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Biomedical subjects

S Seki

Publications and source records attributed to S Seki.

At least 343 records · Page 19Linked to original sources
PubMed1987

The cytotoxicity of cysteinylcatechols and related compounds to human melanoma cells in vitro.

L-3,4-Dihydroxyphenylalanine (L-dopa) and its structural analogs are known to be potently cytotoxic to melanoma cells. We examined the effects of cysteinylcatechols and related compounds, which were newly synthesized as cysteinyl derivatives of L-dopa, on the growth of human melanoma cells in vitro, and their actions were compared with those of L-dopa. 4-S- and 3-S-Cysteinylcatechols showed significantly more potent cytotoxicity to melanoma cells than did L-dopa, and 2-S-cysteinylhydroquinone was next to the catechols in potency. The mechanism of action may involve interaction with the melanocyte-specific enzyme, tyrosinase, for which the cysteinylcatechols could become a better substrate than L-dopa itself. 4-S-Cysteaminylphenol was almost comparable to L-dopa in cytotoxicity, suggesting that this phenol might be oxidized to the corresponding catechol by tyrosinase within the melanoma cells.

Antineoplastic Agents↗
PubMed1987

Bleomycin-induced DNA synthesis in a cell-free system using a permeable mouse sarcoma cell extract.

To investigate factors involved in excision repair DNA synthesis, a soluble extract was prepared from permeable mouse sarcoma (SR-C3H/He) cells by homogenization and ultracentrifugation. DNA synthesis measured by using native calf thymus DNA as the template-primer and the extract as the polymerase source showed low activity. The DNA synthesis was enhanced more than ten-fold by the addition of an appropriate concentration of bleomycin, a radiomimetic DNA-damaging drug. Using selective inhibitors of DNA polymerases, it was shown that the DNA polymerase involved in the bleomycin-induced DNA synthesis was DNA polymerase beta. In addition to DNA polymerase beta, an exonuclease which converts bleomycin-damaged DNA into suitable template-primers for repair DNA synthesis appeared to be present in the permeable cell extract.

Animals↗
PubMed1987

Expression of simian virus 40 small t antigen in Escherichia coli and purification of the antigen.

A simian virus 40 (SV 40) DNA fragment encoding small t antigen was cloned in expression vector pUC8 for the purification of the antigen. The SV40 Hind III B fragment was inserted into the Hind III site of pUC8. A plasmid having the lacZ' and small t antigen genes in the same orientation was designated as pSVt. pSVt encodes the entire small t antigen and an extra 18 amino acids at the amino terminus of the antigen. E. coli transformed with pSVt produced hybrid small t antigen (22 kDa) which comprised about 6% of the total protein. The hybrid small t antigen reacted in immunoblot analysis with SV40-induced tumor-bearing hamster serum. Hybrid small t antigen was extracted from E. coli, and purified by preparative SDS-PAGE. The antigen was extracted from the gel using formic acid solution with high-yield. The gel-purified antigen showed the same antigenic reactivity as crude antigen.

Amino Acid Sequence↗
PubMed1986

Production of histological changes mimicking primary biliary cirrhosis in rabbits by immunization with bile duct antigen.

Histopathological liver changes resembling primary biliary cirrhosis were induced in an experimental animal model. A special strain of rabbit received an antigen prepared from scrapings of bovine gallbladder mucosa. Eventually, 47 out of 84 antigen-treated rabbits displayed histopathological liver features resembling those of chronic non-suppurative destructive cholangitis as seen in humans. In addition, granuloma formation, ductular proliferation and fibrosis were seen in some cases. However, advanced lesions consistent with micronodular cirrhosis have not been found. Lymphocytes seemed to play an important role triggering early pathogenetic mechanisms, judging from the presence of lymphocytes invading the basement membrane of the affected bile ducts. Furthermore, we observed by electron microscopy that the epithelial cells of the involved bile ducts revealed both mitochondrial swelling and dilatation of endoplasmic reticulum cisternae. In summary, our experimental animal model offers interesting possibilities regarding the study of pathogenesis and development of primary biliary cirrhosis.

