Modulation of endogenous FPP synthase causes bisphosphonate resistance in cultured cells
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1
University of Aberdeen, United Kingdom
Nitrogen containing bisphosphonates (N-BPs), such as zoledronic acid (ZOL), are potent inhibitors of osteoclast function and act by preventing the post-translational prenylation of small GTPase signalling proteins such as Rap1A. Isoprenoid lipids, required for prenylation, are generated via the mevalonate pathway which is also responsible for cholesterol biosynthesis. Farnesyl diphosphate (FPP) synthase, a key enzyme in this pathway, is the molecular target for N-BPs and it is likely that modulation of FPP synthase expression may affect flux through the pathway and therefore levels of prenylated proteins within cells. In cell culture, N-BPs can affect many cell types but there is variability between different cells in the sensitivity to N-BPs observed. In addition, not all patients respond in the same way to N-BP therapy and it has been reported that some patients develop resistance. It is not known if upregulation of FPP synthase may contribute to the variability in sensitivity to N-BPs or, indeed to this resistance. Since sterol deficiency induces SRE-mediated upregulation of FPP synthase we postulate that upregulation of endogenous FPP synthase in cultured cells in the presence of lipoprotein depleted serum (LDS) would reduce the effectiveness of N-BP treatment. {BR}When HeLa cells were treated with 2 micromolar or more ZOL for 24 hours in 10% foetal calf serum, unprenylated Rap1A could be detected by western blot analysis and the levels of FPP synthase mRNA and protein remained unchanged, which was probably as a result of the presence of exogenous sterols in the culture medium. However, in the presence of 10% LDS for 48 hours, both the FPP synthase mRNA and protein levels increased by at least 3 fold and unprenylated Rap1A was not detected following treatment with up to 10 micromolar ZOL indicating resistance to ZOL due to upregulation of FPP synthase. Therefore, sterol mediated upregulation of FPP synthase is a model for observing N-BP resistance, but it remains to be determined whether such regulation could occur in different cell types, including osteoclasts, in vivo and whether this could explain some of the variability in response to N-BP treatment in the clinic.
Keywords:
Bones,
Bone Research
Conference:
2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society, Cambridge, United Kingdom, 27 Jun - 29 Jun, 2011.
Presentation Type:
Oral Poster
Topic:
Abstracts
Citation:
Das
S,
Crockett
J and
Rogers
M
(2011). Modulation of endogenous FPP synthase causes bisphosphonate resistance in cultured cells.
Front. Endocrinol.
Conference Abstract:
2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society.
doi: 10.3389/conf.fendo.2011.02.00012
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Received:
30 Sep 2011;
Published Online:
30 Sep 2011.
*
Correspondence:
Mr. S Das, University of Aberdeen, United Kingdom, r08sd9@abdn.ac.uk