Regulation of constitutive p50/c-Rel activity via proteasome inhibitor-resistant IkappaBalpha degradation in B cells

Ectopic CH60 mediates HAPLN1-induced cell survival signaling in multiple myeloma

Multiple myeloma (MM), the second most common hematological malignancy, is generally considered incurable because of the development of drug resistance. We previously reported that hyaluronan and proteoglycan link protein 1 (HAPLN1) produced by stromal cells induces activation of NF-κB, a tumor-supportive transcription factor, and promotes drug resistance in MM cells. However, the identity of the cell surface receptor that detects HAPLN1 and thereby engenders pro-tumorigenic signaling in MM cells remains unknown. Here, we performed an unbiased cell surface biotinylation assay and identified chaperonin 60 (CH60) as the direct binding partner of HAPLN1 on MM cells. Cell surface CH60 specifically interacted with TLR4 to evoke HAPLN1-induced NF-κB signaling, transcription of anti-apoptotic genes, and drug resistance in MM cells. Collectively, our findings identify a cell surface CH60-TLR4 complex as a HAPLN1 receptor and a potential molecular target to overcome drug resistance in MM cells.

HAPLN1 confers multiple myeloma cell resistance to several classes of therapeutic drugs

Multiple myeloma (MM), a malignant plasma cell infiltration of the bone marrow, is generally considered incurable: resistance to multiple therapeutic drugs inevitably arises from tumor cell-intrinsic and tumor microenvironment (TME)-mediated mechanisms. Here we report that the proteoglycan tandem repeat 1 (PTR1) domain of the TME matrix protein, hyaluronan and proteoglycan link protein 1 (HAPLN1), induces a host of cell survival genes in MM cells and variable resistance to different classes of clinical drugs, including certain proteasome inhibitors, steroids, immunomodulatory drugs, and DNA damaging agents, in several MM cell lines tested. Collectively, our study identifies HAPLN1 as an extracellular matrix factor that can simultaneously confer MM cell resistance to multiple therapeutic drugs.

Vitamin D receptor absence does not enhance intestinal tumorigenesis in ApcPirc/+ rats

Epidemiological observations have prompted some to posit that elevated circulating vitamin D is responsible for reduced colon cancer in individuals residing near the equator. We have previously demonstrated that vitamin D has no effect on colon cancer in two rodent models of intestinal tumorigenesis. We have now extended this line of inquiry to ask whether ablation of vitamin D receptor (VDR) affects tumorigenesis. A VDR null rat was developed using Cas9-CRISPR technology, which allowed us to investigate whether 1,25(OH)D₃ signaling through its receptor plays a role in intestinal tumorigenesis. Loss of VDR expression alone did not induce tumorigenesis, even in animals exposed to the inflammatory agent dextran sodium sulfate. These VDR^−/− rats were then crossed with Apc^Pirc/+ rats, which are predisposed to the development of intestinal neoplasms. In combination with the Pirc/+ mutation, VDR loss did not enhance tumor multiplicity, growth, or progression in the colon or small intestine. This study demonstrates that the vitamin D receptor does not impact tumor development, and strongly supports previous findings that vitamin D itself does not play a role in colon cancer development or progression. Alternative explanations are needed for the original latitude hypothesis, as well as observational data in humans.

This article has an associated First Person interview with the first author of the paper.

Summary: Loss of vitamin D receptor, alone or in combination with either an inflammatory agent or the Apc^Pirc/+ rat intestinal tumor model, did not enhance tumor occurrence, growth, or progression.

Hyaluronan and proteoglycan link protein 1 (HAPLN1) activates bortezomib-resistant NF-κB activity and increases drug resistance in multiple myeloma

Nuclear factor-κB (NF-κB) is a family of transcription factors that play a key role in cell survival and proliferation in many hematological malignancies, including multiple myeloma (MM). Bortezomib, a proteasome inhibitor used in the management of MM, can inhibit both canonical and noncanonical activation of NF-κB in MM cells. However, we previously reported that a significant fraction of freshly isolated MM cells harbor bortezomib-resistant NF-κB activity. Here, we report that hyaluronan and proteoglycan link protein 1 (HAPLN1) is produced in bone marrow stromal cells from MM patients, is detected in patients' bone marrow plasma, and can activate an atypical bortezomib-resistant NF-κB pathway in MM cells. We found that this pathway involves bortezomib-resistant degradation of the inhibitor of NF-κB (IκBα), despite efficient bortezomib-mediated inhibition of proteasome activity. Moreover, HAPLN1 can also confer bortezomib-resistant survival of MM cells. We propose that HAPLN1 is a novel pathogenic factor in MM that induces an atypical NF-κB activation and thereby promotes bortezomib resistance in MM cells.

