Glucose depletion accounts for the induction of two transformation-sensitive membrane proteinsin Rous sarcoma virus-transformed chick embryo fibroblasts.

Abstract

Chick embryo fibroblasts transformed by Rous sarcoma virus have an increased content of two membrane proteins of molecular weights 78,000 and 95,000. The increased content of the 95,000-dalton protein and the principal increase in the content of the 78,000-dalton protein are not an early consequence of cell transformation but instead are secondary to the rapid depletion of glucose from the growth medium of transformed cells. When glucose is maintained at high levels in the growth medium of transformed cells, the synthesis of the 95,000-dalton protein is arrested and that of the 78,000-dalton protein is markedly suppressed. Upon removal of glucose from the growth medium of normal cells, these proteins increase to levels comparable to those of transformed cells.Because the amount of these two proteins is influenced by the presence or absence of glucose, we suggest they be referred to as "glucose-regulated proteins," GRP-78 and GRP-95. These proteins may have an important role in regulating the utilization of glucose in cultured cells.Major differences in the composition of cell membrane proteins have been observed for fibroblastic cells transformed by various oncogenic viruses (1-5). For example, chick embryo fibroblasts (CEF) transformed by various strains of Rous sarcoma viruses (RSV) show a substantial decrease in the content of a major cell surface glycoprotein (CSP) with a molecular weight of about 220,000 (2, 3) and a significant increase in two other plasma membrane-associated proteins of molecular weights approximately 90,000 and 75,000 (4, 5). Because alterations of membrane protein composition are associated with the process of malignant transformation, these proteins could have a causative role in transformation. The 220,000 CSP is involved in determining the altered adhesive properties and morphology of transformed chick and other cells (6, 7) but apparently does not have a role in loss of growth control. The biological significance of the changes in the 90,000 and 75,000 membrane proteins and the mechanism by which these alterations take place are unknown.This report presents evidence to suggest that the major increase in the 75,000 and 90,000 cell membrane proteins is not an early consequence of cell transformation but is secondary to rapid depletion of glucose from the medium by RSV-transformed cells. When a high level of glucose is maintained in the growth medium, transformed CEF exhibit low levels of these two proteins. Furthermore, when glucose is removed from the growth medium, normal nontransformed CEF increase their content of these two proteins. Because the synthesis of these two proteins is controlled by glucose, we suggest these proteins be designated "glucose-regulated proteins" (GRP). METHODSCells. CEF were cultivated, propagated, and infected with Schmidt-Ruppin (SR) and Bryan high-titer (BH) strains of RSV as described (8, 9). Subconfluent cells were used in this study.Preparation of Membranes of CEF. Membrane ghosts of normal and transformed CEF were prepared by using a twophas...

Evidence for role of glycoprotein carbohydrates in membrane transport: specific inhibition by tunicamycin.

“…After 24 hr of pretreatment with tunicamycin, there was a significant decrease in the fibronectin band, as we had reported previously (3), but the most apparent alterations were the marked increases of two' major polypeptide bands of apparent molecular weights of 95,000 and 75,000 in homogenates of tunicamycin-treated cultures. The electrophoretic mobilities of these bands are identical to those of the "glucose/glycosylation regulated proteins" (GRP) induced in chick cells subjected to glucose starvation or inhibition of glycosylation (23,24).…”

“…Secondary or tertiary CEF were grown for 24 hr in the presence or absence of tunicamycin (0.05 ,4g/ml or 50 nM) in 35-mm plastic tissue culture dishes (Costar) as described (11).…”

Rapid purification of mammalian 70,000-dalton stress proteins: affinity of the proteins for nucleotides.

“…4D). As we and others have shown, the 80-kDa stress protein is synthesized at high levels in cells either deprived of glucose (i.e., it is one of the so-called glucose-regulated proteins) or in cells treated with the calcium ionophore A23187 (9,10,18,25,26). Indirect immunofluorescence studies with a polyclonal antibody raised against the 80-kDa protein have shown the MOL.…”

The relation between ER stress and HLA-B27 misfolding

“…The inhibitory molecule, Grp78, was first discovered in fibroblastic glucose-free cell culture medium [8]. Grp78 is also referred as immunoglobulin binding protein (BiP) [9].…”