Michio Niinobe

Expression Profiling Reveals Novel Pathways in the Transformation of Melanocytes to Melanomas

Affymetrix and spotted oligonucleotide microarrays were used to assess global differential gene expression comparing normal human melanocytes with six independent melanoma cell strains from advanced lesions. The data, validated at the protein level for selected genes, confirmed the overexpression in melanoma cells relative to normal melanocytes of several genes in the growth factor/receptor family that confer growth advantage and metastasis. In addition, novel pathways and patterns of associated expression in melanoma cells not reported before emerged, including the following: (a) activation of the NOTCH pathway; (b) increased Twist expression and altered expression of additional transcriptional regulators implicated in embryonic development and epidermal/mesenchymal transition; (c) coordinated activation of cancer/testis antigens; (d) coordinated down-regulation of several immune modulation genes, in particular in the IFN pathways; (e) down-regulation of several genes implicated in membrane trafficking events; and (f) down-regulation of growth suppressors, such as the Prader-Willi gene NECDIN, whose function was confirmed by overexpression of ectopic Flag-necdin. Validation of differential expression using melanoma tissue microarrays showed that reduced ubiquitin COOH-terminal esterase L1 in primary melanoma is associated with worse outcome and that increased expression of the basic helix-loop-helix protein Twist is associated with worse outcome. Some differentially expressed genes reside on chromosomal regions displaying common loss or gain in melanomas or are known to be regulated by CpG promoter methylation. These results provide a comprehensive view of changes in advanced melanoma relative to normal melanocytes and reveal new targets that can be used in assessing prognosis, staging, and therapy of melanoma patients.

Microtubule-associated protein 2 as a sensitive marker for cerebral ischemic damage--immunohistochemical investigation of dendritic damage.

We investigated the neuronal distribution of microtubule-associated protein 2 in gerbil brain and monitored the progression of ischemic damage immunohistochemically by using this protein as a dendritic marker. The reaction for microtubule-associated protein 2 in normal gerbil brain clearly visualized neuronal soma and dendrites but other structures such as axonal bundles, glia and endothelial cells exhibited little immunoreactivity. In a reproducible gerbil model of unilateral cerebral ischemia, we could detect the ischemic lesions as early as 3 min after right common carotid occlusion at the subiculum-CA1 region of the ipsilateral hippocampus as faint loss of the reaction in the dendrites. After ischemia for 30 min, the ischemic lesions were clearly detected as loss of the reaction in the nerve cell bodies, dendrites and the neuropil in the hippocampus, cerebral cortex, thalamus and the caudoputamen. Although the mechanism for prompt disappearance of the immunohistochemical reaction for microtubule-associated protein 2 is not clear, the present investigation suggests that dendrites in the vulnerable regions may be quite susceptible to ischemic stress and that the immunohistochemical procedure for microtubule-associated protein 2 may be very useful for demonstration of dendritic damage in various pathophysiological states of the central nervous system.

Free radical generation during brief period of cerebral ischemia may trigger delayed neuronal death

We investigated the pathogenic role of free radical formation in ischemic neuronal death using radical scavenger, superoxide dismutase. Cerebral ischemia was produced in the gerbil by bilateral common carotid occlusion for 5 min, which consistently resulted in delayed neuronal death in the CA1 region of the hippocampus. The effects of free superoxide dismutase and a derivatized superoxide dismutase, pyran copolymer conjugated superoxide dismutase, on early ischemic damages, detected sensitively by the immunohistochemical reaction for microtubule associated protein 2, and a subsequent delayed neuronal death after restoration of blood flow were investigated. Preischemic treatment by pyran conjugated superoxide dismutase showed clear protective effects against both the neuronal damages detected by immunohistochemistry after 5 min ischemia and the delayed neuronal necrosis after one week of recovery, although no clear beneficial effects were observed when this drug was administered just before the recirculation or free superoxide dismutase was used. These results strongly suggest that free radical generation during brief period of ischemia plays a pivotal role in triggering the ischemic neuronal damages causing delayed neuronal death at the selectively vulnerable areas of the brain.

