KLK3

KLK3 (kallikrein-related peptidase 3), also known as prostate-specific antigen (PSA), is a secreted chymotrypsin-like serine protease that is highly expressed in prostate epithelial cells and represents one of the most abundant proteins in prostatic fluid^[1][2][3]. Its core physiological function is the proteolytic processing of seminal plasma proteins involved in semen liquefaction, reflecting its specialized role in the male reproductive tract^[3][4]. Mechanistically, KLK3 acts through protease-dependent extracellular protein cleavage and displays distinctive substrate specificity that differentiates it from other members of the kallikrein family^[5][6]. Beyond its physiological function, KLK3 has been extensively linked to prostate cancer biology and is widely used as a biomarker for disease detection, monitoring, and clinical management^[1][7][8]. Experimental studies further indicate that KLK3 can modulate processes associated with tumor progression, including cell invasion, bone remodeling, osteoblast differentiation, and angiogenesis-related pathways^{[9][10][11][12]}. Compared with closely related kallikrein isoforms such as KLK2, KLK3 exhibits markedly higher prostate-specific expression and unique enzymatic characteristics that support its distinct biological and clinical utility^[4][13]. For experimental applications, selective KLK3 inhibitors and substrate-based probes have been developed to investigate KLK3-mediated mechanisms and to support targeted imaging and therapeutic strategies in prostate cancer models^[7][14][15].