12-O-tetradecanoylphorbol-13-acetate induces apoptosis in renal epithelial cells through a growth signal conflict which is prevented by activated ras.
12-O-Tetradecanoylphorbol-13-acetate (TPA) induced apoptosis in the pig renal epithelial cell line LLC-PK1 after 24 h of treatment as assessed by caspase 3 activation. Cotreatment of the cells with bryostatin markedly reduced the apoptotic effects of TPA. Okadaic acid, another tumor promoter, also induced apoptosis. Expression of an activated ras gene prevented TPA-induced apoptosis, while a dominant negative ras retarded the process. Taken together, these results suggest that TPA-induced apoptosis in LLC-PK1 may be analogous to TPA-induced tumor promotion in the two-stage model of skin carcinogenesis. Mechanistically, TPA-induced apoptosis seemed to be the result of a conflict of the growth-promoting affects of serum and the growth-retarding effects of TPA. This was manifested by a pronounced hypophosphorylation of the retinoblastoma gene product, pRb, which was prevented by activated ras. Apoptosis and pRb hypophosphorylation were associated with a reduction in cyclin D1 levels, suggesting that the growth-retarding effects of TPA were produced by modulation of this cell cycle protein. Interestingly, the mechanism of protection by activated ras did not seem to result from downstream activation of phosphatidylinositol-3-kinase (PI3K) as has been implicated in other systems. Additional analysis revealed that TPA-induced apoptosis was associated with the downregulation of the anti-apoptotic proteins Bcl-x and Mcl-1 and dependent on the activity of the transcription factor Jun.
Lee
R G
RG
Lankenau Institute for Medical Research, Wynnewood, Pennsylvania 19096, USA.
Rosson
D
D
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D054713:Bryostatins; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D011905:Genes, ras / Q000235:genetics; D007668:Kidney / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D007783:Lactones / Q000494:pharmacology; D018942:Macrolides; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013552:Swine; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins
D054713:Bryostatins; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D007783:Lactones; D018942:Macrolides; D008869:Microtubule-Associated Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016755:Proto-Oncogene Proteins c-jun; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019319:Okadaic Acid; C046785:bryostatin 1; D019869:Phosphatidylinositol 3-Kinases; D011493:Protein Kinase C; D053148:Caspase 3; D020169:Caspases; D015689:Oncogene Protein p21(ras); D013755:Tetradecanoylphorbol Acetate