Heat shock proteins: cellular and molecular mechanisms in the central nervous system

Nuclear Ago2/HSP60 contributes to broad spectrum of hATSCs function via Oct4 regulation

AIMS

Argonaute2 (Ago2) plays a fundamental role in microRNA-mediated gene regulation through its intrinsic endonuclease activity. In this study we demonstrate the novel functions and molecular mechanisms by which nuclear Ago2 directly regulates HSP (heat shock protein) 60 expression and stem cell self-renewal. HSP60 is a crucial regulator of ROS (reactive oxygen species), senescence, and apoptotic cell death in several tissues and cell types.

RESULTS

HSP60 is regulated via inactivation of p38/JNK and p53 and binds directly to the regulatory regions of the TERT, c-myc, GPx3, p53, and STAT3 genes. Using HSP60 CHIP-PCR experiments, we show that HSP60 binds directly to the Oct4 and Nanog genes and directly regulates Oct4 and other stemness genes involved in human adipose tissue-derived stem cell (hATSC) differentiation. HSP60 also positively regulates ROS-scavenging factors, including GPx3 and TXNL1, which directly modulate cytosolic ROS in hATSCs. Moreover, our study shows that Oct4 regulates HSP60 expression and controls hATSC survival and self-renewal after binding to the HSP60 gene. Furthermore, HSP60-mediated regulation of Oct4 contributes to neuronal and endodermal β-cell differentiation of hATSCs in vitro and in vivo and downregulates mesoderm-specific gene expression.

INNOVATION AND CONCLUSION

We show that increased levels of Ago2 or HSP60 effectively induce nuclear localization of HSP60, which directly controls Oct4, c-Myc, p53, TERT, and STAT3 for transdifferentiation programs. Collectively, we suggest a novel model in which nuclear Ago2 controls HSP60 in hATSCs.

The heat shock proteins as targets for radiosensitization and chemosensitization in cancer

The heat shock proteins (HSPs) represent a class of proteins which are induced under physiologic stress to promote cell survival in the face of endogenous or exogenous injury. HSPs function predominantly as molecular chaperones, maintaining their "client" proteins in the correct conformational state in order to withstand a biologic stressor. Elevated HSP expression is also found in a range of pathologic conditions, notably malignancy. Cancer cells exploit the pro-survival phenotype endowed by HSPs to bolster their proliferative potential. Consequently, developing means of abrogating HSP expression may provide a way to render cancer cells more susceptible to radiation or chemotherapy. Here, we review the members of the HSP class and their roles in malignancy. We focus on attempts to target these proteins, particularly the small HSPs, in developing potent radiation and chemotherapy sensitizers, as well as proposed mechanisms for this sensitization effect.

Expression of heat shock protein (HSP 72 kDa) during acute methamphetamine intoxication depends on brain hyperthermia: neurotoxicity or neuroprotection?

In the present study, light and electron microscopy were used to examine heat shock protein (HSP 72 kD) expression during acute methamphetamine (METH) intoxication in rats and evaluate its relationships with brain temperature and alterations in a number of other histochemical and morphological parameters. Freely moving rats received METH at the same dose (9 mg/kg, sc) but at different ambient temperatures (23 and 29°C), showing a wide range of brain temperature elevations (37.6-42.5°C); brains were taken for histochemical and morphological evaluations at peak of brain temperature increase. We found that acute METH intoxication induces massive and wide-spread HSP expression in neural and glial cells examined in detail in the cortex, hippocampus, thalamus, and hypothalamus. In each of these structures, the number of HSP-positive cells tightly correlated with brain temperature elevation. The changes in HSP immunoreactivity were also tightly related to alterations in permeability of the blood-brain barrier, acute glial activation, and brain edema assessed by albumin and GFAP immunoreactivity and measuring tissue water content, respectively. While robust and generalized HSP production normally appears to be the part of an adaptive brain response associated with METH-induced metabolic activation, activation of this protective mechanism has its natural limits and could not counteract the damaging effects of oxidative stress, high temperature, and edema--the leading factors of METH-induced neurotoxicity.

Anti-apoptosis and cell survival: a review

Type I programmed cell death (PCD) or apoptosis is critical for cellular self-destruction for a variety of processes such as development or the prevention of oncogenic transformation. Alternative forms, including type II (autophagy) and type III (necrotic) represent the other major types of PCD that also serve to trigger cell death. PCD must be tightly controlled since disregulated cell death is involved in the development of a large number of different pathologies. To counter the multitude of processes that are capable of triggering death, cells have devised a large number of cellular processes that serve to prevent inappropriate or premature PCD. These cell survival strategies involve a myriad of coordinated and systematic physiological and genetic changes that serve to ward off death. Here we will discuss the different strategies that are used to prevent cell death and focus on illustrating that although anti-apoptosis and cellular survival serve to counteract PCD, they are nevertheless mechanistically distinct from the processes that regulate cell death.