Cytosine demethylation of the proteinase-3/myeloblastin primary granule protease gene during phagocyte development

Proteinase-3/Myeloblastin (Mbn) is a neutral serine protease and a major co nstituent of the primary granules of myeloid cells. It can degrade extracel lular matrix proteins and has been discussed as a key factor for the initia tion of terminal differentiation in promyelocytic cells. Regulation of Mbn closely parallels that of another major primary granule protein, myeloperox idase (MPO). We examined the expression and DMA methylation of Mbn in a mod el of in vitro differentiation of CD34(+) enriched peripheral blood progeni tor cells (PBPCs), and in various other myeloid and non-myeloid tissues. Mb n mRNA was undetectable in uncultured PBPCs but was upregulated during thei r in vitro differentiation. Its expression was enhanced in the presence of G-CSF. Mbn expression was also detected in several myeloid cell lines but n ot in mature granulocytes, monocytes and macrophages. Partial demethylation at a CpG site within Mbn intron 1 (analyzed by restriction with Smd) was o bserved during continued in vitro differentiation of PBPCs. This site was f ully demethylated in mature granulocytes, monocytes and macrophages. Variab le methylation of this site and a second Smal site located upstream of the putative Mbn promoter region was present in other myeloid and non-myeloid t issues examined.