CCAAT/enhancer binding protein epsilon (C/EBP epsilon), a myeloid-specific transcription factor, plays an important role in granulopoiesis. A loss-of-function mutation in this protein can result in an abnormal development of neutrophils and eosinophils, known as neutrophil-specific granule deficiency (SGD). The transcriptional activity of C/EBP epsilon is regulated by interactions with other transcription factors and/or post-translational modification, including acetylation. Previously, we reported a novel SGD patient who had a homozygous mutation for two amino acids, arginine (R247) and serine (S248), which were deleted in the basic leucine zipper domain of C/EBP epsilon (Delta RS) and exhibited loss of transcriptional activity with aberrant protein-protein interactions. In the present study, we found that a single amino acid deletion of either R247 (Delta R) or S248 (Delta S) was sufficient for the loss of C/EBP epsilon transcriptional activity, while an amino acid substitution at 5248 to alanine in C/EBP epsilon (SA) had comparable transcriptional activity with the wild-type C/EBP epsilon (WT). Although acetylation at lysine residues (K121 and K198) is indispensable for C/EBP epsilon transcriptional activity, an acetylation mimic form of Delta RS (Delta RS-K121/198Q) did not exhibit the transcriptional activity. Interestingly, we discovered that Delta RS, Delta R, Delta S, and ORS-K121/198Q interacted with histone deacetylase 1 (HDAC1), whereas WT and SA did not. Furthermore, the proteoglycan 2/eosinophil major basic protein induction activity of Delta RS, Delta R, and Delta S could be restored by the HDAC inhibitor, trichostatin A (TSA), and protein protein interactions between Delta RS and Gatal could also be recovered by TSA treatment. Taken together, our results show that TSA has the potential to restore the transcriptional activity of Delta RS, indicating that the inhibition of HDAC1 could be a molecularly targeted treatment for SGD with Delta RS. (C) 2019 Elsevier Inc. All rights reserved.