Gene expression analysis of B-lymphoma cells resistant and sensitive to bortezomib

Selective vulnerability of neurons to acute toxicity after proteasome inhibitor treatment: implications for oxidative stress and insolubility of newly synthesized proteins

Maintaining protein homeostasis is vital to cell viability, with numerous studies demonstrating a role for proteasome inhibition occurring during the aging of a variety of tissues and, presumably, contributing to the disruption of cellular homeostasis during aging. In this study we sought to elucidate the differences between neurons and astrocytes in regard to basal levels of protein synthesis, proteasome-mediated protein degradation, and sensitivity to cytotoxicity after proteasome inhibitor treatment. In these studies we demonstrate that neurons have an increased vulnerability, compared to astrocyte cultures, to proteasome-inhibitor-induced cytotoxicity. No significant difference was observed between these two cell types in regard to the basal rates of protein synthesis, or basal rates of protein degradation, in the pool of short-lived proteins. After proteasome inhibitor treatment neuronal crude lysates were observed to undergo greater increases in the levels of ubiquitinated and oxidized proteins and selectively exhibited increased levels of newly synthesized proteins accumulating within the insoluble protein pool, compared to astrocytes. Together, these data suggest a role for increased oxidized proteins and sequestration of newly synthesized proteins in the insoluble protein pool, as potential mediators of the selective neurotoxicity after proteasome inhibitor treatment. The implications for neurons exhibiting increased sensitivity to acute proteasome inhibitor exposure, and the corresponding changes in protein homeostasis observed after proteasome inhibition, are discussed in the context of both aging and age-related disorders of the nervous system.

Vav-1 expression correlates with NFκB activation and CD40-mediated cell death in diffuse large B-cell lymphoma cell lines

Diffuse large B-cell lymphoma (DLBCL) is an aggressive malignancy with a variable response to therapy. We have previously shown that DLBCL cell lines differ in their susceptibility to CD40-mediated cell death, and that resistance to CD40-targeted antibodies correlated with increased expression of markers of immature B-cell and absence of Vav-1 mRNA. We used gene expression profiling to investigate the mechanism of CD40 resistance in these cell lines, and found that resistance correlated with lack of Vav-1 and inability to activate NFκB upon CD40 ligation. Analysis of tissue microarrays of 213 DLBCL cases revealed that Vav-1 expression correlated with a higher proliferative index and the presence of the post-germinal centre marker Irf-4. Our results suggest that Vav-1 expression may be associated with activated B-cell DLBCL origin and higher proliferative activity, and indicate Vav-1 as a potential marker to identify tumours likely to respond to CD40-targeted therapies.

Caspase 3a: new prognostic marker for diffuse large B-cell lymphoma in the rituximab era

Fewer than half of patients with diffuse large B-cell lymphoma (DLBCL) can be cured. Molecular prognostic factors in the rituximab era must be re-evaluated, because there are few molecular indicators with prognostic value. Samples of DLBCL from 41 newly diagnosed patients with a median follow-up of 52 months were studied. Immunohistochemical staining was performed to investigate the expression of apoptosis-related proteins (Bcl-2 and caspase 3a), cell proliferation (Ki-67), and tumor microenvironmental factors. Two groups were analysed, 23 cases (56%) treated with CHOP and 18 (44%) treated with R-CHOP. Survival analysis showed that cases with overexpression of Bcl-2 had worse overall survival (OS) in the CHOP group. However, OS in the R-CHOP group was adversely affected by lack of caspase 3a staining. In the entire series, cases positive for caspase 3a showed significantly better OS, without significance for other parameters, and caspase 3 was associated with parameters of prognosis and OS in R-CHOP. This is the first study that relates caspase 3a and prognosis in DLBCL.

Anti-malaria drug blocks proteotoxic stress response: anti-cancer implications

The number of physical conditions and chemical agents induce accumulation of misfolded proteins creating proteotoxic stress. This leads to activation of adaptive pro-survival pathway, known as heat shock response (HSR), resulting in expression of additional chaperones. Several cancer treatment approaches, such as proteasome inhibitor Bortezomib and hsp90 inhibitor geldanamycin, involve activation of proteotoxic stress. Low efficacy of these therapies is likely due to the protective effects of HSR induced in treated cells, making this pathway an attractive target for pharmacological suppression. We found that the anti-malaria drugs quinacrine (QC) and emetine prevented HSR in cancer cells, as judged by induction of hsp70 expression. As opposed to emetine, which inhibited general translation, QC did not affect protein synthesis, but rather suppressed inducible HSF1-dependent transcription of the hsp70 gene in a relatively selective manner. The treatment of tumor cells in vitro with a combination of non-toxic concentrations of QC and proteotoxic stress inducers resulted in rapid induction of apoptosis. The effect was similar if QC was substituted by siRNA against hsp70, suggesting that the HSR inhibitory activity of QC was responsible for cell sensitization to proteotoxic stress inducers. QC was also found to enhance the antitumor efficacy of proteotoxic stress inducers in vivo: combinatorial treatment with 17-DMAG + QC resulted in suppression of tumor growth in two mouse syngeneic models. These results reveal that QC is an inhibitor of HSF1-mediated HSR. As such, this compound has significant clinical potential as an adjuvant in therapeutic strategies aimed at exploiting the cytotoxic potential of proteotoxic stress.

