NRP1 and glioblastoma: GBM cells responsive to VEGF-A signaling show a physical interaction between wild-type NRP1 and FMS-related receptor tyrosine kinase 1 (Flt-1), whereas VEGF-A-resistant GBMs show modified chondroitin-sulfated NRP-1 with no interaction with Flt-1, and eliminating the chondroitin sulfate modification in NRP-1 leads to re-sensitization to VEGF-A [97].