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.
View: Text | PDF
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

×

Figure 3

Knockout of GGTase-I results in accumulation of GTP-bound RHO family proteins and has little effect on the subcellular localization of RAC1.

Options: View larger image (or click on image) Download as PowerPoint
Knockout of GGTase-I results in accumulation of GTP-bound RHO family pro...
(A–C) Western blots show levels of GTP-bound and total RAC1 (A), CDC42 (B), and RHOA (C) in lysates from BM macrophages. Actin was used as a loading control. Corresponding graphs show the amount of GTP-bound RAC1 (n = 7), CDC42 (n = 2), and RHOA (n = 4) determined by densitometry. Reduced electrophoretic mobility of affinity-purified RAC1 in lysates from Pggt1bfl/flLC macrophages (run on 12% Protean gels) is also shown in A. (D) Western blots showing the distribution of RAC1, CDC42, RHOA, and np-RAP1A in the cytosol (C), membrane (M), and nuclear (N) fractions of BM macrophages. RHO-GDI, β1-integrin, and lamin A/C were used as markers for cytosol, membrane, and nuclear fractions, respectively. (E) Confocal micrographs showing immunohistochemical staining of BM macrophages with antibodies against RAC1 and Na/K-ATPase. Arrowheads indicate RAC1 at filopodia at the plasma membrane. Scale bars: 10 μm. (F) Immunoprecipitation of RHO-GDI in lysates of BM macrophages followed by Western blot for RAC1, CDC42, and RHOA. Levels of RHO-GDI–bound RAC1 (n = 4), CDC42 (n = 2), and RHOA (n = 4), as determined by densitometry, are also shown. Lanes were run on the same gel but were noncontiguous (white line). (G) Accumulation of unprocessed GGTase-I substrates susceptible to in vitro prenylation by 3H-GGPP and recombinant GGTase-I. The experiment was repeated twice with similar results.