Multiple cellular phenotypes in an insertional mutation in mouse affecting bone development

The 6093 line of transgenic mice exhibits altered bone development as a result of an insertional mutation by the transgene. Female transgenic mice show a marked kyphosis as early as 2 weeks of age. Vertebrae from female mice have lower total bone area and mineral content than age-matched, gender-matched controls, although the bone mineral density is not changed. The femur and tibia exhibit the opposite effect-increased bone area and mineral content. Fluorescent bone label experiments indicated an increased rate of bone mineral deposition in the femur during the early postnatal growth period, and bone marrow from femurs of 6093 females had increased numbers of fibroblast colony-forming units. Transgenic females also are obese and have altered thymocyte development, suggesting that the insertional mutation affects multiple cell populations. We hypothesize that these phenotypes arise as a result of an alteration in the function or developmental potential of a stromal cell or mesenchymal stem cell.

Analysis of oncogene, tumor suppressor gene, and chromosomal alterations in HeLa x osteosarcoma somatic cell hybrids

Using a series of tumorigenic and non-tumorigenic somatic cell hybrids that resulted from the fusion of the human osteosarcoma cell line OHS50-P16T (P16T) with the HeLa cell line D98OR, we investigated the role that genetic mutations, including alterations of oncogenes, tumor suppressor genes, and chromosomes, play in P16T tumorigenicity. Analysis of a previously identified oncogene mutation, c-myc amplification, in the P16T cell line demonstrated that both the tumorigenic and non-tumorigenic hybrids contained the amplified c-myc gene. Analysis of previously identified P16T tumor suppressor gene alterations, p53 mutation, and loss of RB1 expression demonstrated that the mutated p53 gene was selectively maintained in both the non-tumorigenic and tumorigenic hybrids, whereas loss of RB1 expression was not maintained in either the non-tumorigenic or tumorigenic hybrids. Chromosomes 11, 13, 17, and 22 were analyzed for loss of heterozygosity (LOH) to characterize the status of these previously described chromosomal alterations in the tumorigenic and non-tumorigenic hybrids. Loss of HeLa D98OR chromosome 22, with maintenance of P16T chromosome 22, was observed in the tumorigenic hybrids, a result confirmed by LOH analysis, which demonstrated the specific loss of HeLa chromosome 22 genetic material in the tumorigenic segregants. Together, these results demonstrated that amplified c-myc, mutant p53, and RB1 genes seem to be important in osteosarcoma tumorigenicity and that an additional altered gene or genes on chromosome 22 may play a key role in osteosarcoma tumorigenicity.

The combination of epidermal growth factor and transforming growth factor-beta induces novel phenotypic changes in mouse liver stem cell lines

Mouse liver stem cell (oval cell) lines were investigated in order to determine the role which two families of growth and differentiation factors (GDFs), epidermal growth factor (EGF) family and transforming growth factor beta (TGF-beta) family, play in liver regeneration. EGF family members, including EGF, amphiregulin, betacellulin, heparin-binding epidermal growth factor, and TGF-alpha, were mitogenic for oval cell lines while TGF-beta family members, including TGF-beta1, TGF-beta2 and TGF-beta3, inhibited mitogenesis and induced apoptosis in oval cell lines. Surprisingly, the combination of EGF family members and TGF-ss family members resulted in neither proliferation nor apoptosis but instead in a novel cellular response, cellular scattering in tissue culture and morphological differentiation in Matrigel. Analysis of the signal transduction pathways activated by exposure of oval cell lines to either EGF, EGF+TGF-beta, or TGF-beta indicated that novel combinations of intracellular signals result following stimulation of the cells with the combination of EGF+TGF-beta. These data reveal that the dynamics of synergistic GDF action following tissue injury and regeneration results in a new level of complexity not obvious from the study of individual GDFs.

The tetratricopeptide repeat containing Tg737 gene is a liver neoplasia tumor suppressor gene

The Tg737 gene was investigated for gross alterations in a series of rodent/human liver tumors and human tumorigenic cell lines. The Tg737 gene was found to be altered in approximately 40% of the rodent chemically-induced liver tumors, 40% of the human liver tumors, and in liver, kidney and pancreatic human tumor cell lines. Ectopic re-expression of the Tg737 gene in a Tg737 deleted mouse liver tumor cell line resulted in suppression of tumorigenic growth, without altering in vitro cell culture growth. Treatment of mice which are either homozygous normal or heterozygous deleted at the Tg737 locus with the carcinogen diethylnitrosamine resulted in an increase in preneoplastic foci formation in the Tg737 heterozygous deleted mice. Ectopic expression of the Tg737 gene results in multinucleated cells, loss of Tg737 gene expression results in the proliferation of liver stem cells (oval cells) without concomitant differentiation, and reexpression of the Tg737 gene reestablished responsiveness to external differentiation factors. We believe this is the first report demonstrating tumor suppression activity for a tetratricopeptide repeat gene family member and provides insights into the function of this family of genes in mammalian cells.

