Calponin

Protein (present in several isoforms - calopinin 1,2,3) in smooth muscle cells, which binds actin, tropomyosin and calmodulin. Calponin is used as an immunohistological marker and labels analogous to smooth muscle actin, myoepithelia, smooth muscle cells and myofibroblasts.

Calponin is involved in the control of smooth muscle contractions and is phosphorylated by protein kinase C during Ca2+-independent contraction. The expression of basic calponin is restricted to the smooth muscle cells. The protein is used to detect smooth muscle cells (see also alpha smooth muscle actin). If calponin is lost, cells of the smooth muscle of the vessels are transformed into a "synthetic de-differentiated phenotype". This is a crucial stage in arteriosclerosis. It is also assumed that basic calponin exerts its effect via the cortical actin cytoskeleton. It influences the proliferation (and thus also the metastatic potential) of tumor cells.

1. Liu R et al (2016) Calponin isoforms CNN1, CNN2 and CNN3: Regulators for actin cytoskeleton functions in smooth muscle and non-muscle cells. Genes 585:143-153.