A 260-kDa filamin/ABP-related protein in chicken gizzard smooth muscle cells is a new component of the dense plaques and dense bodies of smooth muscle.

A 260-kDa protein, termed cgABP260, which localized in the dense plaques and dense bodies of smooth muscle cells, was found in a low-salt alkaline extract of chicken gizzard smooth muscle. An antibody against cgABP260 was used to screen a chicken gizzard cDNA library, and the nucleotide sequence of the partial cDNA encoding this protein was determined. Comparison of predicted amino acid sequences revealed that the protein had significant homology with human ABP-280 and chicken retina filamin [Barry, C.P. et al. (1993) J. Biol. Chem. 268, 25577-25586], but despite the high homology, cgABP260 was immunologically distinguishable from filamin. Immunoblot analysis showed that an anti-cgABP260 antibody reacted exclusively with the cgABP260 band of smooth, skeletal, and cardiac muscle tissues. By indirect immunofluorescence, the membrane-affinity-purified antibody against cgABP260 intensely stained the dense plaques of the isolated smooth muscle cells. Immunoelectron microscopy showed that immunogold particles representing cgABP260 were found abundantly on the dense plaques and less abundantly on the dense bodies. Its amino acid sequence, molecular size, immunological reactivity, and localization in smooth muscle thus indicated that cgABP260 is a new component of the dense plaques and dense bodies of smooth muscle cells.