Regulation of azurophil granule-associated serine protease genes during myelopoiesis

During myelopoiesis, the primary or azurophil granules are synthesized at the promyelocyte stage of development. The biogenesis of these granules requires the coordinated regulation of a large number of genes that comprise the constituent proteins of the granules themselves. The genes encoding the granule-associated proteins appear to be regulated primarily at the level of gene transcription; that is, most of the granule genes appear to be transcriptionally activated at the beginning of the promyelocyte stage and are transcriptionally repressed at the transition to myelocytes. The cis-acting DNA elements and trans-regulatory factors that control the regulation of granule genes are just beginning to be defined. The granule-associated genes are dispersed throughout the genome; however, several of the serine protease genes expressed in these granules are tightly clustered and the tight clustering may play an important role for their regulation. Recent transgenic studies suggest that DNA elements required for myeloid-specific targeting may be located just upstream from or very near to the granule genes themselves. DNA elements similar to the globin locus control region will probably play a role in the expression of these genes, although locus control elements have not yet been defined for any azurophil granule genes. Future studies directed at defining these key regulatory elements will enhance our understanding of the molecular events that underlie myeloid development.