Tissue Kallikrein and kallikrein-related peptidases (KLKs), encoded, in the human genome, by the largest contiguous cluster of protease genes, are secreted serine proteases with diverse expression patterns. They possess numerous physiological roles, such as the regulation of blood pressure, hormonal processing, apoptosis, inflammation, seminal/skin homeostasis and tissue remodeling.
The expression of KLK genes is detected in a broad spectrum of human tissues where it has been found to be, mainly, regulated by the steroids hormones. Many miRNAs have been reported to comprise targets of the KLKs genes.

Although primarily known for their clinical applicability as cancer biomarkers (e.g PSA/KLK3), recent evidences implicate KLKs in many pathways of cardiovascular, renal, skin and neuron diseases.

Additionally, KLKs were found to be involved in cancer-related processes, including cell-growth regulation, apoptosis, angiogenesis, invasion and metastasis. KLKs have been shown to promote or inhibit neoplastic progression, acting individually and/or in cascades with other KLKs and proteases and might represent good targets for therapeutic intervention. The fact that KLKs represent targets of miRNAs suggests a post-transcriptional regulatory mechanism with further possible therapeutic applications.