Inhibition of protein kinase C prevents asbestos-induced c-fos and c-jun proto-oncogene expression in mesothelial cells.
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.
Fung
H
H
Department of Pathology, University of Vermont, Burlington 05405, USA.
Quinlan
T R
TR
Janssen
Y M
YM
Timblin
C R
CR
Marsh
J P
JP
Heintz
N H
NH
Taatjes
D J
DJ
Vacek
P
P
Jaken
S
S
Mossman
B T
BT
D000818:Animals; D001194:Asbestos / Q000494:pharmacology*; D016227:Benzoquinones; D004848:Epithelium / Q000187:drug effects / Q000201:enzymology*; D015870:Gene Expression; D007527:Isoenzymes; D047029:Lactams, Macrocyclic; D009281:Naphthalenes / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism*; D011809:Quinones / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011916:Rats, Inbred F344; D017828:Rifabutin / Q000031:analogs & derivatives; D013997:Time Factors
D016227:Benzoquinones; D007527:Isoenzymes; D047029:Lactams, Macrocyclic; D009281:Naphthalenes; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D011809:Quinones; D012333:RNA, Messenger; D001194:Asbestos; D017828:Rifabutin; D015240:Phorbol 12,13-Dibutyrate; C020754:herbimycin; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; C058819:calphostin C