Activation of PERK kinase in neural cells by proteasome inhibitor treatment

Inhibition of the proteasome proteolytic pathway occurs as the result of normal aging, as well as in a variety of neurodegenerative conditions, and is believed to promote cellular toxicity in each of these conditions through diverse mechanisms. In the present study, we examined whether proteasome inhibition alters the protein kinase receptor-like endoplasmic reticulum kinase (PERK). Our studies demonstrate that proteasome inhibitors induce the transient activation of PERK in both primary rat neurons as well as the N2a neural cell line. Experiments with siRNA to PERK demonstrated that the modulation of PERK was not significant involved in regulating toxicity, ubiquitinated protein levels, or ribosome perturbations in response to proteasome inhibitor treatment. Surprisingly, PERK was observed to be involved in the up-regulation of p38 kinase following proteasome inhibitor treatment. Taken together, these data demonstrate the ability of proteasome inhibition to activate PERK and demonstrate evidence for novel cross-talk between PERK and the activation of p38 kinase in neural cells following proteasome inhibition. Taken together, these data have implications for understanding the basis by which proteasome inhibition alters neural homeostasis, and the basis by which cell signaling cascades are regulated by proteasome inhibition.

Combination of hyperthermia and bortezomib results in additive killing in mantle cell lymphoma cells

The proteasome inhibitor bortezomib exhibits antitumor activity in many malignancies including mantle cell lymphoma (MCL). Unfortunately, many patients fail to respond to treatment or become refractory. Hyperthermia is an effective chemosensitizer that in combination with some chemotherapeutic agents has shown clinical activity in phase II and III studies. The aim of this study was to use MCL cell lines to investigate the potential benefit of combining clinically relevant doses of bortezomib with two different thermal doses (41.8 degrees C/120 min and 44 degrees C/30 min) that mimic the heterogeneity of the temperature distributions achieved within tumors during hyperthermia. Treated tumor cells were assessed for proliferation using the WST-1 assay and for apoptosis by annexin V staining, while heat shock protein (HSP) levels were determined following western blot analysis. Our results demonstrated that MCL cell lines that are sensitive to bortezomib are also thermosensitive and have low basal expression of hsp27, whereas the bortezomib-resistant MCL cell line strongly expresses hsp27 and is thermoresistant. Interestingly, pre-treatment of MCL cell lines with heat at the two different thermal doses, and the transient elevation of hsp27 and hsp70, do not impair their primary sensitivity to bortezomib. Finally, we show that the concurrent treatment of heat and bortezomib results in additive killing in MCL cell lines.In conclusion, these results suggest that the application of bortezomib, under thermal conditions, in mantle cell lymphoma cells may be beneficial and warrants further investigation.

2-D PAGE-based comparison of proteasome inhibitor bortezomib in sensitive and resistant mantle cell lymphoma

Although gene expression following bortezomib treatment has been previously explored, direct effects of bortezomib-induced proteasome inhibition on protein level has not been analyzed so far. Using 2-D PAGE in five mantle cell lymphoma cell lines, we screened for cellular protein level alterations following treatment with 25 nM bortezomib for up to 4 h. Using MS, we identified 38 of the 41 most prominent reliably detected protein spots. Twenty-one were affected in all cell lines, whereas the remaining 20 protein spots were exclusively altered in sensitive cell lines. Western blot analysis was performed for 17 of the 38 identified proteins and 70.6% of the observed protein level alterations in 2-D gels was verified. All cell lines exhibited alterations of the cellular protein levels of heat shock-induced protein species (HSPA9, HSP7C, HSPA5, HSPD1), whereas sensitive cell lines also displayed altered cellular protein levels of energy metabolism (ATP5B, AK5, TPI1, ENO-1, ALDOC, GAPDH), RNA and transcriptional regulation (HNRPL, SFRS12) and cell division (NEBL, ACTB, SMC1A, C20orf23) as well as tumor suppressor genes (ENO-1, FH). These proteins clustered in a tight interaction network centered on the major cellular checkpoints TP53. The results were confirmed in primary mantle cell lymphoma, thus confirming the critical role of these candidate proteins of proteasome inhibition.