Prediction of preadipocyte differentiation by gene expression reveals role of insulin receptor substrates and necdin

The insulin/IGF-1 (insulin-like growth factor 1) signalling pathway promotes adipocyte differentiation via complex signalling networks. Here, using microarray analysis of brown preadipocytes that are derived from wild-type and insulin receptor substrate (Irs) knockout animals that exhibit progressively impaired differentiation, we define 374 genes/expressed-sequence tags whose expression in preadipocytes correlates with the ultimate ability of the cells to differentiate. Many of these genes, including preadipocyte factor-1 (Pref-1) and multiple members of the Wnt signalling pathway, are related to early adipogenic events. Necdin is also markedly increased in Irs knockout cells that cannot differentiate, and knockdown of necdin restores brown adipogenesis with downregulation of Pref-1 and Wnt10a expression. Insulin receptor substrate proteins regulate a necdin–E2F4 interaction that represses peroxisome-proliferator-activated receptor γ (PPARγ) transcription via a cyclic AMP response element binding protein (CREB)-dependent pathway. Together these define a key signalling network that is involved in brown preadipocyte determination.

Functional Diversity of C2 Domains of Synaptotagmin Family MUTATIONAL ANALYSIS OF INOSITOL HIGH POLYPHOSPHATE BINDING DOMAIN

Synaptotagmins I and II are inositol high polyphosphate series (inositol 1,3,4,5-tetrakisphosphate (IP4), inositol 1,3,4,5,6-pentakisphosphate, and inositol 1,2,3,4,5,6-hexakisphosphate) binding proteins, which are thought to be essential for Ca2+-regulated exocytosis of neurosecretory vesicles. In this study, we analyzed the inositol high polyphosphate series binding site in the C2B domain by site-directed mutagenesis and compared the IP4 binding properties of the C2B domains of multiple synaptotagmins (II-IV). The IP4 binding domain of synaptotagmin II is characterized by a cluster of highly conserved, positively charged amino acids (321 GKRLKKKKTTVKKK 324). Among these, three lysine residues, at positions 327, 328, and 332 in the middle of the C2B domain, which is not conserved in the C2A domain, were found to be essential for IP4 binding in synaptotagmin II. When these lysine residues were altered to glutamine, the IP4 binding ability was completely abolished. The primary structures of the IP4 binding sites are highly conserved among synaptotagmins I through IV. However, synaptotagmin III did not show significant binding ability, which may be due to steric hindrance by the C-terminal flanking region. These functional diversities of C2B domains suggest that not all synaptotagmins function as inositol high polyphosphate sensors at the synaptic vesicle.

Developmental expression and intracellular location of P400 protein characteristic of Purkinje cells in the mouse cerebellum

The developmental expression and intracellular localization of a cerebellum-characteristic 250-kDa glycoprotein, P400 protein, were studied by immunohistochemical and immunoblot methods using a monoclonal antibody against P400 protein. In the cerebellum of normal mouse, the expression of P400 protein increased from Postnatal Day 3 to Day 21. This enhancement of P400 protein expression occurred only in the Purkinje cells and proceeded with the growth of their dendritic arborization. Electron microscopic analysis indicated that P400 protein is present at the plasma membrane, the endoplasmic reticulum, and the postsynaptic densities of Purkinje cells. Immunohistochemistry of the cerebella of neurological mutant mice indicated that the Purkinje cells of reeler, weaver, and pcd mutant mice retain the ability to produce a large amount of P400 protein. However, the Purkinje cells of staggerer mutant mouse proved to be incapable of enhanced P400 protein expression. These results indicate that P400 protein is a Purkinje cell-characteristic plasma membrane-associated glycoprotein, which is also present at the postsynaptic density and endoplasmic reticulum and that the expression of P400 protein in Purkinje cells is closely associated with the growth of their dendritic arborization.

