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 plaqu es and dense bodies of smooth muscle cells, was found in a low-salt al kaline extract of chicken gizzard smooth muscle, An antibody against c gABP260 was used to screen a chicken gizzard cDNA library, and the nuc leotide sequence of the partial cDNA encoding this protein was determi ned, Comparison of predicted amino acid sequences revealed that the pr otein had significant homology with human ABP-280 and chicken retina f ilamin [Barry, C.P. et al, (1993) J. Biol. Chem, 268, 25577-25586], bu t despite the high homology, cgABP260 was immunologically distinguisha ble from filamin, Immunoblot analysis showed that an anti-cgABP260 ant ibody reacted exclusively with the cgABP260 band of smooth, skeletal, and cardiac muscle tissues, By indirect immunofluorescence, the membra ne-affinity-purified antibody against cgABP260 intensely stained the d ense plaques of the isolated smooth muscle cells, Immunoelectron micro scopy showed that immunogold particles representing cgABP260 were foun d abundantly on the dense plaques and less abundantly on the dense bod ies, 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 c ells.