Cystatin-M (CST6) (CST6)

Cystatin-M, also known as Cystatin-E or CST6, is a secreted protein belonging to the type 2 cystatin superfamily of cysteine protease inhibitors. It functions as a potent, high-affinity inhibitor of lysosomal cysteine proteases, including cathepsins B, L, and V, as well as the asparaginyl endopeptidase legumain. Primarily expressed in the epithelia of the skin and mammary glands, Cystatin-M plays a vital role in maintaining epidermal homeostasis, regulating skin barrier formation, and controlling the desquamation process. In the context of oncology, it is frequently characterized as a tumor suppressor that is often silenced by promoter hypermethylation in various malignancies, such as breast cancer, melanoma, and glioma. Its loss leads to uncontrolled proteolytic activity, promoting tumor cell proliferation, invasion, and metastasis. Interestingly, Cystatin-M exhibits a paradoxical dual role, acting as a tumor promoter in specific cancers like triple-negative breast cancer and pancreatic ductal adenocarcinoma. Therapeutic approaches currently under investigation include the use of recombinant Cystatin-M protein to treat osteolytic bone lesions in multiple myeloma and the application of epigenetic modifiers, such as DNMT and HDAC inhibitors, to restore its expression in silenced tumors.

Other names

Cystatin-ECystatin-E/MCysteine protease inhibitor 6CST6

Drugs targeting Cystatin-M primarily act through the epigenetic reactivation of its silenced gene (via DNMT or HDAC inhibition) to restore its tumor-suppressive function, or through the direct administration of recombinant protein to inhibit pathological cysteine protease activity in bone and skin diseases.