PTBP1 and central nervous system cancer: During splicing, three heterogeneous nuclear ribonucleoprotein (hnRNP) proteins-- hnRNPA1, hnRNPA2 and polypyrimidine tract binding protein (hnRNPI, PTB)--bind repressively to exon 9 to facilitate the exclusion of exon 9 and the generation of PKM2 in glioma.[12]