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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Medical molecular morphology 29 (1996), S. 13-22 
    ISSN: 1860-1499
    Keywords: Quick-freezing ; Diabetic nephropathy ; Deep-etching ; Glomerulus ; STZ-diabetic rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The three-dimensional ultrastructure of the glomerular basement membrane (GBM) and mesangial matrix (MM) in streptozotocin (STZ)-induced diabetic rats and in one case of a human diabetic nephropathy were examined using the quick-freezing and deep-etching method. In the diabetic rats, the GBM inner layer was diffusely enlarged, and the meshwork structures in the GBM middle layer and the MM were markedly irregular due to the rupturing of fine fibrils. These irregularities and enlargements of the mesh pores in the diabetic rats developed during the experimental period and were significantly different from those in the control rats. Insulin treatment after STZ injection significantly prevented ultrastructural changes in the GBM and MM. The human diabetic case was a 69-year-old male who had been suffering from non-insulin dependent diabetes mellitus for 29 years. He had a background diabetic retinopathy, microalbuminuria and a decrease in lower limb tendon reflexes. Conventional electron microscopy revealed electron-lucent areas in enlarged subendothelial spaces and mesangium. By the quick-freezing and deep-etching method, the GBM inner layer was diffusely enlarged, and the meshwork structure of the GBM middle layer and the MM showed marked irregularity due to the rupturing of fine fibrils. These findings suggest that the initial morphological changes in diabetic nephropathy include structural abnormalities of fine fibrils in the GBM and MM, which may correspond to the subendothelial and mesangial electron-lucent areas as observed in conventional ultrathin sections.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Polymer bulletin 39 (1997), S. 369-376 
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary. The relationships between lateral force and viscoelastic properties of amorphous polymer surfaces with Tg's lower and higher than room temperature (295 K, RT) and their blend systems have been studied on the basis of lateral force microscopic (LFM) measurement. Under the conditions of scanning rate of 102–105 nm sec-1, normal load of 5 nN and RT, the lateral forces of poly(methyl methacrylate) (PMMA) and polyisoprene (PI) homopolymers with Tg's fairly higher and lower than RT, respectively, did not depend on the scanning rate. Whereas, the lateral force of poly(methyl acrylate) (PMA) with Tg ≤ RT decreased with an increase in the scanning rate. Also, poly(vinyl acetate) (PVAc) with Tg ≥ RT showed slight dependence on the scanning rate. The scanning rate dependence of lateral force was similar to the frequency dependence of mechanical loss modulus. The results indicate that the magnitude of lateral force strongly depends on the state of thermal molecular motion. The lateral force-viscoelastic properties of miscible polymer blends was also investigated by LFM.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Molecular biology reports 21 (1995), S. 21-26 
    ISSN: 1573-4978
    Keywords: antigen processing ; ATPase complex ; cell cycle ; proteasome ; ubiquitin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Eukaryotic proteasomes are unusually large proteins with a heterogeneous subunit composition and have been classified into two isoforms with apparently distinct sedimentation coefficients of 20S and 26S. The 20S proteasome is composed of a set of small subunits with molecular masses of 21–32 kDa. The 26S proteasome is a multi-molecular assembly, consisting of a central 20S proteasome and two terminal subsets of multiple subunits of 28–112 kDa attached to the central part in opposite orientations. The primary structures of all the subunits of mammalian and yeast 20S proteasomes have been deduced from the nucleotide sequences of cDNAs or genes isolated by recombinant DNA techniques. These genes constitute a unique multi-gene family encoding homologous polypeptides that have been conserved during evolution. In contrast, little is yet known about the terminal structures of the 26S proteasome, but the cDNA clonings of those of humans are currently in progress. In this review, I summarize available information of the structural features on eukaryotic 20S and 26S proteasomes which has been clarified by molecular-biological methods.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Molecular biology reports 21 (1995), S. 49-52 
    ISSN: 1573-4978
