JAK2(V617F) is a gain of function mutation that promotes cytokine-independent growth of myeloid cells and accounts for a majority of myeloproliferative neoplasms (MPN). Mutations in p53 are rarely found in these diseases before acute leukemia transformation, but this does not rule out a role for p53 deregulation in disease progression. Using Ba/F3-EPOR cells and ex vivo cultured CD34(+) cells from MPN patients, we demonstrate that expression of JAK2(V617F) affected the p53 response to DNA damage. We show that E3 ubiquitin ligase MDM2 accumulated in these cells, due to an increased translation of MDM2 mRNA. Accumulation of the La autoantigen, which interacts with MDM2 mRNA and promotes its translation, was responsible for the increase in MDM2 protein level and the subsequent degradation of p53 after DNA damage. Downregulation of La protein or cell treatment with nutlin-3, a MDM2 antagonist, restored the p53 response to DNA damage and the cytokine-dependence of Ba/F3-EPOR-JAK2(V617F) cells. Altogether, these data indicate that the JAK2(V617F) mutation affects p53 response to DNA damage through the upregulation of La antigen and accumulation of MDM2. They also suggest that p53 functional inactivation accounts for the cytokine hypersensitivity of JAK2(V617F) MPN and might have a role in disease progression.