Mutations In Transcription Factor NF-E2 Confer Resistance To Interferon Treatment In MPN Patients

Recently, we described insertion and deletion mutations in transcription factor NF-E2 in a subset of patients with Myeloproliferative Neoplasms (MPN), most frequently patients with primary or secondary myelofibrosis (PMF or sMF, respectively) as well as patients with polycythemia vera (PV). These mutations lead to the formation of truncated NF-E2 proteins that lack DNA binding activity. Nonetheless, mutant NF-E2 proteins augment wild-type NF-E2 activity both in vitro and in vivo in a murine bone marrow transplant model. Mice expressing mutant NF-E2 develop erythrocytosis and thrombocytosis.

Here, we demonstrate that, in contrast to mice expressing wild-type NF-E2, treatment of mice expressing mutant NF-E2 with interferon-alpha does not lower red blood cell numbers (RBC), white blood cell counts (WBC) or platelet numbers. While these parameters are significantly decreased by interferon-alpha (IFN) in mice expressing wild-type NF-E2, mice expressing mutant NF-E2 showed no response to interferon treatment in these counts over a four month period.

Two PV patients carrying truncating mutations in NF-E2 received IFN treatment. Blood samples were available both from before treatment as well as from 3 and 4 years after the beginning of therapy, respectively. Purified granulocytes from these samples were analyzed for mutant NF-E2 allele burden by GeneScan analysis. In both patients, the mutant NF-E2 allele burden rose during IFN treatment, increasing from 1% to 30% in one patient and from 24% to 100% in the second.

We have demonstrated that acquisition of an NF-E2 mutation confers a proliferative advantage on cells already carrying the JAK2^V617F mutation. Using colony assays from primary MPN cells, we showed that cells carrying both mutations outcompete cells carrying only the JAK2^V617F mutation in vivo. Cells expressing both mutant NF-E2 and JAK2^V617F are statistically significantly more frequently in the S-phase of the cell cycle and express significantly higher levels of several proteins that promote G1/S transition, cyclin D3, CDK4 and CDK6. The data presented here suggest that IFN treatment is insufficient to counteract the proliferative drive conferred by mutant NF-E2.