IDENTIFICATION OF CYTOPLASMIC ACTIN AS AN ABUNDANT GLUTAMINYL SUBSTRATE FOR TISSUE TRANSGLUTAMINASE IN HL-60 AND U937 CELLS UNDERGOING APOPTOSIS

A lysine derivative, enyl]-amino-n-hexanoyl-L-lysylamido]-propane-1-ol , a novel amine substrate of transglutaminases, was synthesized and de livered into intact HL-60 and U937 human leukemia cells to probe the f unction of the intracellular enzyme. The novel substrate compound was covalently incorporated into intracellular proteins in these cells exp ressing high levels of tissue transglutaminase and undergoing apoptosi s following the induction of their differentiation with dimethyl sulfo xide and retinoic acid. Immunoaffinity purification and microsequencin g of labeled proteins identified cytoplasmic actin as the main endogen ous glutaminyl substrate in these cells. As shown by confocal image an alysis, cells revealed distinct labeling of the microfilament meshwork structures by the novel compound as the result of the intracellular a ction of transglutaminase.