Simultaneous proteosome inhibition and heat shock protein induction by bortezomib is beneficial in experimental pancreatitis

The proteosome inhibitor bortezomib is used in the treatment of patients with multiple myeloma. Proteosomes are responsible for the degradation of I-kappaB, the inhibitory protein of transcription factor nuclear factor kappa B (Nf-kappaB). The heat shock protein (HSP) inducing effect of bortezomib is also documented. The aim of our work was to test the anti-inflammatory effect of bortezomib in cholecystokinin-octapeptide (CCK-8)-induced acute pancreatitis. Male Wistar rats were divided into three groups (n=8 in each). Group P received an i.p. injection of physiological saline (p.s.) 60 min. before the induction of acute pancreatitis by three hourly s.c. injections of 100 microg/kg CCK-8. Group BP received 1 mg/kg bortezomib dissolved in p.s. 1 h previous to pancreatitis induction. Group C was treated with the vehicle (p.s.). Animals were exsanguinated 4 h after the last injection of CCK-8. Bortezomib pre-treatment significantly reduced the pancreatic weight/body weight ratio, and improved the histology by decreasing the extent of vacuolization and infiltration. Bortezomib pre-treatment inhibited I-kappaBbeta degradation, and induced the synthesis of HSP72. The results confirmed the anti-inflammatory effect of bortezomib in acute experimental pancreatitis. This effect of the drug is presumably mediated by the inhibition of Nf-kappaB activation and induction of HSP synthesis.

Different mutants of PSMB5 confer varying bortezomib resistance in T lymphoblastic lymphoma/leukemia cells derived from the Jurkat cell line

OBJECTIVE

To investigate the relationship between bortezomib resistance and mutations in the proteasome beta5 subunit (PSMB5) gene.

MATERIALS AND METHODS

Various bortezomib-resistant lymphoblastic lymphoma/leukemia lines were established by repeated cycles of bortezomib selection. Mutations were detected by sequencing the complementary DNA of the PSMB5 gene. Mutated clones were selected by limited dilution and cultured without bortezomib. Messenger RNA expression levels of PSMB5 in these mutated clones were measured by quantitative reverse transcription polymerase chain reaction. The degree of resistance was determined by cytotoxicity at various bortezomib concentrations. The chymotrypsin-like activities were assayed by measuring the release of the fluorescent 7-amido-4-methylcoumarin from the substrate N-succinyl-Leu-Leu-Val-Tyr-7-amido-4-methylcoumarin.

RESULTS

In addition to the previously reported PSMB5 G322A mutant (Ala49Thr), a C323T mutant (Ala49Val), and G322A, C326T conjoined mutant (Ala49Thr and Ala50Val) were selected and clones containing these mutations (JurkatB-G322A, JurkatB-C323T, and JurkatB-G322A/C326T) were obtained. After being cultured without bortezomib for >2 months, no significant difference in PSMB5 messenger RNA levels was detected between these JurkatB cells and parental Jurkat cells. JurkatB-G322A, JurkatB-C323T, and JurkatB-G322A/C326T clones displayed 22.0-fold, 39.4-fold, and 66.7-fold resistance, respectively, to bortezomib compared to Jurkat cells. There were no significant differences between the chymotrypsin-like activities of these mutants and Jurkat cells. The inhibitory effect of bortezomib on chymotrypsin-like activity was the weakest in JurkatB-G322A/C326T cells, and the strongest in JurkatB-G322A cells, with JurkatB-C323T cells falling in between.

CONCLUSION

Mutations of the PSMB5 gene resulting in substitutions of Ala49 and Ala50 of PSMB5 protein can confer varying bortezomib resistance.

The effects of proteasome inhibitor bortezomib on a P-gp positive leukemia cell line K562/A02

The aim of this study is to clarify the efficacy of proteasome inhibitor bortezomib to multidrug resistant (MDR) acute leukemia cells. We observed the effects of bortezomib on a P-glycoprotein (P-gp) positive leukemia line K562/A02. The results showed that bortezomib has significant effects on P-gp positive K562/A02 cells including cytotoxicity (48 h IC(50): 171.36 nM), induction of apoptosis (31.71 +/- 1.07% apoptotic cells after 24 h treatment at 100 nM), and inhibition of proteasome chymotrypsin-like activity (relative activity to untreated controls: 20.07 +/- 0.66% at 24 h with 10 nM bortezomib). These effects were lower than those observed in K562 cells (IC(50), percentage of apoptotic cells, relative chymotrypsin-like activity to untreated controls were 56.28 nM, 77.95 +/- 0.35%, 5.35 +/- 2.05% after the same treatments, respectively). No synergy between daunorubicin and bortezomib was shown in the killing of K562/A02 cells (synergistic ratios were <1). P-gp expression levels did not decrease in K562/A02 cells after bortezomib treatment. Pretreatment with bortezomib does not improve the intracellular anthracycline concentration in K562/A02 cells. Bortezomib shows a promising effect for the treatment of refractory/relapsed leukemia, but it does not improve the effect of anthracycline to MDR leukemia cells.

