Dual Transforming Activities of the FUS (TLS)-ERG Leukemia Fusion Protein Conferred by Two N-Terminal Domains of FUS (TLS)

Abstract

The FUS (TLS)-ERG chimeric protein associated with t(16;21)(p11;q22) acute myeloid leukemia is structurally similar to the Ewing’s sarcoma chimeric transcription factor EWS-ERG. We found that both FUS-ERG and EWS-ERG could induce anchorage-independent proliferation of the mouse fibroblast cell line NIH 3T3. However, only FUS-ERG was able to inhibit the differentiation into neutrophils of a mouse myeloid precursor cell line L-G and induce its granulocyte colony-stimulating factor-dependent growth. We constructed several deletion mutants of FUS-ERG lacking a part of the N-terminal FUS region. A deletion mutant lacking the region between amino acids 1 and 173 (exons 1 to 5) lost the NIH 3T3-transforming activity but retained the L-G-transforming activity. On the other hand, a mutant lacking the region between amino acids 174 and 265 (exons 6 and 7) lost the L-G-transforming activity but retained the NIH 3T3-transforming activity. These results indicate that the N-terminal region of FUS contains two independent functional domains required for the NIH 3T3 and L-G transformation, which we named TR1 and TR2, respectively. Although EWS intrinsically possessed the TR2 domain, the EWS-ERG construct employed lacked the EWS sequence containing this domain. Since the TR2 domain is always found in chimeric proteins identified from t(16;21) leukemia patients but not in chimeric proteins from Ewing’s sarcoma patients, it seems that the TR2 function is required only for the leukemogenic potential. In addition, we identified three cellular genes whose expression was altered by ectopic expression of FUS-ERG and found that these are regulated in either a TR1-dependent or a TR2-dependent manner. These results suggest that FUS-ERG may activate two independent oncogenic pathways during the leukemogenic process by modulating the expression of two different groups of genes simultaneously.

ACKNOWLEDGMENTS

We thank A. D. Miller for providing pLNCX vector, D. Baltimore for providing BOSC23 cells, T. Honjo for providing L-G cells, Y. Sakamoto for providing NIH 3T3 cells, and T. Ito for making suggestions about the mRNA differential-display technique.

This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science, and Culture; by a grant from the Special Coordination Funds for the Promotion of Science and Technology from the Science and Technology Agency; by a Grant-in-Aid for the 2nd Term Comprehensive 10-year Strategy for Cancer Control and a Research Grant on Human Genome and Gene Therapy from the Ministry of Health and Welfare; and by the Program for Promotion of Fundamental Studies in Health Sciences of the Organization for Drug ADR Relief, R&D Promotion, and Product Review of Japan.