Erythroleukemia induction by Friend leukemia virus. A host gene locus controlling early anemia or polycythemia and the rate of proliferation of late erythroid cells.

This report confirms that the Fv-5 locus controls the types of erythropoiesis induced by Friend erythroleukemia virus (FLV) (21) and extends the study to investigate the mode of action of this locus. With the use of FLV obtained by a variety of procedures, we showed that the polycythemia spleen focus-forming component (SFFVp) was responsible for the contrasting changes of hematocrits observed in FV-Pp (polycythemia strain)-infected DBA/2 (Fv-5pp) or CBA (Fv-5aa) mice. These changes in hematocrits were found to be a direct result of the rise in circulating reticulocytes and erythrocytes in DBA/2 mice and a corresponding drop of these erythroid cells in CBA mice 2 wk after infection. Examination of the FV-P-induced cellular changes indicated that dramatic increase in erythropoietin (epo)-independent erythroid precursor (CFU-E*) cells was detected in the spleens and marrow of both strains of mice. The epo responsiveness of the CFU-E in the uninfected and FV-P-infected CBA and DBA/2 mice was also very similar. Similar to FLV-infected DBA/2 mice, the FV-P-infected CBA mice also developed tumorogenic cells (CFU-FV) relatively early after infection (4-6 wk). Study of the physiological and pathological changes in the marrows and spleens of these infected mice indicated that significant differences were found in the spleens of the two strains of mice. The percent of reticulocytes in the spleen cells of CBA mice remained between 10 and 20%, and level of the DBA/2 mice increased to approximately 50%. This higher rate of erythropoiesis was also reflected in the significantly higher rate of uptake of 59Fe in the spleens of the DBA/2 mice. These results suggest that the Fv-5 locus might control the hematocrit levels of these mice by regulating the rates of erythropoiesis in the spleen levels of these mice, probably by affecting the rate of proliferation of an erythroid cell or cells. The erythroid cell(s) affected is likely to be more mature than the erythroid progenitor, CFU-E, as the levels of CFU-E in these two strains of mice were similar. The hypothesis that Fv-5 may control the rates of proliferation of a late erythroid (cell(s) is also supported by the significantly higher spleen weights found in the infected DBA/2 (approximately 2.5 g/spleen) mice than in the CBA (approximately 1 g/spleen) strain.

HLA DRB4 0101-restricted immunodominant T cell autoepitope of pyruvate dehydrogenase complex in primary biliary cirrhosis: evidence of molecular mimicry in human autoimmune diseases.

We established six T cell clones specific for pyruvate dehydrogenase complex (PDC)-E2 peptides from four different patients with primary biliary cirrhosis using 33 different peptides of 17-20 amino acid residues corresponding to human PDC-E2 as stimulating antigens. The minimal T cell epitopes of these six T cell clones were all mapped to the same region of the PDC-E2 peptide 163-176 (GDLLAEIETDKATI), which corresponds to the inner lipoyl domain of PDC-E2. The HLA restriction molecules for this epitope were all identified as HLA DRB4 0101. The common essential amino acids of this epitope for these T cell clones were E, D, and K at positions 170, 172, and 173, respectively; other crucial amino acids for this epitope differed in each T cell clone. In addition, the alanine-substituted peptides at positions 170 and 173, but not 172, inhibited the proliferation of all T cell clones induced by the original peptide of human PDC-E2 163-176, indicating that amino acid D at position 172 is a critical MHC-binding site for all T cell clones tested. Interestingly, all T cell clones reacted to PDC-E2 peptide 36-49 (GDLIAEVETDKATV), which corresponds to the outer lipoyl domain of human PDC-E2. Furthermore, one T cell clone cross-reacted with exogenous antigens such as Escherichia coli PDC-E2 peptide 31-44/134-147/235-248 (EQSLITVEGDKASM), which has an EXDK sequence. This is a definite demonstration of the presence of molecular mimicry at the T cell clonal level in human autoimmune diseases. It is also considered possible to design peptide-specific immunotherapy based on the findings of T cell autoepitopes in primary biliary cirrhosis.

