MNK-driven eIF4E phosphorylation regulates the fibrogenic transformation of mesenchymal cells and chronic lung allograft dysfunction
Natalie M. Walker, Yuta Ibuki, A. Patrick McLinden, Keizo Misumi, Dylan C. Mitchell, Gabriel G. Kleer, Alison M. Lock, Ragini Vittal, Nahum Sonenberg, Amanda L. Garner, Vibha N. Lama
Natalie M. Walker, Yuta Ibuki, A. Patrick McLinden, Keizo Misumi, Dylan C. Mitchell, Gabriel G. Kleer, Alison M. Lock, Ragini Vittal, Nahum Sonenberg, Amanda L. Garner, Vibha N. Lama
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Research Article Pulmonology

MNK-driven eIF4E phosphorylation regulates the fibrogenic transformation of mesenchymal cells and chronic lung allograft dysfunction

Abstract

Tissue fibrosis remains unamenable to meaningful therapeutic interventions and is the primary cause of chronic graft failure after organ transplantation. Eukaryotic translation initiation factor (eIF4E), a key translational regulator, serves as convergent target of multiple upstream profibrotic signaling pathways that contribute to mesenchymal cell (MC) activation. Here, we investigate the role of MAP kinase–interacting serine/threonine kinase–induced (MNK-induced) direct phosphorylation of eIF4E at serine 209 (Ser209) in maintaining fibrotic transformation of MCs and determine the contribution of the MNK/eIF4E pathway to the pathogenesis of chronic lung allograft dysfunction (CLAD). MCs from patients with CLAD demonstrated constitutively higher eIF4E phosphorylation at Ser209, and eIF4E phospho-Ser209 was found to be critical in regulating key fibrogenic protein autotaxin, leading to sustained β-catenin activation and profibrotic functions of CLAD MCs. MNK1 signaling was upregulated in CLAD MCs, and genetic or pharmacologic targeting of MNK1 activity inhibited eIF4E phospho-Ser209 and profibrotic functions of CLAD MCs in vitro. Treatment with an MNK1/2 inhibitor (eFT-508) abrogated allograft fibrosis in an orthotopic murine lung-transplant model. Together these studies identify what we believe is a previously unrecognized MNK/eIF4E/ATX/β-catenin signaling pathway of fibrotic transformation of MCs and present the first evidence, to our knowledge, for the utility of MNK inhibitors in fibrosis.

Authors

Natalie M. Walker, Yuta Ibuki, A. Patrick McLinden, Keizo Misumi, Dylan C. Mitchell, Gabriel G. Kleer, Alison M. Lock, Ragini Vittal, Nahum Sonenberg, Amanda L. Garner, Vibha N. Lama

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Figure 4

MNK/eIF4E (Ser209) positively regulates ATX expression and activity in fibrotic lung MCs.

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MNK/eIF4E (Ser209) positively regulates ATX expression and activity in f...
(A) MCs isolated from fibrotic (Fib-MCs) or normal (non-Fib-MCs) human lung allografts were infected with lentiviral vectors containing pLenti-LoxEV–eIF4E (S209A) and pLenti-LoxEV–eIF4E (S209D) plasmids, respectively. Protein lysates were analyzed by Western blotting for cellular and secreted ATX expression. Representative immunoblots and densitometry for cellular ATX are shown. (B) Immunoblots for CD44 protein expression in lentiviral-infected MCs described in A. (C and D) Fib-MCs were transfected with MNK1 or scrambled siRNA (C) or treated with eFT-508 (10 μM, 2 hours; D). Protein lysates were analyzed by Western blotting. Representative immunoblots of phospho-eIF4E and total forms of eIF4E, and expression of cellular ATX and CD44 are shown. (E) Conditioned media of Fib-MCs treated with eFT-508 (10 μM, 24 hours) were measured for ATX activity utilizing the fluorogenic substrate FS-3. n = 9. (F) Cultured mouse lung fibroblasts from WT, Eif4eSer209A/A, and Mnk1/2-KO mice were assessed by immunoblotting for cellular ATX, MNK1, phospho-eIF4E, and total eIF4E. (G) Secreted ATX levels were analyzed in the conditioned media by sandwich ELISA. Data are represented as means ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001, unpaired t test (A and B); simple linear regression (E); 1-way ANOVA; post hoc test: Bonferroni’s test (G).