Acts as an inhibitor of cathepsin B (CTSB) activity. Plays a role as a negative regulator of tumor vascular development, cell invasion and metastasis. Monomer. Homodimer; disulfide-linked. Localizes in cytoplasmic granules of neutrophilic precursors (PubMed:8749713). Expressed in myeloid bone marrow cells. Expressed in neutrophilic precursors (at protein level) (PubMed:8749713). Expressed in myeloid bone marrow cells (PubMed:21518852). Up-regulated by CCAAT/enhancer-binding proteins CEBPA and CEBPE and transcription factor SPI1 (at protein level) (PubMed:12515729). Down-regulated in malignant tumor conditioned medium (PubMed:21518852). Up-regulated during early bone marrow differentiation by the granulocyte-macrophage colony-stimulating factor CSF2 and down-regulated during granulocytic maturation (PubMed:8749713). Belongs to the cathelicidin family.