Analysis of oncogenes, tumor suppressor genes, autocrine growth-factor production, and differentiation state of human osteosarcoma cell lines

Human osteosarcoma and fibrosarcoma cell lines were investigated for alterations in oncogenes, tumor suppressor genes, and growth factors, all of which have been implicated in tumor formation. Characterization of oncogenes that are involved in osteosarcoma formation, including the c-fos and c-myc oncogenes, indicated that all six osteosarcoma cell lines examined had 5- to 20-fold amplification of the c-myc oncogene, whereas neither of two fibrosarcoma cell lines c-myc amplification. Interestingly, only three of six osteosarcoma cell lines displayed altered c-myc immediate-early gene function. c-fos was found to be normal, both at the gene and functional levels, in all six osteosarcoma and both fibrosarcoma cell lines tested. Characterization of two tumor suppressor genes, p53 and RB1, that have been implicated in osteosarcoma formation indicated that p53 was altered in five of six osteosarcoma cell lines, whereas RB1 was altered in only two or six of these cell lines. Neither RB1 nor p53 was found to be altered in the fibrosarcoma cell lines tested. An additional transformation marker, autocrine growth-factor production, was observed in all six osteosarcoma cell lines and both fibrosarcoma cell lines examined. Finally, the differentiation state of the osteosarcoma cell lines was investigated via the bone differentiation markers alkaline phosphates and osteocalcin. Alkaline phosphatase activity was observed in four of six osteosarcoma cell lines but not in the two fibrosarcoma cell lines examined. The alkaline phosphatase activity was a result of the expression of the bone/liver/kidney alkaline phosphatase isoform. High-level osteocalcin expression was observed in one of the osteosarcoma cell lines but not in the two fibrosarcoma cell lines examined, although all cell lines demonstrated low-level osteocalcin expression. Together, these data demonstrate that relatively undifferentiated osteosarcomas commonly display c-myc amplification, p53 and RB1 mutation, and autocrine growth-factor production, all of which may play a role in osteosarcomagenesis.

Alterations in cellular differentiation, mitogenesis, cytoskeleton and growth characteristics during Syrian hamster embryo cell multistep in vitro transformation

In vitro Syrian hamster embryo (SHE) cell transformation is a neoplastic process that proceeds through several identifiable consecutive stages including in vitro morphological transformation (mt), acquisition of immortality (I+), acquisition of tumorigenicity (T+) and tumor-derived cells (I'TD). Eight transformed lineages consisting of cells at the mt, I+, T+ and I'TD stages were assayed for alterations in general markers of cell differentiation, mitogenic signaling pathways, cytoskeleton and cellular growth in 3D matrix. Alterations in cellular differentiation markers included a decrease in H19 gene expression and placental alkaline phosphatase enzymatic activity at the mt stage in all lineages examined with a complete absence of H19 gene expression and placental alkaline phosphatase enzymatic activity by the I'TD stage in a majority of transformed lineages. Changes in mitogenic signaling pathways included the production of autocrine growth factors and alterations in growth factor-induced immediate early gene expression by the I'TD stage of transformation in the majority of transformed lineages investigated. By the I'TD stage of transformation in most lineages, changes in both the cytoskeleton (including a decrease in tropomyosin-I gene expression) and the Matrigel growth characteristics of SHE cells were observed.

Tumorigenicity and oncogene expression in pediatric cancers

Cytogenetic and epidemiological studies of pediatric cancers have implicated a loss of genetic information in the development of these tumors. In contrast, other studies have shown that activation of endogenous oncogenes is a common event in these cancer cells. The technique of somatic cell hybridization provides a model for investigating the interaction between loss of genetic elements and oncogene activation in pediatric cancers. A variety of human-human cell hybrids were formed between a tumorigenic adult carcinoma and representative tumorigenic pediatric cell lines. All hybrid cells were completely suppressed for tumor-forming ability when assayed in nu/nu (nude) mice. When the expression of the N-myc, c-myc, and sis oncogenes and tumorigenicity were examined in the same hybrid cells, no correlation was found, suggesting that the expression of these oncogenes in these hybrid cells did not appear to be controlled by putative "tumor suppressor" genes. Thus, tumorigenicity behaves as a recessive genetic trait in pediatric cancers. Furthermore, different genetic elements may be lost during tumor development of adult cancers as opposed to pediatric cancers.

