Glycogen Synthase Kinase-3 regulates multiple myeloma cell growth and bortezomib-induced cell death

Abstract

BackgroundGlycogen Synthase Kinase-3 (GSK-3) α and β are two serine-threonine kinases controlling insulin, Wnt/β-catenin, NF-κB signaling and other cancer-associated transduction pathways. Recent evidence suggests that GSK-3 could function as growth-promoting kinases, especially in malignant cells. In this study, we have investigated GSK-3α and GSK-3β function in multiple myeloma (MM).MethodsGSK-3 α and β expression and cellular localization were investigated by Western blot (WB) and immunofluorescence analysis in a panel of MM cell lines and in freshly isolated plasma cells from patients. MM cell growth, viability and sensitivity to bortezomib was assessed upon treatment with GSK-3 specific inhibitors or transfection with siRNAs against GSK-3 α and β isoforms. Survival signaling pathways were studied with WB analysis.ResultsGSK-3α and GSK-3β were differently expressed and phosphorylated in MM cells. Inhibition of GSK-3 with the ATP-competitive, small chemical compounds SB216763 and SB415286 caused MM cell growth arrest and apoptosis through the activation of the intrinsic pathway. Importantly, the two inhibitors augmented the bortezomib-induced MM cell cytotoxicity. RNA interference experiments showed that the two GSK-3 isoforms have distinct roles: GSK-3β knock down decreased MM cell viability, while GSK-3α knock down was associated with a higher rate of bortezomib-induced cytotoxicity. GSK-3 inhibition caused accumulation of β-catenin and nuclear phospho-ERK1, 2. Moreover, GSK-3 inhibition and GSK-3α knockdown enhanced bortezomib-induced AKT and MCL-1 protein degradation. Interestingly, bortezomib caused a reduction of GSK-3 serine phosphorylation and its nuclear accumulation with a mechanism that resulted partly dependent on GSK-3 itself.ConclusionsThese data suggest that in MM cells GSK-3α and β i) play distinct roles in cell survival and ii) modulate the sensitivity to proteasome inhibitors.

Inhibition of Glycogen Synthase Kinase-3 Increases NKG2D Ligand MICA Expression and Sensitivity to NK Cell–Mediated Cytotoxicity in Multiple Myeloma Cells: Role of STAT3

“…An example of this functional connection between chemotherapy and therapeutical immunomodulation is the finding that several genotoxic agents or drugs, such as inhibitors of histone deacetylases or of the HSP-90 molecular chaperone, can increase the expression of NKG2D ligands, thus facilitating the activation of NKG2D-expressing lymphocytes (including NK cells, NKT cells, and CTLs) against tumor cells (19,20,41,45,46). GSK3 inhibitors are a class of molecules recently studied for their ability to induce apoptosis, to inhibit the proliferation, and to regulate the sensitivity of MM cells to clinically used chemotherapeutics, such as bortezomib (21)(22)(23). Moreover, given that effective inhibition of this kinase is necessary for canonical Wnt signaling and for osteogenic differentiation, GSK3 inhibitors are possible candidates for osteoinductive therapy in MM.…”

“…To characterize novel agents and pathways able to regulate the expression of these ligands in MM cells, we investigated the activity of different GSK3 inhibitors, a class of molecules recently studied for their ability to inhibit the proliferation of malignant lymphoid cells, including MM (21)(22)(23).…”

“…In this regard, it has been shown that inhibition of GSK3 can induce growth arrest or apoptosis in MM cell lines, and enhance the anti-MM cytotoxic effect of bortezomib, by modulating critical signaling pathways in these cells (21)(22)(23).…”

The intersection of genetic and chemical genomic screens identifies GSK-3α as a target in human acute myeloid leukemia

“…For example, GSK-3β missplicing, leading to an increase in β-catenin and enhanced serial replating, was reported in the granulocyte-macrophage progenitors in blast crisis chronic myelogenous leukemia (14). Chemical inhibition of GSK-3 was also reported to induce apoptosis in chronic lymphocytic leukemia and in multiple myeloma (15,28,29). Moreover, GSK-3 was initially reported as a target in MLLrearranged acute leukemia and then more broadly in hematopoietic cells transformed by HOX genes by promoting the conditional association of CREB and its coactivators CBP and TORC with MEIS1 (13,17).…”

Protein Kinase CK2 Protects Multiple Myeloma Cells from ER Stress–Induced Apoptosis and from the Cytotoxic Effect of HSP90 Inhibition through Regulation of the Unfolded Protein Response

“…The internal Institutional Board approved the use of human material. Normal peripheral blood mononuclear cells (PBMC); malignant CD138 þ plasma cells; multiple myeloma cell lines RPMI-8226, U-266, and H-929; and the human stromal cell line HS-5 were isolated and cultured as described previously (23). Primary mesenchymal bone marrow stromal cells from patients with multiple myeloma were obtained as described previously (24).…”