RESUMO
Having found previously that leukemic cells with multidrug resistant (MDR) phenotype, but not their sensitive counterparts, exhibit collateral sensitivity to cold stress in a P-gp-dependent manner, our aim was to study the signaling pathways involved in this phenomenon in sensitive (L1210) and resistant cells (L1210R and CBMC-6). It was observed that the acquisition of MDR phenotype by leukemic cells or their transfection with the extrussion pump, P-gp, modifies the activation profile and regulation of Mitogen-Activated Protein Kinases (MAPK) in cells exposed to low temperatures. More specifically, cold stress provoked the activation of c-Jun N-terminal kinase (JNK) in sensitive cells, while attenuated JNK signaling was observed in MDR cells. This effect was also observed, although with less intensity, in P-gp-transfected cells. Using pharmacological inhibitors to determine the role of MAPK in leukemic cell survival in physiological conditions or under cold stress, a dual temperature-dependent role was observed for JNK in MDR cell survival. At 37°C JNK is necessary for the survival of parental, resistant and P-gp-transfected cells; however, the use of inhibitors of either extracellular signal-regulated protein kinase (ERK) or JNK significantly counteracts cold-induced death of resistant and P-gp-transfected cells, supporting a role for ERK and JNK in cold-stress induced cell death. Finally, a connectivity model concerning MAPK is proposed, summarizing how cold stress and MDR-1 might trigger apoptosis in resistant cell lines. These findings on MDR cells may assist in the design of specific therapeutic strategies to complement current chemotherapy.