Acceleration of Leukemogenesis in CREB Transgenic Mice by Retroviral Insertional Mutagenesis.

Cyclic adenosine monophosphate response element binding protein (CREB) is a 43 KDa transcription factor that promotes cell growth and survival, and is a downstream target of growth factor signaling in myeloid cells. We previously reported that CREB is overexpressed in greater than 60 percent of acute myeloid leukemia (AML) patients and is associated with an increased risk of relapse and decreased survival. Transgenic mice that overexpress CREB in the myeloid lineage develop a myelodysplastic/myeloproliferative (MDS/MPD) syndrome with splenomegaly and aberrant myeloid proliferation after one year, but not leukemia. To accelerate leukemogenesis and identify genes that specifically cooperate with CREB, we infected CREB transgenic and wild type (WT) mice with the retrovirus, MOL4070LTR (kindly provided by Linda Wolff, NCI). MOL4070LTR has been shown to accelerate the onset of leukemia in mice by insertionally activating or mutating cooperating genes. Fifteen newborn CREB transgenic and nineteen control WT mice were injected intraperitoneally with virus (1×10⁵ PFU). The infected mice were monitored at regular intervals for signs and symptoms of disease. We analyzed peripheral blood counts for evidence of blasts and performed physical examination for signs of abdominal distention and lethargy. Three out of the fifteen CREB transgenic mice infected with the virus developed disease at 6 to 7 months of age. WT mice, now 10 to 12 months of age, have yet to develop disease. All three CREB transgenic mice infected with MOL4070LTR had increased white blood cells, hepatosplenomegaly, and abnormal blood smears. One of the three CREB transgenic mice with leukemia developed AML with circulating blasts in the peripheral blood and infiltration of the spleen and liver with myeloblasts by histologic examination. The two other CREB transgenic mice died from acute lymphoblastic leukemia. Our preliminary results demonstrate that CREB transgenic mice but not WT mice infected with MOL4070LTR develop leukemia. We are currently identifying possible oncogenes using DNA from the mouse that developed AML. Our results suggest that CREB has the potential to induce acute leukemia in mice; however, additional mutations are required.