Doxorubicin (DOX) and its derivatives are used as chemotherapeutic drugs to treat
cancer patients. However, production of DOX-mediated
reactive oxygen species (ROS) by prolonged use of these drugs has been found to cause dilative
cardiomyopathy and
congestive heart failure. Thus various preventive modalities have been developed to avoid this side effect. We have found that the DOX-mediated
oxidant-induced toxicity in cardiac cells could be minimized by
hyperthermia-induced small heat shock protein 27 (HSP27); that is, this
protein acts as an
endogenous antioxidant against DOX-derived
oxidants such as H(2)O(2). Heat shock-induced HSP27 was found to act as an antiapoptotic
protein (reducing ROS and Bax-to-Bcl2 ratio) against DOX, and its phosphorylated
isoforms stabilized
F-actin remodeling in DOX-treated cardiac cells and, hence, attenuated the toxicity.
Protein kinase assays and proteomic analyses suggested that higher expression of HSP27 and its phosphorylation are responsible for the protection in heat-shocked cells. Two-dimensional gel electrophoresis showed six
isoforms (nonphosphorylated and phosphorylated) of HSP27. Matrix-assisted
laser desorption/ionization time of flight analyses showed alpha- and beta-
isoforms of HSP27, which are phosphorylated by various
protein kinases. Ser(15) and Ser(85) phosphorylation of HSP27 by MAPK-assisted
protein kinase 2 was found to be the key mechanism in reduction of apoptosis and facilitation of
F-actin remodeling. The present study illustrates that
hyperthermia protects cells from DOX-induced death through induction and phosphorylation of HSP27 and its antiapoptotic and actin-remodeling activities.