Pathway activation in large B-cell non-Hodgkin lymphoma cell lines by doxorubicin reveals prognostic markers of in vivo response

The principal curative agent in the front-line treatment of patients with diffuse large B-cell lymphoma (DLBCL) is the anthracycline, doxorubicin. To define pathways that may have a functional role in the response of DLBCL in vivo to doxorubicin-based therapies, seven DLBCL cell lines were treated with doxorubicin and the cellular response evaluated. Expression profiling of responses revealed changes in levels of genes consistent with discrete pathway activation that were confirmed functionally. The two most sensitive cell lines (Ly3 and Ly10) displayed activation of the TP53 pathway but not in the remaining five (Ly1, Ly2, Ly4, Ly7 and Ly8), where TP53 mutations were identified. In this latter group, a G2/M delay was invoked. NF-kappaB pathway activation was evident in Ly1 which with Ly4 displayed the most chemoresistant response. Treatment of Ly1 after doxorubicin with the proteasomic inhibitor, bortezomib, additively increased the cytotoxic effect of doxorubicin. Chemoresistance of Ly4 was associated with loss of chromosome 2 (0-9 Mbp) that in vivo was highly correlated with adverse outcome. Thus, the response of DLBCL in vivo and in vitro is defined by several distinct molecular and genetic pathways which is, perhaps, not surprising given the heterogeneous clinical, morphologic and genetic nature of DLBCL.

High-content functional screen to identify proteins that correct F508del-CFTR function

Cystic Fibrosis is caused by mutations in CFTR, with a deletion of a phenylalanine at position 508 (F508del-CFTR) representing the most common mutation. The F508del-CFTR protein exhibits a trafficking defect and is retained in the endoplasmic reticulum. Here we describe the development of a high-content screen based on a functional assay to identify proteins that correct the F508del-CFTR defect. Using a HEK293 MSR GripTite cell line that stably expresses F508del-CFTR, we individually co-expressed approximately 450 unique proteins fused to the Cl(-)-sensitive YFP(H148Q/I152L) mutant. We then tested correction of F508del-CFTR function by the CI(-)/l(-) exchange method following stimulation with forskolin/IBMX/genistein, using quantitative recordings in multiple individual cells with a high-content (high-throughput) Cellomics KSR imaging system. Using this approach, we identified several known and novel proteins that corrected F508del-CFTR function, including STAT1, Endothelin 1, HspA4, SAPK substrate protein 1, AP2M1, LGALS3/galectin-3, Trk-fused gene, Caveolin 2, PAP/REG3alpha, and others. The ability of these correctors to rescue F508del-CFTR trafficking was then validated by demonstrating their enhancement of maturation (appearance of band C) and by cell surface expression of F508del-CFTR bearing HA tag at the ectodomain using confocal microscopy and flow cytometry. These data demonstrate the utility of high-content analyses for identifying proteins that correct mutant CFTR and discover new proteins that stimulate this correction. This assay can also be utilized for RNAi screens to identify inhibitory proteins that block correction of F508del-CFTR, small molecule, and peptide screens.

Bortezomib-induced survival signals and genes in human proximal tubular cells

Bortezomib has been introduced recently in the therapy of multiple myeloma (MM), a disease that is frequently associated with progressive renal failure. Because bortezomib-based therapy has been reported to lead to a rapid recovery of kidney function in patients with MM, we decided to study its direct effects in proximal tubular epithelial cells (PTCs) compared with glomerular mesangial cells (GMCs). After 24 h of stimulation, 50 nM bortezomib led to a 6.37-fold induction of apoptosis and markedly activated caspase-9 and -3 in GMCs but not in PTCs. In PTCs but not in GMCs, bortezomib led to a strong time-dependent degradation of IkappaB-alpha and to a long-lasting phosphorylation of both NF-kappaBp65 and extracellular signal-regulated kinase 1/2. Microarray analysis in bortezomib-treated PTCs revealed a time-dependent predominance of antiapoptotic genes compared with proapoptotic genes. Bortezomib (50 nM) induced heat shock protein (Hsp) 70 mRNA and protein levels in PTCs, whereas basal and bortezomib-stimulated Hsp70 protein expression was much weaker in GMCs. Moreover, bortezomib induced Bcl-2-associated athanogene (BAG) 3 mRNA and protein expression but inhibited BAG5 mRNA levels in PTCs. These data suggest that the reduced susceptibility of PTCs to bortezomib-induced cell apoptosis is because of cell type-specific effects of this compound on apoptosis/survival genes and pathways. The concept of bortezomib representing a blocker of both NF-kappaB activation and cell survival should be carefully examined in particular renal cell types.

