Geranylgeranyltransferase type I (GGTase-I) deficiency hyperactivates macrophages and induces erosive arthritis in mice
Omar M. Khan, … , Maria Bokarewa, Martin O. Bergo
Omar M. Khan, … , Maria Bokarewa, Martin O. Bergo
Published January 25, 2011
Citation Information: J Clin Invest. 2011;121(2):628-639. https://doi.org/10.1172/JCI43758.
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Research Article

Geranylgeranyltransferase type I (GGTase-I) deficiency hyperactivates macrophages and induces erosive arthritis in mice

Abstract

RHO family proteins are important for the function of inflammatory cells. They are modified with a 20-carbon geranylgeranyl lipid in a process catalyzed by protein geranylgeranyltransferase type I (GGTase-I). Geranylgeranylation is viewed as essential for the membrane targeting and activity of RHO proteins. Consequently, inhibiting GGTase-I to interfere with RHO protein activity has been proposed as a strategy to treat inflammatory disorders. However, here we show that mice lacking GGTase-I in macrophages develop severe joint inflammation resembling erosive rheumatoid arthritis. The disease was initiated by the GGTase-I–deficient macrophages and was transplantable and reversible in bone marrow transplantation experiments. The cells accumulated high levels of active GTP-bound RAC1, CDC42, and RHOA, and RAC1 remained associated with the plasma membrane. Moreover, GGTase-I deficiency activated p38 and NF-κB and increased the production of proinflammatory cytokines. The results challenge the view that geranylgeranylation is essential for the activity and localization of RHO family proteins and suggest that reduced geranylgeranylation in macrophages can initiate erosive arthritis.

Authors

Omar M. Khan, Mohamed X. Ibrahim, Ing-Marie Jonsson, Christin Karlsson, Meng Liu, Anna-Karin M. Sjogren, Frida J. Olofsson, Mikael Brisslert, Sofia Andersson, Claes Ohlsson, Lillemor Mattsson Hultén, Maria Bokarewa, Martin O. Bergo

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Figure 4

GGTase-I–deficient macrophages exhibit increased activation of proinflammatory signaling pathways.

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GGTase-I–deficient macrophages exhibit increased activation of proinflam...
(A) ROS production was measured in real time after stimulation of BM macrophages with 50 μM PMA. Total ROS production in BM macrophages is also shown (n = 11 per genotype). (B) Western blots of lysates from BM macrophages showing basal and LPS-stimulated p38 phosphorylation. Also shown are levels of phospho-p38 as determined by densitometry, expressed relative to unstimulated Pggt1bfl/+LC BM macrophages (n = 5 per genotype). (C) Western blot of lysates from basal and LPS-stimulated BM macrophages with an antibody to phospho-p65 subunit of NF-κB. Actin was used as a loading control. Lanes were run on the same gel but were noncontiguous (white line). (D) NF-κB p65 activity assay of lysates of BM macrophages (n = 5 per genotype). (E) Data from low-density QPCR array showing the relative change in expression of 15 NF-κB–regulated genes in LPS-stimulated Pggt1bfl/flLC compared with Pggt1bfl/+LC BM macrophages (n = 6 per genotype). (F) Data from low-density QPCR array using the same cDNA as in E, showing the relative change in expression of 8 genes involved in extracellular matrix remodeling and cell adhesion (n = 6 per genotype). Data in E and F are expressed as means. (G) Cytokine concentrations in medium of BM macrophages before and after LPS stimulation (n = 4–6 per genotype, assayed in duplicate). *P < 0.05, ***P < 0.001 versus Pggt1bfl/+LC.