Regulation of silica-induced apoptosis by the tumor supressor gene, p53.
Wang L; Bowman L; Lu Y; Rojanasakul Y; Mercer R; Castranova V; Ding M
Med Lav 2002 Oct; 93(Suppl):S41
Occupational exposure to mineral dusts, such as silica, has been associated with progressive pulmonary inflammation and fibrosis. Increasing evidence suggests that excessive induction of apoptosis (programmed cell death) by silica may be a contributing factor to the development of silicosis. However, the molecular mechanisms involved in this process are poorly understood. Since the tumor suppressor, p53, is a key transcription factor for the regulation of many important apoptosis-related genes, we hypothesized that p53 may play an important role in silica-induced apoptosis and that abnormal regulation of p53 by silica may contribute to exaggerated induction of apoptosis and subsequent lung disorders. To test this hypothesis, p53 activity and apoptosis in silica-treated cells or experimental animals were investigated. The role of p53 in silica-induced apoptosis was also studied by employing p53-deficient (p5J+) cells or p5J+ knockout mice. Using JB6 cells stably transfected with a p53-luciferase reporter plasmid, we found that exposure of cells to freshly fractured silica caused a dose and time dependent transactivation of p53 activity. Western blot analysis indicated that silica stimulated p53 protein expression and its phosphorylation at the FL.393 position. Freshly fractured silica also induced cell apoptosis in a cell culture system, as determined by TUNEL and DNA ladder assays. In contrast, silica-induced apoptosis was significantly blocked in p53-deficient (p53-/o) cells. Similar results were obtained in in vivo studies, using experimental animals. Exposure of wild-type (p53'/" mice to silica via intratracheal instillation (3 mg/100 g body weight) resulted in an increase in lung cell apoptosis with minimal necrosis. In contrast, silica-induced apoptotic and necrotic effects on the lung cells were markedly inhibited in p53-1- knockout mice. These results indicate that: (1) silica induces p53 transactivation in cell culture systems; (2) silica-induced p53 activation is via induction and phosphorylation of p53 protein; (3) silica stimulates apoptosis in both in vitro and in vivo systems; and (4) p53 is required for silica-induced apoptosis. These studies demonstrate for the first time that p53 plays a crucial role in the regulation of silica-induced apoptosis and possibly to silica-induced lung pathogenesis.
Silicates; Silicosis; Silica-dusts; Pulmonary-disorders; Pulmonary-function; Pulmonary-system-disorders; Lung-cells; Lung-disease; Lung-disorders; Lung-irritants; Epidemiology; Occupational-hazards; Occupational-exposure; Respiratory-irritants; Respiratory-system-disorders; Mineral-dusts
Conference/Symposia Proceedings; Abstract
La Medicina del Lavoro. 3rd International Symposium on Silica, Silicosis, Cancer and Other Diseases, S. Margherita Ligure, 21-25 October 2002