title: Tristetraprolin mediates radiation-induced TNF-α production in lung macrophages.
abstract: The efficacy of radiation therapy for lung cancer is limited by radiation-induced lung toxicity (RILT). Although tumor necrosis factor-alpha (TNF-α) signaling plays a critical role in RILT, the molecular regulators of radiation-induced TNF-α production remain unknown. We investigated the role of a major TNF-α regulator, Tristetraprolin (TTP), in radiation-induced TNF-α production by macrophages. For in vitro studies we irradiated (4 Gy) either a mouse lung macrophage cell line, MH-S or macrophages isolated from TTP knockout mice, and studied the effects of radiation on TTP and TNF-α levels. To study the in vivo relevance, mouse lungs were irradiated with a single dose (15 Gy) and assessed at varying times for TTP alterations. Irradiation of MH-S cells caused TTP to undergo an inhibitory phosphorylation at Ser-178 and proteasome-mediated degradation, which resulted in increased TNF-α mRNA stabilization and secretion. Similarly, MH-S cells treated with TTP siRNA or macrophages isolated from ttp (-/-) mice had higher basal levels of TNF-α, which was increased minimally after irradiation. Conversely, cells overexpressing TTP mutants defective in undergoing phosphorylation released significantly lower levels of TNF-α. Inhibition of p38, a known kinase for TTP, by either siRNA or a small molecule inhibitor abrogated radiation-induced TNF-α release by MH-S cells. Lung irradiation induced TTP(Ser178) phosphorylation and protein degradation and a simultaneous increase in TNF-α production in C57BL/6 mice starting 24 h post-radiation. In conclusion, irradiation of lung macrophages causes TTP inactivation via p38-mediated phosphorylation and proteasome-mediated degradation, leading to TNF-α production. These findings suggest that agents capable of blocking TTP phosphorylation or stabilizing TTP after irradiation could decrease RILT.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, United States of America. dipray@umich.edu
authors.forename: Dipankar
authors.initials: D
authors.lastname: Ray
authors.forename: Shirish
authors.initials: S
authors.lastname: Shukla
authors.forename: Uday Sankar
authors.initials: US
authors.lastname: Allam
authors.forename: Abigail
authors.initials: A
authors.lastname: Helman
authors.forename: Susmita Gurjar
authors.initials: SG
authors.lastname: Ramanand
authors.forename: Linda
authors.initials: L
authors.lastname: Tran
authors.forename: Michael
authors.initials: M
authors.lastname: Bassetti
authors.forename: Pranathi Meda
authors.initials: PM
authors.lastname: Krishnamurthy
authors.forename: Matthew
authors.initials: M
authors.lastname: Rumschlag
authors.forename: Michelle
authors.initials: M
authors.lastname: Paulsen
authors.forename: Lei
authors.initials: L
authors.lastname: Sun
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Shanley
authors.forename: Mats
authors.initials: M
authors.lastname: Ljungman
authors.forename: Mukesh K
authors.initials: MK
authors.lastname: Nyati
authors.forename: Ming
authors.initials: M
authors.lastname: Zhang
authors.forename: Theodore S
authors.initials: TS
authors.lastname: Lawrence
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D008168:Lung / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects; D016676:Macrophages, Alveolar / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics; D051816:Tristetraprolin / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D017931:DNA Primers; D012333:RNA, Messenger; D051816:Tristetraprolin; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases