Modulation of VEGFR-2 signal output by the wild-type tail of NRP-1. PAEC expressing VEGFR-2 and NRP-1 were stimulated with VEGF-A₁₆₅a and harvested at the indicated time points. Signaling was monitored with the indicated antibodies. Data were normalized to PAEC expressing only VEGFR-2 (not shown). (A-D) The relative VEGFR-2 phosphorylation was similar in all cell lines. (B-E) Full activation of PLCγ-1 was still observed by the mutant NRP-1-S921X. (C-F) p38 is only fully activated when the complete cytoplasmic tail is present. (G) Spheroids assembled of PAEC expressing VEGFR-2 and the indicated NRP-1 isoform were stimulated for 24 hours with VEGF-A₁₆₅a and then analyzed. Only the full-length form of NRP-1 led to robust sprouting of spheres. Scale bar: 200 μm.