Doxorubicin bypasses the cytoprotective effects of eIF2α phosphorylation and promotes PKR-mediated cell death

Abstract

The eukaryotic cell responds to various forms of environmental stress by adjusting the rates of mRNA translation thus facilitating adaptation to the assaulting stress. One of the major pathways that control protein synthesis involves the phosphorylation of the a-subunit of eukaryotic initiation factor eIF2 at serine 51. Different forms of DNA damage were shown to induce eIF2a phosphorylation by using PERK, GCN2 or PKR. However, the specificity of the eIF2a kinases and the biological role of eIF2a phosphorylation pathway in the DNA damage response (DDR) induced by chemotherapeutics are not known. Herein, we show that PKR is the eIF2a kinase that responds to DDR induced by doxorubicin. We show that activation of PKR integrates two signaling pathways with opposing biological outcomes. More specifically, induction of eIF2a phosphorylation has a cytoprotective role, whereas activation of c-jun N-terminal kinase (JNK) by PKR promotes cell death in response to doxorubicin. We further show that the proapoptotic effects of JNK activation prevail over the cytoprotection mediated by eIF2a phosphorylation. These findings reveal that PKR can be an important inducer of cell death in response to chemotherapies through its ability to act independently of eIF2a phosphorylation. The eukaryotic cell has established intricate mechanisms to cope with environmental stress. It does so by changing protein expression in a manner that promotes adaptation to the assaulting stress. Protein expression within the cell is regulated at the transcriptional, translational and posttranslational levels. Translational control is often used under conditions of cellular stress because it allows immediate and selective changes in protein levels. 1 Translation itself is divided into three distinct phases: initiation, elongation and termination. By far the most explored step is that of initiation, which has been shown to be regulated by different extracellular stimuli. 1 One of the major pathways that control translation initiation is that of the phosphorylation of the a-subunit of translation initiation factor eIF2. 2 Phosphorylation of eIF2a at serine 51 (S51) leads to the inhibition of global protein synthesis providing the cell with the opportunity to elicit adaptive responses not only by saving energy but also by preventing the accumulation of unwanted proteins that could interfere with cellular functions. 1 There are four eIF2a kinases that share a homologous kinase domain (KD) but possess different regulatory domains that enable them to become activated by distinct stimuli. 2 The eIF2a kinases are the heme-regulated inhibitor, which is found mainly in erythroid cells and is activated by heme deficiency; the endoplasmic reticulum (ER)-resident kinase (PERK), which is activated by ER stress and inhibits protein synthesis as part of the unfolded protein response; the general aminoacid nonderepressing kinase 2 (GCN2), which responds to amino-acid deprivation and becomes activated by uncharged tRNA and the RNA-dependent protein kinase PKR, an interfer...

Blocking Double-Stranded RNA-Activated Protein Kinase PKR by Japanese Encephalitis Virus Nonstructural Protein 2A

“…6). The chemotherapeutic doxorubicin has been shown to promote PKR-mediated cell death, and other eIF2␣ kinases such as PERK and GCN2 did not contribute to doxorubicin-induced cell death (54). Compared to the GFP control cells, cells with JNS2A expression showed suppressed PKR and eIF2␣ phosphorylation triggered by doxorubicin (Fig.…”

eIF2α Kinase PKR Modulates the Hypoxic Response by Stat3-Dependent Transcriptional Suppression of HIF-1α

“…Furthermore, chemotherapeutic drugs such as etoposide, doxorubicin, and related topoisomerase inhibitors lead to an inhibition of HIF-1α synthesis and accumulation in response to hypoxia (47)(48)(49). Given that PKR becomes activated by doxorubicin (50) and other chemotherapeutic means (43), its activation may significantly contribute to suppression of tumor growth by drugs targeting HIF-1α.…”

Bacterial Cytological Profiling Reveals the Mechanism of Action of Anticancer Metal Complexes

“…62,64 Both cisplatin and doxorubicin were able to induce phosphorylation of JNK in A549 and HL60 cells at 24 h, though different phosphorylation levels in HL60 cells were observed, which might indicate possible phosphorylation time course differences. Phospho-JNK was seen as early as 6 h after doxorubicin treatment in HL60 cells, while cisplatin induced phospho-JNK was seen to increase to its maximum level at 24 h. 65,66 Surprisingly, compound 1 did not activate the JNK pathway to the same extent as cisplatin or doxorubicin. The phosphorylation level was slightly increased within 6 to 12 h of treatment with compound 1 in both cell lines but then decreased over time.…”