Downregulation of microRNA‑574 in cancer stem cells causes recurrence of prostate cancer via targeting REL

miR‑574‑5p has been reported involved in the pathogenesis of numerous human malignancies such as colorectal and lung cancer. In this study, we aimed to explore the roles of REL and miR‑574 in the recurrence of prostate cancer (PCa) and to identify the underlying molecular mechanisms. Our literature search found that miR‑574 is regulated in cancer stem cells (CSCs), and next we used the microRNA (miRNA) database (www.mirdb.org) to find REL as a target of miR‑574. Luciferase assay was performed to verify the miRNA/target relationship. Oligo-transfection, real‑time PCR and western blot analysis were used to support the conclusions. We validated REL to be the direct gene via luciferase reporter assay system, and real‑time PCR and western blot analysis were also conducted to study the mRNA and protein expression level of REL between different groups (recurrence and non‑recurrence) or cells treated with scramble control, miR‑574 mimics, REL siRNA and miR‑574 inhibitors, indicating the negative regulatory relationship between miR‑574 and REL. We also investigated the relative viability of prostate CSCs when transfected with scramble control, miR‑574 mimics, REL siRNA and miR‑574 inhibitors to validate miR‑574 to be positively interfering with the viability of prostate CSCs. We then investigated the relative apoptosis of prostate CSCs when transfected with scramble control, miR‑574 mimics, REL siRNA and miR‑574 inhibitors. The results showed miR‑574 inhibited apoptosis. In conclusion, miR‑574 might be a novel prognostic and therapeutic target in the management of PCa recurrence.

Prognostic impact of c-Rel nuclear expression and REL amplification and crosstalk between c-Rel and the p53 pathway in diffuse large B-cell lymphoma

Dysregulated NF-κB signaling is critical for lymphomagenesis. The regulation, function, and clinical relevance of c-Rel/NF-κB activation in diffuse large B-cell lymphoma (DLBCL) have not been well studied. In this study we analyzed the prognostic significance and gene-expression signature of c-Rel nuclear expression as surrogate of c-Rel activation in 460 patients with de novo DLBCL. Nuclear c-Rel expression, observed in 137 (26.3%) DLBCL patients frequently associated with extranoal origin, did not show significantly prognostic impact in the overall- or germinal center B-like-DLBCL cohort, likely due to decreased pAKT and Myc levels, up-regulation of FOXP3, FOXO3, MEG3 and other tumor suppressors coincided with c-Rel nuclear expression, as well as the complicated relationships between NF-κB members and their overlapping function. However, c-Rel nuclear expression correlated with significantly poorer survival in p63⁺ and BCL-2⁻ activated B-cell-like-DLBCL, and in DLBCL patients with TP53 mutations. Multivariate analysis indicated that after adjusting clinical parameters, c-Rel positivity was a significantly adverse prognostic factor in DLBCL patients with wild type TP53. Gene expression profiling suggested dysregulations of cell cycle, metabolism, adhesion, and migration associated with c-Rel activation. In contrast, REL amplification did not correlate with c-Rel nuclear expression and patient survival, likely due to co-amplification of genes that negatively regulate NF-κB activation. These insights into the expression, prognostic impact, regulation and function of c-Rel as well as its crosstalk with the p53 pathway underscore the importance of c-Rel and have significant therapeutic implications.

Acetyl-L-carnitine (ALCAR) for the prevention of chemotherapy-induced peripheral neuropathy in patients with relapsed or refractory multiple myeloma treated with bortezomib, doxorubicin and low-dose dexamethasone: a study from the Wisconsin Oncology Network

Purpose

Retreatment with bortezomib (B) is often considered for patients with relapsed multiple myeloma (MM), but this strategy is hindered by uncertainty of response and emergence of B-induced peripheral neuropathy (PN). We incorporated acetyl-l-carnitine (ALCAR) to prevent PN and allow for adequate dosing. We also investigated the correlation between B-inducible NF-κB activation and response to therapy.

