Fractionated radiation suppresses Kruppel-like factor 2 pathway to a greater extent than by single exposure to the same total dose

• Published in: Scientific reports Vol. 10; no. 1; p. 7734
• Main Authors: Sadhukhan, Ratan, Leung, Justin W. C., Garg, Sarthak, Krager, Kimberly J., Savenka, Alena V., Basnakian, Alexei G., Pathak, Rupak
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07-05-2020; Nature Publishing Group
• Subjects: 13/1; 13/106; 13/31; 14/63; 631/337/572/2102; 631/80/86/2366; Activated protein C; Cell adhesion; Dose Fractionation, Radiation; Dose-Response Relationship, Radiation; Endothelial cells; Extracellular signal-regulated kinase; Fractionation; Gene Expression Regulation - radiation effects; Human Umbilical Vein Endothelial Cells - metabolism; Human Umbilical Vein Endothelial Cells - radiation effects; Humanities and Social Sciences; Humans; Intercellular adhesion molecule 1; Intercellular Adhesion Molecule-1 - genetics; Irradiation; Krueppel-like factor; Kruppel-Like Transcription Factors - genetics; MEF2 Transcription Factors - genetics; Mevalonate pathway; Mevalonic acid; Mitogen-Activated Protein Kinase 7 - genetics; multidisciplinary; Myocyte enhancer factor 2; Neoplasms - genetics; Neoplasms - pathology; Neoplasms - radiotherapy; Nitric oxide; Nitric Oxide Synthase Type III - genetics; Nitric-oxide synthase; Radiation; Radiation therapy; Science; Science (multidisciplinary); Signal Transduction - radiation effects; Thorax; Thrombin; Thrombomodulin; Thrombomodulin - genetics; Toxicity; Transcription; Upstream
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-64672-3

Kruppel-like factor 2 (KLF2) is a positive transcriptional regulator of several endothelial protective molecules, including thrombomodulin (TM), a surface receptor, and endothelial nitric oxide synthase (eNOS), an enzyme that generates nitric oxide (NO). Loss of TM and eNOS causes endothelial dysfunction, which results in suppressed generation of activated protein C (APC) by TM-thrombin complex and in upregulation of intercellular adhesion molecule 1 (ICAM-1). Mechanistic studies revealed that activation of extracellular signal-regulated kinase 5 (ERK5) via upregulation of myocyte enhancer factor 2 (MEF2) induces KLF2 expression. Radiation causes endothelial dysfunction, but no study has investigated radiation’s effects on the KLF2 pathway. Because fractionated radiation is routinely used during cancer radiotherapy, we decided to delineate the effects of radiation dose fractionation on the KLF2 signaling cascade at early time points (up to 24 h). We exposed human primary endothelial cells to radiation as a series of fractionated or as a single exposure, with the same total dose delivered to each group. We measured the expression and activity of critical members of the KLF2 pathway at subsequent time points, and determined whether pharmacological upregulation of KLF2 can reverse the radiation effects. Compared to single exposure, fractionated radiation profoundly suppressed KLF2, TM, and eNOS levels, subdued APC generation, declined KLF2 binding ability to TM and eNOS promoters, enhanced ICAM-1 expression, and decreased expression of upstream regulators of KLF2 (ERK5 and MEF2). Pharmacological inhibitors of the mevalonate pathway prevented fractionated-radiation–induced suppression of KLF2, TM, and eNOS expression. Finally, fractionated irradiation to thoracic region more profoundly suppressed KLF2 and enhanced ICAM-1 expression than single exposure in the lung at 24 h. These data clearly indicate that radiation dose fractionation plays a critical role in modulating levels of KLF2, its upstream regulators, and its downstream target molecules in endothelial cells. Our findings will provide important insights for selecting fractionated regimens during radiotherapy and for developing strategies to alleviate radiotherapy-induced toxicity to healthy tissues.