Work

Involvement of p38-βTrCP-Tristetraprolin-TNFα axis in radiation pneumonitis

Year: 2017

Type: article

Abstract: // Pranathi Meda Krishnamurthy 1, 3, * , Shirish Shukla 1, 2, * , Paramita Ray 1 , Rohit Mehra 2 , Mukesh K. Nyati 1 , Theodore S. Lawrence 1 and Dipankar Ray 1 1 Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, USA 2 Department of Pathology, University of Michigan, Ann Arbor, MI, USA 3 Current address: RNA Therapeutics Institute, University of Massachusetts Medical School, Worcester, MA, USA * These authors have contributions equal to this work Correspondence to: Dipankar Ray, email: [email protected] Keywords: radiation pneumonitis, TNF-α, Tristetraprolin, p38 MAPK, β-TrCP1 Received: December 21, 2016 Accepted: April 14, 2017 Published: May 10, 2017 ABSTRACT Early release of tumor necrosis factor-alpha (TNF-α) during radiotherapy of thoracic cancers plays an important role in radiation pneumonitis, whose inhibition may provide lung radioprotection. We previously reported radiation inactivates Tristetraprolin (TTP), a negative regulator of TNF-α synthesis, which correlated with increased TNF-α release. However, the molecular events involved in radiation-induced TTP inactivation remain unclear. To determine if eliminating Ttp in mice resulted in a phenotypic response to radiation, Ttp -null mice lungs were exposed to a single dose of 15 Gy, and TNF-α release and lung inflammation were analyzed at different time points post-irradiation. Ttp -/- mice with elevated (9.5±0.6 fold) basal TNF-α showed further increase (12.2±0.9 fold, p <0.02) in TNF-α release and acute lung inflammation within a week post-irradiation. Further studies using mouse lung macrophage (MH-S), human lung fibroblast (MRC-5), and exogenous human TTP overexpressing U2OS and HEK293 cells upon irradiation (a single dose of 4 Gy) promoted p38-mediated TTP phosphorylation at the serine 186 position, which primed it to be recognized by an ubiquitin ligase (E3), beta transducing repeat containing protein (β-TrCP), to promote polyubiquitination-mediated proteasomal degradation. Consequently, a serine 186 to alanine (SA) mutant of TTP was resistant to radiation-induced degradation. Similarly, either a p38 kinase inhibitor (SB203580), or siRNA-mediated β-TrCP knockdown, or overexpression of dominant negative Cullin1 mutants protected TTP from radiation-induced degradation. Consequently, SB203580 pretreatment blocked radiation-induced TNF-α release and radioprotected macrophages. Together, these data establish the involvement of the p38-βTrCP-TTP-TNFα signaling axis in radiation-induced lung inflammation and identified p38 inhibition as a possible lung radioprotection strategy.

Source: Oncotarget

DOI: 10.18632/oncotarget.17770