PHORBOL ESTER-INDUCED MEMBRANE-PROTEINS IN CHRONIC LEUKEMIC B-LYMPHOCYTES - CANDIDATE PROTEINS FOR THE L-SYSTEM AMINO-ACID TRANSPORTER

Chronic lymphocytic leukemia (CLL) B-lymphocytes have markedly diminis hed membrane L-system amino acid transport as compared with normal mat ure B- and T-lymphocytes. L-system functional recovery is induced in C LL B-cells by the maturational agent, 12-O-tetradecanoylphorbol-13-ace tate ( TPA). The studies reported here extend the analysis of CLL B-ce ll maturation by comparing membrane protein expression in untreated an d TPA-treated CLL B-cells, with the identification of candidate protei ns for the L-system transporter. Cell membrane proteins of resting and TPA-treated CLL B-lymphocytes were studied using ultra-high resolutio n giant two-dimensional gel electrophoresis. Cellular proteins were me tabolically labeled with [S-35]methionine, and, in separate experiment s, membrane proteins were photoaffinity labeled with [I-125] iodoazido phenylalanine, an amino acid transported by the L-system and which bin ds at or near the L-system transport carrier. In a partially purified membrane preparation, approximately 1400 proteins were identified by m etabolic labeling. Following TPA treatment for 17 h, 14 new metabolica lly labeled membrane proteins were identified, and five of these also were labeled by the L-system photoprobe. Photolabeling of four of thes e proteins was inhibited by an excess of the L-system prototype amino acid, 2-aminobicyclo(2.2.1)heptane-2-carboxylic acid. Given these labe ling characteristics, one or more of these four proteins may be relate d to the L-system amino acid transport carrier.