Purification and Characterization of P400 Protein, a Glycoprotein Characteristic of Purkinje Cell, from Mouse Cerebellum

Abstract: P400 protein is a concanavalin A (Con A)‐binding, 250–kilodalton glycoprotein characteristic of cerebellum. Extraction conditions for P400 protein were investigated, and complete solubilization of P400 protein from a submicrosomal fraction (P31 fraction) of mouse cerebellum was attained by the combination of 4% Zwittergent 3–14 and 4 M guanidinium chloride. The solubilized P400 protein was purified using Sepharose CL‐4B and Con A‐Sepharose chromatography. A monoclonal antibody (18A10) was prepared against P400 protein. Endo‐β‐N‐acetylglucosaminidase F digestion of P400 protein revealed that P400 protein has a small number of asparagine‐linked oligosaccharide chains and that the epitope that is recognized by 18A10 monoclonal antibody is not on the asparagine‐linked oligosaccharide portion. Tissue distribution of P400 protein was investigated by immunoblot analysis using 18A10 monoclonal antibody. P400 protein was abundant in the cerebellum, but a very small amount of P400 protein or related antigen was also detected in other parts of the nervous system and in nonneural tissues. Immunohis‐tochemical studies indicated that P400 protein was distributed abundantly in the soma, the dendritic arborization, and the axon of the Purkinje cell. No immunoreaction was observed in the other types of cells.

Two types of ryanodine receptors in mouse brain: Skeletal muscle type exclusively in Purkinje cells and cardiac muscle type in various neurons

Two types of ryanodine receptors, channels for Ca2+ release from intracellular stores, are known. We detected the skeletal muscle type only in cerebellum by immunoblot analysis of microsomes and partially purified proteins. The cardiac muscle type was found in all parts of the mouse brain. Immunohistochemical study showed that the cardiac muscle type was localized mainly at the somata of most neurons. Analysis of mutant cerebella suggested that the skeletal muscle type was present exclusively in Purkinje cells. These results suggest that Ca(2+)-induced Ca2+ release, probably mediated by the cardiac muscle receptor, functions generally in various neurons, whereas depolarization-induced Ca2+ release, probably mediated by the skeletal muscle receptor, functions specifically in Purkinje cells.

Msx2 and Necdin Combined Activities Are Required for Smooth Muscle Differentiation in Mesoangioblast Stem Cells

Little is known about the molecular mechanism underlying specification and differentiation of smooth muscle (SM), and this is, at least in part, because of the few cellular systems available to study the acquisition of a SM phenotype in vitro. Mesoangioblasts are vessel-derived stem cells that can be induced to differentiate into different cell types of the mesoderm, including SM. We performed a DNA microarray analysis of a mesoangioblast clone that spontaneously expresses an immature SM phenotype and compared it with a sister clone mainly composed of undifferentiated progenitor cells. This study allowed us to define a gene expression profile for “stem” cells versus smooth muscle cells (SMCs) in the absence of differentiation inducers such as transforming growth factor β. Two transcription factors, msx2 and necdin, are expressed at least 100 times more in SMCs than in stem cells, are coexpressed in all SMCs and tissues, are induced by transforming growth factor β, and, when coexpressed, induce a number of SM markers in mesoangioblast, fibroblast, and endothelial cell lines. Conversely, their downregulation through RNA interference results in a decreased expression of SM markers. These data support the hypothesis that Msx2 and necdin act as master genes regulating SM differentiation in at least a subset of SMCs.

Cellular and Subcellular Localization of Necdin in Fetal and Adult Mouse Brain

Necdin is a 325-amino-acid residue protein encoded by a cDNA clone isolated from neurally differentiated embryonal carcinoma cells. Ectopic expression of necdin induces growth arrest of proliferative cells. Necdin binds to major transcription factors E2F1 and p53, suggesting that necdin exerts its functions through the interactions with these cell-cycle-regulating factors. However, information about precise localization of endogenous necdin protein is currently lacking. A rabbit polyclonal antibody was raised against a bacterially expressed recombinant protein of necdin (amino acids 83–325). Immunoblot analysis revealed that necdin protein was expressed almost exclusively in the brain of adult mice. A relative molecular mass of endogenous necdin was estimated at approximately 43,000. In developing mouse brain, necdin was most abundant during fetal and neonatal periods. Necdin was highly enriched in the cytoplasm of hypothalamic neurons in fetal and adult mice. The subcellular fractionation analysis revealed that necdin was concentrated in the cytosol fraction of brain cells. These results suggest that endogenous necdin protein is localized predominantly in the cytoplasm of differentiated neurons and moves into the nucleus under specific conditions.