High-density lipoprotein (HDL) stimulates the growth of many types of cells, including those of breast cancer. High levels of HDL are associated with an increased risk of breast cancer development. A scavenger receptor of the B class (SR-BI)/human homolog of SR-BI, CD36, and LIMPII analogous-1 (CLA-1) facilitates the cellular uptake of cholesterol from HDL and thus augments cell growth. Furthermore, HDL is also believed to have antiapoptotic effects on various cell types, and this feature adds to its ability to promote cell growth. These collaborative roles of HDL and CLA-1 prompted us to assess the function of these components on human breast cancer cells. In this study, we created a mutant CLA-1 (mCLA) that lacked the COOH-terminal tail to determine its potential role in breast cancer cell growth. Expression of mCLA inhibited the proliferation of breast cancer cell line MCF-7. This inhibitory action of mCLA required the transcriptional factor activator protein-1 (AP-1), and the mutant receptor also affected the antiapoptotic features of HDL. The effect of HDL on AP-1 activation and [ 3 H]thymidine incorporation was abrogated by wortmannin, a specific inhibitor of phosphoinositide 3-kinase. Furthermore, the dominant negative mutant of Akt abolished the ability of HDL to activate AP-1. These findings raise the possibility that the inhibitors of the effects of HDL may be of therapeutic value for breast cancer.

Hyperleptinaemia is observed in obese animals and humans, suggesting that leptin resistance rather than leptin deficiency is a characteristic feature of obesity. This study was designed to determine whether peripherally or centrally administered leptin is effective on the short-term food intake and expression of Fos protein in the hypothalamus in the Otsuka Long-Evans Tokushima Fatty (OLETF) or Long-Evans Tokushima Otsuka (LETO) rat, as a control. The OLETF rat exhibits a polygenic syndrome of hyperphagia, obesity, hyperinsulinaemia, and hyperglycaemia. Male OLETF rats of 5, 8, and 14 weeks of age became heavier than LETO rats. Serum leptin concentrations were not significantly different between LETO and OLETF rats at the age of 5 weeks, but in 8- and 14-week-old OLETF rats were increased to 3.4 and 2.9 times those of LETO rats, respectively. The 8-week-old OLETF and LETO rats were given intraperitoneal (i.p.) injections with recombinant mouse leptin to measure the kinetics. There was a dramatic increase in plasma leptin concentration at 1 h, a decline by 3 h, and the concentrations 6 h after injection were similar to the basal levels. There were no significant difference between OLETF and LETO rats. In LETO rats at 5, 8 and 14 weeks of age, i.p. injection of leptin significantly decreased food intake. Whereas 5-week-old OLETF rats responded to leptin with a decrease in food intake, 8- and 14-week-old OLETF rats became resistant to peripherally administered leptin. In contrast, intracerebroventricular (i.c.v.) injections of leptin were very effective in inhibiting food intake in both OLETF and LETO rats at 14 weeks of age. Intraperitoneal injection of leptin in the LETO rats at each age increased the number of Fos-positive nuclei detected in the ventromedial hypothalamic (VMH), the dorsomedial hypothalamic (DMH) and arcuate nuclei, whereas there was no significant increase in the number of cells expressing c-fos protein in the hypothalamus of the 8- and 14 week-old OLETF rats with hyperleptinaemia. On the other hand, increased expression of c-fos protein in the VMH, DMH and arcuate nuclei following i.c.v. injection of leptin was observed in both OLETF and LETO rats at 5, 8 and 14 weeks of age. These data demonstrated that obese OLETF rats are peripherally leptin resistant, while they retain sensitivity to centrally administered leptin.

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Neuropeptide S (NPS) is a newly identified transmitter that modulates arousal and anxiety. To determine potential neuronal targets for NPS, we studied the pattern of neuronal activation as indicated by the expression of Fos. Centrally administered NPS increased Fos-like immunoreactivity (FLI) in the paraventricular, dorsomedial nuclei and lateral hypothalamic area (LHA) of the hypothalamus, the midline thalamic nuclei, and the amygdala, many parts of which are involved in the regulation of emotion, arousal, and feeding. In particular, we noted that Fos-immunoreactive (Fos-ir) levels were increased in orexin-expressing neurons in the LHA. We then studied whether an icv injection of NPS increased food intake. The injection of NPS (1 nmol) significantly stimulated feeding at 2 h in rats, but there was no difference in food intake at 4 h or 24 h. These results suggest that arousal and feeding induced by NPS in the central nervous system may be related to the activation of orexin-expressing neurons.

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Neuromedin U (NMU) is a peptide isolated from the porcine spinal cord. Recently, two receptors for NMU have been identified and characterized. A recent study indicated that NMU is an anorectic chemical in the brain. The present study shows that NMU has an action in the brain to inhibit food intake in rats. Intracerebroventricular injection of NMU inhibited dark-phase feeding. Animals injected with NMU showed a strong increase in Fos-immunoreactive nuclei in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus, and in the parabrachial nucleus of the brain stem. Double immunohistochemistry revealed that a high number of oxytocin-immunoreactive neurons in the PVN and SON contained Fos after intracerebroventricular injection of NMU. In addition, a small proportion of vasopressinergic cells within the PVN and SON were found to contain Fos. The effect of NMU on the hypothalamus and brain stem contributes to the inhibitory effects of NMU on feeding behavior.

Menin is a protein encoded by the gene mutated in multiple endocrine neoplasia type 1 (MEN1) characterized by multiple endocrine tumors of the parathyroid glands, pancreatic islets and the anterior pituitary, especially prolactinoma. In this study, we examined the effects of menin on human prolactin (hPRL) expression. In rat pituitary GH3 cells stably expressing menin, both PRL gene expression/ secretion and thymidine incorporation into DNA were inhibited as compared with mock-transfected cells. The transcriptional activity of PRL promoter in GH3 cells co-transfected with menin was significantly decreased. A deletion mutation (569 delC), which we identified in a Japanese MEN1 family, was introduced into menin. When GH3 cells were transfected with a mutant menin expression vector, inhibition of hPRL promoter activity was partially reversed. These observations suggest that menin inhibits hPRL promoter activity and cell proliferation, raising the possibility that menin might play an important role in the tumorigenesis of prolactinoma.

No abstract