Fibronectin Stimulates Endothelial Cell ¹⁸F-FDG Uptake Through Focal Adhesion Kinase–Mediated Phosphatidylinositol 3-Kinase/Akt Signaling

¹ Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

^* To whom correspondence should be addressed. E-mail: khleenm{at}yahoo.co.kr.

	Abstract

There has been recent interest in the relationship between ¹⁸F-FDG uptake and the angiogenic activity of endothelial cells (ECs). The angiogenic process is strongly dependent on the interaction of ECs with matrix fibronectin (FN), a key regulator of EC survival, migration, and proliferation. Therefore, we investigated how FN influences EC glucose uptake and elucidated the signaling pathways that mediate this effect. Methods: Human umbilical vein ECs were allowed to adhere to FN-coated plates and were compared with control cells for ¹⁸F-FDG uptake, membrane GLUT1 levels, and hexokinase activity. The roles of focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3K), and Akt were evaluated with Western blotting, small interfering RNA (siRNA), and specific inhibitors. Results: FN adhesion significantly enhanced the protein-corrected ¹⁸F-FDG uptake in HUVEC, to 2.1-, 2.7-, and 4.3-fold that in control cells by 2, 3, and 5 d, respectively. This effect was mediated by the upregulation of both membrane GLUT1 expression and hexokinase activity and was accompanied by FAK activation. Silencing of FAK signaling by siRNA completely abrogated both FN-induced FAK phosphorylation and ¹⁸F-FDG uptake. FN also activated PI3K and Akt, well-known angiogenesis mediators, and the inhibition of either pathway totally abolished the effect of FN on ¹⁸F-FDG uptake. Nitric oxide, a downstream Akt effector that stimulates glucose uptake, was not involved in the metabolic effect of FN. Conclusion: The results of this study demonstrated that an EC–FN interaction induces strong enhancement of ¹⁸F-FDG uptake through the upregulation of GLUT1 expression and hexokinase activity. The findings also showed that the response occurs through FAK-mediated activation of PI3K and Akt, indicating a role for this pathway in modulating EC glucose metabolism.

Key Words: endothelial cell, fibronectin, ¹⁸F-FDG, angiogenesis, focal adhesion kinase