ERG is a megakaryocytic oncogene.

Ets-related gene (ERG) is a member of the ETS transcription factor gene family located on Hsa21. ERG is known to have a crucial role in establishing definitive hematopoiesis and is required for normal megakaryopoiesis. Truncated forms of ERG are associated with multiple cancers such as Ewing's sarcoma, prostate cancer, and leukemia as part of oncogenic fusion translocations. Increased expression of ERG is highly indicative of poor prognosis in acute myeloid leukemia and ERG is expressed in acute megakaryoblastic leukemia (AMKL); however, it is unclear if expression of ERG per se has a leukemogenic activity. We show that ectopic expression of ERG in fetal hematopoietic progenitors promotes megakaryopoiesis and that ERG alone acts as a potent oncogene in vivo leading to rapid onset of leukemia in mice. We observe that the endogenous ERG is required for the proliferation and maintenance of AMKL cell lines. ERG also strongly cooperates with the GATA1s mutated protein, found in Down syndrome AMKL, to immortalize megakaryocyte progenitors, suggesting that the additional copy of ERG in trisomy 21 may have a role in Down syndrome AMKL. These data suggest that ERG is a hematopoietic oncogene that may play a direct role in myeloid leukemia pathogenesis.

Constitutional aneuploidy and cancer predisposition.

Constitutional aneuploidies are rare syndromes associated with multiple developmental abnormalities and the alterations in the risk for specific cancers. Acquired somatic chromosomal aneuploidies are the most common genetic aberrations in sporadic cancers. Thus studies of these rare constitutional aneuploidy syndromes are important not only for patient counseling and clinical management, but also for deciphering the mechanisms by which chromosomal aneuploidy affect cancer initiation and progression. Here we review the major constitutional aneuploidy syndromes and suggest some general mechanisms for the associated cancer predisposition.

Trisomy of chromosome 21 in leukemogenesis.

Extra copies of chromosome 21 are often found in sporadic leukemias. Constitutional trisomy 21 of Down syndrome (DS) is associated with markedly increased risk for childhood leukemia. Thus the oncogenic role of trisomy 21 in the more common sporadic childhood leukemias may be revealed through the investigations of the relatively rare leukemias of DS. Recent studies of the megakaryoblastic leukemias of Down syndrome have uncovered a developmental leukemogenic mechanism characterized by a unique pre-natal collaboration between overexpressed genes from chromosome 21 and an acquired mutation in the transcription factor GATA1. The base of the markedly enhanced risk for acute lymphoblastic leukemia conferred by trisomy 21 is still unclear. Studies of the leukemias of DS are likely to contribute to the general understanding of the oncogenic mechanisms of chromosomal aneuploidies, the most common abnormalities in cancer.