Protein Kinase R as Mediator of the Effects of Interferon (IFN) γ and Tumor Necrosis Factor (TNF) α on Normal and Dysplastic Hematopoiesis

Abstract

IFN␥ and TNF␣ are potent inhibitors of hematopoiesis and have been implicated in the pathophysiology of bone marrow failure and myelodysplastic syndromes (MDS). We examined the role of protein kinase R (PKR) in the generation of the inhibitory effects of these myelosuppressive cytokines on hematopoiesis. Our data demonstrate that PKR is rapidly phosphorylated/ activated in response to engagement of IFN␥ or TNF␣ receptors in normal human hematopoietic progenitors. Such engagement of PKR is important for the suppressive effects of these cytokines on normal hematopoiesis. Pharmacological targeting of PKR using a specific inhibitor or siRNA-mediated PKR knockdown results in partial reversal of the suppressive effects of IFN␥ and TNF␣ on normal human CD34؉-derived myeloid (colonyforming unit-granulocyte-monocytic) and erythroid (burstforming unit-erythroid) progenitors. Importantly, inhibition of PKR activity or expression increases hematopoietic colony formation from human MDS progenitors, suggesting that drugs that target PKR may provide a novel approach for the treatment of MDS and marrow failure syndromes. Altogether, our data establish that beyond its key role in the induction of IFN-antiviral responses, PKR plays important roles in signaling for IFN␥ and other myelosuppressive cytokine receptors as a common mediator of signals for hematopoietic suppression.

Regulatory Effects of Programmed Cell Death 4 (PDCD4) Protein in Interferon (IFN)-Stimulated Gene Expression and Generation of Type I IFN Responses

“…The effects of IFN-␣ on CFU-L colony formation from KT1 cells transfected with control siRNA or siRNAs specific for PDCD4 or HA-tagged PDCD4(S67/71A) were determined essentially as previously described (3). Myeloid progenitor (granulocyte-macrophage CFU [CFU-GM]) colony formation from normal CD34 ϩ cells was assessed in clonogenic assays in methylcellulose, as previously described (45).…”

eIF2α phosphorylation controls thermal nociception

“…TNF-α induces a robust up-regulation of eIF2α phosphorylation in cultured cells and in the nervous system via activation of PKR (32)(33)(34)(35)(36). Because TNF-α is a major proinflammatory cytokine (37)(38)(39)(40), which plays a critical role in the pathogenesis of inflammatory pain (41,42), we examined whether inflammationinduced TNF-α promotes eIF2α phosphorylation.…”

IFN-γ-mediated hematopoietic cell destruction in murine models of immune-mediated bone marrow failure

“…12,34 In our murine models of immune-mediated marrow destruction, infusion of H2 or minor histocompatibility antigen mismatched lymph node (LN) cells rapidly induces AA with elevated circulating IFN-g. 35 Development of marrow failure can be ameliorated by both broadly acting immunosuppressive agents and monoclonal antibody specific to IFN-g. 36,37 Inhibitory effects of IFN-g on human hematopoietic cells have been localized molecularly to an essential role for Mnk kinases and sprouty proteins. 38,39 IFN-g appears to suppress HSC self-renewal and multilineage differentiation, thus impairing normal hematopoiesis. The online version of this article contains a data supplement.…”