Regulation of alpha 2 integrin gene expression in cells with megakaryocytic features: a common theme of three necessary elements.

The alpha 2 beta 1 integrin mediates interactions between cells and the extracellular matrix molecules, collagen and/or laminin. The alpha 2 beta 1 integrin is expressed in a variety of cell types, but in cells of hematopoietic lineage, expression is restricted to megakaryocytes and platelets. Increased expression of the alpha 2 beta 1 integrin during megakaryocytic differentiation is a consequence of transcriptional activation of the alpha 2 gene. We have begun to characterize the role of the 5' flanking region of the alpha 2 integrin gene in regulating expression during megakaryocyte differentiation. A 5-kb fragment of the 5' region directs both cell type and differentiation-dependent expression of a reporter gene in the pluripotent hematopoietic K562 cells upon megakaryocytic differentiation and in the megakaryocytic cell line, Dami. Analysis of a series of 5' deletion mutants indicates that expression of the alpha 2 integrin gene in cells with megakaryocytic features requires a core promoter region, a silencer region, and megakaryocytic enhancers in the distal 5' end. The organization of these three distinct regulatory regions of the alpha 2 promoter/enhancer suggests a common theme for megakaryocytic gene regulation shared with other megakaryocyte-specific proteins, including alpha IIb integrin subunit and platelet factor 4.