Neutrophil-specific granule deficiency (SGD) is a rare congenital disorder, and neutrophils of SGD patients lack secondary and tertiary granule gene expression. Neutrophils of SGD patients are deficient for bactericidal activity; therefore, the patients display immunodeficiency and suffer from severe infections. The transcription factor C/EBP epsilon is the responsible gene for the disease. At least two homozygous germline mutations (5bp deletion and A-nucleotide insertion) of C/EBP epsilon, which are functionally defective, have been reported.
Previously, we reported a novel 2 amino acids deletion of the C/EBP epsilon gene in a 55 years-old female patient. Sequencing of the gene revealed a homozygous deletion of 6 base-pairs (arginine and serine residues deletion; ΔRS) within the leucine zipper domain. Promoter activity of the G-CSFR gene was not induced by ΔRS, and endogenous expression of granule genes (B9, NGAL and lactoferrin) was induced by wild-type (WT) C/EBP epsilon but not by ΔRS in mouse embryonic stem (ES) cells, indicating that transcriptional activity of ΔRS was diminished. Also, artificial single amino acid deletion of either ΔR or ΔS exhibited transcriptional deficiency. Synergistic transcriptional activity with p300 was diminished in ΔRS. GFP-ΔRS was localized to the nucleus in NIH3T3 cells, and DNA binding activity of ΔRS was intact. Interestingly, WT C/EBP epsilon associated with Gata1 and PU.1; however, ΔRS did not interact with them. Interestingly, ΔRS acquired a novel association with HDAC1. Our results indicated that the ΔRS likely impairs protein-protein interaction of other transcription factors resulting in loss of transcriptional activation of C/EBP epsilon.