Identification of a functional receptor for granulocyte colony-stimulating factor on platelets.

Since granulocyte colony-stimulating factor (G-CSF) is thought to be a granulocyte lineage-specific cytokine, G-CSF receptors on blood cells other than those of granulocyte or monocyte lineage have not been well investigated. We now report that G-CSF receptors are present on platelets. The expression of G-CSF receptors on platelets was demonstrated by flow cytometry and radioreceptor assay. The mean number of G-CSF-binding sites per cell was 41 and the binding affinity was high (Kd 300 pM), similar to the affinity observed on granulocytes. Cross-linking assay revealed that G-CSF receptors were present on a single subunit protein of approximately 150 kD on the platelets. To clarify whether or not G-CSF might produce some direct functional influence on platelet response, the effects on platelet aggregation were studied. Although G-CSF itself did not affect platelet aggregation in vitro, preincubation with G-CSF augmented a secondary aggregation of platelets induced by low concentrations of adenosine diphosphate (ADP). There was a dose-response relationship for this G-CSF activity at concentrations of up to 10 ng/ml. Furthermore, the augmented ADP-induced secondary aggregation of platelets on G-CSF receptors was completely abrogated in the presence of anti-G-CSF polyclonal antibodies. These results indicate that platelets possess functional G-CSF receptors.

Interleukin 4 suppresses the spontaneous growth of chronic myelomonocytic leukemia cells.

We studied the effects of IL-4 on the spontaneous proliferation of chronic myelomonocytic leukemia (CMMoL) cells in vitro. IL-4 (100 U/ml) suppressed the spontaneous DNA synthesis by approximately 50% in 5 of 8 cases examined. IL-4 (100 U/ml) also inhibited the spontaneous colony formation by CMMoL cells in a methylcellulose culture by 50-97% in all of the 10 cases in which spontaneous colonies were formed. This IL-4-mediated suppression of the growth of CMMoL cells was completely abolished by the addition of anti-IL-4 neutralizing antibodies. The spontaneous CMMoL colonies were substantially suppressed by the addition of either anti-IL-6 or anti-granulocyte/macrophage colony-stimulating factor (GM-CSF) antibodies to the colony assay system: the addition of both anti-IL-6 and anti-GM-CSF antibodies resulted in greater than 80% inhibition of the colony formation by CMMoL cells. On the other hand, none of anti-IL-1-beta, anti-granulocyte-CSF, anti-macrophage-CSF, or anti-tumor necrosis factor-alpha antibodies affected the CMMoL colony formation. In the supernatants from 24-h cultures of CMMoL cells, high levels of IL-6 and GM-CSF were demonstrated in 9 of 9 and 2 of 9 cases examined, respectively. IL-4 (100 U/ml) almost completely inhibited the secretion of IL-6 and GM-CSF by CMMoL cells. These observations suggest that IL-4 suppresses the spontaneous proliferation of CMMoL cells by inhibiting their production of IL-6 and/or GM-CSF, both of which could act in vitro as an autocrine growth factor for CMMoL cells.

Deficiency of coagulation factor XIII A subunit caused by the dinucleotide deletion at the 5' end of exon III.

A congenital deficiency of the coagulation Factor XIII A subunit (F XIII A) is a rare autosomal recessive disorder that is characterized by a life-long bleeding tendency complicated by a difficulty in healing. Thus far, no molecular genetic analysis of this disorder has been reported. In this study, we demonstrate the molecular abnormalities in a family with this disorder. We performed Northern blot analysis of peripheral blood monocytes obtained from the propositus and found a 4-kb single band of F XIII A mRNA whose size was identical with that of normal subjects. Exons II-XV, which encode all the amino acids, were individually amplified by a polymerase chain reaction (PCR). All PCR products from the propositus had lengths indistinguishable from those of the wild type on agarose gel, suggesting that this defect results from either a point mutation or a short deletion/insertion. The sequencing of F XIII A cDNA from the propositus revealed a deletion of the dinucleotide AG within the AGAG repeat at the position of 210 to 213. Concerning the genomic sequence, a deletion of dinucleotide AG was also demonstrated in the intron B-exon III boundary. This deletion appeared to cause a frameshift mutation making a new stop codon shortly thereafter, and leading to a deficiency of plasma F XIII A. The heterozygosity of the F XIII A deficiency in the patient's offspring was documented by the nucleotide sequences of their exon III.

