Takamasa Nishiuchi

Interferon α decreases expression of human scavenger receptor class BI, a possible HCV receptor in hepatocytes

Background: Infection with the hepatitis C virus (HCV) causes acute hepatitis. This disease has a high probability of becoming chronic and leading to cirrhosis, but a more deadly consequence is hepatocellular carcinoma. Interferon α (IFNα)-based treatment combined with ribavirin is the major therapeutic choice available for the treatment of chronic HCV infection. Aims: The scavenger receptor class B type I (SR-BI) or its human homologue CD36 and LIMPII Analogous-1 (hSR-BI/CLA-1) has recently been shown to interact with HCV envelope glycoprotein E2, thus suggesting that it might participate in entry of the virus into host cells. This rationale underlies current interest in the potential role of IFNα in hSR-BI/CLA-1 expression in HepG2 cells. Results: It was shown that endogenous hepatocyte expression of hSR-BI/CLA-1 was suppressed by exposure to IFNα. Decreased hSR-BI/CLA-1 expression in IFNα-treated cells was due to lower transcriptional activity of the promoter. A potential pathway for the effect of IFNα on hSR-BI/CLA-1 promoter activity was identified when the inhibitory action of IFN was abrogated in signal transducer and activator of transcription 1 (STAT1)/STAT2 knocked-down cells. Exposure of HepG2 cells to IFNα elicited a rapid phosphorylation of STAT1/STAT2, a known target of IFNα signalling. In addition, the mutagenesis of a STAT1/STAT2 response element in the hSR-BI/CLA-1 promoter abolished the ability of IFNα to suppress promoter activity. Conclusions: Together, these results indicate that the STAT1/STAT2 pathway participates in IFNα inhibtion of hSR-BI/CLA-1 expression, and raise the possibility that lowering the expression of this gene may be of therapeutic value for treating HCV infections.

Regulation of Scavenger Receptor Class BI Gene Expression by Angiotensin II in Vascular Endothelial Cells

High-density lipoprotein mediates a normal physiological process called reverse cholesterol transport. In this process, a scavenger receptor of the B class (SR-BI)/human homologue of SR-BI, CD36, and LIMPII analogous-1 (hSR-BI/CLA-1) facilitates the cellular uptake of cholesterol from high-density lipoprotein. In endothelial cells, high-density lipoprotein activates endothelial NO synthase via hSR-BI/CLA-1. Angiotensin II (Ang II) is a powerful accelerator of atherosclerosis and modulates the expression of endothelial NO synthase. In the present study, we have examined the role of Ang II on hSR-BI/CLA-1 expression in human umbilical vein endothelial cells. Our results showed that endogenous expression of hSR-BI/CLA-1 was suppressed by exposure to Ang II in human umbilical vein endothelial cells. Administration of the Ang II type-1 receptor blocker olmesartan inhibited Ang II–induced hSR-BI/CLA-1 protein repression. In Ang II–treated cells, high-density lipoprotein had no effect on endothelial NO synthase activation. Ang II decreased transcriptional activity of the hSR-BI/CLA-1 promoter. The inhibitory effect of Ang II on hSR-BI/CLA-1 promoter activity was abrogated by wortmannin and LY294002, specific inhibitors of phosphatidylinositol 3-kinase. Exposure of human umbilical vein endothelial cells to Ang II elicited a rapid phosphorylation of Akt and FoxO1, a known target of Akt signaling. Constitutively active Akt inhibits the activity of the hSR-BI/CLA-1 promoter, and a dominant-negative mutant of Akt or mutagenesis of a FoxO1 response element in the hSR-BI/CLA-1 abolished the ability of Ang II to suppress promoter activity. Together, these results indicate that the phosphatidylinositol 3-kinase/Akt/FoxO1 pathway participates in Ang II suppression of hSR-BI/CLA-1 expression and suggests that the endothelial receptor for hSR-BI/CLA-1 is downregulated by the renin–angiotensin system.

Platelet derived growth factor regulates ABCA1 expression in vascular smooth muscle cells

The ATP‐binding cassette transporter A1 (ABCA1) regulates lipid efflux from peripheral cells to High‐density lipoprotein. The platelet‐derived growth factor (PDGF) is a potent mitogen that enables vascular smooth muscle cells to participate in atherosclerosis. In this report, we showed that PDGF suppressed endogenous expression of ABCA1 in cultured vascular smooth muscle cells. Exposure of CRL‐208 cells to PDGF elicited a rapid phosphorylation of a kinase downstream from PI3‐K, Akt. The constitutively active form of both p110, a subunit of PI3‐K, and Akt inhibited activity of the ABCA1 promoter. In conclusion, PI3‐K‐Akt pathways participate in PDGF‐suppression of ABCA1 expression.

