Expression of PML-RARα protein in leukemic spleen cells. Western blots were performed for RARα and actin on transiently transfected U937 cells (harvested 4 hours after transfection) and on independent tumors from each model. Lane 1 represents U937 cells electroporated with an empty expression plasmid; lane 2, U937 cells expressing the RARα portion of human PML-RARα (RARα exons 3-9); and lane 3, U937 cells expressing full-length human PML-RARα (importantly, high-level expression of PML-RARα in these cells is highly toxic, causing the death of most U937 cells within 24 hours of transfection27 ). Lanes 4-6 represent hCG-PR tumors; lanes 7-8, mCG+/PR (ΔPGK-neo) tumors. The positions of RARα (∼55 kDa) and full-length PML-RARα (∼120 kDa) are marked. A band of approximately 50 kDa marked * represents an unknown protein recognized by the RARα antibody in hCG–PML-RARα tumors. It could potentially represent an altered PML-RARα protein.