Methods

Nineteen patients with relapsed/refractory MM received up to 8 cycles of intravenous bortezomib, doxorubicin and oral low-dose dexamethasone (BDD) to evaluate response and toxicity. Thirteen additional patients received prophylactic ALCAR (BDD-A). Patients receiving BDD-A were evaluated by FACT-GOG-TX, FACIT-Fatigue, Neuropathic Pain index (NPI) and Grooved Pegboard (GP) testing. Primary MM cells from 11 patients were tested for B-inducible NF-κB activation.

Results

Seventy-six percent of subjects were refractory to previous treatment, 39 % refractory to bortezomib. Median cycles received were 5. CR + PR for the entire group were 53 % and did not differ between groups. Incidence of ≥3 PN was 32 % in the BDD group versus 15 % in the BDD-A group (p = ns). Patient-reported fatigue and PN measured by FACT-GOG-TX increased throughout the treatment period in the BDD-A group, although time to complete GP testing declined. In a sub-study examining constitutive bortezomib-inducible NF-κB activity in primary subject-specific MM cells, the presence of NF-κB activation correlated with lower likelihood of response.

Conclusions

Addition of ALCAR to BDD did not alter the incidence or severity of PN in relapsed MM patients receiving a B-based regimen. Bortezomib-inducible NF-κB activation in patient-derived primary MM cells may be associated with poorer response.

Overcoming bortezomib resistance in multiple myeloma

The introduction of the proteasome inhibitor bortezomib in 2003 significantly improved treatment of the B-cell malignancy MM (multiple myeloma). Relapse following bortezomib therapy is inevitable, however, and MM remains an incurable disease. In the present mini-review, we explore the mechanisms by which bortezomib resistance occurs in MM, including inherent and acquired mutation, and inducible pro-survival signalling. We also outline the importance of MM cell interaction with the BMSC (bone marrow stromal cell) microenvironment as a pro-survival mechanism, and examine some potential druggable targets within this milieu, such as IGFs (insulin-like growth factors) and Btk (Bruton's tyrosine kinase). Although our understanding of bortezomib resistance is far from complete, there are a number of scientific developments that can help inform clinical decisions in relapsed MM.

Identification of new IκBα complexes by an iterative experimental and mathematical modeling approach

The transcription factor nuclear factor kappa-B (NFκB) is a key regulator of pro-inflammatory and pro-proliferative processes. Accordingly, uncontrolled NFκB activity may contribute to the development of severe diseases when the regulatory system is impaired. Since NFκB can be triggered by a huge variety of inflammatory, pro-and anti-apoptotic stimuli, its activation underlies a complex and tightly regulated signaling network that also includes multi-layered negative feedback mechanisms. Detailed understanding of this complex signaling network is mandatory to identify sensitive parameters that may serve as targets for therapeutic interventions. While many details about canonical and non-canonical NFκB activation have been investigated, less is known about cellular IκBα pools that may tune the cellular NFκB levels. IκBα has so far exclusively been described to exist in two different forms within the cell: stably bound to NFκB or, very transiently, as unbound protein. We created a detailed mathematical model to quantitatively capture and analyze the time-resolved network behavior. By iterative refinement with numerous biological experiments, we yielded a highly identifiable model with superior predictive power which led to the hypothesis of an NFκB-lacking IκBα complex that contains stabilizing IKK subunits. We provide evidence that other but canonical pathways exist that may affect the cellular IκBα status. This additional IκBα:IKKγ complex revealed may serve as storage for the inhibitor to antagonize undesired NFκB activation under physiological and pathophysiological conditions.

In unstimulated cells, the transcription factor NFκB resides in the cytosol bound to its inhibitor IκBα. Canonical activation of NFκB by numerous stimuli leads to proteasomal depletion of IκBα, thereby liberating NFκB to translocate into the nucleus to induce transcription of genes leading to proliferation, angiogenesis, metastasis, or chronic inflammation. Consequently, only transient activity needs to be warranted by immediate NFκB-dependent induction of negative regulatory mechanisms, including up-regulation of its inhibitor IκBα. Resynthesized IκBα consequently terminates NFκB activity by binding to its nuclear localization sequence. However, under physiological or pathophysiological conditions, random NFκB activation may occur, which needs to be avoided in order to guarantee proper cellular function. Using detailed dynamical modeling, we have now identified an additional IκBα containing complex to exist in un-stimulated cells which lacks NFκB but includes IKKγ (IκBα:IKKγ complex). This additional IκBα is not depleted from cells in the canonical fashion and may therefore serve as a cellular backup to avoid random NFκB activation.

