Plasma membrane-associated sialidase is a key enzyme for ganglioside hydrolysis, thereby playing crucial roles in regulation of cell surface functions. Here we demonstrate that mice overexpressing the human ortholog (NEU3) develop diabetic phenotype by 18 -22 weeks associated with hyperinsulinemia, islet hyperplasia, and increased ␤-cell mass. As compared with the wild type, insulin-stimulated phosphorylation of the insulin receptor (IR) and insulin receptor substrate I was significantly reduced, and activities of phosphatidylinositol 3-kinase and glycogen synthase were low in transgenic muscle. IR phosphorylation was already attenuated in the younger mice before manifestation of hyperglycemia. Transient transfection of NEU3 into 3T3-L1 adipocytes and L6 myocytes caused a significant decrease in IR signaling. In response to insulin, NEU3 was found to undergo tyrosine phosphorylation and subsequent association with the Grb2 protein, thus being activated and causing negative regulation of insulin signaling. In fact, accumulation of GM1 and GM2, the possible sialidase products in transgenic tissues, caused inhibition of IR phosphorylation in vitro, and blocking of association with Grb2 resulted in reversion of impaired insulin signaling in L6 cells. The data indicate that NEU3 indeed participates in the control of insulin signaling, probably via modulation of gangliosides and interaction with Grb2, and that the mice can serve as a valuable model for human insulin-resistant diabetes.Gangliosides are a family of sialic acid-containing glycosphingolipids present in the cell surface membranes. Several lines of evidence suggest their important functional roles in regulating a wide range of biological processes including cell growth, cell differentiation, and transmembrane signaling (1-3). Most of the observations on ganglioside function, however, have been performed so far by using bacterial sialidases and exogenous gangliosides to mimic in vivo expression. To obtain further insights into their physiological significance and regulation mechanism, it is necessary to focus on endogenous sialidases responsible for ganglioside hydrolysis inside the cells. Three types of mammalian sialidase have been cloned and established to have low identity with each other in their primary structure. They differ in enzymatic properties and subcellular localization, being mainly found in lysosomes (Neu1), cytosol (Neu2), and plasma membranes (Neu3). Other than the contribution of lysosomal sialidase to glycoconjugate catabolism in lysosomes, their cellular roles are not well understood. The fact that plasma membrane sialidase is unique in specifically hydrolyzing gangliosides (4 -10) and in its subcellular localization in plasma membranes, where levels of other glycosidases are very low, suggests participation in cell surface events through modulation of gangliosides. To obtain evidence of this, we previously cloned sialidase cDNAs of mammalian origin (8, 9, 11, 12), and we have recently investigated effects of overexpression in transgenic...

Our goal in the present study was to evaluate antitumor effects and frequency of tumor-infiltrating immune cells upon intratumoral injection of RGD fiber-mutant adenoviral vector (AdRGD) encoding the chemokines CCL17, CCL19, CCL20, CCL21, CCL22, CCL27, XCL1, and CX3CL1. Among eight kinds of chemokine-expressing AdRGDs, AdRGD-CCL19 injection most efficiently induced infiltration of T cells into established B16BL6 tumor parenchyma, whereas most of these T cells were perforin-negative in immunohistochemical analysis. Additionally, the growth of AdRGD-CCL19-injected tumors decreased only slightly as well as that of other tumors treated with each chemokine-expressing AdRGD, which indicated that accumulation of naive T cells in tumor tissue does not effectively damage the tumor cells. Tumor-bearing mice, in which B16BL6-specific T cells were elicited by dendritic cellbased immunization, demonstrated that intratumoral injection of AdRGD-CCL17, -CCL22, or -CCL27 could considerably suppress tumor growth and attract activated T cells. On the other hand, AdRGD-CCL19-injection in the immunized mice showed slight increase of tumor-infiltrating T cells compared to treatment using control vector. Collectively, although AdRGD-mediated chemokine gene transduction into established tumors would be very useful for augmentation of tumor-infiltrating immune cells, a combinational treatment that can systemically induce tumor-specific effector T cells is necessary for satisfactory antitumor efficacy.

Dendritic cells (DCs) are the most potent professional antigen-presenting cells for the initiation of antigen-specific immune responses, and antigen-loaded DCs have been regarded as promising vaccines in cancer immunotherapy. We previously demonstrated that RGD fiber-mutant adenovirus vector (AdRGD) could attain highly efficient gene transduction into human and murine DCs. The aim of the present study is to demonstrate the predominance of ex vivo genetic DC manipulation using AdRGD in improving the efficacy of DC-based immunotherapy targeting gp100, a melanoma-associated antigen (MAA). Vaccination with murine bone marrow-derived DCs transduced with AdRGD encoding gp100 (AdRGD-gp100/mBM-DCs) dramatically improved resistance to B16BL6 melanoma challenge and pulmonary metastasis as compared with immunization with conventional Ad-gp100-transduced mBM-DCs. The improvement in antimelanoma effects upon immunization with AdRGD-gp100/mBM-DCs correlated with enhanced cytotoxic activities of natural killer (NK) cells and B16BL6-specific cytotoxic T lymphocytes (CTLs). Furthermore, in vivo depletion analysis demonstrated that CD8 þ CTLs and NK cells were the predominant effector cells responsible for the anti-B16BL6 immunity induced by vaccination with AdRGDgp100/mBM-DCs, and that helper function of CD4 þ T cells was necessary for sufficiently eliciting effector activity. These findings clearly revealed that highly efficient MAA gene transduction to DCs by AdRGD could greatly improve the efficacy of DC-based immunotherapy against melanoma.

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