MEK5 is Activated by Shear Stress, Activates ERK5 and Induces KLF4 to Modulate TNF Responses in Human Dermal Microvascular Endothelial Cells

P>Objective: ECs lining arteries respond to LSS by suppressing pro-inflammatory changes, in part through the activation of MEK5, ERK5 and induction of KLF4. We examined if this anti-inflammatory pathway operates in human ECs lining microvessels, the principal site of inflammatory responses. Methods: We used immunofluorescence microscopy of human skin to assess ERK5 activation and KLF4 expression in HDMECs in situ. We applied LSS to or overexpressed MEK5/CA in cultured HDMECs and assessed gene expression by microarrays and qRT-PCR and protein expression by Western blotting. We assessed effects of MEK5/CA on TNF responses using qRT-PCR, FACS and measurements of HDMEC monolayer electrical resistance. We used siRNA knockdown to assess the role of ERK5 and KLF4 in these responses. Results: ERK5 phosphorylation and KLF4 expression is observed in HDMECs in situ. LSS activates ERK5 and induces KLF4 in cultured HDMECs. MEK5/CA-transduced HDMECs show activated ERK5 and increased KLF4, thrombomodulin, eNOS, and ICAM-1 expression. MEK5 induction of KLF4 is mediated by ERK5. MEK5/CA-transduced HDMECs are less responsive to TNF, an effect partly mediated by KLF4. Conclusions: MEK5 activation by LSS inhibits inflammatory responses in microvascular ECs, in part through ERK5-dependent induction of KLF4.