Evidence for a novel RasGAP-associated protein of 105 kDa in both mature trophoblasts and differentiating choriocarcinoma cells

A novel tyrosine-phosphorylated, RasGAP-associated protein of 105 kDa (p105 ) is found in normal human term placental trophoblasts, as well. as in JEG- 3 human choriocarcinoma cells induced to differentiate by okadaic acid (OA) . This p105 RasGAP-associated protein is distinct from other RasGAP-associa ted proteins described so far, none of which has either a molecular size cl ose to p105 or a trophoblastic cell origin. The p105 appears, accompanied b y p120 and p100 RasGAP expression, after OA treatment of JEG-3 cells but is almost undetectable in the absence of stimulation. Moreover, the p105 is t he first discovered RasGAP-associated protein bound to p100 RasGAP. The nat ural occurrence of the p105 in normal mature trophoblasts isolated from hum an term placenta suggests that it may be linked to the differentiation stat e of human trophoblasts. Hence, this p105 RasGAP-associated protein might b e considered a marker of human trophoblast differentiation. (C) 1999 Academ ic Press.