Associate Professor of Molecular Microbiology and Immunology and Pathology
Member, USC/Norris Comprehensive Cancer Center
Keck School of Medicine
Associate Professor of Molecular Pharmacology and Pharmaceutical Sciences
School of Pharmacy
Member of Free Radical Institute
University of Southern California
- Chemical Carcinogenesis
- Chemically Induced Morphological and Neoplastic Cell Transformation
- Nickel and Chromium(VI) Compound-Induced Morphological and Neoplastic Cell Transformation of Cultured Murine and Human Fibroblasts
- Molecular Biology of Nickel Compound and Chromium (VI) Compound-Induced Morphological and Neoplastic Cell Transformation
Research OverviewDr. Landolph’s laboratory studies the molecular mechanisms and molecular and cell biology of chemically induced morphological and neoplastic transformation of murine and human fibroblasts. This is a good model for the induction of sarcomas by chemical carcinogens. Carcinogens of interest to his laboratory are insoluble nickel (Ni) compounds and soluble and insoluble chromium (Cr) (VI) compounds. Ni compounds induce human nasal and respiratory cancer in workers in the nickel refineries, in conjunction with cigarette smoking. Hence, insoluble Ni compounds are occupational carcinogens for humans. Cr(VI) compounds induce nasal and respiratory cancer in the chromium electroplating industries, and in the manufacturing of chromate pigments. Hence, soluble and insoluble Cr(VI) compounds are occupational carcinogens for humans. In addition, nickel and chromium (VI) compounds are part of particulate matter of a size of 2.5 um and less, called PM2.5. Exposure of humans to air pollution particles in the form of PM2.5 induces human lung cancer, which insoluble Ni compounds and Cr(VI) compounds are partially responsible for. Therefore, insoluble Ni compounds and soluble and insoluble Cr(VI) compounds are also environmental carcinogens for humans.
Nickel Compound-Induced Morphological and Neoplastic Cell Transformation of Mammalian Cells
His laboratory has shown that carcinogenic insoluble Ni compounds, such as crystalline nickel monosulfide (Nis), green NiO, crystalline black NiO, and nickel subsulfide (Ni3S2) are phagocytosed into C3H/10T1/2 Cl 8 (10T1/2) mouse embryo cells and induce dose-dependent cytotoxicity (reduction in plating efficiency), dose-dependent chromosomal aberrations, and dose-dependent morphological and neoplastic transformation of 10T1/2 mouse embryo cells.
To date, using mRNA differential display, our laboratory has found that the ect-2 proto-oncogene is amplified and expressed higher steady-state levels at the mRNA and protein levels, in NiO and NiS-transformed 10T1/2 mouse embryo cells. Higher steady-state levels of the ect-2 mRNA and protein lead to an over-expression of microtubules in the transformed cell lines, leading to changes in the distribution of microtubules and to changes in the shapes of the transformed cell lines, which will lead to changes in gene expression in the transformed cell lines. In addition, the calnexin gene is over-expressed at the mRNA and protein levels, which may perturb Ca+2 gradients in the transformed cell lines. Also, the Wdr1 stress-responsive gene is over-expressed at the mRNA level, in Ni compound transformed cell lines.
Further, a number of genes are expressed in non-transformed 10T1/2 cells, but are either expressed at reduced levels or are not expressed at detectable levels, in NiO and NiS-transformed 10T1/2 cells lines. We found that the b-centaurin-2 gene, which functions in a signal transduction pathway that leads to the disaggregation of microfilaments, has become quiescent at the mRNA and hence protein levels, in Ni-compound transformed 10T1/2 cell lines. This leads to over-expression of microfilaments in the transformed cell lines, due to a failure of the cells to disaggregate microfilaments during the cell cycle. This leads to changes in cell shape, which will also lead to changes in gene expression in the transformed cell lines.
Overall, we have found that 130 genes are differentially expressed in the Ni compound-transformed cell lines. Our current model is that 15 primary genes are aberrantly expressed in the transformed cell lines. One-third of these proto-oncogene-like genes, or 5 genes, are over-expressed. This leads to a further over-expression of 43 genes. Each over-expression of each proto-oncogene or proto-oncogene like gene, causes over-expression of approximately 9 additional genes in signal transduction pathways. Two thirds of these primary genes, or 10 genes, are tumor suppressor-like genes. Two thirds of these total genes, or 87 genes, are tumor suppressor–like genes. We postulate that each suppression of expression of one tumor suppressor gene or tumor suppressor-like gene, leads to inhibition of expression of an additional 9 tumor suppressor genes/tumor suppressor-like genes. This would lead to suppressor of an additional 87 genes. Our current working model is 5 proto-oncogenes are over-expressed in the transformed cell lines, leading to over-expression of an additional 43 genes, and that 10 tumor suppressor genes are inhibited in expression, leading to further inhibition of an additional 87 tumor suppressor genes/tumor suppressor-like genes. Hence a total of 130 gens are differentially expressed in th Ni compound transformed cell lines. We are working to determine the effect that each over-expression of each of the five proto-oncogenes causes, and the effect that each knockout of each tumor suppressor gene causes.
Our laboratory has also found that black NiO and nickel subsulfide are phagocytosed into diploid human fibroblasts, and induce dose-dependent cytotoxicity and dose-dependent anchorage independent colonies in cultured diploid human fibroblasts.
Cr(VI) Compound-Induced Morphological and Neoplastic Transformation of Mammalian Cells
A second project that we are working on is the genotoxicity of soluble and insoluble Cr(VI) compounds. We have found that soluble and insoluble Cr(VI) compounds, such as calcium chromate, potassium dichromate, and lead chromate, all induce dose-dependent cytotoxicity to cultured 10T1/2 mouse embryo cells. Interestingly, insoluble lead chromate induced a small but dose-dependent yield of morphological transformation (foci) in 10T1/2 cells, but the other Cr(VI) compounds did not induce morphological transformation. Currently, we are studying the effects of adding reductants to the 10T1/2 cells prior to adding the Cr(VI) compounds. Preliminary data indicates that this causes increases in cytotoxicity and increases in morphological transformation of 10T1/2 cells.
In addition, w have found that both soluble and insoluble Cr(VI) compounds induce dose-dependent cytotoxicity and dose-dependent mutants to 6-thioguanine resistance in cultured diploid human fibroblasts. Soluble and insoluble Cr(III) compound induce dose-dependent cytotoxicity in diploid human fibroblasts, but at doses 1,00-fold higher than those of Cr(VI) compounds utilized. Cr(VI) compounds also induce dose-dependent numbers of anchorage-independent colonies in diploid human fibroblasts.