The principal goal of the proposed research is to characterize transmembrane signaling events triggered by Cd, Ni, Fe, and some other divalent metals. It appears that the metals stimulate a receptor,provisionally called the Cd receptor. Receptor activation causes a rapid production of inositol polyphosphates and releases sequestered Ca. The receptor is present in a variety of mammalian cells including lung and skin fibroblasts, smooth muscle, neuroblastoma, and endothelial cells. The receptor is probably on the external surface of the cells because extracellular rather than intracellular Cd elicits Ca mobilization. The potency order of the divalent metals that stimulate the receptor is: Cd>Co>Ni>Fe>Mn. Zn(II) and Cu(II) are potent antagonists of Cd-evoked Ca mobilization. The hypothesis that certain carcinogenic metals act as growth promoters by stimulating the Cd receptor will be investigated. The hypothesis that Cd receptor stimulation produces diacylglycerol and activates protein kinase C will be tested. Measurements of changes in inositol lipids and diacylglycerol produced by Cd receptor stimulation are needed to conclusively show lipid hydrolysis and may help to identify the phospholipase(s) involved. The incorporation of radiolabeled phosphate into specific proteins in intact cells be measured to find out if stimulating the Cd receptor activates protein kinase C and a Ca/calmodulin protein kinase. The cellular location of protein C before and after Cd receptor stimulation will be determined to find out if the enzyme translocates from the cytosolic to membrane and nuclear fractions. The hypothesis that a GTP-binding protein mediates receptor activation of inositol polyphosphate formation will be tested. Cd receptor stimulation may cause cell proliferation,k at least in part, by eliciting changes in cell metabolism which are similar to those evoked by Ca-mobilizing hormones or phorbol ester tumor promoters. The effects of Cd receptor stimulation on proto-oncogene expression will be examined. Cells that are less susceptible to the toxic effects of intracellular metal may be more susceptible to the growth promoting effect of Cd receptor stimulation. The role of the Cd receptor in the promotion of cell growth by Fe(II) will be assessed because Fe(II) stimulates the Cd receptor and previous growth studies did not consider an extracellular site of Fe(II) action. Methods will be developed which might be useful for cloning or purifying the Cd receptor. Poly(A)+RNA from cells that have the Cd receptor will be injected into Xenopus oocytes to find out if they express functional Cd receptors. High affinity 109Cd binding to membrane proteins after gel electrophoresis and transfer to nitrocellulose will be examined.
| Smith, J B; Smith, L; Pijuan, V et al. (1994) Transmembrane signals and protooncogene induction evoked by carcinogenic metals and prevented by zinc. Environ Health Perspect 102 Suppl 3:181-9 |
| Lyu, R M; Smith, J B (1993) Genistein inhibits calcium release by platelet-derived growth factor but not bradykinin or cadmium in human fibroblasts. Cell Biol Toxicol 9:141-8 |
| Chen, Y C; Smith, J B (1992) A putative lectin-binding receptor mediates cadmium-evoked calcium release. Toxicol Appl Pharmacol 117:249-56 |
| Smith, L; Pijuan, V; Zhuang, Y et al. (1992) Reversible desensitization of fibroblasts to cadmium receptor stimuli: evidence that growth in high zinc represses a xenobiotic receptor. Exp Cell Res 202:174-82 |
