DDT mimicks estradiol stimulation of breast cancer cells to enter the cell cycle

Estrogens play a critical role in the etiology of found breast cancer. Estradiol promotes the growth of breast cancer cells in vivo and in vitro. Exogenous estrogens in both the environment and in the human diet increase the growth of breast cancer cells in vitro. A role for xenoestrogens in breast cancer etiology has been proposed but remains controversial. We examined the effects of the xenoestrogenic pesticide 1,1,1-trichloro-2,2-bis(chlorophenyl)ethane (DDT) on estrogen-receptor (ER)-positive MCF-7 and T-47D human breast cancer cells as well as on ER-negative HS 578Bst breast cancer cells and rat liver cells. Estradiol and DDT were found to increase the growth of MCF-7 cells in the presence of insulin. The activity of cyclin-dependent kinase (Cdk)2 increased in growth-arrested T-47D and MCF-7 cells treated with beta-estradiol or DDT. The steroidal antiestrogen ICI 182,780 prevented both growth and Cdk2 activation induced by estradiol or DDT. Increased phosphorylation of Cdk2 and the retinoblastoma protein (pRb1O5) was observed in ER-positive cells treated with DDT or estradiol. Cdk2 activity was not affected by DDT or estradiol in ER-negative HS 578Bst breast cancer cells or in rat liver epithelial cells. Cyclin D1 protein synthesis was increased by DDT and estradiol in MCF-7 cells. DDT and estradiol-induced ER-dependent transcriptional activation of estrogen response elements (EREs) in stably transfected MVLN cells, and ERE activation by low doses of DDT was increased by insulin. These findings suggest that DDT can stimulate breast cancer cells to enter into the cell cycle by directly affecting key regulatory elements. The relative potency of DDT in inducing cell-cycle progression appears to be only 100-300 times less than that of estradiol when measured in the presence of insulin. Therefore, the cancer risks associated with DDT exposure may be greater than first thought, especially when additional mitogenic stimuli are present.

Carcinogenic potential of benzene and toluene when evaluated using cyclin-dependent kinase activation and p53-DNA binding

Benzene is carcinogenic, whereas toluene is thought to have little carcinogenic potential. Benzene and toluene were found to activate cyclin-dependent kinase 2 in rat liver epithelial (RLE) and HL60 cells. pRb105 was hyperphosphorylated in RLE cells treated with either solvent. Kinase activation and subsequent hyperphosphorylation of pRb105 and p53 by benzene or toluene may be responsible for their growth promotional effects, but it does not account for increased potential of benzene to induce cancer. Therefore, we examined the ability of these solvents to increase p53-DNA site-specific binding in RLE cells. Benzene increased p53-DNA site-specific DNA binding in RLE cells compared to control levels or the effects of toluene. Increased p53-DNA site-specific binding by benzene may be caused by damage to cellular DNA. If so, although both solvents appear to have promotional activity, the increased potential of benzene to damage DNA may be responsible to the difference in the ability of benzene to cause cancer.

Transforming growth factor-beta 1 as a signal for induction of cell death by apoptosis

Cell death by apoptosis is a major determinant of growth of normal tissues and tumours. The present study aimed to elucidate signal factors involved in its regulation. Epithelial cells in control liver, during regression of cyproterone acetate induced liver hyperplasia, in liver (pre)neoplasia and in uterus undergoing apoptosis in vivo show immunostaining for transforming growth factor beta 1 (TGF-beta 1) as detected by anti-pre(266-278) TGF-beta 1 antibodies. Positive immunostaining is also seen in a few intact cells of hyperplastic, regressing liver apparently preparing for apoptosis, but is virtually not found in hepatocytes of normal or growing liver nor in cells undergoing death by necrosis. Recombinant latency associated protein (rLAP, dimer of the pro-region non-covalently associated with the mature region) complex and mature TGF-beta 1 induce apoptosis in isolated hepatocytes cultured in vitro. These findings suggest an involvement of TGF-beta 1 in the induction of apoptosis in certain epithelia in vivo.

