Bcl-2 differentially targets K-, N-, and H-Ras to mitochondria in IL-2 supplemented or deprived cells: implications in prevention of apoptosis.

IL-2 deprivation triggers apoptosis in the murine T cell line TS1alphabeta, a process that can be blocked by overexpression of Bcl-2. Here we show that Bcl-2 and Ras proteins interact in mitochondria from TS1alphabeta cells in the presence or absence of IL-2, as evidenced by co-immunoprecipitation. All three Ras proteins, K-, N- and H-Ras, interact with Bcl-2; however, their mitochondrial localization is differentially regulated in IL-2-supplemented or -deprived cells. K-Ras is found in mitochondria only in IL-2-supplemented cells, whereas H-Ras is observed in mitochondria only after IL-2 withdrawal. N-Ras is detected in mitochondria under both experimental conditions. Bcl-2 transfection partially restored K- and N-Ras association with mitochondria in IL-2-deprived cells and rendered H-Ras association independent of IL-2 withdrawal. Inhibitors of Ras posttranslational processing did not alter the IL-2-induced differential pattern of mitochondrial localization. The processed forms of K- and N-Ras associated with mitochondria, although unprocessed H-Ras was also detected in mitochondria from mevastatin-treated cells. These results evidence a distinct behavior among the three Ras proteins in TS1alphabeta cells, depending on IL-2 supply, and suggest homologue-specific roles for Ras proteins in IL-2-dependent events.