AML1 (CBF alpha 2) cooperates with B cell-specific activating protein (BSAP/PAX5) in activation of the B cell-specific BLK gene promoter

AML1 plays a critical role during hematopoiesis and chromosomal translocati ons involving ARML1 are commonly associated with different forms of leukemi a, including pre-B acute lymphoblastic leukemia. To understand the function of AML1 during B cell differentiation, we analyzed regulatory regions of B cell-specific genes for potential AML1-binding sites and have identified a putative AML1-binding site in the promoter of the B cell-specific tyrosine kinase gene, blk, Gel mobility shift assays and transient transfection ass ays demonstrate that AML1 binds specifically to this site in the blk promot er and this binding site is important for blk promoter activity. Furthermor e, in vitro binding analysis revealed that the AML1 runt DNA-binding domain physically interacts with the paired DNA-binding domain of BSAP, a B cell- specific transcription factor. BSAP has been shown previously to be importa nt for B cell-specific regulation of the blk gene. Physical interaction of AML1 with BSAP correlates with functional cooperativity in transfection stu dies where AML1 and BSAP synergistically activate blk promoter transcriptio n by more than 50-fold. These results demonstrate physical and functional i nteractions between AML1 and BSAP and suggest that AML1 is an important fac tor for regulating a critical B cell-specific gene, blk.