Animals↗
PubMed1986

DNA repair synthesis in bleomycin-pretreated permeable HeLa cells.

To establish an in vitro system for studying DNA repair, bleomycin-induced unscheduled DNA synthesis in permeable HeLa cells was investigated. Permeable HeLa cells were incubated at 0 degree C for 60 min with 0.11 mM bleomycin, washed to remove free bleomycin and assayed for DNA synthesis. Optimum [3H]deoxythymidine monophosphate incorporation occurred at pH 7.6-8.0 (adjusted at 20 degrees C with Tris-HCl buffer), 3-6 mM MgCl2, 40-60 mM NaCl, and 2.5-5 mM ATP in the presence of four deoxynucleoside triphosphates. The unscheduled nature of DNA synthesis in bleomycin-pretreated permeable cells was confirmed by the BrdUMP density shift technique. Exonuclease III sensitivity of repaired DNA was measured to determine whether or not the completion of repair patches and ligation occurred in bleomycin-pretreated permeable cells. Gap-filling and ligation were suggested to occur in the presence of ATP. Studies using the selective inhibitors (aphidicolin, 2',3'-dideoxythymidine 5'-triphosphate and N-ethylmaleimide) for DNA synthesis showed that DNA polymerases alpha and beta were involved in the repair process. Inhibitor studies suggested that DNA polymerase alpha plays a preferential role in repair label in the intranucleosomal region of nuclear chromatin and DNA polymerase beta in the completion of repair patches in bleomycin-pretreated permeable cells.

Adenosine Triphosphate↗
PubMed1986

Deoxyribonuclease I sensitivity of DNA replicated in permeable mouse sarcoma cells.

To study chromatin structure at the sites of DNA replicated in permeable cells, deoxyribonuclease I (DNase I) sensitivity of newly replicated DNA in permeable mouse sarcoma cells was compared with that of newly replicated DNA in intact cells. About 35% of the DNA replicated in permeable cells was hypersensitive to DNase I, and the remaining DNA showed the same DNase I sensitivity as that of parental chromatin DNA. The sensitivity of DNA replicated in permeable cells was higher than that of DNA newly replicated in intact cells, and was close to that of DNA replicated in the presence of cycloheximide. The sensitivity of DNA pulse-labeled with [3H]deoxythymidine triphosphate by replication in permeable cells was reduced significantly by chasing with cold deoxythymidine triphosphate. The present results suggest that chromatin structure at the sites of DNA replicated in permeable cells is similar to that at the sites of DNA replicated in living cells in the absence of protein synthesis, and that some structural change (possibly toward the maturation) of newly replicated chromatin occurs after the DNA replication in permeable cells.

Animals↗
PubMed1986

Karyotype aberrations and surface marker analyses of the tumor cells of Hodgkin's disease: a case report and review of literature.

Fresh tumor cells from pleural effusion of a patient with Hodgkin's disease were analyzed cytogenetically, immunologically and enzymocytochemically. They were characterized by the presence of alpha-naphthyl butyrate esterase activity, Fc gamma-receptor, HLA-DR antigen and No. 9 antigen which has been shown to be present in Hodgkin's cells and granulocytes, and the absence of definite T-, B- and myeloid cell markers. The karyotype analysis of these tumor cells revealed chromosome instability, but the clonality was confirmed by the many common abnormalities such as -4, -6, -10, -12, -13, -14, +21, del(X) (q22,q26), del(7) (q32q36), and +der(19)t(19;?). In addition, there were more duplicated tetraploid clones than near-diploid clones. The karyotype of the near-diploid clone was interpreted as: 48, X, del(X) (q22q26), -4, -6, -10, -12, -13, -14, +20, +21, +der(4)t(4;?) (p16;?), del(7) (q32q36), +der(19)t(19;?) (p13;?), +mar1, +mar2, +mar3. The karyotype abnormalities characteristic of lymphomas or leukemias were not found. These results indicate that the tumor cells are not of lymphoid or myeloid lineage. Further studies are needed to determine the cellular origin of the tumor cells of Hodgkin's disease.

Adult↗