Cadmium-induced hormetic effect in differentiated Caco-2 cells: ERK and p38 activation without cell proliferation stimulation.
Cadmium (Cd) is a toxic metal that enters the food chain. Following oral ingestion, the intestinal epithelium may in part protect against Cd toxicity but is also a target tissue. Using human enterocytic-like Caco-2 cells, we have previously shown differences in sensitivity to Cd according to the differentiation status. The present study focuses on Cd effects on differentiated cells. Concentration and time-dependent increases in MTT (3-[4,5-dimethyl-2-thiazol-2-yl]-2,5-diphenyltetrazolium bromide assay) activity were observed in post-confluent cultures exclusively, with a twofold maximal stimulation in 21-day-old cells exposed to 10 microM Cd for 24 h. No concomitant increase in [methyl-(3)H] thymidine incorporation was noted and Cd did not modify cell distribution in the cell-cycle phases. However, Cd-induced increase in MTT activity was inhibited by cycloheximine as well as by inhibitors of ERK1/2 and p38, but not by that of JNK. Consistently, Cd increased the levels of ERK1/2 and p38 phosphorylation. Inhibition of Ras-GTP or PI3K enhanced the stimulatory effect of Cd, whereas mTOR inhibition had no effect. Inhibition of G protein-phospholipase and PKC decreased MTT stimulation. These results show a hormesis-like stimulation of Cd on MTT activity in differentiated intestinal cells exclusively. This effect is not related to cell proliferation but more likely to increased protein synthesis which involves ERK1/2 and p38 cascades and possibly PLC-beta signaling pathways. Because growth-related differentiation of intestinal cells is linked to the selective and sequential activation of MAPKs, the impacts that these Cd-induced perturbations in signaling pathways may have on intestinal functions clearly deserve to be investigated.
Mantha
Marc
M
Département des Sciences Biologiques, Centre TOXEN, Université du Québec à Montréal, Montréal, Québec, Canada.
Jumarie
Catherine
C
D018938:Caco-2 Cells; D002104:Cadmium / Q000494:pharmacology*; D002454:Cell Differentiation; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000201:enzymology; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010084:Oxidation-Reduction; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
D002104:Cadmium; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D047428:Protein Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D058570:TOR Serine-Threonine Kinases; D010738:Type C Phospholipases; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins; C546842:MTOR protein, human