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It is well known that MVA 1 is required for growth of mammalian cells (1-4) as well as constituting the key metabolite in the biosynthesis of cholesterol and a variety of nonsterol isoprenoid derivatives (e.g. dolichyl-phosphate, farnesyl pyrophosphate, isopentenyladenine, and ubiquinone). The formation of MVA from HMG-CoA, which is catalyzed by HMG-CoA reductase, is the principal regulatory step in the pathway (1). Increasing evidence suggests that the MVA-derived product critical for cell growth is an isoprene of nonsterol type (1-4).A possible mechanism for MVA-regulated cell growth is the involvement of dolichyl-phosphate in N-linked glycosylation. De novo synthesized dolichyl-phosphate acts as a carrier of oligosaccharides in the assembly of glycoproteins in the lumen of the endoplasmic reticulum (ER) (5, 6). In a recent study we investigated the potential regulatory role of N-linked glycosylation in initiation of DNA synthesis in human fibroblasts stimulated by serum (7). Our results suggested that N-linked glycosylation of proteins of 90 -240 kDa in the prereplicative phase may be critical for induction of DNA replication. These high molecular mass glycoproteins may include growth factor receptors. This raises the possibility that MVA may regulate the expression of growth factor receptors through limiting the biosynthesis of dolichyl-phosphate. The existence of such a mechanism would constitute a substantial link between HMGCoA reductase and cell growth. The aim of the present study was to investigate this issue in detail. Our experiments provide evidence that MVA is critical for the translocation of insulinlike growth factor-1 receptor (IGF-1R) to the cell surface.

Fertilization and oocyte cleavage rates have previously been demonstrated to be lower for women with endometriosis undergoing IVF compared with controls. This might be related to impaired oocyte function, possibly due to an inflammatory milieu in the pelvis of these women, where an elevated concentration of many cytokines is documented. The aim of this study was to examine whether granulosa cells from women with endometriosis deviated with respect to production of the inflammatory cytokines interleukin-1beta, interleukin-6, interleukin-8 and tumour necrosis factor alpha (TNFalpha) compared with granulosa cells from healthy women, undergoing IVF for male infertility. The effect of human chorionic gonadotrophin on cytokine production was also investigated. Granulosa cells in follicular fluid were obtained at oocyte retrieval for IVF. Incubated cell culture media were analysed by enzyme-linked immunosorbent assay. The basal production of all four cytokines was higher in cells from women with endometriosis when compared to controls, although the increase was only significant for TNFalpha. Chorionic gonadotrophin had no significant effect, although it had a tendency to suppress cytokine release in both patient categories. Whether aberrant cytokine production in granulosa cells from women with endometriosis may disturb fertilizing capacity of oocytes requires study.

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.

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