Down-regulation of phospho-Akt is a major molecular determinant of bortezomib-induced apoptosis in hepatocellular carcinoma cells

Bortezomib, a proteasome inhibitor, has been clinically approved for the treatment of myeloma and lymphoma. Here, we report a differential effect of bortezomib on apoptosis in four hepatocellular carcinoma (HCC) cell lines and identify the major molecular event that determines sensitivity. Although bortezomib inhibited proteasome activity to a similar extent in all HCC cell lines, it showed differential effects on their viability: Huh-7 (IC(50) 196 nmol/L), Sk-Hep1 (IC(50) 180 nmol/L), Hep3B (IC(50) 112 nmol/L), and resistant PLC5 (IC(50) >1,000 nmol/L). Bortezomib caused cell cycle arrest at G(2)-M phase in all HCC cells tested whereas apoptotic induction was found only in sensitive cells but not in PLC5 cells. No significant bortezomib-induced NF-kappaB changes were noted in Huh-7 and PLC5. Bortezomib down-regulated phospho-Akt (P-Akt) in a dose- and time-dependent manner in all sensitive HCC cells whereas no alterations of P-Akt were found in PLC5. Down-regulation of Akt1 by small interference RNA overcame the apoptotic resistance to bortezomib in PLC5 cells, but a constitutively activated Akt1 protected Huh-7 cells from bortezomib-induced apoptosis. Furthermore, bortezomib showed suppression of tumor growth with down-regulation of P-Akt in Huh-7 tumors but not in PLC5 tumors. Down-regulation of P-Akt represents a major molecular event of bortezomib-induced apoptosis in HCC cell lines and may be a biomarker for predicting clinical response to HCC treatment. Targeting Akt signaling overcomes drug resistance to bortezomib in HCC cells, which provides a new approach for the combinational therapy of HCC.

Mechanisms of proteasome inhibitor action and resistance in cancer

Proteasome inhibitors (PIs), such as bortezomib, carfilzomib or NPI-0052, have excellent clinical activity in patients with multiple myeloma and mantle cell lymphoma, and they are currently being evaluated in combination with other agents in patients with solid tumors. Although they exert broad effects on cancer cells, their ability to (1) stabilize pro-apoptotic members of the BCL-2 family, (2) inhibit the two major pathways leading to NFkappaB activation, and (3) cause the build-up of misfolded proteins appear to be particularly important. In addition, PIs may disrupt tumor-stromal interactions that drive NFkappaB activation and angiogenesis and in such a way sensitize cancer cells to other agents. Still, drug resistance ultimately emerges in all tumors that initially respond to PIs. This review provides an overview of the current thinking about how PIs may kill cancer cells exemplified for pancreatic cancer and the possible mechanisms involved in resistance to PIs.

Noxa mediates bortezomib induced apoptosis in both sensitive and intrinsically resistant mantle cell lymphoma cells and this effect is independent of constitutive activity of the AKT and NF-kappaB pathways

Bortezomib is more active against mantle cell lymphoma (MCL) than against most other lymphoma subtypes. Nevertheless, up to half of patients with MCL have bortezomib resistant disease. Factors contributing to intrinsic resistance to bortezomib have not been determined. Here we used a panel of eight bortezomib sensitive (median IC(50) 5.9 nM) and three relatively bortezomib resistant cell lines (median IC(50) 12.9 nM) to investigate differences in tumor biology that could determine sensitivity to bortezomib. Bortezomib effectively inhibited high baseline proteasome activity and induced a comparable degree of proteasome inhibition in both sensitive and resistant cells. At 10 nM, bortezomib induced the proapoptotic BH3-only protein Noxa in sensitive but not resistant cells. At higher concentrations of bortezomib, however, Noxa was also upregulated in resistant cells and this effect was sufficient to induce apoptosis. Silencing of Noxa with siRNA rescued these cells from apoptosis, arguing against a defect in Noxa regulation or function as the basis of bortezomib resistance. Bortezomib was equally effective against cells with high and low constitutive NF-kappaB signaling. Also, sensitive and resistant MCL cell lines showed comparable activation of the AKT pathway. We conclude that bortezomib can overcome classic mechanisms of resistance to apoptosis and that determinants of bortezomib sensitivity in MCL are due to differences in signaling or stress pathways upstream of Noxa.

