Gene fusions and RNA trans-splicing in normal and neoplastic human cells

Chimeric gene products, most often resulting from chromosome translocations, have been considered unique features of cancer, or at least of cells at high risk for becoming cancerous. Chimeric JAZF1-JJAZ1 mRNA transcribed from DNA spanning the site of recombination in the (7;17)(p15;q21) chromosomal translocation found in half of endometrial stromal sarcomas and most cases of benign stromal nodules is one such example. The recent finding that chimeric JAZF1-JJAZ1 mRNA can also be detected in normal endometrial stromal cells suggests that chimeric gene products are not limited to cancer or pre-cancerous cells. The JAZF1-JJAZ1 mRNA and the protein encoded by it appear to be identical to that synthesized from the gene fusion in neoplastic cells. In cultured cells, the chimeric protein has anti-apoptotic properties and is pro-proliferative when unrearranged JJAZ1 alleles are silenced, as they are in endometrial stromal sarcomas but not in the stromal nodules. These observations are consistent with the conclusion that chromosomal rearrangements and gene fusions in neoplastic cells may represent mechanisms for the deregulated expression of chimeric gene products that are generated at specific stages in cell development and have physiologic functions in normal cells. Furthermore, it may be possible that other means for abnormal production of chimeric gene products, such as hyperactive trans-splicing of RNA, may be another mechanism underlying the neoplastic properties of tumor cells.