Functional characterization of PDGFRA alterations in cancer reveals a gain-of-function V536E transmembrane mutant as well as loss-of-function and passenger mutations

Activating mutations in the PDGF receptor alpha (PDGFRA) have been described in patients with gastrointestinal stromal tumors (GIST) or myeloid malignancies associated with hypereosinophilia. These patients respond well to imatinib, raising the question as to whether all cancer patients with a PDGF receptor mutation should receive a tyrosine kinase inhibitor treatment. We characterized eleven novel somatic point PDGFRA mutations that have been reported in glioblastoma, melanoma, acute myeloid leukemia, peripheral nerve sheath tumors and neuroendocrine carcinoma. The PDGFRA transmembrane domain mutation V536E stimulated Ba/F3 cell growth and signaling via ERK and STAT5 in the absence of ligand. This mutant, identified in glioblastoma, was strongly inhibited by imatinib. Surprisingly, three mutations in highly conserved residues blocked the response to PDGF: PDGFRA-C235Y was quickly degraded by proteasomes; W349C failed to traffic to the cell surface and F808L was devoid of kinase activity. The relevance of these loss-of-function mutations remains to be established. The other mutations had no constitutive activity but responded to PDGF like wild type receptors and may thus represent passenger mutations. Our results underline the importance of characterizing new PDGFRA cancer mutations before selecting patients eligible for tyrosine kinase inhibitor therapy.