PFAAP5 is a 583 amino acid nuclear protein that potentially is involved in transcriptional regulation. PFAAP5 is phosphorylated on Ser 199 in response to DNA damage, probably by ATM or ATR. Primarily expressed in bone marrow, PFAAP5 is dramatically down-regulated after exposure to arsenic compounds, an event which precedes neutropenia. PFAAP5 interacts with both Gfi-1 and Neutrophil Elastase, two proteins that are implicated in neutropenia disorders. Defects in the gene encoding Neutrophil Elastase, ELA2, are the cause of cyclic haematopoiesis, which, with decreased numbers of circulating neutrophils, leads to an increased risk for opportunistic infection. Gfi1 is a transcriptional repressor that targets the ELA2 gene among others. With PFAAP5 expression, Neutrophil Elastase can potentiate repression of Gfi1 target genes, leading to the transcription of ELA2 and subsequent neutrophil differentiation. There are two isoforms of PFAAP5 that are produced as a result of alternative splicing events.