The tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) provokes a prolonged morphologic response and ERK activation in Tsc2-null renal tumor cells.
Loss of tumor suppressor function dramatically alters the cellular response to chemicals. The phorbol ester tumor promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), stimulates cell proliferation through rapid activation of protein kinase C (PKC), followed by gradual degradation of the kinase. TPA also activates the GTPase Rap1 in some cell types. The tumor suppressor protein Tsc2 has a proposed GTPase activating protein (GAP) function for Rap1, providing a common mechanistic target for Tsc2 and TPA. We compared the cellular response of Tsc2-null (ERC-18) and Tsc2-competent (NRK-52E) renal epithelial cells to TPA treatment. Treatment of ERC-18 cells with 100 ng/ml TPA for 24 h resulted in loss of cell-cell contact, retraction of the cell periphery and rounding. These changes were reversed 1 h after treatment in NRK-52E cells and were apparent 24 h after treatment of ERC-18 cells. Expression of Tsc2 in ERC-18 cells abrogated the prolonged morphologic response. TPA treatment rapidly increased phosphorylation of ERK, a reported downstream effector of both PKC and Rap1, in ERC-18 cells, but induced weak Rap1 activation. TPA-induced ERK phosphorylation was prolonged in ERC-18 cells compared to NRK-52E cells and expression of Tsc2 in ERC-18 cells did not inhibit prolonged ERK activation. The selective PKC inhibitor, bisindolylmaleimide VIII, however, inhibited TPA-induced changes in morphology and ERK activation. These results imply that TPA-induced changes in morphology and ERK activation are mediated primarily through PKC and not Rap1 in renal epithelial cells. These data also imply that Tsc2 expression modulates TPA-induced changes in renal epithelial cell morphology via an ERK-independent mechanism.
Kolb
Todd M
TM
Program in Toxicology, University of Maryland, School of Medicine, Baltimore 21201, USA.
Davis
Myrtle A
MA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002273:Carcinogens / Q000633:toxicity*; D002292:Carcinoma, Renal Cell / Q000378:metabolism* / Q000473:pathology*; D016923:Cell Death / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D015151:Immunoblotting; D007150:Immunohistochemistry; D007680:Kidney Neoplasms / Q000378:metabolism* / Q000473:pathology*; D000090204:Mesothelin; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000235:genetics; D011493:Protein Kinase C / Q000378:metabolism; D051571:Protein Kinase C-alpha; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics*; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins
D002273:Carcinogens; C000715529:Msln protein, rat; D012097:Repressor Proteins; D000089804:Shelterin Complex; C440809:TERF2IP protein, human; C000624653:TSC2 protein, human; D034501:Telomere-Binding Proteins; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D020928:Mitogen-Activated Protein Kinases; D000090204:Mesothelin; D013755:Tetradecanoylphorbol Acetate