Bleomycin treatment of A549 human lung cancer cells results in association of MGr1-Ag and caveolin-1 in lipid rafts

Bleomycin treatment of A549 cells induces senescence rather than apoptosis, a more usual response of cancer cells to cytotoxic drugs. We have previously shown that upregulation of caveolin-1, the main structural component of caveolae, plays a key role in this process. In order to gain a better understanding of the molecular basis of this phenomenon, caveolin-1-enriched microdomains of untreated and bleomycin-treated growth-arrested A549 cells were analysed for differential protein expression using 2-D DIGE followed by LC-MS/MS. One of these differentially expressed proteins was found to be the multidrug resistance-associated protein (MGr1-Ag). We show that MGr1-Ag becomes partly localised in lipid rafts following bleomycin treatment, and that MGr1-Ag and caveolin-1 occur in a common protein complex in vivo using co-immunoprecipitation studies. GST pull-down assays demonstrated an increased interaction between MGr1-Ag and caveolin-1 following bleomycin treatment in vitro. Our results reveal MGr1-Ag as a novel lipid raft protein; its increased association with caveolin-1 in bleomycin-induced cell cycle arrest and subsequent cellular senescence might contribute to the success of chemotherapy.