The human tissue Kallikrein gene family encodes 15 serine proteases. All Kallikreins share structural similarities including cysteine residues, a catalytic triad of His, Asp, and Ser residues, typically five coding exons, and varied intron phases. Kallikreins are predominantly secreted as inactive zymogens prior to activation by cleavage of an N-terminal peptide, and all function extracellularly. Kallikreins can be activated autocatalytically, via other Kallikreins, or additional proteases. While structurally similar, Kallikrein family members have distinct functions and have key roles in many physiological and pathological processes. Many human tissue Kallikreins also show promise as cancer biomarkers, which may facilitate earlier detection and characterization of many forms of cancer.
Kallikrein 12, also known as Kallikrein-like5 (KLK-L5), is a trypsin-like serine proteinase. It was discovered by cloning the kallikrein locus on chromosome 19, and was found to be similar to the other kallikrein family genes. It is produced by a number of tissues, including pancreas, salivary gland, breast, prostate, uterus, lung, thymus, thyroid, brain, stomach and colon. Kallikrein 12 message has been reported to be decreased in breast cancer. Different splice variants of kallikrein-12 have been identified; a 254 amino acid form, 248 amino acids form, and a truncated 111 amino acid form.