Development of a rapid chemosensitivity test for anticancer drugs with contact-sensitive monolayers of Balb/3T3 cells.

We investigated whether lethally irradiated, contact-sensitive Balb/3T3 cell confluent monolayers, termed "cell mats," could be used for the screening of human tumors for sensitivity to anticancer drugs. Cell mats greatly inhibited the growth of normal Balb/3T3 cells and normal human fibroblasts but did not inhibit the growth of human tumor cells. To assess chemosensitivity of tumor cells, we measured the [14C]thymidine (dThd) incorporation by tumor cells that had been plated and then treated with various anticancer drugs on the cell mats. Although the [14C]dThd incorporation assay, when compared with the colony-formation assay, underestimated the toxicity of certain drugs, the assays gave similar results with regard to the degree of colony inhibition and to the decrease in [14C]dThd incorporation when various anticancer drugs were used at the same concentration ranges. Therefore, the method we used for measuring the isotope uptake in the cell mats could also be used to test for tumor-specific chemosensitivity. Because our results from this assay on various human tumor cells, including those from primary human tumors, can be obtained within 5 days, we believe that the system is potentially useful for testing anticancer drugs against human tumors in vitro.

Marked granulocytosis in C57BL/6 mice bearing a transplanted BMT-11 fibrosarcoma.

When a 3-methylcholanthrene (CAS: 56-49-5)-induced fibrosarcoma, BMT-11, and its eight clones were transplanted sc into syngeneic C57BL/6 mice, leukemoid reaction characterized by a progressive increase in peripheral white blood cells (WBCs) and by splenomegaly was observed as the tumors grew. The WBC count reached about forty-fold of the normal level, and more than 90% of WBCs were found to be polymorphonuclear leukocytes. The increase in WBCs was correlated with tumor size, and its count decreased to normal level within 7 days after surgical excision of subcutaneous tumors. Moreover, a high level of colony-stimulating activity was detected in the supernatant of BMT-11 culture. These results suggest that the colony-stimulating factor produced by BMT-11 cells caused granulocytosis in mice. This is the first report of the marked degree of granulocytosis induced by a transplanted tumor in C57BL/6 strain mice.

Production of interleukin 6 from human liver cell lines: production of interleukin 6 is not concurrent with the production of alpha-fetoprotein.

The production of interleukin (IL) 6 from six human liver cell lines, including Chang liver, HLF, HLE, HepG2, PLC/PRF/5, and HuH-7, was investigated using enzyme-linked immunosorbent assay and Northern blot analysis. When cells were cultured in the presence of 12-O-tetradecanoylphorbol-13-acetate, significant amounts of IL6 were detected in the culture supernatants of Chang liver cells, HLF cells, and HLE cells. However, IL6 was not detected in the culture supernatants from HepG2 cells, PLC/PRF/5 cells, or HuH-7 cells which had been treated similarly. To further investigate the production of IL6, expression of the IL6 gene was studied. Results of Northern blot analysis using IL6 complementary DNA as a probe showed that the induction was initiated at the mRNA level. Moreover, IL6 mRNA was also induced by IL1 beta and tumor necrosis factor but not by a calcium ionophore (A23187) or IL6 itself in Chang liver cells. This is the first study to demonstrate the production of human IL6 in liver cells. Furthermore, when the production of alpha-fetoprotein (AFP) from the liver cell lines was examined, the three that were able to produce IL6 failed to produce AFP, whereas the other three cell lines succeeded in producing AFP. These observations may indicate the heterogeneous origin of the liver cell lines.

