Genome profiling revealed the activation of IL2RG/JAK3/STAT5 in peripheral T­cell lymphoma expressing the ITK­SYK fusion gene.

Peripheral T­cell lymphomas (PTCLs) are heterogeneous malignancies that are types of non­Hodgkin lymphomas; patients with this disease have poor prognoses. The IL­2­inducible T­cell kinase­spleen tyrosine kinase (ITK­SYK) fusion gene, the first recurrent chromosome translocation in PTCL­not otherwise specified (NOS), can drive cellular transformation and the development of T­cell lymphoma in mouse models. The aim of the current study was to investigate the signal transduction pathways downstream of ITK­SYK. The authors constructed a lentiviral vector to overexpress the ITK­SYK fusion gene in Jurkat cells. By using Signal­Net and cluster analyses of microarray data, the authors identified the tyrosine­protein kinase JAK (JAK)3/STAT5 signalling pathway as a downstream pathway of ITK­SYK, activation of which mediates the effects of ITK­SYK on tumourigenesis. JAK3­selective inhibitor tofacitinib abrogated the phosphorylation of downstream signalling molecule STAT5, supressed cell growth, induced cell apoptosis and arrested the cell cycle at the G1/S phase in ITK­SYK+ Jurkat cells. In a xenograft mouse model, tumour growth was significantly delayed by tofacitinib. Since JAK3 associates with interleukin­2 receptor subunit γ (IL2RG) only, siRNA­specific knockdown of IL2RG showed the same effect as tofacitinib treatment in vitro. These results first demonstrated that the activation of the IL2RG/JAK3/STAT5 signalling pathway contributed greatly to the oncogenic progress regulated by ITK­SYK, supporting further investigation of JAK3 inhibitors for the treatment of PTCLs carrying the ITK­SYK fusion gene.