Characterization of a complex chromosomal rearrangement maps the locus for in vitro complementation of xeroderma pigmentosum group D to human chromosome band 19q13

Microcell-mediated chromosome transfer (MMCT) is a powerful genetic technique that permits the transfer of a single chromosome from one mammalian cell to another. The utility of MMCT for gene mapping strategies is critically dependent on the careful characterization of the chromosomes being transferred. We have recently reported the identification of a single rearranged human chromosome, designated Tneo, which corrects the UV sensitivity and excision repair defect of cells of xeroderma pigmentosum genetic complementation group D (XP-D) in culture (Flejter WL et al., Proc Natl Acad Sci USA 89:261-265, 1992). Additionally, those studies demonstrated a role for the excision repair cross-complementing 2 (ERCC2) gene in the observed phenotypic correction. We now report the results of detailed conventional and molecular cytogenetic characterization of the complementing Tneo chromosome. This analysis revealed a complex rearrangement involving material from human chromosomes 16, 17, and 19. Characterization of deletions of Tneo which retained or lost XP-D complementing ability mapped the gene responsible for phenotypic correction to a small region of the terminal q-arm of this chromosome. This region includes the previously described human DNA repair gene cluster located in the region 19q13.2-q13.3, a result consistent with the notion that the in vitro correction of XP-D cells by the Tneo chromosome is rendered by the ERCC2 locus. The data illustrate the potential value of detailed cytogenetic characterization of a human chromosome present in a somatic cell hybrid, even when that material involves complex rearrangements.

Effects of sympathetic innervation on size of myocytes in embryonic rat heart cultured in oculo

Embryonic rat myocardium cultured in the anterior eye chamber of an adult rat increases in mass and differentiates into mature myocardium by most morphological criteria [1]. When sympathetic innervation of grafted heart tissue was prevented by superior cervical ganglionectomy (SCGx), growth of the grafts was severely compromised. The present study used morphometric methods to examine the contribution of myocyte size to the differential growth of grafts in sympathetically denervated and intact eye chambers. For this purpose, atria or ventricles from 12-day gestation rat hearts were grafted into sympathetically denervated and intact eye chambers of male host rats. Tissue was harvested after either 2 or 8 weeks in oculo. Myocyte diameter and the ratio of cytoplasmic area to nuclear area increased between 2 and 8 weeks in oculo in both atrial and ventricular grafts. In these unloaded heart grafts, estimated myocyte size did not differ between atrial and ventricular myocytes. Grafts into sympathetically innervated and denervated eye chambers did not differ in myocyte diameter or in the ratio of cytoplasmic to nuclear area, suggesting that myocyte size cannot explain the smaller mass of grafts in sympathetically denervated eye chambers. Thus, it is likely that other factors such as myocyte proliferation, myocyte survival or altered tissue composition underlie the lesser growth of grafts not innervated by sympathetic nerves.

Induction of dermal and subcutaneous inflammation by recombinant cachectin/tumor necrosis factor (TNF alpha) in the mouse

The ability of cachectin/tumor necrosis factor (TNF alpha) to induce acute dermal and subcutaneous inflammation was examined in a murine model. A number of other proteins, and diluent alone were examined as controls. After subcutaneous injection into the mouse footpad, recombinant human TNF alpha (rHuTNF alpha) induced acute inflammation with an initial marked dermal and subcutaneous neutrophil infiltrate by approximately 3 h, with a peak between 4 and 24 h and resolution by 79 h. Recombinant interleukin-2, cytochrome c, and heat-inactivated rHuTNF alpha induced negligible inflammation. Recombinant human lymphotoxin (TNF beta), another control protein, also induced acute inflammation in our system. Because TNF alpha and TFN beta are partially homologous, they may be acting through a similar mechanism. This pro-inflammatory effect of TNF alpha may result from chemotactic activity as well as by induction of secondary mediators. Inflammation induced by TNF alpha was partially suppressed by indomethacin treatment, suggesting that products of the cyclo-oxyganase pathway may mediate a portion of the inflammation involved. Five daily injections of rHuTNF alpha into the mouse footpad resulted in a predominantly mononuclear infiltrate and focal fibrosis. These results suggest that TNF alpha may be an important mediator of acute inflammation in vivo and might provide a signal for the production of collagen.

