The Role of an Adhesion Molecule in Cell Differentiation: HL-60 Cells as a Model System
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Cells ditfferentiation is an important process in the cycle of life. To study this phenomena a good model is needed. HL-60 cells, a promyelocytic leukemic cell line, provide a good model for studying cell differentiation, in vitro. When exposed to such factors such as phorbol esters and α.1,25 dihydroxyvitamin D3 these cells differentiate along the monocyte pathway and cell adhesion is associated with differentiation along this pathway. In contrast, cell adhesion is never observed when HL-60 cells are induced to differentiate along the granulocyte pathway. The studies performed here were based on the hypothesis that cells which differentiate along the monocyte/macrophage pathway express the adhesion molecule, osteopontin (OPN). To address this hypothesis cells were exposed to a granulocyte differentiating agent, retinoic acid and two monocyte/macrophage differentiating agents, α.1,25 dihydroxyvitamin D3 and PMA and then specific different assays were performed, i.e. proliferation/toxicity assay, NBT reduction assay, NAE reaction assay, and Northern analysis, which was used to determine expression of OPN in cells exposed to agents that allow cells to differentiate along the monocyte pathway versus the granulocyte pathway. The result obtained demonstrated that cells which differentiated along the monocyte pathway expressed OPN, a cell adhesion molecule linked with osteoclast function. In contrast, differentiation along the granulocyte pathway did not result on OPN expression. Importantly, these studies demonstrated that HL-60 cells are a valuable tool to use to further our understanding as to the role of OPN's involvement with the monocyte/macrophage pathway.