Connexin 37 sequestering of activated-ERK in the cytoplasm promotes p27-mediated endothelial cell cycle arrest

Connexin37-mediated regulation of cell cycle modulators and, consequently, growth arrest lack mechanistic understanding. We previously showed that arterial shear stress up-regulates Cx37 in endothelial cells and activates a Notch/Cx37/p27 signaling axis to promote G1 cell cycle arrest, and this is required to enable arterial gene expression. However, how induced expression of a gap junction protein, Cx37, up-regulates cyclin-dependent kinase inhibitor p27 to enable endothelial growth suppression and ar-terial specification is unclear. Herein, we fill this knowledge gap by expressing wild-type and regulatory domain mutants of Cx37 in cultured endothelial cells expressing the Fucci cell cycle re-porter. We determined that both the channel-forming and cy-toplasmic tail domains of Cx37 are required for p27 up-regulation and late G1 arrest. Mechanistically, the cytoplasmic tail domain of Cx37 interacts with, and sequesters, activated ERK in the cyto-plasm. This then stabilizes pERK nuclear target Foxo3a, which up -regulates p27 transcription. Consistent with previous studies, we found this Cx37/pERK/Foxo3a/p27 signaling axis functions downstream of arterial shear stress to promote endothelial late G1 state and enable up-regulation of arterial genes.

Automated summary

We provide mechanistic insights into the role of Cx37 in regulating cell cycle modulators and growth arrest. Both the channel-forming and cytoplasmic tail domains of Cx37 are involved in up-regulating p27 and causing late G1 arrest. The cytoplasmic tail domain of Cx37 interacts with activated ERK, leading to stabilization of pERK nuclear target Foxo3a and subsequent up-regulation of p27 transcription.