Platelet-derived growth factor receptor alpha in glioma: a bad seed

Abstract

Recent collaborative, large-scale genomic profiling of the most common and aggressive brain tumor glioblastoma multiforme(GBM) has significantly advanced our understanding of this disease. The gene encoding platelet-derived growth factor receptor alpha(PDGFRα) was identified as the third of the top 11 amplified genes in clinical GBM specimens. The important roles of PDGFRα signaling during normal brain development also implicate the possible pathologic consequences of PDGFRα over-activation in glioma. Although the initial clinical trials using PDGFR kinase inhibitors have been predominantly disappointing, diagnostic and treatment modalities involving genomic profiling and personalized medicine are expected to improve the therapy targeting PDGFRα signaling. In this review, we discuss the roles of PDGFRαsignaling during development of the normal central nervous system(CNS) and in pathologic conditions such as malignant glioma. We further compare various animal models of PDGF-induced gliomagenesis and their potential as a novel platform of pre-clinical drug testing. We then summarize our recent publication and how these findings will likely impact treatments for gliomas driven by PDGFRα overexpression. A better understanding of PDGFRα signaling in glioma and their microenvironment, through the use of human or mouse models, is necessary to design a more effective therapeutic strategy against gliomas harboring the aberrant PDGFRα signaling.

Figure 1.. Progression and genetic alterations in human malignant gliomas.

Astrocytoma may arise from astrocytes or progenitor cells that accumulate genetic alterations and become transformed. IDH1 and TP53 mutations are believed the first alterations occurring in these tumors. Oligodendrogliomas can develop from the same progenitor cells or mature oligodendrocytes that acquire a distinct set of genetic changes. The earliest changes that occur include IDH1 mutation and a 1p/19p loss. Representative genetic changes are shown with the estimated frequency of occurrence within each type of tumor. OE, overexpression; mut, mutation; del, deletion; met, promoter methylation; amp, amplification.

Figure 2.. PDGFRα/PDGF-A signaling.

PDGF-AA homodimers bind and induce the dimerization and autophosphorylation of the PDGFRαα homodimer receptor. Subsequently, SH2 domain-containing signaling effectors are recruited to the receptor by binding to specific phosphorylated tyrosine residues, initiating downstream signaling cascades.