Chaperones assist in the correct folding of newly synthesised proteins in the endoplasmic reticulum (ER) of cells, this being essential for the translocation of protein molecules to specific subcellular compartments, extracellular matrix or to biological fluids. The biosynthesis of some ER chaperones is regulated by glucose. They are named "glucose-regulated proteins" (GRPs). The function of some GRPs depends on oxygen, a subgroup named "oxygen-regulated proteins" (ORPs). The biosynthesis of ORPs is induced by deprivation of glucose or oxygen. Exposure of HeLa cells to glucose starvation induces the biosynthesis of various GRPs including ORP 150. The expression of ORP 150 is regulated by the concentration of glucose in the culture medium, being induced by a shortage and repressed by a presence of glucose. We have shown that both glucose starvation and transfection of cells with siRNA (specific to ORP 150 mRNA) evoke similar, but quantitatively different, effects. The cells grown for 72 h in a 4.5 mg/ml glucose-containin medium demonstrated low apoptosis (3.7%) whereas in a 0.5 mg/ml glucose-containing medium the apoptosis was increased to 10%. The effect of transfection on apoptosis was distinctly higher with almost 22% of apoptotic cells detected in 72 h cultures. One may conclude that ORP 150 reduces the pro-apoptotic effects of glucose starvation. Such a hypothesis is supported by the observation that the transfection procedure makes HeLa cells resistant to the regulatory effect of glucose on ORP 150 production. The transfected cells do not respond to glucose starvation with an overexpression of ORP 150. It is apparent from our experiments that ORP 150 plays an important role in adaptation of cells to the shortage of glucose and reduces the pro-apoptotic effect of glucose starvation. (c) 2005 Elsevier Inc. All rights reserved.