Xanthogranuloma of the intrasellar region presenting in pituitary dysfunction: a case report.

IntroductionDifferentiation of cystic mass lesions of the sellar and parasellar regions may pose a diagnostic dilemma for physicians, neurosurgeons, radiologists and pathologists involved in treating patients with these entities. A considerable number of tumors previously identified as craniopharyngiomas may, in fact, have been xanthogranulomas. We report a case of pituitary dysfunction caused by xanthogranuloma of the intrasellar region.Case presentationA 47-year-old man of Japanese descent presented to our institution with a tumor located exclusively in the intrasellar region which manifested as severe hypopituitarism. MRI revealed a clearly defined intrasellar mass that was heterogeneously hyperintense on T1-weighted images and markedly hypointense on T2-weighted images. We preoperatively diagnosed the patient with Rathkes cleft cyst or non-functioning pituitary adenoma. Although the tumor was completely removed using a transsphenoidal approach, the improvement of the patients endocrine function was marginal, and continued endocrine replacement therapy was needed. Postoperatively, a histological examination revealed the tumor to be a xanthogranuloma of the intrasellar region. His visual field defects and headache improved.ConclusionBecause diagnosis depends on surgical intervention and xanthogranulomas of the intrasellar region are very rare, the natural history of xanthogranuloma is still unknown. Therefore, this entity is difficult to diagnose preoperatively. We suggest that xanthogranuloma should be included in the differential diagnosis, even in the case of sellar lesions, to formulate appropriate postoperative management and improve endocrine outcomes.

17β-Estradiol regulates scavenger receptor class BI gene expression via protein kinase C in vascular endothelial cells

High-density lipoprotein (HDL) mediates reverse cholesterol transport. In this process, the human homolog of the B class, type I scavenger receptor (SR-BI), CD36, and LIMPII analogous-1 (hSR-BI/CLA-1) facilitates the cellular uptake of cholesterol from HDL. In endothelial cells, HDL activates endothelial nitric oxide synthase (eNOS) via hSR-BI/CLA-1, and 17β-estradiol (E2) modulates nitric oxide (NO) synthesis. In this study, we elucidated the effect of E2 on hSR-BI/CLA-1 expression in human umbilical vein endothelial cells (HUVECs). HSR-BI/CLA-1 expression was examined by real-time PCR, western blot analysis and reporter gene assay in HUVECs incubated with E2. eNOS activity was assessed by detection of phosphorylation (Ser 1179) of eNOS. We investigated the effect of the constitutively active form or dominant negative form of protein kinase C on hSR-BI/CLA-1 promoter activity. Our results showed that E2 increased the endogenous expression of hSR-BI/CLA-1. E2 also enhanced the activity of the hSR-BI/CLA-1 promoter and the expression of its mRNA. However, bisindolylmaleimide I, an inhibitor of protein kinase C, blocked the stimulatory effect of E2 on hSR-BI/CLA-1 promoter activity. Moreover, constitutively active PKC increased the activity of the hSR-BI/CLA-1 promoter, and a dominant-negative mutant of PKC prevented E2 from stimulating promoter activity. In cells treated with E2, HDL stimulated the phosphorylation of serine 1179 of eNOS in HUVECs. These results suggested that E2 upregulates the expression of the endothelial hSR-BI/CLA-1 via the PKC pathway, which may be a novel mechanism of the anti-atherosclerotic potential of E2 in vascular endothelial cells.

Suprasellar Germinoma Masquerading As Lymphocytic Hypophysitis Associated With Central Diabetes Insipidus, Delayed Sexual Development, and Subsequent Hypopituitarism

We report the case of an 18-year-old woman with suprasellar germinoma masquerading as lymphocytic hypophysitis, which was associated with central diabetes insipidus, delayed sexual development, and hypopituitarism. Magnetic resonance imaging revealed an enlarged pituitary gland, thickened pituitary stalk, and a mass lesion in the inferior hypothalamus; these findings are typical of lymphocytic hypophysitis. Despite the administration of prednisolone therapy for 3 months, an enlarged irregular cystic mass lesion developed in the pituitary stalk and inferior hypothalamus. Open cranial surgery of the posterior pituitary revealed the presence of a germinoma. Therefore, chemotherapy and stereotactic radiation therapy were administered, resulting in complete remission of the germinoma. This case illustrates that the presence of an intrasellar mass lesion in association with pituitary stalk thickening can often cause difficulties in differential diagnosis. We believe that lymphocytic hypophysitis in pubertal children may be the first sign of a host reaction to an occult germinoma.

