Naoko Yamauchi

Adiponectin and AdipoR1 regulate PGC-1α and mitochondria by Ca2+ and AMPK/SIRT1

Adiponectin is an anti-diabetic adipokine. Its receptors possess a seven-transmembrane topology with the amino terminus located intracellularly, which is the opposite of G-protein-coupled receptors. Here we provide evidence that adiponectin induces extracellular Ca2+ influx by adiponectin receptor 1 (AdipoR1), which was necessary for subsequent activation of Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ), AMPK and SIRT1, increased expression and decreased acetylation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), and increased mitochondria in myocytes. Moreover, muscle-specific disruption of AdipoR1 suppressed the adiponectin-mediated increase in intracellular Ca2+ concentration, and decreased the activation of CaMKK, AMPK and SIRT1 by adiponectin. Suppression of AdipoR1 also resulted in decreased PGC-1α expression and deacetylation, decreased mitochondrial content and enzymes, decreased oxidative type I myofibres, and decreased oxidative stress-detoxifying enzymes in skeletal muscle, which were associated with insulin resistance and decreased exercise endurance. Decreased levels of adiponectin and AdipoR1 in obesity may have causal roles in mitochondrial dysfunction and insulin resistance seen in diabetes.

Inhibition of RXR and PPARγ ameliorates diet-induced obesity and type 2 diabetes

PPARgamma is a ligand-activated transcription factor and functions as a heterodimer with a retinoid X receptor (RXR). Supraphysiological activation of PPARgamma by thiazolidinediones can reduce insulin resistance and hyperglycemia in type 2 diabetes, but these drugs can also cause weight gain. Quite unexpectedly, a moderate reduction of PPARgamma activity observed in heterozygous PPARgamma-deficient mice or the Pro12Ala polymorphism in human PPARgamma, has been shown to prevent insulin resistance and obesity induced by a high-fat diet. In this study, we investigated whether functional antagonism toward PPARgamma/RXR could be used to treat obesity and type 2 diabetes. We show herein that an RXR antagonist and a PPARgamma antagonist decrease triglyceride (TG) content in white adipose tissue, skeletal muscle, and liver. These inhibitors potentiated leptins effects and increased fatty acid combustion and energy dissipation, thereby ameliorating HF diet-induced obesity and insulin resistance. Paradoxically, treatment of heterozygous PPARgamma-deficient mice with an RXR antagonist or a PPARgamma antagonist depletes white adipose tissue and markedly decreases leptin levels and energy dissipation, which increases TG content in skeletal muscle and the liver, thereby leading to the re-emergence of insulin resistance. Our data suggested that appropriate functional antagonism of PPARgamma/RXR may be a logical approach to protection against obesity and related diseases such as type 2 diabetes.

The glypican 3 oncofetal protein is a promising diagnostic marker for hepatocellular carcinoma

Expression profiling of hepatocellular carcinoma has demonstrated that glypican 3 (GPC3), a heparan sulfate proteoglycan anchored to the membrane, is expressed at a markedly elevated level in hepatocellular carcinoma. In this paper, two monoclonal antibodies against GPC3, GPC3-C02 and A1836A, were confirmed to specifically recognize GPC3 molecule in cells from hepatocellular carcinoma and hepatoblastoma cell lines by immunoblotting, and both were confirmed to recognize different epitopes of the GPC3 molecule by epitope mapping. Then, we evaluated the feasibility of GPC3-immunohistochemistry in the pathological diagnosis of benign and malignant hepatocellular lesions by applying these monoclonal antibodies to formalin-fixed and paraffin-embedded specimens. The immunoreactivity turned out to be identical in the two monoclonal antibodies and was thus confirmed to represent the actual expression of the GPC3 molecule. The expression was observed in the fetal liver, but not in normal adult liver, liver cirrhosis or hepatitis except for a tiny focus of a regenerative nodule of fulminant hepatitis. Diffusely positive staining of GPC3 was observed in malignant hepatocytes in hepatoblastomas and in hepatocellular carcinomas (47/56, 84%). GPC3 expression was independent of the differentiation and size of the hepatocellular carcinoma. On the other hand, there was only weak and focal staining in low-grade (2/8) and high-grade dysplastic nodules (6/8). GPC3 immunoreactivity was detected in only one of 23 metastatic lesions of colorectal carcinoma, and its expression was entirely absent in the liver cell adenoma (0/7), carcinoid tumor (0/1), and cholangiocellular carcinoma (0/16). When compared with immunohistochemistry of hepatocyte antigen and alpha-fetoprotein, GPC3-immunohistochemistry was siginificantly much more specific and sensitive for hepatocellular carcinomas. Thus, GPC3 was confirmed to be one of the oncofetal proteins now attracting attention for their promise both as markers of hepatocellular carcinoma in routine histological examination and as targets in monoclonal antibody-based hepatocellular carcinoma therapy.

