Cysteine auxotrophy of human leukemic lymphoblasts is associated with decreased amounts of intracellular cystathionase protein

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Abstract
A series of human lymphoblastoid cell lines derived from nonleukemic donors are cysteine prototrophs (cys+), while several lymphoblastoid lines derived from leukemic donors are cysteine auxotrophs (cys-). Representative cell lines of each type were tested for their content of cystathionase enzyme activity by a specific catalytic assay and their total cystathionase protein content by immunoprecipitation of in vivo labeled protein. There was a close correlation between the cellular content of the enzyme as determined in the 2 assays. Specifically, those cys+ lines having readily measurable enzyme by catalytic assay contained significantly higher levels of immunoprecipitable MW 43,000 cystathionase subunit than those cys- lines tested which were depleted in active enzyme. The absolute cysteine requirement of the leukemic, cys- cell lines tested is likely due to an intracellular reduction of cystathionase protein.