TRAF7 is an essential regulator of vascular integrity

Targeted deletion of TRAF7 revealed that it is a crucial part of shear stress-responsive MEKK3-MEK5-ERK5 signaling pathway induced in endothelial cells by blood flow. Similarly, to Mekk3-, Mek5- or Erk5-deficient mice, Traf7-deficient embryos died in utero around midgestation due to impaired endothelial cell integrity. They displayed significantly lower expression of transcription factor Klf2, an essential regulator of vascular hemodynamic forces downstream of the MEKK3-MEK-ERK5 signaling pathway. Deletion of Traf7 in endothelial cells of postnatal mice was also associated with severe cerebral hemorrhage. Here, we show that besides MEKK3 and MEK5, TRAF7 associates with a planar cell polarity protein SCRIB. SCRIB binds with an N-terminal region of TRAF7, while MEKK3 associates with the C-terminal WD40 domain. Downregulation of TRAF7 as well as SCRIB inhibited fluid shear stress-induced phosphorylation of ERK5 in cultured endothelial cells. These findings suggest that TRAF7 and SCRIB may comprise an upstream part of the MEKK3-MEK5-ERK5 signaling pathway. Objective: to present first in vivo experimental evidence of TRAF7 function by using global and endothelium-specific TRAF7 knockout mice and comparing transcriptomes of developing embryos. Overall design: RNA-seq was performed to determine and compare transcriptome profiles in whole mouse embryos of different genotypes at E9.5. Genotypes include wild type, global, and endothelium-specific TRAF7 knockouts.