Characterization of a low-molecular-weight growth inhibitor formed by density-inhibited, tumorigenic V79 Chinese hamster cells.

A novel type of low-molecular-weight growth-inhibitory factor responsible for the density inhibition of tumorigenic V79 Chinese hamster cells has been purified, if not homogenously, by a series of reverse-phase and gel filtration high-performance liquid chromatography. The factor is an acid-stable, heat-labile substance distinct from antiproliferative nucleoside analogues or polyamines and has a molecular weight of approximately 2000. The biological activity of this inhibitor was enhanced nearly 5-fold by trypsin treatment, thereby suggesting that the inhibitor may be a precursor peptide which becomes an oligopeptide with intense biological activity by proteolysis, or that trypsin treatment allows resultant small molecules to efficiently transfer across the cytoplasmic membrane. This inhibitor reversibly inhibits the growth of a broad spectrum of cell types from neoplastic and nonneoplastic cells from various species. These data suggest that this inhibitor is primarily a growth-regulatory molecule common to mammalian cells and may play an important role in regulating growth of both normal and neoplastic cells.

Serum acid ribonuclease in myelogenous leukemia.

Acid and alkaline RNase activities in serum were measured with yeast RNA as the substrate in normal subjects and in leukemic patients pretreatment and posttreatment, and the acid/alkaline ratios of activities were 0.63 +/- 0.08 (S.D.) (N, 12), 2.28 +/- 0.82 (N, 8), and 0.60 +/- 0.13 (N, 9), respectively. The mean value for the ratio in the pretreated leukemia was significantly higher than that in the other 2 groups (p less than 0.01). By separating these acid and alkaline RNases from normal and leukemic sera by phosphocellulose chromatography, it was further confirmed that acid RNase alone increased markedly in leukemic serum. From serum and leukocytes of leukemic patients, acid RNases were purified about 2000-fold and 300-fold, respectively, by phosphocellulose and Sephadex G-75 chromatography. Both enzymes displayed properties nearly identical with those of normal serum and leukocytes, except that leukemic serum acid RNase had about a 2.4-fold greater affinity for polyuridylate than for polycytidylate as substrate, in contrast to normal serum acid RNase that degraded polycytidylate exclusively. On the other hand acid RNases from serum leukocytes of leukemia showed a similar substrate preference. These results suggest that the high RNase levels of leukemic sera are due to an excessive leakage of acid RNase into the blood stream from abnormal leukocytes.

Effect of human recombinant granulocyte/macrophage colony-stimulating factor and native granulocyte colony-stimulating factor on clonogenic leukemic blast cells.

The effects of human recombinant granulocyte/macrophage colony-stimulating factor (GM-CSF) and human native purified granulocyte colony-stimulating factor (G-CSF) on the growth of clonogenic leukemic blast cells from eight Japanese patients with acute myeloblastic leukemia were studied, using an in vitro leukemic blast colony assay. The results showed that GM-CSF stimulated leukemic blast colony formation in all cases examined, whereas G-CSF stimulated colony formation in four of the eight cases. The maximum stimulating activity of GM-CSF on the growth of clonogenic leukemic blast cells was higher than that of G-CSF in the majority of cases, while sometimes GM-CSF and G-CSF worked synergistically. Thus, the clonogenic leukemic blast cell populations seemed to be heterogeneous with respect to their in vitro response to growth regulators.

Identification and partial purification of a low-molecular-weight growth inhibitor formed by density-inhibited, tumorigenic V79 Chinese hamster cells.

