Keisei Okamoto

Persistent oxidative stress in cancer

DNA of cancers such as renal cell carcinoma and mammary invasive ductal carcinoma, is persistently exposed to more oxidative stress than that of adjacent nornal tissue. We suggest that the concept of ‘persistent oxidative stress in cancer’ may open up a new research area, explaining part of the characteristic tumor biology of cancer such as activated transcription factors and proto‐oncogenes, genomic instability, chemotherapy‐resistance, invasion and metastasis.

Overexpression of human mutT homologue gene messenger RNA in renal-cell carcinoma: Evidence of persistent oxidative stress in cancer

Data regarding oxidatively modified DNA bases suggest that cancer cells are more exposed to oxidative stress than adjacent non‐tumorous tissue. This novel concept may contribute to the understanding of certain aspects of tumor biology such as activated transcription factors, genetic instability, chemotherapy‐resistance and metastasis. We therefore tested this concept in human renal‐cell carcinomas (RCCs) by evaluating the expression of hMTH1, an enzyme preventing the misincorporation into DNA of 8‐oxo‐dGTP (8‐oxo‐7,8‐dihydrodeoxyguanosine triphosphate), an oxidized form of dGTP in the nucleotide pool. The expression of hMTH1 messenger RNA (mRNA) in tumorous kidney. Moreover, advanced‐stage tumors showed significantly higher hMTH1 mRNA expression than early‐stage tumors, and there was a modest linear correlation between hMTH1 expression and c‐myc expression. The results provide logical support for the concept of “persistent oxidative stress in cancer” and suggest a role of hMTH1 mRNA level as a prognostic marker.

Low Incidence of Point Mutations in H- ,K- and N-ras Oncogenes and p53 Tumor Suppressor Gene in Renal Cell Carcinoma and Peritoneal Mesothelioma of Wistar Rats Induced by Ferric Nitrilotriacetate

An iron chelate, ferric nitrilotriacetate (Fe‐NTA), induces renal proximal tubular damage, a consequence of iron‐catalyzed free radical reactions, that finally leads to a high incidence of renal cell carcinoma (RCC) in rodents. Previous studies have identified, within 24 h after administration of Fe‐NTA, lipid peroxidation products, aldehyde‐modified proteins and a variety of modified DNA bases such as 8‐hydroxyguanine that may be mutagenic in vivo. In the present study, pathological features of the RCCs were studied, and, in an effort to correlate them with carcinogen‐specific molecular events in Fe‐NTA‐induced carcinogenesis, the H‐, K‐ and N‐ras oncogenes and the p53 tumor suppressor gene were investigated for the presence of mutations. Fe‐NTA‐induced RCCs showed similarity to human RCCs in that they are often invasive, metastatic and fatal. None (0 of 12) of the tumors had mutation in codons 12, 13 and 61 of the H‐, K‐ and N‐ras genes by direct sequencing. Only one (1 of 12) tumor with high grade histology revealed a CGC‐to‐CTC (Arg to Leu) transversion in codon 246 of the p53 gene by the use of single strand conformation polymorphism (SSCP) analysis and direct sequencing. High expression of mutant p53 protein was confirmed by Western blotting and immunohistochemistry. Study of three peritoneal mesotheliomas induced by Fe‐NTA revealed no mutation in ras and p53 genes. These results suggest that the ras and p53 genes are not the major targets of mutation in Fe‐NTA‐induced carcinogenesis of kidney and mesothelium. Instead, p53 mutation may work for potentiation of malignant character in Fe‐NTA‐induced renal carcinogenesis.

SL/KH strain of mice: a model of spontaneous pre-B-lymphomas.

The SL/Kh strain of mice spontaneously develop two types of non-thymic lymphomas at a high incidence and very short latency. The major type of lymphomas induce systemic lymph node enlargement and hepatosplenomegaly, and the minor type, proliferation predominantly in bone marrow often associated with spinal paralysis. Phenotypes of both types of lymphomas are indistinguishable: they express B220, 6C3, c-kit but not Thy-1.1, Mac-1 and surface Ig. In both types of lymphomas, the immunoglobulin heavy chain gene is found clonally rearranged in the order of VH-D-JH, whereas the light chain gene remains in germ line configuration. About half of the primary lymphomas are dual or oligoclonal in origin. R-PCR also demonstrates expression of lambda 5, RAG-1 and RAG-2, which are specifically associated with pre-B stage lymphocytes. All these observations indicate that both types of the SL/Kh lymphomas are pre-B-lymphomas.