the induction of IL-1β expression in many regions of the brain via STAT3-independent mechanisms.

Leptin Signaling Deficiency Impairs Humoral and Cellular Immune Responses and Attenuates Experimental Arthritis

Leptin is produced almost exclusively by adipocytes and regulates body weight at the hypothalamic level. In addition, recent studies showed that leptin plays an important role in T lymphocyte responses. To examine the role of leptin in Ag-induced arthritis, the development of joint inflammation was assessed in immunized leptin-deficient mice (ob/ob), +/?, and wild-type mice (+/+) following the administration of methylated BSA into the knees. The results showed that ob/ob mice developed less severe arthritis compared with control mice. The levels of IL-1beta and TNF-alpha mRNA in the synovium of arthritic knees were lower in ob/ob than in +/? mice. In vitro Ag-specific T cell proliferative responses were significantly decreased in ob/ob mice with lower IFN-gamma and higher IL-10 production, suggesting a shift toward a Th2-type response in ob/ob mice. The serum levels of anti-methylated BSA Abs of any isotype were significantly decreased in arthritic ob/ob mice compared with controls. Essentially identical results were obtained in db/db mice, which lack the expression of the long isoform of leptin receptor. By RT-PCR, we observed that B lymphocytes express leptin receptor mRNA, indicating that in addition to its effect on the cellular response, leptin may exert a direct effect on B cell function. In conclusion, leptin contributes to the mechanisms of joint inflammation in Ag-induced arthritis by regulating both humoral and cell-mediated immune responses.

Leptin and leptin receptor expression in rat and mouse pituitary cells.

Leptin is a circulating hormone secreted mainly by adipose tissue. Recent studies have shown leptin production by other tissues, including the placenta, stomach, and mammary tissues. Various reports have suggested that the anterior pituitary may have a role in the regulatory effects of leptin. We recently localized leptin in the human anterior pituitary, but analysis of leptin in rodent pituitary has not been previously reported. In this study we examined rat and mouse pituitary tissues and various cell lines for leptin by RT-PCR, immunohistochemistry, and Western blotting. Leptin receptor messenger RNA was also examined in these tissues by RT-PCR. Leptin was present in a small percentage of rat (4.8 +/- 0.7%) and mouse (7 +/- 2%) pituitary cells. Colocalization studies with leptin and pituitary hormones showed leptin expression mainly in TSH cells (24 +/- 2% of TSH cells in the rat pituitary and 31 +/- 1% of TSH cells in the mouse pituitary). A folliculo-stellate (FS) cell line, TtT/GF, also expressed leptin. The long isoform of leptin receptor (OB-Rb) was present in normal pituitary and in various pituitary cell lines, including FS, GH3, and alphaT3-1 cells. Treatment of GH3 and FS cells with leptin (1 x 10(-8) M) inhibited cell proliferation assessed by [3H]thymidine incorporation in GH3, but not in FS, cells. These findings show for the first time that leptin is expressed in rat and mouse anterior pituitaries mainly by TSH cells and by a mouse FS cell line. The finding of leptin and of the long isoform of leptin receptor in normal rat and mouse pituitaries and in various cell lines implicates an autocrine/paracrine loop in the production and regulation of leptin and leptin receptor in the rodent pituitary.

Expression of leptin receptor mRNA (long form splice variant) in the human cerebellum.

Primers specific to the long isoform of leptin receptor (OB-Rb) mRNA were used in reverse transcriptase-linked polymerase chain reactions (RT-PCR) to investigate the expression of this receptor in the hypothalamus and cerebellum of human and rat. For both regions, we observed RT-PCR cDNAs as well as restriction enzyme cleavage fragments of expected sizes. Additionally, in situ hybridization of human cerebellum using two independent [35S]oligonucleotide probes complementary to the OB-Rb mRNA sequence revealed a prominent hybridization signal within the granular layer. Overall, our findings demonstrate the expression of OB-Rb mRNA in the cerebellum and suggest that in such a location, leptin receptors may mediate a function presumably not linked to body weight homeostasis.