Inhibition of Grb2 expression demonstrates an important role in BCR-ABL-mediated MAPK activation and transformation of primary human hematopoietic cells

Chronic myeloid leukemia (CML) results from expression of the BCR/ABL oncogene in a primitive hematopoietic cell. However BCR/ABL-activated signaling mechanisms are dependent on the cellular context in which it is expressed, and mechanisms underlying primitive human hematopoietic cell transformation by BCR-ABL are not well understood. Our previous studies have shown that BCR/ABL-Y177 plays an essential role in Ras activation and human hematopoietic progenitor transformation in CML. The adapter protein growth factor receptor binding protein-2 (Grb2) can bind phosphorylated BCR/ABL-Y177, induce Grb2-SoS complex formation, and activate Ras signaling. We investigated the role of Grb2 in CML progenitor transformation by co-transducing human CD34+ cells with lentivirus vectors expressing shRNA to Grb2 and retrovirus vectors expressing BCR/ABL. We show that Grb2 knockdown significantly inhibits proliferation and survival of BCR-ABL-expressing CD34+ cells, but not control CD34+ cells. Grb2 knockdown reduced MAPK activity in BCR-Abl-expressing hematopoietic cells. We conclude that inhibition of Grb2 expression demonstrates an important role in BCR-ABL mediated MAPK activation and transformation of primary human hematopoietic cells. These results support further investigation of downstream effectors of Grb2-mediated signals and targeting of Grb2 interactions in the treatment of CML.