FGFR1 and Kaposi's sarcoma: To test whether or not the PDGFRA activation, which is prominent in lytically-induced K-Pα(+)S KS cells but not in K-Pα(+)S MSC cells, is necessary for enabling cell proliferation upon KSHV lytic reactivation, we inhibited this pathway using a highly selective PDGFR tyrosine kinase inhibitor (PDGFR Tyrosine Kinase Inhibitor IV, IC50: PDGFR-α: IC50 = 45 nM; PDGFR-β: IC50 = 4.2 nM; c-Abl: IC50 = 22 nM; c-Src: IC50 = 185 nM; VEGFR: IC50 = 3.1 μM; bFGFR-1: IC50 = 45.8 μM; EGFR: IC50 = >100 μM).