Inhibition of the Raf–MEK1/2–ERK1/2 Signaling Pathway, Bcl-xL Down-Regulation, and Chemosensitization of Non-Hodgkin’s Lymphoma B Cells by Rituximab

Abstract

Rituximab (Rituxan, IDEC-C2B8) has been shown to sensitize nonHodgkin's lymphoma (NHL) cell lines to chemotherapeutic drug-induced apoptosis. Rituximab treatment of Bcl-2-deficient Ramos cells and Bcl-2-expressing Daudi cells selectively decreases Bcl-xL expression and sensitizes the cells to paclitaxel-induced apoptosis. This study delineates the signaling pathway involved in rituximab-mediated Bcl-xL down-regulation in Ramos and Daudi NHL B cells. We hypothesized that rituximab may interfere with the extracellular signal-regulated kinase (ERK) 1/2 pathway, leading to decreased Bcl-xL expression. Rituximab (20 g/mL) inhibited the kinase activity of mitogen-activated protein kinase kinase (MEK) 1/2 and reduced the phosphorylation of the components of the ERK1/2 pathway (Raf-1, MEK1/2, and ERK1/2) and decreased activator protein-1 DNA binding activity and Bcl-xL gene expression. These events occurred with similar kinetics and were observed 3 to 6 hours after rituximab treatment. Rituximab-mediated effects were corroborated by using specific inhibitors of the ERK1/2 pathway, which also reduced Bcl-xL levels and sensitized the NHL B cells to paclitaxel-induced apoptosis. Previous findings implicated a negative regulatory role of the Raf-1 kinase inhibitor protein (RKIP) on the ERK1/2 pathway. Rituximab treatment of NHL B cells significantly up-regulated RKIP expression, thus interrupting the ERK1/2 signaling pathway through the physical association between Raf-1 and RKIP, which was concomitant with Bcl-xL downregulation. These novel findings reveal a signaling pathway triggered by rituximab, whereby rituximab-mediated up-regulation of RKIP adversely regulates the activity of the ERK1/2 pathway, Bcl-xL expression, and subsequent chemosensitization of drug-refractory NHL B cells. The significance of these findings is discussed.

Agonists of an ecdysone-inducible mammalian expression system inhibit Fas Ligand- and TRAIL-induced apoptosis in the human colon carcinoma cell line RKO

“…29,30,[32][33][34] We could show that muristerone A treatment increases phosphorylation of p42/ 44 MAPK , and inhibitors of the p42/44 MAPK and PKC pathways abolished protection by muristerone A, as the inhibitors of the PI3K pathway did. It is possible that activation of one of these pathways stimulates one or both of the other signaling cascades; however, we did not observe changes in Akt phosphorylation level when the PKC inhibitor had been applied, and vice versa (data not shown), arguing for an independent activation of at least these two pathways by muristerone A.…”

“…31 One mechanism how activated p42/44 MAP kinases (extracellular signal-regulated kinase 1/2 (ERK1/2)) suppress apoptosis is by upregulating Bcl-x L , [32][33][34] and in mammary epithelial cells a significant decrease in Bcl-x L protein has been reported by using pharmacological inhibitors of both the PI3K/Akt and the p42/44 MAPK pathways. 35 We used a specific inhibitor of the activation of mitogen-activated protein kinase kinase (MAPKK), PD 98,059, 36 to investigate the role of p42/44 MAP kinases in muristerone A-induced inhibition of RKO cell apoptosis.…”

Rituximab (chimeric anti-CD20) sensitizes B-NHL cell lines to Fas-induced apoptosis

“…Recent findings demonstrated that rituximab treatment of B-NHL cell lines triggers the cells and inhibits survival signaling pathways and sensitizes drug-resistant cells to drug-induced apoptosis Jazirehi et al, 2004. Thus, we examined whether rituximab also sensitizes cells to Fas-induced apoptosis.…”

Absence of RKIP expression is an independent prognostic biomarker for gastric cancer patients

“…In non-Hodgkin's lymphoma cell lines it was shown that treatment with Rituximab induced RKIP upregulation, with further sensitization to chemotherapeutic induced apoptosis (48). Other studies reported that RKIP can be induced by nitric oxide or the proteasome inhibitor NPI-0052, via NF-κB inhibition (49)(50)(51).…”