Constitutive tyrosine phosphorylation of ErbB-2 via Jak2 by autocrine secretion of prolactin in human breast cancer.

Overexpression of the oncogene for ErbB-2 is an unfavorable prognostic marker in human breast cancer. Its oncogenic potential appears to depend on the state of tyrosine phosphorylation. However, the mechanisms by which ErbB-2 is constitutively tyrosine-phosphorylated in human breast cancer are poorly understood. We now show that human breast carcinoma samples with ErbB-2 overexpression have higher proliferative and metastatic activity in the presence of autocrine secretion of prolactin (PRL). By using a neutralizing antibody or dominant negative (DN) strategies or specific inhibitors, we also show that activation of Janus kinase Jak2 by autocrine secretion of PRL is one of the significant components of constitutive tyrosine phosphorylation of ErbB-2, its association with Grb2 and activation of mitogen-activated protein (MAP) kinase in human breast cancer cell lines that overexpress ErbB-2. Furthermore, the neutralizing anti-PRL antibody or erbB-2 antisense oligonucleotide or DN Jak2 or Jak2 inhibitor or DNRas or MAP kinase kinase inhibitor inhibits the proliferation of both untreated and PRL-treated cells. Our results indicate that autocrine secretion of PRL stimulates tyrosine phosphorylation of ErbB-2 by Jak2, provides docking sites for Grb2 and stimulates Ras-MAP kinase cascade, thereby causing unrestricted cellular proliferation. The identification of this novel cross-talk between ErbB-2 and the autocrine growth stimulatory loop for PRL may provide new targets for therapeutic and preventive intervention of human breast cancer.

Identification of ROBO1 as a Novel Hepatocellular Carcinoma Antigen and a Potential Therapeutic and Diagnostic Target

Purpose: Hepatocellular carcinoma is the most common primary malignancy of the liver and accounts for as many as one million deaths annually worldwide. The present study was done to identify new transmembrane molecules for antibody therapy in hepatocellular carcinoma. Experimental Design: Gene expression profiles of pooled total RNA from three tissues each of moderately differentiated and poorly differentiated hepatocellular carcinoma were compared with those of normal liver, noncancerous liver tissue in hepatocellular carcinoma patients, 30 normal tissue samples, and five fetal tissue samples. Target genes up-regulated specifically in hepatocellular carcinoma were validated by immunohistochemical analysis and complement-dependent cytotoxicity assay using monoclonal antibodies generated against target molecules. Results: The human homologue of the Drosophila Roundabout gene, axon guidance receptor homologue 1, ROBO1/DUTT1, a member of the immunoglobulin superfamily, was highly expressed in hepatocellular carcinoma, whereas it showed only a limited distribution in normal tissues. On immunohistochemical analysis using a newly generated anti-ROBO1 monoclonal antibody, positive signals were observed in 83 of 98 cases of hepatocellular carcinoma (84.7%). The mAb B2318C induced complement-dependent cytotoxicity in ROBO1-expressing cell lines and in the liver cancer cell line PLC/PRF/5. Strikingly, the ectodomain of ROBO1 was detected not only in the culture medium of liver cancer cell lines (PLC/PRF/5, HepG2, etc.) but also in sera from hepatocellular carcinoma patients (6 of 11). Conclusions: This is the first report that ROBO1 is overexpressed in hepatocellular carcinoma and shed into serum in humans. These observations suggest that ROBO1 is a potential new serologic marker for hepatocellular carcinoma and may represent a new therapeutic target.

