Membrane associated SI factor, LIF(Leukemia inhibitory factor)and bFGF synergistically stimulate proliferation of murine primordial germ cells in primary culture. Moreover, pluripotential embryonic germ cell line can be derived from primordial germ cells after prolonged culture. Although growth of primordial germ cells in primary culture is affected by genetical background, we have successfully got EG cell lines from all inbered mice that we tested. STO feeder cells seem to provide unknown factor that may be important for EG cells to remain in undifferentiation.

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In order to find a new type of hypolipidemic drug, we carried out screening of an inhibitor of cholesterol synthesis from microorganisms and found ML-236B, as a potent and specific inhibitor of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, the ratelimiting enzyme in the pathway of cholesterol biosynthesis. Among many derivatives of ML-236B, pravastatin sodium (pravastatin) was finally selected because of its potency and tissue selectivity.
Pravastatin strongly inhibited sterol synthesis in rat hepatocytes, but only weakly inhibited that in cells from nonhepatic tissues. The selective inhibitory activity of pravastatin in sterol synthesis was further confirmed by ex vivo and in vivo experiments using rats and mice. This characteristic of pravastatin is based on its hydrophilic nature a hydrophilic compound hardly permeates plasma membrane, whereas a hydrophobic (lipophilic) one easily permeates it. In hepatocytes, on the other hand, pravastatin is actively incorporated via organic anion transporter.
Pravastatin demonstrated a preventive effect on the development of coronary atherosclerosis and xanthomatosis in young Watanabe heritable hyperlipidemic (WHHL)rabbits, as a consequence of keeping their serum cholesterol levels low. In clinical study, pravastatin preferentially reduced low-density lipoprotein cholesterol by 27% at 10-20mg/day with low side effects.

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There are characteristic G-rich repeats, i. e. telomeric repeats, at every chromosome end in eukaryotes. The telomeric repeats are considered to be lost in proportion to cell divisions in somatic cells and cultured cells. We analyzed the length of telomeric repeats in natural occurring human tumors, neuroblastomas and lung cancers, to investigate whether the length of telomeric repeats simply reflects the number of cell divisions the tumor cell has passed. In neuroblastoma, reduction of telomeric repeats demonstrated a significant correlation with stage at diagnosis, poor prognosis, and percentage of tumor cells in S-phase. In lung cancer, the occurrence of reduction or elongation of telomeric repeats was observed only in late stage, in metastatic lesions, or in cancer tissues with a high percentage of cells in S-phase, except for adenocarcinoma. According to the telomere hypothesis, the length of telomeric repeats is stably maintained by re-activation of telomerase in immortalized transformed cells. Such re-activation of telomerase, elongation or convergence of telomeric repeats, was suspected only in 7.3% and 6.5% cases in neuroblastoma and lung cancer, respectively.

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A culture model for invasion of rat mesothelial cell layer by rat ascites hepatoma cells has been developed. By using this quantitative model, we have recently found that the invasiveness of tumor cells is not only genetically determined but is greatly influenced by their interactions with host cells and host mediators. The preculture with macrophages was found to enhance both the in vitro and in vivo invasive potentials of the tumor cells. This potentiation appears to be mediated partly by oxygen radicals generated by the cocultured macrophages. The in vitro invasive capacity was also augmented by pretreating the tumor cells with TGF-β, or with activated platelets. In this culture model, tumor cells did not invade mesothelial cell monolayers without fetal calf serum. Serum could be completely substituted by oleoyl-lysophosphatidic acid (LPA) or bacterial phospholipase D (PLD), suggesting a possible participation of particular signaling cascade, PLD-LPA/PA system, in the invasion of tumor cells.

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Androgen-unresponsive cancer cells were established from androgen-dependent tumor, and role of androgen receptor (AR) in these cells was studied. Next, in human prostatic cancer at untreated and endocrine therapy-resistant stages structure of AR were examined. From the results, Following classification on relationship between changes of AR and loss of response is proposed; a) loss of AR is the causal event. This type of response to androgen was found in rat prostatic cancer cell line. b) loss of AR is not required on progression to unresponsive tumor. This type was found in a mouse mammary tumor cell line. c) abnormal AR accompanying with loss or change of response to androgen. This type was found in human prostatic cancer tissues. It is indicated that loss of response to androgen occurs through many ways; some of which may require change of AR, the other is independent on state of AR.

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Many lines of evidence indicate that immortalization of human cells is a rate-limiting step in their malignant transformation. We immortalized normal human fibroblasts with ⁶⁰Co gamma rays (KMST-6 line) and 4-nitroquinoline 1-oxide (SUSM-1 and OUMS-24F lines). Immortalization of normal human cells with gamma rays and 4-nitroquinoline 1-oxide (4NQO) required repeated treatments, suggesting that several mutational events are involved in the immortalization process. The immortalization of human cells itself may be a multistep process. None of these immortalized cells showed either anchorageindependent growth or tumorigenicity and therefore were not malignant. It was possible to further transform the KMST-6 and OUMS-24F lines into malignant cells by treatment with the ras oncogene, but not by transfection with the mutant p53 gene. The immortalized cells showed epithelial-like morphology, prominent numerical and structural abnormalities, requirement of serum growth factors for their growth, enhanced or aberrant expression of c-myc, and elongation of telomere. It is clear from these observations that these immortalized human cell lines are useful for studying many of the factors that are known to contribute to cellular aging, immortalization, and malignant transformation of human cells.

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