Lead may affect glucocorticoid signal transduction in cultured hepatoma cells through inhibition of protein kinase C
| Autor: | Ann S. Heiman, Lisa E. Tonner |
|---|---|
| Rok vydání: | 1997 |
| Předmět: |
medicine.medical_specialty
Carcinoma Hepatocellular Blotting Western chemistry.chemical_element Calcium Biology Toxicology Dexamethasone Calcium Chloride Internal medicine Organometallic Compounds Tumor Cells Cultured medicine Animals Enzyme Inhibitors Glucocorticoids Protein Kinase C Protein kinase C Tyrosine Transaminase Kinase Liver Neoplasms Protein-Tyrosine Kinases Genistein Isoflavones Molecular biology Isoenzymes Cytosol Endocrinology Lead Mechanism of action chemistry Cell culture Lead acetate Enzyme Induction Tetradecanoylphorbol Acetate medicine.symptom Signal transduction Signal Transduction |
| Zdroj: | Toxicology. 119:155-166 |
| ISSN: | 0300-483X |
| Popis: | Specific cellular sites of lead action have not been completely defined. To elucidate the effects of lead exposure on glucocorticoid-mediated signal transduction in hepatic hormonal target tissues, the induction of tyrosine aminotransferase (TAT) specific activity in the H4-IIE-C3 hepatoma cell culture model system was employed. It had been found that lead acetate (3-10 microM) exposure of HTC cells significantly reduced TAT specific activity in a concentration- and time-dependent manner. Two possible molecular targets of the lead-induced effect were investigated: interference with calcium-mediated cellular processes and calcium- and phospholipid-dependent protein kinase C (PKC) activity and isoform-type interactions. Lead acetate treatment (5 microM) reduced TAT specific activity below sodium acetate treated controls by 31%. One-half of the TAT specific activity was recovered by co-treatment with 5 microM lead acetate and 10 mM calcium chloride. As the concentration of lead acetate was increased to 10 microM, interference in calcium-mediated events also increased. Potentiation of glucocorticoid induction by phorbol myristate acetate (PMA) (300 nM) in control cells was 34%, but was abolished by exposure of cells to 10 microM lead acetate (48 h). Treatment with the kinase inhibitor genistein decreased TAT specific activity by 55% and 45% in control and lead acetate exposed cells, respectively. Following treatment with dexamethasone (100 nM), significant increases in both cytosolic and particulate PKC were noted in control cells but not lead acetate exposed cells. Western blot results indicated that lead exposure may increase PKC beta and decrease PKC alpha translocation from cytosolic to particulate fractions, respectively. Taken together, these results suggest that glucocorticoid signal transduction pathways in HTC cells involve calcium-mediated cellular events and PKC isoforms. Exposure of cells to lead results in interference with calcium-mediated events and aberrant modulation of PKC activities. Within hormonal target cells, these may be toxic molecular sites of action of the heavy metal lead and may contribute to the overall toxicity of lead exposure. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect