Proximal Events in 712-Dimethylbenzaanthracene-Induced Stromal Cell-Dependent Bone Marrow B Cell Apoptosis: Stromal Cell-B Cell Communication and Apoptosis Signaling

摘要

Intercellular communication is an essential process in stimulating lymphocyte development and in activating and shaping an immune response. B celldevelopment requires cell-to-cell contact with and cytokine production by bone marrow stromal cells. However, this intimate relationship also may be responsible for the transfer of death-inducing molecules to the B cells. 7,12-dimethylbenz[a]anthracene (DMBA), a prototypicalpolycyclic aromatic hydrocarbon, activates caspase-3 in pro/pre-B cells in a bone marrow stromal cell-dependent manner, resulting in apoptosis. Thesestudies were designed to examine the hypothesis that an intrinsic apoptotic pathway is activated by DMBAand that the ultimate death signal is a DMBA metabolitegenerated by the stromal cell sand transferred to the B cell s. Whilea loss of mitochondrial membrane potentialdid not occur in the DMBA/stromal cell -induced pathway, cytochrome c release was stimulated in B cells. Caspase-9 was activated, and formation of the apoptosome was essential to support apoptosis, as demonstrated by suppression of death in Apaf-1^fogmutant pro -B cells. Investigation of signaling upstream of the mitochondria demonstrated an essential role for p53. Furthermore, DMBA-3,4-dihydrodiol-1,2-epoxide, a DNA-reactive metabolite of DMBA, wassufficient to upregulate p53, induce caspase-9 cleavage and initiate B cell apoptosis in the absence of stromal cells, suggesting that production of this metabolite by the stromal cellsand transfer to the B cell sis a proximal event in triggering apoptosis. Indeed, we provide evidencethat metabolite transfer from bone marrow stromal cells occurs through membrane exchange, which may represent a novel communication mechanismbetween developing B cells and stromal cells.