Point mutation of the proteasome beta5 subunit gene is an important mechanism of bortezomib resistance in bortezomib-selected variants of Jurkat T cell lymphoblastic lymphoma/leukemia line

To study the mechanism of acquired resistance to bortezomib, a new antitumor drug that is the first therapeutic proteasome inhibitor, we established a series of bortezomib-resistant T lymphoblastic lymphoma/leukemia cell lines, designated the JurkatBs, from the parental Jurkat line via repeated drug selection. There were no significant differences in the growth curves or colony formation between the JurkatB cells and parental Jurkat cells. The effects of bortezomib on cytotoxicity, cell cycle arrest, and induction of apoptosis were decreased in JurkatB cells compared with parental Jurkat cells. A mutation in the proteasome beta5 subunit (PSMB5) gene (G322A), which encodes an amino acid change from Ala to Thr at polypeptide position 108, was detected by sequencing full-length cDNA clones and direct polymerase chain reaction products of the PSMB5 gene. Bortezomib caused less inhibition of chymotrypsin-like activity in resistant cells. When the G322A mutant PSMB5 was retrovirally introduced into parental Jurkat cells, it conferred bortezomib resistance to these cells, resulting in decreased cytotoxicity, apoptosis, and inhibition of chymotrypsin-like activity. The predicted structure of A108T-mutated PSMB5 shows a conformational change that suggests decreased affinity to bortezomib. In short, the G322A mutation of the PSMB5 gene is a novel mechanism for bortezomib resistance.

Abnormal AP-1 protein expression in primary cutaneous B-cell lymphomas

BACKGROUND

Primary cutaneous B-cell lymphoma (PCBCL) consists mainly of primary cutaneous marginal zone B-cell lymphoma (PCMZL), primary cutaneous follicle centre lymphoma (PCFCL) and primary cutaneous large B-cell lymphoma, leg type (PCLBCL-LT). The activator protein 1 (AP-1) transcription factor includes JUN, FOS and other family members.

OBJECTIVES

To assess the expression pattern of AP-1 transcription factors in PCBCL.

METHODS

We analysed paraffin tissue sections from nine cases of PCMZL, seven PCFCL, six PCLBCL-LT and two unspecified PCBCL cases by using immunohistochemistry with antibodies against c-JUN, JUNB, JUND, c-FOS, RAF1, alphaPAK, CD30 and CCND1.

RESULTS

A positive staining for JUND (++) was observed in six cases of PCFCL (86%), five PCLBCL-LT (83%) and five PCMZL (56%). Positive CCND1 protein expression was present in four cases of PCLBCL-LT (67%), four PCFCL (57%) and four PCMZL (44%), and the two unspecified PCBCL cases. Expression of alphaPAK protein was seen in three cases of PCLBCL-LT (50%), two PCMZL (22%) and one PCFCL. However, c-JUN, c-FOS and RAF1 protein were rarely expressed in the PCBCL cases analysed; JUNB and CD30 protein expression was absent in these cases.

CONCLUSIONS

These findings suggest that the presence of abnormal AP-1 protein expression is associated with upregulation of JUND, CCND1 and alphaPAK and downregulation of JUNB in PCBCL.

Overexpression of the PSMB5 gene contributes to bortezomib resistance in T-lymphoblastic lymphoma/leukemia cells derived from Jurkat line

OBJECTIVE

To study the mechanism of bortezomib resistance in JurkatB lines derived from T-lymphoblastic lymphoma/leukemia Jurkat line.

MATERIALS AND METHODS

Cytotoxicities of popular chemotherapeutic drugs to JurkatB cells were analyzed by trypan blue assay. Functional drug efflux in JurkatB cells was determined by flow cytometry utilizing daunorubicin and the expression of P-glycoprotein (P-gp) was detected by Western blot. mRNA expression levels of proteasome beta5 subunit (PSMB5) were measured by quantitation real-time reverse transcription polymerase chain reaction. In situ hybridization was performed to detect the amplification of PSMB5 gene. The chymotrypsin-like activities were assayed by measuring the release of the fluorescent 7-amido-4-methylcoumarin (AMC) from the substrate N-succinyl-Leu-Leu-Val-Tyr-AMC. Cytogenetic studies were performed using R-banded metaphases and fluorescence in situ hybridization (FISH) analysis. IkappaB-alpha levels were detected by Western blot.

RESULTS

No cross-resistance to daunorubicin, adriamycin, vindesine, and etoposide was found in JurkatB cells. No evidence of drug efflux was found in JurkatB cells and the expression of P-gp was negative. The PSMB5 mRNA was overexpressed in highly resistant JurkatB5 and JurkatB1 lines compared with parental Jurkat, corresponding well with the increase of chymotrypsin-like activity and a karyotype of i(14q). Amplification of PSMB5 gene was demonstrated by in situ hybridization and FISH. The decreased IkappaB-alpha level in JurkatB5 cells after bortezomib treatment indicating an upregulation of nuclear factor-kappaB (NF-kappaB) activity.

CONCLUSION

The mechanism of bortezomib resistance is different from that of multidrug resistance. Overexpression of PSMB5 is an important mechanism for bortezomib resistance in JurkatB lines. NF-kappaB may play a critical role in evading the apoptotic effects.

