Relation of cell proliferation to expression of peripheral benzodiazepine receptors in human breast cancer cell lines

Peripheral benzodiazepine receptor (PBR) agonist [H-3]Ro5-4864 has been shown to bind with high affinity to the human breast cancer cell line BT-20. Therefore, we investigated different human breast cancer cell lines with regard to binding to [H-3]Ro5-4864 and staining with the PER-specific monoclonal antibody 8D7. Results were correlated with cell proliferation characteristics. In flow cytometric analysis, the estrogen receptor (ER)-negative breast cancer cell lines BT-20,MDA-MB-435-S, and SK-BR-3 showed significantly higher PER expression (relative fluorescence intensity) than the ER-positive cells T47-D, MCF-7 and BT-474 (P < 0.05). Accordingly, BT-20 and MDA-MB-435-S had the highest capacity for binding [H-3] Ro5-4864, while the ER-positive cells exhibited only low binding of the benzodiazepine. PER expression correlated inversely with cell doubling time (r = 0.78) and positively with Ki-67 expression (r = 0.77). The amount of mitochondria was significantly higher in cells with high PER expression. As PER could be demonstrated only after permeabilization of cells, PER is suggested to be localized within the cytoplasm. Moreover, colocalization of PER and mitochondria was shown by confocal microscopy analysis. The highest amounts of both PER and mitochondria were found in cell lines with high mitotic activity. Therefore, it is concluded that the level of PER is dependent on the number of mitochondria. PER and its putative endogenous ligand diazepam-binding inhibitor are possibly involved in the regulation of cell proliferation of human breast cancer cell lines. BIOCHEM PHARMACOL 60;3:397-402, 2000. (C) 2000 Elsevier Science Inc.