The megakaryocyte/platelet-specific enhancer of the alpha(2)beta(1) integrin gene: Two tandem AP1 sites and the mitogen-activated protein kinase signaling cascade

The alpha(2)beta(1) integrin, a collagen receptor on platelets and megakary ocytes, is required for normal platelet function. Transcriptional regulatio n of the alpha(2) integrin gene in cells undergoing megakaryocytic differen tiation requires a core promoter between bp -30 and -92, a silencer between bp -92 and -351, and megakaryocytic enhancers in the distal 5' flank. We h ave now identified a 229-bp region of the distal 5' flank of the alpha(2) i ntegrin gene required for high-level enhancer activity in cells with megaka ryocytic features. Two tandem AP1 binding sites with dyad symmetry are requ ired for enhancer activity and for DNA-protein complex formation with membe rs of the c-fos/c-jun family The requirement for AP1 activation suggested a role for the mitogen-activated protein kinase (MAPK) signaling pathway in regulating at integrin gene expression. Inhibition of the MAP kinase cascad e with PD98059, a specific inhibitor of MAPK kinase 1, prevented the expres sion of the alpha(2) integrin subunit in cells induced to become megakaryoc ytic. We provide a model of megakaryocytic differentiation in which express ion of the alpha(2) integrin gene requires signaling via the MAP kinase pat hway to activate two tandem AP1 binding sites in the alpha(2) integrin enha ncer (C) 1999 by The American Society of Hematology.