    Keywords: cancer cells ; cell cycle ; cell growth ; proteasomes ; proteolysis ; ubiquitin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Proteasomes are large, unique protein complexes catalyzing energy- and ubiquitin-dependent proteolysis. Recent studies have revealed that these complexes are involved in two important cellular functions. One is to make antigen fragments for major histo-compatibility complex (MHC) class I-restricted antigen presentation and the other is to regulate the cell cycle by proteolysis. Here we review only the latter function of proteasomes. Proteasomes are widely distributed in eukaryotic cells, but their levels have been shown to be particularly high in various immature cells, such as cancerous, fetal and lymphoblastic cells, and agents inducing cell differentiation were found to suppress their expression. These conditions also regulate the expression of ubiquitin genes in a similar way, suggesting that proteasomes act ubiquitin-dependently in their 26S form in immature cells. High levels of proteasomes were found immunochemically in the nuclei of rapidly growing cells, indicating that proteasomes are important for eukaryotic cell growth. Indeed, gene disruptions of most subunits of proteasomes in yeast resulted in total suppression of cell growth and cell death. Short-lived regulatory factors of the cell cycle, such as Fos, p53, Mos, and cyclins are degraded by the proteasome-ubiquitin pathway under phosphorylated or dephosphorylated conditions. Ornithine decarboxylase, which is also a short-lived enzyme and is involved in the early phase of cell growth, is quickly degraded by proteasomes with antizyme, but without ubiquitination. Recently, we found that one of the regulatory factors of 26S proteasomes, p31, is a homologue of Ninlp, whose mutation caused inhibition of the cell cycle in yeast. These results indicate that proteasomes play important roles in regulation of the cell cycle in eukaryotes.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Molecular biology reports 26 (1999), S. 3-9 
    ISSN: 1573-4978
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The 20S proteasome is an intriguingly large complex that acts as a proteolytic catalytic machine. Accumulating evidence indicates the existence of multiple factors capable of regulating the proteasome function. They are classified into two different categories, one type of regulator is PA700 or PA28 that is reversibly associated with the 20S proteasome to form enzymatically active proteasomes and the other type including a 300-kDa modulator and PI31 indirectly influences proteasome activity perhaps by promoting or suppressing the assembly of the 20S proteasome with PA700 or PA28. Thus, there have been documented two types of proteasomes composed of a core catalytic proteasome and a pair of symmetrically disposed PA700 or PA28 regulatory particle. Moreover, the recently-identified proteasome containing both PA28 and PA700 appears to play a significant role in the ATP-dependent proteolytic pathway in cells, as can the 26S proteasome which is known as a eukaryotic ATP-dependent protease.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Molecular biology reports 26 (1999), S. 95-101 
    ISSN: 1573-4978
    Keywords: cancer cachexia ; pentoxifylline ; protein breakdown ; skeletal muscle ; ubiquitin-proteasome system ; tumor necrosis factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The development of pharmacological approaches for preventing the loss of muscle proteins would be extremely valuable for cachectic patients. For example, severe wasting in cancer patients correlates with a reduced efficacy of chemotherapy and radiotherapy. Pentoxifylline (PTX) is a very inexpensive xanthine derivative, which is widely used in humans as a haemorheological agent, and inhibits tumor necrosis factor transcription. We have shown here that a daily administration of PTX prevents muscle atrophy and suppresses increased protein breakdown in Yoshida sarcoma-bearing rats by inhibiting the activation of a nonlysosomal, Ca2+-independent proteolytic pathway. PTX blocked the ubiquitin pathway, apparently by suppressing the enhanced expression of ubiquitin, the 14-kDa ubiquitin conjugating enzyme E2, and the C2 20S proteasome subunit in muscle from cancer rats. The 19S complex and 11S regulator associate with the 20S proteasome and regulate its peptidase activities. The mRNA levels for the ATPase subunit MSS1 of the 19S complex increased in cancer cachexia, in contrast with mRNAs of other regulatory subunits. This adaptation was suppressed by PTX, suggesting that the drug inhibited the activation of the 26S proteasome. This is the first demonstration of a pharmacological manipulation of the ubiquitin-proteasome pathway in cachexia with a drug which is well tolerated in humans. Overall, the data suggest that PTX can prevent muscle wasting in situations where tumor necrosis factor production rises, including cancer, sepsis, AIDS and trauma.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Molecular biology reports 24 (1997), S. 3-11 
    ISSN: 1573-4978
