THE SH3 DOMAIN CONTRIBUTES TO BCR ABL-DEPENDENT LEUKEMOGENESIS IN-VIVO - ROLE IN ADHESION, INVASION, AND HOMING/

To determine the possible role of the BCR/ABL oncoprotein SH3 domain i n BCR/ABL-dependent leukemogenesis, we studied the biologic properties of a BCR/ABL SH3 deletion mutant (Delta SH3 BCR/ABL) constitutively e xpressed in murine hematopoietic cells. Delta SH3 BCR/ABL was able to activate known BCR/ABL-dependent downstream effector molecules such as RAS, PI-3kinase, MAPK, JNK, MYC, JUN, STATs, and BCL-2. Moreover, exp ression of Delta SH3 BCR/ABL protected 320cl3 murine myeloid precursor cells from apoptosis, induced their growth factor-independent prolife ration, and resulted in transformation of primary bone marrow cells in vitro. Unexpectedly, leukemic growth from cells expressing Delta SH3 BCR/ABL was significantly retarded in SCID mice compared with that of cells expressing the wild-type protein. In vitro and in vivo studies t o determine the adhesive and invasive properties of Delta SH3 BCR/ABL- expressing cells showed their decreased interaction to collagen IV- an d laminin-coated plates and their reduced capacity to invade the strom a and to seed the bone marrow and spleen. The decreased interaction wi th collagen type IV and laminin was consistent with a reduced expressi on of alpha 2 integrin by Delta SH3 BCR/ABL-transfected 32Dcl3 cells. Moreover, as compared with wild-type BCR/ABL, which localizes primaril y in the cytoskeletal/membrane fraction, Delta SH3 BCR/ABL was more ev enly distributed between the cytoskeleton/membrane and the cytosol com partments. Together, the data indicate that the SH3 domain of BCR/ABL is dispensable for in vitro transformation of hematopoietic cells but is essential for full leukemogenic potential in vivo. (C) 1998 by The American Society of Hematology.