Oncofetal protein glypican-3 in testicular germ-cell tumor

The expression of an oncofetal protein, the glypican-3 (GPC3), was immunohistochemically evaluated in a wide variety of primary testicular germ-cell tumors (GCTs) in comparison with other markers, alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG)-beta, and OCT3/4. Eighty-nine cases of GCT including 22 cases of mixed GCT were evaluated with reference to each tumor component. GPC3 expression was observed in neoplastic cells of yolk-sac tumor (YST) (25/25), teratoma (2/10), components of syncytiotrophoblastic giant cells (STGCs) (10/14), and choriocarcinoma (1/3), but none in intratubular germ-cell neoplasias, unclassified type (0/33), seminomas (0/61), or embryonal carcinoma (0/19). All cases of YST showed diffuse labeling of neoplastic cells in cytoplasmic and membranous patterns, and the positive area of GPC3 was much larger than that of AFP. Glandular structures in teratomas showed GPC3 immunostaining as well as AFP. Although the number of GPC3-positive cells was smaller in STGC components and choriocarcinoma, there was no diffusion artifact in GPC3 immunostaining, as was frequently encountered in hCG-beta staining. Thus, GPC3 is a unique oncofetal protein, which is useful as an immunohistochemical marker for GCT differentiated to extraembryonic tissue, especially YST.

Hepatocellular oncofetal protein, glypican 3 is a sensitive marker for α-fetoprotein-producing gastric carcinoma

Aims Glypican 3 (GPC3) is a cell surface heparan sulphate proteoglycan expressed specifically in the fetal liver and malignant neoplasms of hepatocyte lineage. The aim was to evaluate the significance of GPC3 in α‐fetoprotein (AFP)‐producing gastric carcinoma (GC) and other forms of GC.

Immunohistochemical analysis of endometrial adenocarcinoma for bcl-2 and p53 in relation to expression of sex steroid receptor and proliferative activity

In order to clarify the factors that affect growth of endometrial carcinoma, immunohistochemical analyses of bcl-2, p53, sex steroid receptors, and Ki-67 were performed in 35 cases of endometrial carcinoma (32 endometrioid and three clear-cell carcinomas). Correlation of antigen expression with clinicopathological features was analyzed. Expression of bcl-2 was found in 58.8, 33.3, and 20.0% of grade 1 (G1), grade 2 (G2), and grade 3 (G3) endometrial carcinomas, respectively. Estrogen receptor (ER) was observed in 70.6, 22.2, and 0% of G1, G2, and G3 cases (p < 0.01), respectively. In contrast, expression of p53 was found in 5.8, 33.3, and 60.0% of G1, G2, and G3 cases, respectively. The labeling index of Ki-67 correlated with p53 overexpression (p < 0.01). Lymph node metastases were observed in 6.6 and 5.5% of ER- and PR (progesterone receptor)-positive carcinomas, whereas metastases were observed in 44.4 and 53.3% of ER- and PR-negative carcinomas, respectively (p < 0.05). Lymph node metastases were observed in 50.0% of p53-positive carcinomas, whereas metastases were observed in 22.2% of p53-negative carcinomas (p < 0.05). These results suggest that bcl-2 expression in endometrial carcinomas is regulated in a hormone-dependent manner. Expression of bcl-2 may occur more frequently in estrogen-related, low-grade endometrial carcinomas, whereas p53 overexpression is found more often in endometrial carcinomas in estrogen-unrelated, high-grade endometrial carcinomas with prominent proliferative activity and a high frequency of lymph node metastases.