Medium conditioned by exposure to density-inhibited, tumorigenic V79 Chinese hamster cell cultures reversibly inhibited the growth and DNA synthesis of sparse, proliferating cultures, not only of the same cell line but also of the BALB/c 3T3 A31 murine cell line. This species nonspecific inhibitory activity was found to be mediated by the soluble inhibitor produced endogenously by V79 cells at the time of density inhibition. The molecular weight of this inhibitor is approximately 2000, and production of this compound seems to be serum dependent. Partial purification was done by reverse-phase fast protein liquid chromatography. The inhibitory activity was linearly dependent on the concentration in the inhibitory fraction. This partially purified inhibitor did not include lactic acid, a growth-inhibitory metabolite. These data indicate that a growth-regulatory factor is also operant in tumorigenic V79 cells and suggest that growth of neoplastic cells cannot only be explained by an enhanced positive growth potential but rather by the balance between a positive and negative growth potential.

Inhibition by 5-fluorouracil of cis-diamminedichloroplatinum(II)-induced DNA interstrand cross-link removal in a HST-1 human squamous carcinoma cell line.

To elucidate the mechanism of the synergistic cytotoxicity of 5-fluorouracil (5-FU) and cis-diamminedichloroplatinum(II) (CDDP), we studied the interaction of these agents using a human squamous carcinoma cell line (HST-1). Exposure to 5-FU for 24 h and to CDDP for 1 h produced a 50% inhibitory concentration of 1.0 micrograms/ml (7.7 microM) and 2.5 micrograms/ml (8.3 microM), respectively. The cytotoxic action of CDDP was augmented, and a greater than additive effect was observed when the cells were exposed to 5-FU (1.0 micrograms/ml; 7.7 microM) for 24 h before the CDDP treatment. This synergistic activity was maximal when the interval between 5-FU and CDDP exceeded 24 h. In contrast, the cytotoxicity of CDDP was attenuated when it preceded the exposure to 5-FU. Thymidine did not alter the 5-FU-CDDP interaction. Evaluation of the kinetics of the removal of DNA interstrand cross-links, measured by alkaline elution, showed a significant reduction of this removal in the cells exposed to 5-FU followed by CDDP with a drug-free interval of 48 h, as compared with cells exposed to CDDP alone, or to 5-FU immediately followed by CDDP, although no differences were found in the formation of DNA interstrand cross-links by CDDP among these cells. No significant differences in the accumulation of intracellular platinum were detected by atomic absorption spectrophotometry. These findings suggest that 5-FU modulates the repair of platinum-DNA adducts, thereby potentiating the antitumor activity of CDDP.

Establishment of Epstein-Barr virus-negative diffuse large cell lymphoma cell line with an 8;22 chromosomal translocation.

A new human B-cell lymphoma cell line was established from a pleural effusion of a patient with a diffuse large cell lymphoma which originated from an ileocecal tumor. The cell line, designated KAL-1, has been passaged 280 times over a period of 22 months. This cell line was successfully maintained in a chemically defined serum-free medium; its doubling time is approximately 24 h. Immunologically, the cells were demonstrated to express IgM lambda on the cell surface and to react with monoclonal antibodies to B-cell antigen including B1, B4, HLA-DR, and common acute lymphoblastic leukemic antigen but not with B2 and all the T-cell markers. Immunoglobulin gene analysis revealed rearrangements of both JH and C lambda. These data indicate that this cell line represents the B-cell lineage at the immature B-cell stage. This cell line was negative for Epstein-Barr virus nuclear antigen and had no detectable Epstein-Barr virus genome in cellular DNA. Chromosome analyses revealed that the cells carried an 8;22 chromosome translocation, reminiscent of variant type Burkitt's lymphoma. However, there was no histological evidence for Burkitt's lymphoma. Molecular studies showed that KAL-1 had deregulated high constitutive expression of c-myc. This cell line was demonstrated to be highly tumorigenic when injected into athymic nude mice. This tumor model should provide clues about the molecular mechanism involved in the pathogenesis of B-cell malignancy and appears to be a useful in vivo model for the study of molecular events during B-cell differentiation and therapeutic investigations.

