Role of Epac1, an exchange factor for Rap GTPase, in endothelial microtubule dynamics and barrier function

Abstract

Vascular leakage leading to excessive tissue fluid accumulation often has severe pathological consequences and contributes to morbidity and mortality in disease. 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 co‐localize with microtubules in human umbilical vein endothelial cells. Importantly, Epac activation with a cAMP analogue, 8‐pCPT‐2′O‐Me‐cAMP (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 was attributed to microtubule growth as assessed by time‐lapse microscopy of HUVEC expressing flourophore‐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 was not required for Rap activation. Finally, Epac activation reversed microtubule dependent reductions in vascular permeability induced by TNFα and TGFβ. Thus Epac can directly promote microtubule growth in endothelial cells. This, together with Epac mediated Rap activation leads to an increase in cortical actin, which has functional significance for vascular permeability. Elucidation of the mechanism of Epac regulation of MT and actin may lead to potential therapies for edema in acute vascular syndromes.Funding was provided by NIH HL (PPG), NIH HL036028 (TNM), HL68130 (JI). XC was supported by KO1AR054984, and SP by training grant HL066978 (L. Silberstein) and a Ruth L. Kirschstein fellowship HL082133‐01.