Calponins: adaptable modular regulators of the actin cytoskeleton.

Over 20 years ago Katsuhito Takahashi isolated a heat stable, calmodulin and actin binding protein from chicken gizzard smooth muscle. Considered initially as a mainly structural component of the vertebrate smooth muscle contractile machinery, the 34-kDa calcium- and calmodulin-binding troponin T-like protein, calponin quickly appeared to also be involved in a number of regulatory and signal transduction events in the actin cytoskeleton. Calponins regulate actomyosin contraction, and reduce metastatic cell motility and tissue invasion. From these various cellular functions the biological role of calponin is now slowly emerging, namely that of an actin filament-stabilizing molecule that contributes to physiological thin filament turnover rates in different cell types.