title: Shear flow attenuates serum-induced STAT3 activation in endothelial cells.
abstract: Vascular endothelial cells (ECs) are constantly exposed to flow-induced shear stress. Shear stress is known to induce signaling cascades, including the extracellular signal-regulated protein kinase (ERK) pathway. STAT3 transcription factor plays a key role in cytokine stimulation. Recent studies indicate that STAT3 is involved in growth factor-induced cell cycle. In the present study, we have examined STAT3 activation of ECs under conditions of shear flow. Bovine aortic ECs cultured with serum at static state show a serum concentration-dependent phosphorylation at Tyr-705 of STAT3, whereas there is a constant basal phosphorylation at Ser-727. In ECs subjected to shear flow, a shear dose-dependent phosphorylation of Ser-727 and ERK1/2 was observed. In contrast, a concomitantly shear dose-dependent inhibition of phosphorylation at Tyr-705 was exhibited. Shear stress on ECs increased the association of ERK1/2 to STAT3. ECs treated with MEK inhibitor (U0126 or PD98059) consistently and significantly reduced the shear-induced ERK1/2 and Ser-727 phosphorylation, indicating that ERK1/2 is upstream of Ser-727 phosphorylation. Interestingly, shear-induced inhibition in Tyr-705 phosphorylation was abolished in these same inhibitor-treated ECs. Similarly, ECs transfected with a dominant positive mutant of MEK1 enhanced the phosphorylation of Ser-727 with the attenuation of the Tyr-705 phosphorylation. In contrast, when ECs were transfected with dominant positive mutant of MEKK1, JNK upstream, no change in the phosphorylation of Ser-727 and Tyr-705 was observed. These results indicate that shear flow induces the phosphorylation of Ser-727 via ERK1/2 pathway, and this Ser-727 phosphorylation inhibits Tyr-705 phosphorylation in STAT3. As a result, shear flow reduced the translocation of STAT3 into nucleus. This study shows for the first time that shear flow may play a significant role by attenuating STAT3 activation and thus may reduce inflammatory responses and/or serum-induced endothelial proliferation.
authors.affiliation: Cardiovascular Division, Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan 11529.
authors.forename: Chih-Wen
authors.initials: CW
authors.lastname: Ni
authors.forename: Hsyue-Jen
authors.initials: HJ
authors.lastname: Hsieh
authors.forename: Yuen-Jen
authors.initials: YJ
authors.lastname: Chao
authors.forename: Danny Ling
authors.initials: DL
authors.lastname: Wang
mesh_terms: D000818:Animals; D001769:Blood; D002417:Cattle; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D050796:STAT3 Transcription Factor; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; D014443:Tyrosine; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases