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Vol. 19, Issue 3, 1261-1270, March 2008

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Role of Epac1, an Exchange Factor for Rap GTPases, in Endothelial Microtubule Dynamics and Barrier Function

Seema Sehrawat^*,, Xavier Cullere^*,, Sunita Patel, Joseph Italiano, Jr., and Tanya N. Mayadas^*

*Center of Excellence in Vascular Biology, Department of Pathology, and Translational Medicine Division, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115

Submitted November 1, 2006; Revised December 10, 2007; Accepted December 26, 2007
Monitoring Editor: Asma Nusrat

Rap1 GTPase activation by its cAMP responsive nucleotide exchange factor Epac present in endothelial cells increases endothelial cell barrier function with an associated increase in cortical actin. Here, Epac1 was shown to be responsible for these actin changes and to colocalize with microtubules in human umbilical vein endothelial cells. Importantly, Epac activation with a cAMP analogue, 8-pCPT-2'O-Me-cAMP resulted in a net increase in the length of microtubules. This did not require cell–cell interactions or Rap GTPase activation, and it was attributed to microtubule growth as assessed by time-lapse microscopy of human umbilical vein endothelial cell expressing fluorophore-linked microtubule plus-end marker end-binding protein 3. An intact microtubule network was required for Epac-mediated changes in cortical actin and barrier enhancement, but it was not required for Rap activation. Finally, Epac activation reversed microtubule-dependent increases in vascular permeability induced by tumor necrosis factor- and transforming growth factor-β. Thus, Epac can directly promote microtubule growth in endothelial cells. This, together with Rap activation leads to an increase in cortical actin, which has functional significance for vascular permeability.

These authors contributed equally to this work.

Address correspondence to: Tanya N. Mayadas (tmayadas{at}rics.bwh.harvard.edu)

Abbreviations used: EB3, end-binding protein 3; F, forskolin; GEF, guanine exchange factor; HUVEC, human umbilical vein endothelial cell; MT, microtubule; O-Me-cAMP, 8-pCPT-2'O-Me-cAMP; R, rolipram; TER, transelectrical resistance.