Activating Mutations In Fyn Kinase In Peripheral T-Cell Lymphomas

Peripheral T-cell lymphomas (PTCLs) are a heterogeneous group of aggressive non Hodgkin lymphomas with poor prognosis. Molecular and cytogenetic studies have shown a prominent role for kinase fusion oncogenes, mostly NPM-ALK, in ALK+ anaplastic large cell lymphomas (ALCLs) and ITK-SYK kinase in unspecified PTCLs. To gain further insight on the genetics and pathogenic mechanisms of aggressive PTCLs we performed an integrated mutation analysis using whole exome sequencing (n=12) and RNAseq (n=35) data. This analysis identified 288 candidate coding somatic mutations in 268 genes including known recurrent mutations in the TET2, DNMT3A and IDH2 epigenetic factor genes and pointed to the FYN kinase gene as a new recurrently mutated oncogene in T-cell transformation. The FYN tyrosine kinase is, with LCK, the predominant SRC family kinase found in T lymphocytes and plays an important role in T-cell activation upon T-cell receptor (TCR) stimulation. FYN mutations in PTCL included a FYN L174R mutation detected in one AITL patient sample, a FYN R176C allele recurrently found in two PTCL NOS cases and a FYN Y531H mutation present in a PTCL NOS sample. Notably, each of these alleles are predicted to specifically disrupt the inhibition of FYN kinase activity by the C terminal SRC kinase (CSK). Thus, structure analysis of FYN and FYN mutant proteins predicted that FYN L174R and, most prominently, FYN R176C and FYN Y531H can disrupt the inhibitory interaction of the FYN SH2 domain with the CSK-phosphorylated Y531. Consistently, pull down assays using GST-FYN-SH2 recombinant proteins and biotinylated C-terminal FYN peptides encompassing Y531 showed abrogation of the interaction between FYN-SH2 and P-Y531 in each of these mutants. In agreement with these results, expression of FYN L174R, FYN R176C and FYN Y531H resulted in increased levels of FYN activation. Moreover, CSK expression effectively inhibited wild type FYN, but failed to abrogate FYN L174R, FYN R176C or FYN Y531H activation. In contrast, pharmacologic kinase inhibition with dasatinib, a multikinase inhibitor which blocks ABL1 and SRC kinases, effectively abrogated the activity of FYN L174R, FYN R176C and FYN Y531H mutant proteins and suppressed the growth of cells transformed via expression of activated FYN mutant alleles. Overall these results support an oncogenic role for FYN activating mutations in the pathogenesis of PTCL and support a role for SRC kinase inhibitors for the treatment of this disease.