streptavidin-agarose complexes were harvested by centrifugation and washed five times with RIPA buffer. Proteins bound to beads were eluted in Laemmli sample buffer and analyzed by SDS- PAGE and western blotting. The ratio of internalized EGFR was determined by densitometric analysis. Internalization of 125I-EGF HeLa cells grown in 12-well dishes were treated with 125I-EGF at 37uC and the ratio of internalized and surface radioactivity was determined during linear 3-min to calculate the specific internal- ization rate constant ke as described previously [7]. In vivo PLD activity assays PLD activity analysis was performed as previously described [25]. After 24 h of fasting, the HeLa cells were incubated with 10 mCi [3H]myristic acid (PerkinElmer Life Sciences) for 3 h. PLD activity was determined using the transphosphatidylation reaction in the presence of 0.4% 1-butanol. 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