Transforming Growth Factor-β1 Sensitivity Is Altered inAbl-Myc- andRaf-Myc-Induced Mouse Pre-B-Cell Tumors

Understanding the mechanisms leading to transformation of early B-lineage precursors is an important step leading to rational design of new treatments for precursor (pre)-B-cell leukemia. We used normal mouse pre-B cells to determine if and how transforming growth factor (TGF)-beta 1 affects these precursors to the B-cell lineage and whether transformed pre-B cells respond to TGF-beta 1. We found that normal pre-B cells proliferating in the presence of interleukin (IL)-7 enter cell-cycle arrest after exposure to TGF-beta 1. However, clonally related IL-7-independent tumors induced by oncogenes abl + myc or raf + myc have reduced sensitivity to TGF-beta 1. In contrast, tumor cells induced by myc alone remain sensitive to TGF-beta 1 growth suppression. These results suggest that lesions in different molecular signaling pathways can lead to loss of TGF-beta 1 sensitivity in a single cell type. The approach of using normal pre-B-cell lines and transformation by overexpression of different oncogenes provides a system to compare and contrast molecular pathways that lead to full malignancy.