KLK13

KLK13 (kallikrein-related peptidase 13) is a secreted trypsin-like serine protease belonging to the human kallikrein family and is predominantly expressed in epithelial tissues, including the esophagus, salivary glands, tonsils, and testis^[1][2]. As a proteolytic enzyme, KLK13 participates in extracellular protein processing and has been implicated in extracellular matrix degradation and tissue remodeling, suggesting a role in regulating epithelial homeostasis and cell-cell interactions^[3][4]. Mechanistically, KLK13-mediated proteolysis has been linked to cellular adhesion pathways, and loss of KLK13 expression is associated with reduced expression of adhesion-related molecules and enhanced invasive behavior in squamous epithelial cancers^[5][6]. In disease models, altered KLK13 expression has been reported in multiple malignancies, including oral, esophageal, lung, bladder, gastric, and breast cancers, where its expression level is frequently associated with tumor progression, metastasis, or patient prognosis^[5][7][8]. Compared with related kallikrein isoforms, KLK13 displays a distinct tissue distribution pattern and clinical association profile, although its physiological substrates and regulatory network remain less completely characterized than those of several other KLK family members^[1][2]. For experimental applications, KLK13 has attracted interest as a candidate biomarker and functional regulator of tumor invasion, while recent evidence also identified KLK13 as a host protease that can facilitate human coronavirus HKU1 entry through proteolytic activation of the viral spike protein^[9]. Therefore, KLK13 represents a biologically relevant protease connecting extracellular proteolysis, epithelial disease progression, and host-pathogen interactions^[3][5][9].