Epidermal cells in activation of suppressor lymphocytes: further characterization

Intravenous administration of hapten-coupled, high-density (density greater than 1.077) epidermal cells (HD-EC) to mice results in the appearance of transferable splenic T suppressor (Ts) cells as assayed in adoptive transfer experiments. Depletion of I-A bearing cells from the HD-EC population before hapten coupling prevents these cells from inducing Ts cell formation, whereas depletion of Thy-1-bearing cells from the HD-EC cell preparation has no effect. When HD-EC are adhered to glass for 2 hr, the ability to induce Ts cell formation resides in the adherent population. Exposure of HD-EC to a dose of ultraviolet radiation (UVR) that largely abrogates the ability of hapten-coupled EC to immunize mice for a DTH response does not affect the ability of these cells to activate Ts cells. Treatment of mice with i.p. administration of 20 mg/kg of cyclophosphamide 2 days before EC harvesting abrogates the ability of HD-EC from these mice to induce Ts cell formation. HD-EC from B10.A(3R) (I-Jb) but not B10.A(5R) (I-Jk) mice induce Ts cell formation in B10.A(3R) mice, demonstrating that the ability to do so is restricted by the I-J locus. Transmission electron microscopy of adherent HD-EC populations demonstrated that two cell types were present. One type had the characteristics of keratinocytes; the other was monocyte-like and resembled Langerhans cells or indeterminate cells in many aspects. Immunoelectron microscopy revealed this second cell type to bear I-A/I-E antigen. These cells were T-200 positive and Mac-1 negative by immunoperoxidase staining. Extensive examination by light and electron microscopy failed to reveal any dermal components in the EC populations; however, a very small degree of dermal contamination cannot be excluded. Thus, EC that activate afferent-acting Ts cells are high-density, I-A+, Thy-1-, I-J restricted, glass adherent, and functionally UVR resistant and cyclophosphamide sensitive.

Epidermal cells in activation of suppressor lymphocytes: further characterization

Intravenous administration of hapten-coupled, high-density (density greater than 1.077) epidermal cells (HD-EC) to mice results in the appearance of transferable splenic T suppressor (Ts) cells as assayed in adoptive transfer experiments. Depletion of I-A bearing cells from the HD-EC population before hapten coupling prevents these cells from inducing Ts cell formation, whereas depletion of Thy-1-bearing cells from the HD-EC cell preparation has no effect. When HD-EC are adhered to glass for 2 hr, the ability to induce Ts cell formation resides in the adherent population. Exposure of HD-EC to a dose of ultraviolet radiation (UVR) that largely abrogates the ability of hapten-coupled EC to immunize mice for a DTH response does not affect the ability of these cells to activate Ts cells. Treatment of mice with i.p. administration of 20 mg/kg of cyclophosphamide 2 days before EC harvesting abrogates the ability of HD-EC from these mice to induce Ts cell formation. HD-EC from B10.A(3R) (I-Jb) but not B10.A(5R) (I-Jk) mice induce Ts cell formation in B10.A(3R) mice, demonstrating that the ability to do so is restricted by the I-J locus. Transmission electron microscopy of adherent HD-EC populations demonstrated that two cell types were present. One type had the characteristics of keratinocytes; the other was monocyte-like and resembled Langerhans cells or indeterminate cells in many aspects. Immunoelectron microscopy revealed this second cell type to bear I-A/I-E antigen. These cells were T-200 positive and Mac-1 negative by immunoperoxidase staining. Extensive examination by light and electron microscopy failed to reveal any dermal components in the EC populations; however, a very small degree of dermal contamination cannot be excluded. Thus, EC that activate afferent-acting Ts cells are high-density, I-A+, Thy-1-, I-J restricted, glass adherent, and functionally UVR resistant and cyclophosphamide sensitive.