Immunocytochemical Identification and Localization of the Mr 22,000 Calcium‐binding Protein (Sorcin) in an Adriamycin‐resistant Myelogenous Leukemia Cell Line

Monoclonal antibody against the Mr 22,000 calcium‐binding protein (sorcin) from an adriamycin‐resistant myelogenous leukemia cell line K562 (K562/ADM) was prepared and used as a probe to study the localization of sorcin in K562/ADM cells and the parental cell line, K562. Analysis of extracts from K562/ADM cells by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and fluorescence image analysis showed that K562/ADM cells possessed abundant sorcin in the cytoplasm which was almost entirely absent from the drug‐sensitive parental cell line, K562. Furthermore, immuno‐electron microscopic studies revealed that sorcin was closely associated with free ribosomes, rough endoplasmic reticulum, mitochondria, microfilament bundles and perinuclear membranes. These observations provide the first clue that the Ca‐binding protein, sorcin, may play an important role in the development of the multidrug resistance phenomenon, although the relationship between sorcin and P‐glycoprotein is still unknown.