Activation of Ca2+ influx by transforming Ha-ras.
The effect of an induction of transforming Ha-ras on Ca2+ influx into NIH3T3 cells was studied employing Fura-2 quenching by Mn2+. The expression of transforming p21Ha-ras caused a significant increase in Mn2+ influx which was blocked by Cd2+, La3+, niguldipine and the Ca(2+)-channel blocker SK&F96365. This effect was specific for transforming Ha-ras and was not seen after overexpression of the Ha-ras proto-oncogene or v-mos. In addition to the enhanced Mn2+ influx, transforming p21Ha-ras elicited an increased efflux of the K(+)-congener 86Rb+ which was inhibitable by Ca(2+)-channel blockers and charybdotoxin, a selective inhibitor of high and intermediate conductance Ca(2+)-dependent K+ channels. Charybdotoxin did not reduce the increase in Mn2+ influx by ras, demonstrating that the activation of Ca(2+)-dependent K+ channels was not required for the sustained Mn2+/Ca2+ influx in the presence of transforming Ha-ras. In ras-expressing cells, the bradykinin-induced Mn2+ influx and charybdotoxin sensitive 86Rb+ efflux were markedly potentiated. The increase in the inositol- 1,4,5-trisphosphate and inositol-1,3,4,5-tetrakisphosphate levels by ras is not sufficient to explain the elevated Mn2+ influx. The mitogenic response to an expression of transforming Ha-ras was inhibited by the Ca(2+)-channel blockers not, however, by charybdotoxin. These data suggest the existence of an agonist-independent activation of a receptor- or second messenger-operated Ca2+ channel by transforming Ha-ras which is necessary for the mitogenic response to the activation of the oncogene.
Maly
K
K
Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Austria.
Kindler
E
E
Tinhofer
I
I
Grunicke
H H
HH
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D051379:Mice; D015221:Potassium Channels / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism
D015220:Calcium Channels; D007295:Inositol Phosphates; D015221:Potassium Channels; D008345:Manganese; D003907:Dexamethasone; D016283:Proto-Oncogene Proteins p21(ras); D012413:Rubidium; D001920:Bradykinin; D002118:Calcium