Expression of the insulin-like growth factor 1 receptor (IGF-1R) in breast cancer cells: evidence for a regulatory role of dolichyl phosphate in the transition from an intracellular to an extracellular IGF-1 pathway.
In this study we provide evidence that the low expression of IGF-1R at the cell surface of estrogen-independent breast cancer cells is due to a low rate of de novo synthesis of dolichyl phosphate. The analyses were performed on the estrogen receptor-negative breast cancer cell line MDA231 and, in comparison, the melanoma cell line SK-MEL-2, which expresses a high number of plasma membrane-bound IGF-1R. Whereas the MDA231 cells had little or no surface expression of IGF-1R, they expressed functional (i.e., ligand-binding) intracellular receptors. By measuring the incorporation of [3H]mevalonate into dolichyl phosphate, we could demonstrate that the rate of dolichyl phosphate synthesis was considerably lower in MDA231 cells than in SK-MEL-2 cells. Furthermore, N-linked glycosylation of the alpha-subunit of IGF-1R was 8-fold higher in the melanoma cells. Following addition of dolichyl phosphate to MDA231 cells, N-linked glycosylation of IGF-1R was drastically increased, which in turn was correlated to a substantial translocation of IGF-1R to the plasma membrane, as assayed by IGF-1 binding analysis and by Western blotting of plasma membrane proteins. The dolichyl phosphate-stimulated receptors were proven to be biochemically active since they exhibited autophosphorylation. Under normal conditions MDA231 cells, expressing very few IGF-1R at the cell surface, were not growth-arrested by an antibody (alphaIR-3) blocking the binding of IGF-1 to IGF-1R. However, after treatment with dolichyl phosphate, leading to a high cell surface expression of IGF-1R, alphaIR-3 efficiently blocked MDA231 cell growth. Taken together with the fact that the breast cancer cells produce IGF-1 and exhibit intracellular binding, our data suggest that the level of de novo -synthesized dolichyl phosphate may be critical for whether the cells will use an intracellular or an extracellular autocrine IGF-1 pathway.
Dricu
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Cellular and Molecular Tumor Pathology, CCK, R8:04, Karolinska Hospital, S-17176, Stockholm, Sweden.
Kanter
L
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Wang
M
M
Nilsson
G
G
Hjertman
M
M
Wejde
J
J
Larsson
O
O
D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D004288:Dolichol Phosphates / Q000096:biosynthesis / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D014415:Tunicamycin / Q000494:pharmacology
D004288:Dolichol Phosphates; D014415:Tunicamycin; C028306:dolichol monophosphate; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1