Mitochondrial functions play a central role in energy metabolism and provide survival fitness to both normal and tumor cells. Mitochondrial chaperonin Hsp60 is involved in both pro- and anti-apoptotic functions, but how Hsp60 senses the mitochondria selective oxidative stress response is unknown. In this study, by using rotenone, an irreversible inhibitor of oxidative phosphorylation against IMR-32 and BC-8 tumor cells containing differential heat shock transcriptional machinery, we studied whether the oxidative stress response is related to Hsp60. The accelerated cytotoxicity in response to rotenone has been correlated with enhanced production of O2•−, H2O2, reactive oxygen species, and Hsp60 translocation from the mitochondria to the cytoplasm. The inability of cells to resist oxidative stress mediated Hsp60 translocation appeared to depend on mitochondrial oxyradical scavenging system and Bax translocation. A delayed oxidative stress response in hsp60 shRNA-treated cells was found to be due to increased mitochondrial translocation of Hsp60 on shRNA pre-sensitization. Overexpression of Hsp60 failed to protect cells from oxidative stress due to a lack of its mitochondrial retention upon post-rotenone treatment. These results also revealed that Hsp60 mitochondrial localization is indispensable for decreasing O2•− levels, but not H2O2 and ROS levels. However, cycloheximide treatment alone induced Hsp60 translocation, while rotenone combination delayed this translocation. In contrast to oxidative stress, MG132 and 17AAG treatments showed mitochondrial retention of Hsp60; however, MG132 combination either with hsp60 shRNA or 17AAG induced its translocation. Additionally, overexpression of Huntingtin gene also resulted in Hsp60 mitochondrial accumulation. We suggest that Hsp60 may act as a barrier to pharmacological targeting of mitochondria.

Mitosis-targeted anti-cancer therapies gained much attention in recent years. However, lack of tumor selectivity poses limitations to the current anti-mitotic drugs to be used as broad-spectrum anti-cancer agents. In this study, we show that combination treatment of colcemid, an inhibitor of microtubule polymerization with geldanamycin, an inhibitor of cancer chaperone, Hsp90 irreversibly targets mitosis through mitotic kinase bubR1 stabilization. When the individual and combination drugs treatments were tested against tumor cells (IMR-32 and HeLa) and non-tumor cells (SRA01), the combination treatment showed significant increase in cytotoxicity only in tumor cells followed by G2/M cell cycle block. The IMR-32 cells showed enhanced cytotoxicity in response to combination treatments, compared to HeLa cells. Further studies revealed that the G2/M arrest in IMR-32 correlates with both increased bubR1 nuclear localization and metaphase arrest. The siRNA knockdown of bubR1 has decreased tumor cell response to geldanamycin suggesting Hsp90-dependent regulation of bubR1. The combination treatment also showed inactivation of non-canonical β-catenin signaling suggesting inhibition of cancer growth. In addition, the combination treatment has significantly affected the distribution and functions of bubR1 downstream mitotic kinases such as aurks and plk1 indicating the combinatorial attack of combination treatment. In conclusion, we demonstrate that colcemid and GA combination treatment compromises the division potential of tumor cells interfering with the mitosis through bubR1 kinase.

non disponibile