Effect of bortezomib on human neuroblastoma: analysis of molecular mechanisms involved in cytotoxicity

Background

Bortezomib, a specific and selective inhibitor of the 26S proteasome with antitumor activity against a wide range of malignancies, has been approved for the treatment of relapsed or refractory multiple myeloma and other cancers. Recently, bortezomib has been identified as an effective inhibitor of neuroblastoma cell growth and angiogenesis.

Results

In the present study, we demonstrate that some neuroblastoma cell lines are actually resistant to bortezomib. We have sought to characterize the main pathway by which proteasome inhibition leads to apoptosis, and to define the mechanism responsible for resistance to bortezomib in neuroblastoma cells. Our results show that SB202190, an inhibitor of mitogen-activated protein kinase (MAPK) p38, enhances the ability of bortezomib to induce apoptosis by preventing the phosphorylation of the heat shock protein (HSP) 27.

Conclusion

This study opens the way to further clinical investigations and suggests a potential benefit of using a combination of bortezomib with an inhibitor of p38 MAPK for the treatment of neuroblastoma relapse.

ATF4 is an oxidative stress-inducible, prodeath transcription factor in neurons in vitro and in vivo

Oxidative stress is pathogenic in neurological diseases, including stroke. The identity of oxidative stress–inducible transcription factors and their role in propagating the death cascade are not well known. In an in vitro model of oxidative stress, the expression of the bZip transcription factor activating transcription factor 4 (ATF4) was induced by glutathione depletion and localized to the promoter of a putative death gene in neurons. Germline deletion of ATF4 resulted in a profound reduction in oxidative stress–induced gene expression and resistance to oxidative death. In neurons, ATF4 modulates an early, upstream event in the death pathway, as resistance to oxidative death by ATF4 deletion was associated with decreased consumption of the antioxidant glutathione. Forced expression of ATF4 was sufficient to promote cell death and loss of glutathione. In ATF4^−/− neurons, restoration of ATF4 protein expression reinstated sensitivity to oxidative death. In addition, ATF4^−/− mice experienced significantly smaller infarcts and improved behavioral recovery as compared with wild-type mice subjected to the same reductions in blood flow in a rodent model of ischemic stroke. Collectively, these findings establish ATF4 as a redox-regulated, prodeath transcriptional activator in the nervous system that propagates death responses to oxidative stress in vitro and to stroke in vivo.

The proteasomal and apoptotic phenotype determine bortezomib sensitivity of non-small cell lung cancer cells

Bortezomib is a novel anti-cancer agent which has shown promising activity in non-small lung cancer (NSCLC) patients. However, only a subset of patients respond to this treatment. We show that NSCLC cell lines are differentially sensitive to bortezomib, IC50 values ranging from 5 to 83 nM. The apoptosis-inducing potential of bortezomib in NSCLC cells was found to be dependent not only on the apoptotic phenotype but also on the proteasomal phenotype of individual cell lines. Upon effective proteasome inhibition, H460 cells were more susceptible to apoptosis induction by bortezomib than SW1573 cells, indicating a different apoptotic phenotype. However, exposure to a low dose of bortezomib did only result in SW1573 cells, and not in H460 cells, in inhibition of proteasome activity and subsequent apoptosis. This suggests a different proteasomal phenotype as well. Additionally, overexpression of anti-apoptotic protein Bcl-2 in H460 cells did not affect the proteasomal phenotype of H460 cells but did result in decreased bortezomib-induced apoptosis. In conclusion, successful proteasome-inhibitor based treatment strategies in NSCLC face the challenge of having to overcome apoptosis resistance as well as proteasomal resistance of individual lung cancer cells. Further studies in NSCLC are warranted to elucidate underlying mechanisms.

Knockdown of PgP resensitizes leukemic cells to proteasome inhibitors

Overexpression of MDR-1 represents a critical mechanism of drug resistance in cancer. Proteasome inhibitors recently entered the clinic for treatment of multiple myeloma. We provide evidence that the proteasome-inhibitors Bortezomib and MLN273 are both substrates of MDR-1 by using knockdown of MDR-1 via a transposon-based vector system stably expressing siRNA against MDR-1 in MDR-1-overexpressing K562/Dox cells. Notably, the efficacy of MLN273 (EC(50) from 253 ng/ml in MDR-1(+) to 9.7 ng/ml in MDR-1(-) cells) was much more dependent on MDR-1 expression than Bortezomib (EC(50) from 24.9 ng/ml in MDR-1(+) to 4.5 ng/ml in MDR-1(-) cells). Growth inhibition in MDR-1 negative cells was in part due to increased rate of apoptosis. The enhanced inhibitory effect on the proteasome by loss of MDR-1 was corroborated by a reduced proteasomal activity. Our report provides evidence that MLN273 and, to a lesser degree, Bortezomib are both MDR-1-substrates, which might be relevant for drug-resistance in cancer.

