Mevalonate-regulated mechanisms in cell growth control: role of dolichyl phosphate in expression of the insulin-like growth factor-1 receptor (IGF-1R) in comparison to Ras prenylation and expression of c-myc.
One or more mevalonate derivatives of non-sterol type have been proposed to be of indispensable importance for cell growth. Conceivable mevalonate-dependent mechanisms involved in growth control are farnesylation of Ras proteins, regulation of c-myc expression, and N-linked glycosylation of the IGF-1 receptor. The latter mechanism might be rate-limited by dolichyl phosphate, which acts as a donor of oligosaccharides in glycoprotein synthesis in the endoplasmic reticulum. In order to study the significance for cell proliferation of the three aforementioned mevalonate-dependent processings, their inhibitory response due to mevalonate deprivation was explored and compared with the effect on DNA synthesis in the malignant melanoma cell line SK-MEL-2. We found that mevalonate depletion due to treatment with 3 microM lovastatin for 24 h, which efficiently growth-arrested the cells, hardly at all affected the expression of c-myc, and although Ras prenylation was inhibited by 50%, the most pronounced effect of lovastatin was seen on N-linked glycosylation of IGF-1 receptors, which was inhibited by more than 95%. The order and magnitude of the decreased IGF-1 receptor glycosylation, which was followed by a decreased expression of IGF-1 receptors at the cell membrane, correlated well with the inhibition of DNA synthesis. We investigated whether dolichol, and in particular dolichyl phosphate, through its participation in N-linked glycosylation, act as regulators of IGF-1 receptor expression. First, we could confirm that exogenous dolichol became phosphorylated and in this form took part in the glycosylation processing. Secondly, we showed that dolichyl phosphate, in a dose-dependent manner, could increase the number of IGF-1 receptors at the cell membrane, simultaneously as DNA synthesis was stimulated. Taken together, our results provide direct evidence for an important role of dolichyl phosphate as a regulator of cell growth through limiting N-linked glycosylation of the IGF-1 receptor.
Dricu
A
A
Department of Tumor Pathology, Karolinska Institutet, Stockholm, Sweden.
Wang
M
M
Hjertman
M
M
Malec
M
M
Blegen
H
H
Wejde
J
J
Carlberg
M
M
Larsson
O
O
D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism; D003110:Colonic Neoplasms; D004273:DNA, Neoplasm / Q000096:biosynthesis / Q000187:drug effects; D004288:Dolichol Phosphates / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007700:Kinetics; D008148:Lovastatin / Q000494:pharmacology*; D008545:Melanoma; D008798:Mevalonic Acid / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism; D016133:Polymerase Chain Reaction; D017368:Protein Prenylation; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis* / Q000378:metabolism; D012878:Skin Neoplasms; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000378:metabolism*
D004273:DNA, Neoplasm; D004288:Dolichol Phosphates; D009363:Neoplasm Proteins; C028306:dolichol monophosphate; D008148:Lovastatin; D017526:Receptor, IGF Type 1; D018631:ras Proteins; D008798:Mevalonic Acid