Chaperone Proteins Involved in Troglitazone-Induced Toxicity in Human Hepatoma Cell Lines

Abstract

Troglitazone (TRO), an effective thiazolidinedione antidiabetic agent, was reported to produce idiosyncratic hepatotoxic effects in some individuals. In contrast, rosiglitazone (RSG), in the same group of agents, has no significant toxic effects and now is widely used. In this study, human hepatoma (HepG2) cell lines were exposed to various doses of TRO as well as RSG (0, 25, 50, and 75 microM) for 48 h. Cell lysates were separated by two-dimensional electrophoresis, and the gels were stained with coomassie brilliant blue to compare the spot profiles. The greatest protein expression at a MW of 75 kDa and isoelectric point of 5 was specifically increased with TRO treatments of 50 and 75 microM. The spot was identified as a mixture of immunoglobulin heavy chain binding protein (BiP) and, to a lesser extent, protein disulfide isomerase-related protein (PDIrp). Immunoblot analyses showed that the BiP protein was dose-dependently increased by TRO treatment and, to a lower degree, by RSG. These effects were also correlated with the high induction of BiP mRNA by TRO (50 and 75 microM) and the lower induction by RSG. However, both treatments showed no significant effects on PDIrp expression. The toxic effects of TRO in relation to the overexpression of BiP were also demonstrated in HLE cells, another human hepatoma cell line. In HLE cells, the inhibition of BiP expression by small interference RNA rendered cells more susceptible to the toxic effects of TRO. These results suggest that the overexpression of BiP is a defense mechanism of the endoplasmic reticulum in response to TRO-induced toxicity.

Activation of the Unfolded Protein Response Is Associated with Favorable Prognosis in Acute Myeloid Leukemia

“…Induction of these endoplasmic reticulum chaperones is crucial for cell survival by re-establishing correct folding of proteins, preventing their aggregation and ultimately protecting cancer cells against endoplasmic reticulum stress-induced apoptosis (14,15). GRP78 expression was reported to be induced in a variety of human solid tumors (16)(17)(18)(19)(20)(21)(22)(23), whereas its expression in hematologic malignancies has not been investigated thus far. Here, we observed that malignant cells from AML patients with activated unfolded protein response expressed higher GRP78 and CHOP levels.…”

PGJ2-stimulated β-cell apoptosis is associated with prolonged UPR activation

“…The attenuation of protein synthesis is one hallmark of UPR activation, as ER stress stimulates eIF2␣ phosphorylation, resulting in a translational blockade (21)(22)(23). It has now been reported in a number of cell types that PGJ 2 is capable of stimulating the expression of ER stress-responsive genes such as CHOP and glucose-regulated protein 78 (BiP), the phosphorylation of eIF2␣, and the attenuation of translation (19,38,48,55).…”

Troglitazone

“…This results in the accumulation of incompletely folded proteins and activates the transcription of ER chaperone genes (Liu et al 1998;Lodish and Kong 1990). We found that troglitazone treatment of hepatoma cell lines led to overexpression of immunoglobulin heavy chain binding protein (BiP), an abundant chaperone protein in the ER (Maniratanachote et al 2005a). The important role of this chaperone protein was indicated by the phenotypic change in cell viability when BiP expression was inhibited by small interference RNA (Maniratanachote et al 2005a).…”