Sorcin (V19), a soluble acidic calcium-binding protein overproduced in multidrug-resistant cells. Identification of the protein by anti-sorcin antibody.

Sorcin (soluble resistance-related calcium-binding protein), an acidic (pI = 5.7) protein (Mr approximately 20 kDa) previously designated V19, was originally identified in cells selected for high levels of resistance to vincristine. Two-dimensional gel electrophoresis and/or Western blot techniques now show sorcin to be overproduced in cells selected for resistance to actinomycin D (QUA/ADj), colchicine (CHRC5), and adriamycin (BE(2)-C/ADR). Not all cell lines selected for resistance to these drugs overproduced sorcin; e.g. cells of an independently selected actinomycin D-resistant subline of QUA, QUA/ADsx, did not contain increased amounts of sorcin. Sorcin was purified by preparative gel electrophoresis from QUA/ADj cells and used to generate specific antiserum in chickens. By Western blot analyses the antiserum was shown to recognize sorcin in QUA/ADj and in vincristine-resistant mouse and Chinese hamster lung, colchicine-resistant Chinese hamster ovary, and adriamycin-resistant human neuroblastoma lines. Low level expression of the protein was detectable in control, drug-sensitive cells. Direct binding assays with 45Ca2+ showed that sorcin was a calcium-binding protein. QUA/ADj cells contained increased numbers of double minute chromosomes (DMs), cytogenetic indicators of gene amplification. As found for two other multidrug-resistant sublines, sorcin overproduction in QUA/ADj cells may be the result of amplification of the sorcin-encoding gene. The overproduction of this protein in multidrug-resistant cells of various species implies that sorcin plays a role in expression of the resistant phenotype.