Activation of β1 Integrin Fibronectin Receptors on HL60 Cells After Granulocytic Differentiation

Abstract

AbstractPhorbol esters upregulate the functional affinity of β1 integrin receptors for fibronectin on human neutrophils and other leukocytes. We investigated the ability of phorbol myristate acetate (PMA) to stimulate the human promyelocyte cell line HL-60 to adhere to fibronectin, either in its undifferentiated state (HL60) or after dimethylsulfoxide-in-duced differentiation along the granulocytic pathway (dHL60). PMA stimulated little adherence of undifferentiated HL60 to fibronectin or to the 120-kD chymotryptic cell-binding domain (CBD) of fibronectin. In contrast, PMA stimulated dHL60 cells to rapidly adhere to both fibronect-in- and to CBD-coated plastic. PMA-stimulated dHL60 adherence to fibronectin was largely mediated by both α4β1 and α5β1, whereas PMA-stimulated dHL60 adherence to CBD was largely mediated by α5β1. There was little contribution from β2 integrins to PMA-stimulated dHL60 adherence to fibronectin or CBD. The inability of undifferentiated HL60 to adhere to fibronectin and CBD did not result from lack of expression of α4β1 or α5β1 because HL60 and dHL60 express similar amounts of both α4β1, and α5β1, on their surface. In addition, 1 mmol/LMn2+ induced similar amounts of α5β1-dependent adherence of both HL60 and dHL60, showing that α5β1 on undifferentiated HL60 is capable of binding to its ligand. These data suggest that activation of protein kinase C cannot functionally upregulate these β1 integrins on undifferentiated HL60 cells. The development of PMA-stimulated β1-dependent adherence after granulocytic differentiation of HL60 cells suggests that the differentiated HL60 cell is a useful model for investigating functional coupling of protein kinase C to β1 integrin in myeloid cells.