Characterization of an RNase P activity from HeLa cell mitochondria. Comparison with the cytosol RNase P activity

A ribonuclease P-like activity was partially purified from HeLa cell mitochondria by DEAE-cellulose and octyl-Sepharose chromatography. RNase P-like activity can be quantitatively recovered from intact mitochondrial preparations treated with micrococcal nuclease, strongly suggesting that the enzyme is localized within the organelles. Mitochondrial RNase P (mtRNase P) cleaves the precursor to Escherichia coli suppressor tRNATyr at the same site as E. coli RNase P, producing the mature 5'-end of tRNATyr. The sensitivity of mtRNase P to pretreatment with nucleases or Pronase indicates that the enzyme has essential RNA and protein components. Although the ionic requirements of mtRNase P are similar to those of the RNase P activity isolated from the post-mitochondrial cytosol fraction, the chromatographic properties of mtRNase P are distinct. Mitochondrial RNase P is probably a part of the mitochondrial RNA processing machinery of mammalian mitochondria, being responsible for the endonucleolytic cleavage of the RNA transcripts at the 5'-side of the tRNA sequences.

Nuclear Inheritance of Erythromycin Resistance in Human Cells: New Class of Mitochondrial Protein Synthesis Mutants

The characterization of two new erythromycin-resistant mutants of HeLa cells is described. The strains ERY2305 and ERY2309 both exhibited resistance to erythromycin in growth assays and cell-free mitochondrial protein synthesis assays. The erythromycin resistance phenotype could not be transferred by cybridization. The mutation appeared to be encoded in the nucleus and inherited as a recessive trait. These two mutants, therefore, represent a new class of erythromycin-resistant mutants in human cells that is distinct from the cytoplasmically inherited mutation in strain ERY2301 described previously.

Human cell hybrids: analysis of transformation and tumorigenicity

Intraspecific human-human cell hybrids provide a stable model system with which to investigate the genetic control of transformed and tumorigenic phenotypes. Using this system it has been shown that these phenotypes are under separate genetic control. Furthermore, the tumorigenic phenotype can be complemented by fusion of different tumorigenic cells, resulting in nontumorigenic hybrids. This system also provides information on the control of differentiated function. Molecular cytogenetic techniques should reveal the nature of the chromosomal control of neoplastic transformation.

Effects of mycoplasma contamination on phenotypic expression of mitochondrial mutants in human cells

HeLa cells sensitive to the mitochondrial protein synthesis inhibitors erythromycin (ERY) and chloramphenicol (CAP) and HeLa variants resistant to the effects of these drugs were purposefully infected with drug-sensitive and -resistant mycoplasma strains. Mycoplasma hyorhinis and the ERY-resistant strain of Mycoplasma orale, MO-ERYr, did not influence the growth of HeLa and ERY-resistant ERY2301 cells in the presence or absence of ERY. M. hyorhinis also did not affect the growth of HeLa and CAP-resistant Cap-2 cells in the presence or absence of CAP. However, both HeLa and Cap-2 cells infected with the CAP-resistant strain of M. hyorhinis, MH-CAPr, were more sensitive to the cytotoxic effect of CAP. This may be due to the glucose dependence of the cells, which was compromised by the increased utilization of glucose by MH-CAPr in these infected cell cultures. In vitro protein synthesis by isolated mitochondria was significantly altered by mycoplasma infection of the various cell lines. A substantial number of mycoplasmas copurified with the mitochondria, resulting in up to a sevenfold increase in the incorporation of [3H]leucine into the trichloroacetic acid-insoluble material. More importantly, the apparent drug sensitivity or resistance of mitochondrial preparations from mycoplasma-infected cells reflected the drug sensitivity or resistance of the contaminating mycoplasmas. These results illustrate the hazards in interpreting mitochondrial protein synthesis data derived from mycoplasma-infected cell lines, particularly putative mitochondrially encoded mutants resistant to inhibitors of mitochondrial protein synthesis.

Cytoplasmic inheritance of erythromycin resistance in human cells

An erythromycin-resistant mutant, ERY2301, was isolated from ethidium bromide-treated HeLa cells in the presence of erythromycin at 300 micrograms/ml. ERY2301 cells were enucleated and the anucleate cytoplasts were fused with D98/AH-2, a hypoxanthine phosphoribosyltransferase-deficient variant of HeLa cells. The resultant cybrids were isolated in a double selective medium containing erythromycin and 6-thioguanine. Cybrid formation occurred at a frequency of 10(-3) to 10(-4). In vitro protein synthesis by intact and Triton X-100 treated mitochondria isolated from ERY2301 was resistant to the macrolide antibiotics erythromycin and carbomycin, but was sensitive to chloramphenicol. These results suggest that the site of erythromycin resistance in ERY2301 may be at the level of mitochondrial protein synthesis and indicate that this trait is cytoplasmically inherited and, therefore, presumably encoded in the mitochondrial genome.