Disruption of the ARF transcriptional activator DMP1 facilitates cell immortalization, Ras transformation, and tumorigenesis

The DMP1 transcription factor induces the ARF tumor suppressor gene in mous e fibroblasts, leading to cell cycle arrest in a p53-dependent manner. We d isrupted sequences encoding the DNA-binding domain of DMP1 in mouse embryon ic stem cells and derived animals lacking the functional protein. DMP1-null animals are small at birth, and males develop more slowly than their wild- type littermates. Some adult animals exhibit seizures and/or obstuctive uro pathy, each of unknown cause. The growth of explanted DMP1-null mouse embry o fibroblasts (MEFs) is progressively retarded as cells are passaged in cul ture on defined transfer protocols; but, unlike the behavior of normal cell s, p19(ARF), Mdm2, and p53 levels remain relatively low and DMP1-null MEFs do not senesce. Whereas the establishment of cell lines from MEFs is usuall y always accompanied by either p53 or ARF loss of function, continuously pa ssaged DMP1-null cells readily give rise to established 3T3 and 3T9 cell li nes that retain wild-type ARF and functional p53 genes. Early-passage DMP1- null cells, like MEFs from either ARF-null or p53-null mice, can be morphol ogically transformed by oncogenic Ha-Ras (Val-12) alone. Splenic lymphocyte s harvested from both DMP1-null and ARF-null mice exhibit enhanced prolifer ative responses in long-term cultures when stimulated to divide with antibo dy to CD3 and interleukin-2. Although only 1 of 40 DMP1-null animals sponta neously developed a tumor in the first year of life, neonatal treatment wit h dimethylbenzanthracene or ionizing radiation induced tumors of various hi stologic types that were not observed in similarly treated DMP+/+ animals. Karyotypic analyses of MEFs and lymphomas from DMP1-null animals revealed p seudodiploid chromosome numbers, consistent with the retention of wild-type p53. Together, these data suggest that ARI: function is compromised, but n ot eliminated, in animals lacking functional DMP1.