    Keywords: 20S proteasome ; 26S proteasome ; ubiquitin ; ATPase ; non-ATPase subunit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The 26S proteasome is an eukaryotic ATP-dependent, dumbbell-shaped protease complex with a molecular mass of approximately 2000 kDa. It consists of a central 20S proteasome, functioning as a catalytic machine, and two large V-shaped terminal modules, having possible regulatory roles, composed of multiple subunits of 25–110 kDa attached to the central portion in opposite orientations. The primary structures of all the subunits of mammalian and yeast 20S proteasomes have been determined by recombinant DNA techniques, but structural analyses of the regulatory subunits of the 26S proteasome are still in progress. The regulatory subunits are classified into two subgroups, a subgroup of at least 6 ATPases that constitute a unique multi-gene family encoding homologous polypeptides conserved during evolution and a subgroup of approximately 15 non-ATPase subunits, most of which are structurally unrelated to each other.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Molecular biology reports 24 (1997), S. 95-102 
    ISSN: 1573-4978
    Keywords: muscle wasting ; 19S complex ; PA28 activator ; proteasome ; xanthine derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A precise knowledge of the role of subunits of the 19S complex and the PA28 regulator, which associate with the 20S proteasome and regulate its peptidase activities, may contribute to design new therapeutic approaches for preventing muscle wasting in human diseases. The proteasome is mainly responsible for the muscle wasting of tumor-bearing and unweighted rats. The expression of some ATPase (MSS1, P45) and non ATPase (P112-L, P31) subunits of the 19S complex, and of the two subunits of the PA28 regulator, was studied in such atrophying muscles. The mRNA levels for all studied subunits increased in unweighted rats, and analysis of MSS1 mRNA distribution profile in polyribosomes showed that this subunit entered active translation. By contrast, only the mRNA levels for MSS1 increased in the muscles from cancer rats. Thus, gene expression of the proteasome regulatory subunits depends on a given catabolic state. Torbafylline, a xanthine derivative which inhibits tumor necrosis factor production, prevented the activation of protein breakdown and the increased expression of 20S proteasome subunits in cancer rats, without reducing the elevated MSS1 mRNA levels. Thus, the increased expression of MSS1 is regulated independently of 20S proteasome subunits, and did not result in accelerated proteolysis.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Plant molecular biology 34 (1997), S. 307-316 
    ISSN: 1573-5028
    Keywords: gene cloning ; proteasome ; senescence ; Spinacia oleracea ; seedlings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Three kinds of cDNAs encoding 26S proteasome subunits have been cloned from spinach (Spinacia oleracea L.). These genes, designated as SOPSC8, SOPSC1 and SOPRS7, encode an α-type and a β-type subunit of the 20S catalytic core, and an ATPase subunit of the 19/22S regulatory complex, respectively. The deduced protein sequences showed high sequence similarities to other proteasome α- and β-type and ATPase subunit proteins. Southern blot analysis indicates that there are additional members of these dispersed proteasome families in the spinach genome. These three subunit genes are expressed simultaneously during germination and reach a maximum one day after sowing followed by a decline. The expression of these genes also increases during cotyledon senescence.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Medical electron microscopy 33 (2000), S. 115-122 
    ISSN: 1437-773X
    Keywords: Key words Diabetic nephropathy ; Glomerular hypertrophy ; GBM thickening ; Mesangial expansion ; Renal structural heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Details of renal structural changes and structural-functional relationships at the early stage of diabetic nephropathy (DN) in type 2 diabetes are not well known. The present review focuses on these topics from previous studies using light and electron microscopic morphometric analysis. Glomerular hypertrophy, one of the histological changes in DN, is present in type 2 as well as in type 1 diabetic patients. However, mechanisms of increased glomerular size might be different from those in type 1 diabetes. Other typical glomerular changes, glomerular basement membrane thickening and mesangial expansion, are present in normoalbuminuric type 2 diabetic patients as a group. However, these parameters are similar between normo- and microalbuminuric patients. Renal structural-functional relationships cannot be seen in type 2 diabetic patients and therefore urinary albumin might not be a reliable indicator for glomerular structural changes in type 2 diabetic patients. Although previous reports showed reversibility of advanced diabetic glomerulosclerosis in type 1 diabetes by 10 years of strict glycemic control, there is no report regarding histological reversibility by therapeutic interventions in type 2 diabetic patients. In addition, it is unclear whether DN lesions are concordant or discordant with diabetic retinopathy grade in type 2 diabetes. From this information, renal structural changes or structural-functional relationships in type 2 diabetic patients might be heterogeneous and different from those in type 1 diabetic patients. Careful longitudinal study of renal structure and function including serial renal biopsy at the early stage of DN in type 2 diabetes is necessary.
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