PTPN2 Negatively Regulates Oncogenic JAK1 in T-cell Acute Lymphoblastic Leukemia

We have recently reported inactivation of the tyrosine phosphatase PTPN2 (also known as TC-PTP) through deletion of the entire gene locus in ∼ 6% of T-cell acute lymphoblastic leukemia (T-ALL) cases. T-ALL is an aggressive disease of the thymocytes characterized by the stepwise accumulation of chromosomal abnormalities and gene mutations. In the present study, we confirmed the strong association of the PTPN2 deletion with TLX1 and NUP214-ABL1 expression. In addition, we found cooperation between PTPN2 deletion and activating JAK1 gene mutations. Activating mutations in JAK1 kinase occur in ∼ 10% of human T-ALL cases, and aberrant kinase activity has been shown to confer proliferation and survival advantages. Our results reveal that some JAK1 mutation-positive T-ALLs harbor deletions of the tyrosine phosphatase PTPN2, a known negative regulator of the JAK/STAT pathway. We provide evidence that down-regulation of Ptpn2 sensitizes lymphoid cells to JAK1-mediated transformation and reduces their sensitivity to JAK inhibition.