Translocation of cytoplasmic HSP70 onto the surface of EL‐4 cells during apoptosis

Abstract

Heat shock proteins (HSPs) are involved in a variety of intracellular processes and can have both pro- and anti-apoptotic action. However, little is known about the role of HSPs in the progression of apoptosis. Translocation of HSPs to the surface of apoptotic cells is a previously observed phenomenon demonstrating participation of these proteins in execution of the terminal stages of apoptosis. In a previous study we showed that development of EL-4 lymphoma cell apoptosis in vitro is accompanied by elevation of surface HSP expression. In this study we used this model to analyse the relationship of HSP70 expression and its translocation to the cell surface during apoptosis with some key intracellular events. Our data demonstrate a synchronization of surface and intracellular HSP70 expression with bcl-2 expression, intracellular reactive oxygen species (ROS) concentration and caspase-3 activity. A maximum level of surface and intracellular HSP70 expression was observed at an irreversible phase of EL-4 cell apoptosis after mitochondrial potential depolarization. In addition, an enhancement of the relative level of cytoplasmic HSP70 translocation to the cell surface was concomitant with EL-4 cell apoptosis. However, the size of surface and intracellular pools of HSP70, increasing for initial and intermediate stages of cell death, decreased at the terminal phase of apoptosis. Western blot analysis of HSP70 in conditioned supernatant obtained from EL-4 cell tissue showed that the observed decrease of HSP70 cell content might be due to surface HSP70 shedding into the intercellular space.

Heat Shock 70‐kDa Protein 8 Isoform 1 Is Expressed on the Surface of Human Embryonic Stem Cells and Downregulated upon Differentiation

“…Originally, HSPs were known to play an important role in chaperoning by transiently associating with nascent polypeptides to facilitate correct folding in the cytoplasm and nucleus [35]. However, recently it has been demonstrated that HSP70 does occur on the surface of a number of cell types [25,26,[36][37][38][39][40][41][42]. In most studies, the extracellular presence of HSP70 was considered to be the outcome of necrotic or apoptotic cell death of neighboring cells, but recent evidence strongly supports active release of HSP70s from cells in response to stresses, including cytokines, acute psychological stress, and exercise [43,44].…”

“…As HSP70 was expressed on the surface of several cancer cell lines [25,26,[36][37][38][39][40][41][42], we examined the surface expression of the HSPA8 protein in some cancer cell lines by flow cytometry. As in Miz-hES1, we could observe its surface expression in Choi-CK, SH-J1, and HeLa cells.…”

Global Profiling of the Cell Surface Proteome of Cancer Cells Uncovers an Abundance of Proteins with Chaperone Function

“…been demonstrated that HSP70 does occur on the surface of a number of cell types (37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48). However, our ability to comprehensively profile cell surface proteins has uncovered the high abundance of heat-shock proteins compared with other cell surface proteins.…”

Roles of Heat Shock Proteins and γδT Cells in Inflammation

“…Although Hsp70 expression by PMN requires de novo protein synthesis and the transport of the protein to the cell surface (7), the question of whether this mechanism is universal for surface expression of Hsp in other cells as well remains to be investigated. Several studies have shown that cells can externalize Hsp molecules during apoptotic transformation (23)(24)(25). Another possible mechanism is through the binding of Hsp molecules that are produced by other cells.…”