Inhibition of protein kinase C prevents asbestos-induced c-fos and c-jun proto-oncogene expression in mesothelial cells

• Published in: Cancer research (Chicago, Ill.) Ill.), 1997-08, Vol.57 (15), p.3101-3105
• Main Authors: FUNG, H, QUINLAN, T. R, JANSSEN, Y. M. W, TIMBLIN, C. R, MARSH, J. P, HEINTZ, N. H, TAATJES, D. J, VACEK, P, JAKEN, S, MOSSMAN, B. T
• Format: Article
• Language: English
• Subjects: Animals; Asbestos - pharmacology; Benzoquinones; Biological and medical sciences; Carcinogenesis, carcinogens and anticarcinogens; Chemical agents; Epithelium - drug effects; Epithelium - enzymology; Gene Expression; Isoenzymes; Lactams, Macrocyclic; Medical sciences; Naphthalenes - pharmacology; Phorbol 12,13-Dibutyrate - pharmacology; Protein Kinase C - physiology; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - metabolism; Proto-Oncogene Proteins c-fos - genetics; Proto-Oncogene Proteins c-fos - metabolism; Proto-Oncogene Proteins c-jun - genetics; Proto-Oncogene Proteins c-jun - metabolism; Quinones - pharmacology; Rats; Rats, Inbred F344; Rifabutin - analogs & derivatives; RNA, Messenger - analysis; Time Factors; Tumors
• ISSN: 0008-5472; 1538-7445

Asbestos and the phorbol ester tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), increase c-fos and c-jun mRNA levels and AP-1 DNA binding activity in rat pleural mesothelial (RPM) cells, a target cell of asbestos-induced mesotheliomas (N. H. Heintz et al., Proc. Natl. Acad. Sci. USA, 90: 3299-3303, 1993). Because protein kinase C (PKC) is the intracellular receptor of phorbol ester tumor promoters and asbestos is a putative tumor promoter in the respiratory tract, we hypothesized that PKC might play a critical role in asbestos-induced cell signaling pathways associated with regulation of proto-oncogenes. Using a panel of PKC antibodies, we identified PKC alpha as the major PKC isozyme in RPM cells. We then pretreated cells with phorbol ester dibutyrate to down-modulate PKC or with calphostin C, a specific PKC inhibitor, to determine if depletion of PKC alpha could block asbestos-induced c-fos/c-jun expression. Quantitation of Northern blots showed that fiber-associated c-fos/c-jun mRNA levels were significantly lower either after PKC alpha down-modulation or pretreatment with calphostin C. In addition, to determine whether tyrosine kinases also were involved in proto-oncogene activation by asbestos, tyrphostin AG82 or herbimycin A was added to RPM cells before exposure to asbestos. These inhibitors decreased crocidolite-induced c-fos but not c-jun levels, suggesting that tyrosine kinases have different regulatory roles in asbestos-induced c-fos versus c-jun signaling pathways. The ability to block induction of asbestos-induced proto-oncogene expression using pharmacological intervention may be important in prevention and treatment of asbestos-induced proliferative diseases including lung cancers, mesothelioma, and pulmonary fibrosis.