Effect of the chimeric soluble granulocyte colony-stimulating factor receptor on the proliferation of leukemic blast cells from patients with acute myeloblastic leukemia.

The biological roles of the soluble granulocyte colony-stimulating factor (G-CSF) receptor, which arises as a result of alternative RNA splicing, are as yet unknown. In this study, we examined the in vitro effect of a chimeric protein composed of the extracellular region of a murine G-CSF receptor and the human IgG1 Fc region because a human natural soluble G-CSF receptor was not available. First, we found that this chimeric soluble G-CSF receptor could inhibit the biological activity of G-CSF on normal bone marrow colony formation. Because G-CSF also plays an important role in the proliferation of leukemic blast cells, we next examined the effect of the soluble G-CSF receptor on leukemic blast colony formation in 10 acute myeloblastic leukemia cases. Although G-CSF stimulated the proliferation of leukemic progenitor cells to form leukemic blast colonies, the chimeric soluble G-CSF receptor completely inhibited this stimulatory effect. Furthermore, the chimeric soluble G-CSF receptor also inhibited spontaneous leukemic blast colony formation in two cases. Because a high concentration of G-CSF was observed in the supernatants of leukemic blast cells from these two cases, it seems likely that the soluble G-CSF receptor cut off the autocrine growth mechanism of leukemic blast cells mediated by G-CSF. These findings suggest the possibility that the soluble G-CSF receptor could be used in a clinical application for acute myeloblastic leukemia patients in the future.

Dominant negative isoform of the Ikaros gene in patients with adult B-cell acute lymphoblastic leukemia.

Gene targeting studies in mice have shown that the transcription factor Ikaros plays an essential role in lymphoid development and as a tumor suppressor in T cells, whereas the related gene Aiolos functions as a tumor suppressor in B cells. We analyzed the expression levels of the Ikaros gene family, Ikaros and Aiolos, in human bone marrow samples from patients with adult acute lymphoblastic leukemia [ALL (n = 46; B-cell ALL = 41; T-cell ALL = 5)]. Overexpression of the dominant negative isoform of Ikaros gene Ik-6 was observed in 14 of 41 B-cell ALL patients by reverse transcription-PCR, and the results were confirmed by sequencing analysis and immunoblotting. None of the other dominant negative isoforms of the Ikaros gene were detected by reverse transcription-PCR analysis. Southern blotting analysis with PstI digestion revealed that those patients with the dominant negative isoform Ik-6 might have small mutations in the Ikaros locus. We did not detect any overexpression of dominant negative isoforms of Aiolos in adult ALL patients. These results suggest that Ikaros plays a key role in human B-cell malignancies through the dominant negative isoform Ik-6.

Decreases in Ikaros activity correlate with blast crisis in patients with chronic myelogenous leukemia.

Gene targeting studies in mice have shown that the lack of Ikaros activity leads to T-cell hyperproliferation and T-cell neoplasia, establishing the Ikaros gene as a tumor suppressor gene in mice. This prompted us to investigate whether mutations in Ikaros play a role in human hematological malignancies. Reverse transcription-PCR was used to determine the relative expression levels of Ikaros isoforms in a panel of human leukemia/lymphoma cell lines and human bone marrow samples from patients with hematological malignancies. Among the cell lines examined, only BV-173, which was derived from a chronic myelogenous leukemia (CML) patient in lymphoid blast crisis, overexpressed the dominant-negative isoform, Ik-6. In 9 of 17 samples of patients in blast crisis of CML, Ikaros activity had been reduced either by drastically reducing mRNA expression (4 of 17) or by overexpressing the dominant-negative isoform Ik-6 (5 of 17). Significantly, expression of Ikaros isoforms seemed normal in chronic phase CML patients and patients with other hematological malignancies. In some cases, overexpression of the dominant-negative Ik-6 protein was confirmed by Western blot analysis, and Southern blot analysis indicated that decreases in Ikaros activity correlated with a mutation in the Ikaros locus. In summary, these findings suggest that a reduction of Ikaros activity may be an important step in the development of blast crisis in CML and provide further evidence that mutations that alter Ikaros expression may contribute to human hematological malignancies.