A case of non-Hodgkin's lymphoma primary arising in both adrenal glands associated with adrenal failure.

It is known that adrenal insufficiency is one of the complications in primary adrenal lymphoma, especially those with bilateral adrenal involvement. A 73-year-old man was referred for general fatigue and high fever to the nearest hospital. The patient was transferred to our hospital for evaluation of bilateral adrenal tumors and hyponatremia. He was diagnosed as having non-Hodgkin’s lymphoma (NHL) with primaries arising in both adrenal glands. Primary adrenal lymphoma (PAL) is a rare extra-nodal NHL. Although an appropriate treatment of this disease has not been established, our case has demonstrated that the combination of rituximab and THP-COP chemotherapy could be administered, and that it improved clinical manifestations. This case raises the suggestion that malignant lymphoma should be suspected in patients with bilateral adrenal tumors that present with progressive adrenal insufficiency.

The transcription factor prolactin regulatory element-binding protein mediates prolactin transcription induced by thyrotropin-releasing hormone in GH3 cells

The prolactin regulatory element-binding protein (PREB) is a transcription factor that regulates prolactin (PRL) promoter activity in the rat anterior pituitary. PRL gene expression and secretion are regulated by various hormones and growth factors, including dopamine, epidermal growth factor, and thyrotropin-releasing hormone (TRH). We examined the effect of TRH on PREB expression in pituitary cells. Western blots probed with a PREB-specific antiserum showed that the relative abundance of PREB in GH3 cells increased on treatment with TRH in a dose-dependent manner. The relative abundance of PREB mRNA also increased in a dose-dependent manner after treatment with TRH. TRH induced the expression of the luciferase reporter protein under the PREB promoter control. We used inhibitors of certain signal transduction pathways to show that TRH-induced PREB induction is sensitive to the protein kinase A (PKA) inhibitor. TRH stimulated the activity of the wild-type PRL promoter, whereas mutation of the PREB core-binding element on the PRL promoter reduced this ability. In summary, we have shown that TRH stimulated PREB expression in GH3 cells via the PKA pathway. PREB can function as a transcriptional regulator of PRL promoter activity and might be involved in TRH-induced PRL gene transcription.

The prolactin regulatory element-binding regulates of the 11β-hydroxylase gene

Prolactin regulatory element-binding (PREB) protein is a transcription factor not only in pituitary but also adrenal gland. Steroid 11beta-hydroxylase (CYP11B1), a member of the cytochrome p-450 superfamily, is responsible for the last step of glucocorticoid biosynthesis in the adrenal cortices of many kinds of animals. In the present study, we have examined the role of PREB in regulating CYP11B1. CYP11B1 expression was found to be regulated by cAMP, which stimulated the expression of PREB. In addition, PREB induced the expression of the luciferase reporter protein that was under the control of the CYP11B1 promoter. Electrophoretic mobility shift analysis (EMSA) showed that PREB mediates its transcriptional effect by binding to the PREB-responsive cis-element (PRCE) of the CYP11B1 promoter. The knockdown of PREB expression attenuated the effects of cAMP on CYP11B1 expression. In summary, our data showed that in the adrenal gland, PREB regulates the transcription of the CYP11B1 gene via cAMP.

Hyperglycemia Suppresses ABCA1 Expression in Vascular Smooth Muscle Cells

Hyperglycemia is a major risk factor for atherosclerotic disease. The ATP-binding cassette transporter A1 (ABCA1) functions as a pivotal regulator of lipid efflux from cells to apolipoproteins and is thus involved in lowering the risk of atherosclerosis. In this study, we have examined the glucose-mediated regulation of the ABCA1 gene expression in vascular smooth muscle cells. ABCA1 expression was examined by real-time polymerase chain reaction (PCR), Western blot analysis, and reporter gene assay. The results showed that the expression of the ABCA1 mRNA and protein decreased after the cells were treated with 22.4 mM glucose for 48 h. The transcriptional activity of the ABCA1 promoter paralleled the endogenous expression of the ABCA1 gene. Next, we used inhibitors of certain signal transduction pathways to demonstrate that the glucose-induced ABCA1 suppression is sensitive to the p38-mitogen-activated protein kinase (MAPK) inhibitors. The expression of a constitutively active form of p38-MAPK in the cells inhibited the ABCA1 promoter activity, irrespective of the presence of glucose. A dominant-negative mutant of p38-MAPK abrogated the inhibitory effect of glucose on the ABCA1 promoter activity. These results indicate that the glucose-induced suppression of ABCA1 expression is partially mediated by the activation of the p38-MAPK pathway.