Differential sensitivity of normal and H-ras oncogene-transformed rat kidney epithelial cells to okadaic acid-induced apoptosis.
H-ras oncogenes have been identified in greater than 50% of the most common forms of human neoplasia. Ras-related proteins have been postulated to mediated signal transduction pathways involving mitogen-activated protein (MAP) kinases and nuclear responses that may be involved in the induction of apoptosis. We examined whether expression of H-ras oncogene conferred resistance or susceptibility to the morphologic effects of the protein phosphatase inhibitor, okadaic acid, using a tumorigenic H-ras-transformed normal rat kidney epithelial cell line, NRK-H/6.1. We also examined whether okadaic acid induced apoptosis correlated with a differential effect on kinase activity in H-Ras-transformed cells as compared to the nontransformed NRK-52E cells. Treatment with various concentrations of okadaic acid produced rapid and extensive morphologic changes characteristic of apoptosis in both cell types. Equimolar okadaic acid concentrations for 2 or 4 hr resulted in cell detachment and loss of membrane integrity (as measured by propidium iodide uptake) in 74% (0.5 microM) and 78% (1.0 microM) of the H-Ras-transformed cells as compared to 8 and 25%, respectively, in the non-transformed cells. Furthermore, a higher basal level of kinase activity was observed in the H-Ras-transformed cells as compared to the nontransformed cells. Okadaic acid-induced apoptosis correlated with activation of members of the MAP kinase family, raf-1 and protein kinase C (PKC). These studies show that H-ras oncogene expression imparts selective susceptibility to cell death induced by phosphatase inhibition. The observed increase in susceptibility to okadaic acid-induced apoptosis appears to involve the modulation of raf-1, PKC, and MAP kinase activities. These findings may be significant in the elucidation of mechanisms for selective induction of cell death in tumor cells expressing H-ras oncogene.
Davis
M A
MA
Department of Pathology, University of Maryland, School of Medicine, Baltimore 21201, USA.
Chang
S H
SH
Trump
B F
BF
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016923:Cell Death; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D053938:DNA Fragmentation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D019319:Okadaic Acid / Q000633:toxicity*; D015689:Oncogene Protein p21(ras) / Q000494:pharmacology*; D010770:Phosphotransferases / Q000378:metabolism*; D051381:Rats
D004791:Enzyme Inhibitors; D019319:Okadaic Acid; D010770:Phosphotransferases; D015689:Oncogene Protein p21(ras)