Heat shock protein inhibition is associated with activation of the unfolded protein response pathway in myeloma plasma cells

Plasma cells producing high levels of paraprotein are dependent on the unfolded protein response (UPR) and chaperone proteins to ensure correct protein folding and cell survival. We hypothesized that disrupting client-chaperone interactions using heat shock protein 90 (Hsp90) inhibitors would result in an inability to handle immunoglobulin production with the induction of the UPR and myeloma cell death. To study this, myeloma cells were treated with Hsp90 inhibitors as well as known endoplasmic reticulum stress inducers and proteasome inhibitors. Treatment with thapsigargin and tunicamycin led to the activation of all 3 branches of the UPR, with early splicing of XBP1 indicative of IRE1 activation, upregulation of CHOP consistent with ER resident kinase (PERK) activation, and activating transcription factor 6 (ATF6) splicing. 17-AAG and radicicol also induced splicing of XBP1, with the induction of CHOP and activation of ATF6, whereas bortezomib resulted in the induction of CHOP and activation of ATF6 with minimal effects on XBP1. After treatment with all drugs, expression levels of the molecular chaperones BiP and GRP94 were increased. All drugs inhibited proliferation and induced cell death with activation of JNK and caspase cleavage. In conclusion, Hsp90 inhibitors induce myeloma cell death at least in part via endoplasmic reticulum stress and the UPR death pathway.

The Proteasome Inhibitor Bortezomib Acts Independently of p53 and Induces Cell Death via Apoptosis and Mitotic Catastrophe in B-Cell Lymphoma Cell Lines

Bortezomib is a proteasome inhibitor with proven efficacy in multiple myeloma and non-Hodgkin's lymphoma. This study reports the effects of bortezomib in B-cell lymphoma cell lines with differing sensitivity to bortezomib to investigate factors that influence sensitivity. Bortezomib induced a time- and concentration-dependent reduction in cell viability in five lymphoma cell lines, with EC(50) values ranging from 6 nmol/L (DHL-7 cells) to 25 nmol/L (DHL-4 cells) after 72 h. Bortezomib cytotoxicity was independent of p53 function, as all cell lines exhibited mutations by sequence analysis. The difference in sensitivity was not explained by proteasome or nuclear factor-kappaB (NF-kappaB) inhibition as these were similar in the most and least sensitive cells. NF-kappaB inhibition was less marked than that of a specific NF-kappaB inhibitor, Bay 11-7082. Cell cycle analysis showed a marked G(2)-arrested population in the least sensitive DHL-4 line only, an effect that was not present with Bay 11-7082 treatment. Conversely, in DHL-7 cells, bortezomib treatment resulted in cells moving into an aberrant mitosis, indicative of mitotic catastrophe that may contribute to increased sensitivity to bortezomib. These studies show that although bortezomib treatment had similar effects on apoptotic and NF-kappaB signaling pathways in these cell lines, different cell cycle effects were observed and induction of a further mechanism of cell death, mitotic catastrophe, was observed in the more sensitive cell line, which may provide some pointers to the difference in sensitivity between cell lines. An improved understanding of how DHL-7 cells abrogate the G(2)-M cell cycle checkpoint may help identify targets to increase the efficacy of bortezomib.

Novel etodolac analog SDX-308 (CEP-18082) induces cytotoxicity in multiple myeloma cells associated with inhibition of beta-catenin/TCF pathway

We have reported previously that R-enantiomer of etodolac (R-etodolac), which is under investigation in phase 2 clinical trials in chronic lymphocytic leukemia, induces potent cytotoxicity at clinically relevant concentrations in multiple myeloma (MM) cells. In this study, we demonstrated that SDX-308 (CEP-18082), a novel analog of etodolac, has more potent cytotoxicity than R-etodolac against both MM cell lines and patient MM cells, including tumor cells resistant to conventional (dexamethasone, doxorubicine, melphalan) and novel (bortezomib) therapies. SDX-308-induced cytotoxicity is triggered by caspase-8/9/3 activation and poly (ADP-ribose) polymerase cleavage, followed by apoptosis. SDX-308 significantly inhibits beta-catenin/T-cell factor pathway by inhibiting nuclear translocation of beta-catenin, thereby downregulating transcription and expression of downstream target proteins including myc and survivin. Neither interleukin-6 nor insulin-like growth factor-1 protect against growth inhibition triggered by SDX-308. Importantly, growth of MM cells adherent to bone marrow (BM) stromal cells is also significantly inhibited by SDX-308. Our data therefore indicate that the novel etodolac analog SDX-308 can target MM cells in the BM milieu.