The Kinase Inhibitor Sorafenib Induces Cell Death through a Process Involving Induction of Endoplasmic Reticulum Stress

Abstract

Sorafenib is a multikinase inhibitor that induces apoptosis in human leukemia and other malignant cells.Recently, we demonstrated that sorafenib diminishes Mcl-1 protein expression by inhibiting translation through a MEK1/2-ERK1/2 signaling-independent mechanism and that this phenomenon plays a key functional role in sorafenib-mediated lethality. Here, we report that inducible expression of constitutively active MEK1 fails to protect cells from sorafenib-mediated lethality, indicating that sorafenib-induced cell death is unrelated to MEK1/2-ERK1/2 pathway inactivation. Notably, treatment with sorafenib induced endoplasmic reticulum (ER) stress in human leukemia cells (U937) manifested by immediate cytosolic-calcium mobilization, GADD153 and GADD34 protein induction, PKR-like ER kinase (PERK) and eukaryotic initiation factor 2␣ (eIF2␣) phosphorylation, XBP1 splicing, and a general reduction in protein synthesis as assessed by [35 S]methionine incorporation. These events were accompanied by pronounced generation of reactive oxygen species through a mechanism dependent upon cytosolic-calcium mobilization and a significant decline in GRP78/Bip protein levels. Interestingly, enforced expression of IRE1␣ markedly reduced sorafenib-mediated apoptosis, whereas knockdown of IRE1␣ or XBP1, disruption of PERK activity, or inhibition of eIF2␣ phosphorylation enhanced sorafenib-mediated lethality. Finally, downregulation of caspase-2 or caspase-4 by small interfering RNA significantly diminished apoptosis induced by sorafenib. Together, these findings demonstrate that ER stress represents a central component of a MEK1/2-ERK1/2-independent cell death program triggered by sorafenib.The discovery that aberrant activation of the Ras-Raf-MEK1/2-ERK1/2 module occurs in a high percentage (30%) of human cancers (12, 42, 48, 57) provided a rationale for attempting to disrupt this pathway as a candidate anticancer strategy. Recently, a number of specific inhibitors designed to interrupt this pathway at the level of Ras, Raf, or MEK1/2 have been developed. Among these, sorafenib, a biaryl urea, also known as BAY 43-9006 or Nexavar, was initially developed as a specific inhibitor of C-Raf and B-Raf. However, subsequent studies revealed that it also inhibits several other tyrosine kinases involved in tumor progression, including VEGFR-2, VEGFR-3, PDGFR-␤, Flt3, c-Kit, and Ret (6, 60). Interestingly, sorafenib has been shown to inhibit mutant (V600E) B-Raf kinase activities in vitro and to diminish MEK/extracellular signal-regulated kinase (ERK) activation in various tumor cell lines, including those harboring mutant Ras or B-Raf (25,56,60). Although this compound has potent activity in preclinical tumor xenograft models against a variety of tumor cell types (60), has shown promising activity in a number of clinical trials, and has recently been approved for the treatment of advanced renal cell carcinoma (51), the mechanism(s) by which it exerts its antitumor activity has not been fully elucidated and is currently the subject of ongoing i...

Induction of Endoplasmic Reticulum Stress by Sorafenib and Activation of NF-κB by Lestaurtinib as a Novel Resistance Mechanism in Hodgkin Lymphoma Cell Lines

“…The sorafenib-induced deactivation of intracellular signaling molecules was often accompanied by losses of total amounts of these proteins, and sorafenib can cause ER stress with reduced translation in leukemia cells (25). As we observed typical features of ER stress also in the sorafenib-treated HRS cell lines, it is likely that the losses of total amounts of signaling molecules are due to ER stress induced reduction in translation combined with their fast turnover rates.…”

“…Sorafenib can cause endoplasmic reticulum (ER) stress with a general reduction of translation and caspase-3-independent cell death in human leukemia cells (25), and ER stress could thus also account for the reduction in total protein amounts of several signaling molecules and caspase-3-independent cell death in HRS cell lines. Therefore, we analyzed the effect of sorafenib on different ER stress markers in HRS cell lines by Western blotting and quantitative real-time PCR (qRT-PCR).…”

“…Therefore, we analyzed the effect of sorafenib on different ER stress markers in HRS cell lines by Western blotting and quantitative real-time PCR (qRT-PCR). The phosphorylation of PERK, one of the ER resident proteins inducing the stress response (26), and the expression of genes induced by ER stress, GADD34 and GADD153 (25)(26)(27), were monitored (Fig. 5).…”

The multikinase inhibitor sorafenib induces caspase-dependent apoptosis in PC-3 prostate cancer cells

“…Rahmani et al [39] found that constitutive activation of MEK1 failed to protect leukaemia cells from sorafenib-induced lethality. Their data suggested that endoplasmic reticulum (ER) stress represents a central component of an MEK1/2-ERK1/2-independent cell death program that is triggered by sorafenib treatment.…”

A SPRY2 mutation leading to MAPK/ERK pathway inhibition is associated with an autosomal dominant form of IgA nephropathy

“…Treatment was maintained until the 7th day. In spite of the reduced cell number and block of protein synthesis 21 IgA production increased, and, as a result of ERK1/2 inhibition, expression of SPRY2 transcript was reduced (Figure 3c). This finding supports the hypothesis that a block in the MAPK/ERK leads to an increased IgA production.…”