Biomedical subjects

Michio Niimi

Publications and source records attributed to Michio Niimi.

4 recordsLinked to original sources

PubMed2005

Neuropeptide W as a stress mediator in the hypothalamus.

Neuropeptide W (NPW) was isolated and found to be an endogenous peptide ligand for the orphan receptors GPR7 and GPR8. Centrally administered NPW caused a dose-dependent increase in corticosterone levels in rats. This observation indicates that NPW may play an important role in the hypothalamic organization of the endocrine response to stress. We examined the effects of immobilization stress and cold exposure on NPW-containing neurons in the hypothalamus of the rat, using dual immunostaining for NPW and Fos. In addition, to analyze the function of NPW, we studied the effect of intracerebroventricular (icv) NPW administration on Fos protein accumulation in the brain. Double immunohistochemistry for NPW and Fos showed that the percentage of Fos expression in the NPW-immunoreactive cells of the perifornical nucleus was significantly increased by immobilization stress compared with that in nonstressed rats. Similarly, the results indicated that cold exposure activates NPW-immunoreactive neurons in the perifornical nucleus. An icv administration of NPW resulted in significant Fos expression in the paraventricular nucleus, as compared with saline-infused controls. These results suggest that NPW is related to stress-responsive signal transduction, and that NPW may modulate the hypothalamus-pituitary-adrenal axis.

Animals↗

PubMed2005

[Leptin].

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Biomarkers↗

PubMed2004

A mutant high-density lipoprotein receptor inhibits proliferation of human breast cancer cells.

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.

Apoptosis↗

PubMed2004

The role of calcium/calmodulin-dependent protein kinase cascade in glucose upregulation of insulin gene expression.

A number of factors have been reported to affect insulin synthesis in beta-cells. Although glucose is the most important regulator of insulin gene expression in pancreatic beta-cells, the mechanisms whereby glucose stimulates insulin gene transcription in response to changes in glucose concentration have not been clarified yet. In this study, we examined the role of the Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaM-K) cascade in transcriptional activation of insulin. RT-PCR, Western blotting, and immunohistochemical staining analysis revealed that CaM-K kinase-alpha (CaM-KKalpha) and CaM-KIV were localized in rat pancreatic beta-cells and their cell line, INS-1. Exposure of INS-1 cells to 11.2 mmol/l glucose elicited an increase of insulin promoter activity as well as upregulation of CaM-KIV activity within 2 min after stimulation. We investigated the influence on insulin promoter activity of the constitutively active form (CaM-KIVc) or dominant-negative mutant (CaM-KIVdn) of CaM-KIV in transfected INS-1 cells. CaM-KIVc alone was sufficient, and the upstream kinase, CaM-KK, was enhanced to upregulate the insulin promoter activity in INS-1 cells. Furthermore, cotransfection of CaM-KIVdn suppressed to a significant degree the glucose-upregulated activity of the insulin promoter. Taken together, these results indicated that the CaM-KK/CaM-KIV cascade might play an important role in glucose-upregulated transcriptional activation of the insulin gene.

Animals↗