Calpain small subunit 1

Calpain small subunit 1 (CSS1) is a protein that in humans is encoded by the CAPNS1 gene.

Calpains are a ubiquitous, well-conserved family of calcium-dependent, cysteine proteases. Calpain families have been implicated in neurodegenerative processes, as their activation can be triggered by calcium influx and oxidative stress. Calpain I and II are heterodimeric with distinct large subunits associated with common small subunits, all of which are encoded by different genes. The small regulatory subunit consists of an N-terminal domain, containing about 30% glycine residues and a C-terminal Ca-binding domain. Two transcript variants encoding the same protein have been identified for this gene.

This gene encodes a small subunit common to both calpain I and II and is associated with myotonic dystrophy.

'Elevated expression of CAPNS1 has been found to be associated with progression of various cancers such as hepatocellular and renal carcinoma.