Transcriptional control of Bactericidal/permeability increasing protein (BPI) and cathepsin G in myeloid cells

Abstract: The neutrophil store its effector proteins in several distinct types of cytoplasmic granules, developed sequentially during cell maturation. The different subtypes of granules have unique protein content and functional characteristics. The formation of each granule subtype coincides with the biosynthesis of its content. Granule proteins synthesised during the formation of a granule subtype are thus stored in that granule type. Therefore, the temporal regulation of granule protein expression is an important mechanism by which sorting into different granule subtypes is achieved. BPI (bactericidal/permeability increasing protein) is a cationic protein with antibacterial activity, present in azurophil (primary) granules of neutrophils. BPI neutralises the pro-inflammatory effects of LPS and is of potential clinical use in the treatment of fulminant gram-negative infections. The expression of BPI occurs during the promyelocyte stage of neutrophil maturation, but absence of BPI in patients with specific granule deficiency indicates a transcriptional control distinct from that of other azurophil granule proteins. In the present thesis have I show that AML1, Sp3 and PU.1 activate the BPI promoter in HL60 cells. Moreover, all trans retinoic acid (ATRA)-induced BPI expression in NB4 cells correlates with C/EBP binding to BPI promoter. Furthermore, have I identified a mouse BPI orthologue that is expressed in both bone marrow and testis. Cathepsin G is a haematopoietic serine protease also stored in azurophil granules of neutrophils. I show that transcription of cathepsin G is activated by assembly of an enhanceosome including cis-elements for C/EBP and c-myb, and a GC-rich region, and corresponding trans-factors. Binding of trans-factors C/EBPa and C/EBPe to the enhancesome is shown by chromatin immunoprecipitation. Furthermore, PU.1 binding to the cathepsin G promoter in monocytic cells confers a high cathepsin G mRNA expression.