Autocrine Tnf signaling favors malignant cells in myelofibrosis in a Tnfr2-dependent fashion

William L Heaton,Russell N Bell,Dongqing Yan,Anthony D Pomicter,Phillip M Clair,Mohamed E Salama,Jeremy M Gililland,Michael W Deininger,Anna V Senina,Thomas O’Hare,Josef T Prchal

doi:10.1038/s41375-018-0131-z

William L Heaton, Russell N Bell + Show 9 more

Open Access

https://doi.org/10.1038/s41375-018-0131-z

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Abstract

Tumor necrosis factor alpha (TNF) is increased in myelofibrosis (MF) and promotes survival of malignant over normal cells. The mechanisms altering TNF responsiveness in MF cells are unknown. We show that the proportion of marrow (BM) cells expressing TNF is increased in MF compared to controls, with the largest differential in primitive cells. Blockade of TNF receptor 2 (TNFR2), but not TNFR1, selectively inhibited colony formation by MF CD34+ and mouse JAK2V617F progenitor cells. Microarray of mouse MPN revealed reduced expression of X-linked inhibitor of apoptosis (Xiap) and mitogen-activated protein kinase 8 (Mapk8) in JAK2V617F relative to JAK2WT cells, which were normalized by TNFR2 but not TNFR1 blockade. XIAP and MAPK8 were also reduced in MF CD34+ cells compared to normal BM, and their ectopic expression induced apoptosis. Unlike XIAP, expression of cellular IAP (cIAP) protein was increased in MF CD34+ cells. Consistent with cIAP’s role in NF-κB activation, TNF-induced NF-κB activity was higher in MF vs. normal BM CD34+ cells. This suggests that JAK2V617F reprograms TNF response toward survival by downregulating XIAP and MAPK8 through TNFR2. Our results reveal an unexpected pro-apoptotic role for XIAP in MF and identify TNFR2 as a key mediator of TNF-induced clonal expansion.

Highlights

Myelofibrosis (MF) is a myeloproliferative neoplasm (MPN) characterized by bone marrow (BM) reticulin fibrosis, anemia, and splenomegaly due to extramedullary hematopoiesis
Despite TNF receptor 1 (TNFR1)’s ability to form this pro-apoptotic complex, the initial signaling event following tumor necrosis factor (TNF) engagement is the formation of a membrane bound complex (Complex I) where TNFR1-associated death domain (TRADD) associates with TNF receptor (TNFR)-associated factor 2 (TRAF2), cellular inhibitor of apoptosis and poly-ubiquitinated receptorinteracting serine/threonine protein kinase 1 (RIPK1) leading to nuclear factor-κB (NF-κB) activation
TNF expression is increased in MPN cells from multiple hematopoietic cell compartments To determine the cellular origin of TNF, we assessed expression by FACS in BM or blood of MF patients compared to normal controls (Fig. 1a)

Summary

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Myelofibrosis (MF) is a myeloproliferative neoplasm (MPN) characterized by bone marrow (BM) reticulin fibrosis, anemia, and splenomegaly due to extramedullary hematopoiesis. The aging BM is characterized by inflammation, a bias toward myelomonocytic differentiation and somatic mutations in genes related to myeloid malignancies, including JAK2 [9,10,11,12,13,14] This suggests that MPNs such as MF may arise through a process in which clones carrying JAK2 activating mutations are selected in the inflammatory environment, a concept supported by the steep increase of MPN incidence with age [15]. Despite TNFR1’s ability to form this pro-apoptotic complex, the initial signaling event following TNF engagement is the formation of a membrane bound complex (Complex I) where TRADD associates with TNFR-associated factor 2 (TRAF2), cellular inhibitor of apoptosis (cIAP) and poly-ubiquitinated RIPK1 leading to nuclear factor-κB (NF-κB) activation. We show that blocking TNFR2 but not TNFR1 selectively inhibits MPN cells over normal controls and implicate Xlinked inhibitor of apoptosis (XIAP), cIAP and mitogenactivated protein kinase 8 (MAPK8) as key mediators of differential responses to TNF

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