H2O2 mediated MAPK-mTOR crosstalk determines the XIAP and FLIP degradation pathways and development of resistance to Imatinib

Abstract

Abnormal or aggregated proteins degradation is very crucial to protect the cell against proteotoxic stress. Cellular proteins are usually degraded in a ubiquitin-dependent manner by proteasomes and macro-autophagy/autophagy. Both processes use ubiquitin, binding of which target them to proteasomes via ubiquitin-like domains or to phagophores (the precursors to autophagosomes) via Atg8/LC3 binding motifs. Since both pathways use ubiquitin, the question that arises is how degradative pathway choice is achieved. Here in this paper, we have shown that mTOR pathway acts as major player in deciding which degradation pathway to choose. Here, we used Imatinib resistant (K562R) and Imatinib-sensitive (K562S) K562 cell as our previous study showed that Ubiquitin-proteasome pathway is selected for degradation of two proteins XIAP and FLIP in Imatinib-resistant K562 cells. H2O2 treatment in K562R cells degrades XIAP and FLIP via proteasomal pathway whereas H2O2 degrades them via lysosomal pathway in K562S cells. We found H2O2 mediated mTOR activation suppressed autophagy pathway in K562R cells and protein takes proteasomal degradation rout. However, proteins get degraded via autophagy when mTOR remains suppressed in K562S cells. We also found that H2O2-mediated activation of activation of ERK in turn activated mTOR in K562R cells because ROS inhibited ERK phosphorylation and thus mTOR remained inhibited in K562S cells. Moreover, we found that endogenous H2O2 levels are way higher in K562R cells than in K562S cells. Finally, and most interestingly, our data clearly suggested that activation of mTOR is responsible for developing resistance to Imatinib in K562R cells. Thus, this paper delineates a very crucial role of H2O2 and mTOR in both the selection of protein degradation pathway and development of drug resistant.