MTG8 proto-oncoprotein interacts with the regulatory subunit of type II cyclic AMP-dependent protein kinase in lymphocytes.

AML1-MTG8 chimeric oncogene is generated in acute myelogenous leukemia with t(8;21), and seems to be responsible for the pathogenesis of the disease. However, the role of MTG8 is ambiguous. Here we found that MTG8 interacted with the regulatory subunit of type II cyclic AMP-dependent protein kinase (PKA RIIalpha). The binding site of MTG8 was NHR3 domain, and that of RIIalpha was the N-terminus for interacting with PKA anchoring proteins (AKAPs). NHR3 contains a putative alpha-amphipathic helix which is characteristic in binding of AKAPs with RII. Indirect immunofluorescence microscopy showed that MTG8 and RIIalpha were overlapped at the centrosome-Golgi area in lymphocytes. These findings suggest that MTG8 may function as an AKAP at the centrosome-Golgi area in lymphocytes.

Progressive impairment of kidneys and reproductive organs in mice lacking Rho GDIalpha.

The Rho small G protein family members regulate various actin cytoskeleton-dependent cell functions. The Rho GDI (GDP dissociation inhibitor) family, consisting of Rho GDIalpha, -beta, and -gamma, is a regulator that keeps the Rho family members in the cytosol as the GDP-bound inactive form and translocates the GDP-bound form from the membranes to the cytosol after the GTP-bound form accomplishes their functions. Rho GDIalpha is ubiquitously expressed in mouse tissues and shows GDI activity on all the Rho family members in vitro. We have generated mice lacking Rho GDIalpha by homologous recombination to clarify its in vivo function. Rho GDIalpha -/- mice showed several abnormal phenotypes. Firstly, Rho GDIalpha -/- mice were initially viable but developed massive proteinuria mimicking nephrotic syndrome, leading to death due to renal failure within a year. Histologically, degeneration of tubular epithelial cells and dilatation of distal and collecting tubules were readily detected in the kidneys. Secondly, Rho GDIalpha -/- male mice were infertile and showed impaired spermatogenesis with vacuolar degeneration of seminiferous tubules in their testes. Thirdly, Rho GDIalpha -/- embryos derived from Rho GDIalpha -/- female mice were defective in the postimplantation development. In addition, these morphological and functional abnormalities showed age-dependent progression. These results suggest that the signaling pathways of the Rho family members regulated by Rho GDIalpha play important roles in maintaining the structure and physiological function of at least kidneys and reproductive systems in adult mice.

Evidence for the involvement of endogenous thymidine in the density-inhibition of tumorigenic Chinese hamster V79 cells.

Two distinct low-molecular-weight growth inhibitory activities were isolated from supernatants of a density-inhibited, tumorigenic V79 Chinese hamster cell line. By chromatographic analyses, one of these was purified to homogeneity and eventually proved to be thymidine (dThd). In order to investigate the biological role of dThd in a density-inhibited culture of these cells, a dThd-kinase deficient (TK-) clone resistant to the excess of dThd was isolated from V79 cells and the effect of the supernatants on growth of these TK- or TK-proficient (TK+) cells was examined. As a result, the growth of TK- cells was not inhibited but enhanced by the supernatant at the concentrations which significantly inhibited the growth of TK+ cells. Such TK-dependent differential responses to supernatants suggest the presence of deoxyribonucleosides including a high level of dThd in the supernatants. Since it is unlikely that dThd might derive from denatured DNA of dead cells, an accumulation of endogenous dThd in confluent culture appears to be responsible for dThd triphosphates which are synthesized de novo, degraded and excreted into the medium rather than incorporated into DNA as a consequence of aberrant growth in the presence of certain growth inhibitors produced by density-inhibited V79 cells.