The role of PKCα and RLIP76 in transport-mediated doxorubicin-resistance in lung cancer

In deletion mutant analyses of potential phosphorylation sites in RLIP76, we identified T297 and S509 as targets for phosphorylation by PKCα. Phosphorylation at T297 increased doxorubicin (DOX)-transport activity ∼2-fold for RLIP76 purified from recombinant source, or from three small (H69, H1417, H1618) and three non-small cell, one each derived from H226 (squamous), H358 (bronchio alveolar), and H1395 (adenocarcinoma) lung cancer cell lines. T297 phosphorylation conferred sensitivity to tryptic digestion at R293. The specific activity for DOX-transport by RLIP76 purified from non-small cell, which was primarily in the phosphorylated form, was approximately twice that in small cell lung cancer cell lines. These finding offer a novel explanation for the observed intrinsic differences in sensitivity to DOX between non-small cell and small cell lung cancer cell lines.