Concurrent Activation of Acetylation and Tri-Methylation of H3K27 in a Subset of Hepatocellular Carcinoma with Aggressive Behavior

Analysis of acetylation and tri-methylation of the same residue of histone molecules might identify a subset of hepatocellular carcinoma (HCC) with aggressive behavior. In the present study, we examined acetylation and tri-methylation of lysine 27 on histone H3 (H3K27ac and H3K27me3, respectively) because these two modifications are known to exhibit opposite effects (enhancing and silencing) on gene expression. Neoplastic and non-neoplastic tissues from 198 HCC cases were immunostained with specific monoclonal antibodies against H3K27ac and H3K27me3. The stained tissues were evaluated by an image analyzing program to generate histological scores (H-scores, range 0–300), which were determined by multiplying the percentage of positive-stained cells with the classified immunohistochemical marker intensity (0–3). HCC tissues showed significantly higher H3K27ac (156.7±86.8) and H3K27me3 H-scores (151.8±78.1) compared with the background liver (40.3±33.0 and 64.7±45.6, respectively) (both P<0.001). The cases with H-scores of high-H3K27ac/high-H3K27me3 (n = 54) showed significant correlation with poor differentiation of morphology (P<0.01) and p53-positive staining (P<0.05), and poor prognosis (P<0.01). Confocal microscopy revealed segregated intranuclear localization of both modifications in the individual cancer cells: H3K27ac localization in central euchromatin regions and H3K27me3 in peripheral heterochromatin regions. Concurrent acetylation and methylation at H3K27 occurs in HCC cells in association with p53 abnormalities. These findings demonstrate that image analyzer-assisted H-scores of H3K27ac and H3K27me3 identified an aggressive subgroup of HCC, and could serve as a prognostic marker for HCC.

Expression levels of adiponectin receptors are decreased in human endometrial adenocarcinoma tissues.

Adiponectin is a cytokine secreted by adipocytes, whose plasma levels are decreased in obesity. Adiponectin has insulin-sensitizing, antiatherogenic, and antidiabetogenic effects. It has been shown that adiponectin may also exert antineoplastic activity through suppression of tumor proliferation and neoangiogenesis and through induction of apoptosis. Recently, low adiponectin serum concentration has been found in obesity-related malignancies, including endometrial cancer. In addition, the expression of adiponectin receptors (AdipoR1 and AdipoR2) has been documented in several human cancer tissues, but the expression has previously not been assessed in human endometrial cancer tissues. In this study, we analyzed the immunohistochemical expression of AdipoR1 and AdipoR2 in a series of surgically resected human endometrioid adenocarcinoma tissues from a total of 141 cases. Decreased AdipoR1 or AdipoR2 expression was significantly associated with histological higher grade (P=0.0026 and 0.0004, respectively). Decreased expression of AdipoR1 was associated with myometrial invasion and lymph node metastasis of endometrioid adenocarcinoma (P=0.0039 and P=0.0069, respectively). AdipoR1 and AdipoR2 immunoexpression was significantly associated with the expression of the progesterone receptor, although it was not significantly correlated with the expression of the estrogen receptor, Ki-67 or p53. Our present study raises the possibility that decreased expression of adiponectin receptors is implicated in the development, invasion, and metastasis of human endometrioid adenocarcinoma. Our findings, moreover, indicate that adiponectin receptors could be considered as therapeutic targets for endometrioid adenocarcinoma. In adiponectin receptor-positive endometrioid adenocarcinoma, we think adiponectin-based anticancer therapy is useful; however, in histological high-grade endometrioid adenocarcinoma, in which the expression levels of adiponectin receptors are relatively low, adiponectin therapy supported by adiponectin receptor induction is needed.