Modulation of actin filament dynamics by actin-binding proteins residing in lamellipodia.

Lamellipodial extension depends essentially on the polymerisation cycle of actin. In this cellular compartment the rate and extent of actin polymerisation is tightly regulated by a large number of actin-binding proteins. The main regulators comprise proteins of the actin-depolymerising factor (ADF)/cofilin family, which stimulate actin cycling, but there are also minor constituents like gelsolin and certain variants of tropomyosin that have so far not been considered to be lamellipodial constituents.

Activated cofilin colocalises with Arp2/3 complex in apoptotic blebs during programmed cell death.

Etoposide inhibits topoisomerase II and induces apoptosis in human epidermoid cancer cells (A431) and normal rat fibroblasts (NRK) as verified by apoptotic morphology and chromatin degradation. Here we examine changes in the localisation of actin, cofilin and the Arp2/3 complex during the apoptotic process in response to etoposide. Twenty-four hours after etoposide addition, a large number of cells of both lines exhibited nuclear and cytoplasmic fragmentation with the formation of numerous blebs typical of apoptosis.

Binding of a C-terminal fragment (residues 369 to 435) of vitamin D-binding protein to actin.

The vitamin D-binding protein (DBP) binds to monomeric actin with high affinity. The variation in DBP isoforms is due to genetic polymorphism and varying glycosylation. To obtain a homogeneous preparation, the cDNA for human DBP and truncations thereof were cloned and various systems were applied for heterologous bacterial and yeast expression.

Gelsolin as a calcium-regulated actin filament-capping protein.

Various concentrations of gelsolin (25-100 nM) were added to 2 microM polymerized actin. The concentrations of free calcium were adjusted to 0.05-1.

Co-operative binding of Ca2+ ions to the regulatory binding sites of gelsolin.

The rate of association of actin with gelsolin was measured at various Ca2+ and ATP concentrations. The fraction of Ca2+-activated gelsolin was determined by quantitative evaluation of the association rates thereby assuming that Ca2+-binding gelsolin associates with actin and Ca2+-free gelsolin does not. A plot of the fraction of Ca2+-activated gelsolin vs.