In vitro and in vivo immunostimulatory effects of hot water extracts from the leaves of Artemisia princeps Pampanini cv. Sajabal

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia princeps Pampanini (Asteraceae) is used as a traditional medicine to immune function-related diseases, such as dysmenorrhea, inflammation, cancer, and ulcers.

AIM OF THE STUDY

The purpose of this study is to evaluate the immunostimulatory effects of the hot water extract from the leaves of Artemisia princeps Pampanini (WAPP) in recombinant interferon-γ (rIFN-γ)-primed RAW 264.7 macrophages and in cyclophosphamide (20mg/kg, i.p.)-induced immunosuppressed Sprague-Dawley rats.

MATERIALS AND METHODS

RAW 264.7 macrophages were treated with WAPP and production and expressions of nitric oxide (NO) and tumor necrosis factor-α (TNF-α) via nuclear factor-κB (NF-κB) were detected by immunoassay, western blot, qRT-PCR and reporter gene assay. In addition, in vivo immunomodulatory activity was studied by cyclophosphamide-induced myelosuppression in rats.

RESULTS

In rIFN-γ-primed RAW 264.7 macrophages, pretreatment with WAPP increased the productions of nitric oxide (NO) and tumor necrosis factor-α (TNF-α),and increased the expressions of inducible nitric oxide synthase (iNOS) at the protein level and of iNOS and TNF-α at the mRNA level. Molecular data revealed that WAPP upregulated the transcriptional activity and translocation of nuclear factor-κB (NF-κB) by activating inhibitory kappa B-α (IκB-α) degradation and phosphorylation. Furthermore, WAPP upregulated the phosphorylations of p38 MAP kinase, c-Jun NH2-terminal kinase (JNK), and extracellular signal-regulated kinase 1/2 (ERK1/2). In cycloheximide-induced immunosuppressed rats, pretreatment with WAPP (100, 200, or 400mg/kg, p.o.) increased the serum levels of albumin and globulin, and reduced immobility times.

CONCLUSION

Our results suggest that upregulations of the expressions of iNOS and TNF-α via the activations of NF-κB and MAPK are responsible for the immunostimulatory effects of WAPP.

Direct Rel/NF-κB inhibitors: structural basis for mechanism of action

The Rel/NF-κB transcription factors have emerged as novel therapeutic targets for a variety of human diseases and pathological conditions, including inflammation, autoimmune diseases, cancer, ischemic injury, osteoporosis, transplant rejection and neurodegeneration. Several US FDA-approved drugs may, in part, attribute their therapeutic effects to the inhibition of the Rel/NF-κB pathway. Strategies for blocking the Rel/NF-κB signaling pathway have inspired the pharmaceutical industry to develop inhibitors for I-κB kinase, however, this article focuses instead on identifying natural compounds that directly target and inhibit DNA binding and transcription activity of Rel/NF-κB. These include compounds containing a quinone core, an α,β unsaturated carbonyl and a benzene diamine. By investigating the mechanisms of action of existing natural inhibitors, novel strategies and synthetic approaches can be devised that will facilitate the development of novel and selective Rel/NF-κB inhibitors with better safety profiles.

Nuclear export of the NF-κB inhibitor IκBα is required for proper B cell and secondary lymphoid tissue formation

The N-terminal nuclear export sequence (NES) of inhibitor of nuclear factor kappa B (NF-κB) alpha (IκBα) promotes NF-κB export from the cell nucleus to the cytoplasm, but the physiological role of this export regulation remains unknown. Here we report the derivation and analysis of genetically targeted mice harboring a germline mutation in IκBα NES. Mature B cells in the mutant mice displayed nuclear accumulation of inactive IκBα complexes containing a NF-κB family member, cRel, causing their spatial separation from the cytoplasmic IκB kinase. This resulted in severe reductions in constitutive and canonical NF-κB activities, synthesis of p100 and RelB NF-κB members, noncanonical NF-κB activity, NF-κB target gene induction, and proliferation and survival responses in B cells. Consequently, mice displayed defective B cell maturation, antibody production, and formation of secondary lymphoid organs and tissues. Thus, IκBα nuclear export is essential to maintain constitutive, canonical, and noncanonical NF-κB activation potentials in mature B cells in vivo.

Fibromodulin suppresses nuclear factor-kappaB activity by inducing the delayed degradation of IKBA via a JNK-dependent pathway coupled to fibroblast apoptosis

Fibulin-5 (FBLN5) belongs to the Fibulin family of secreted extracellular matrix proteins, and our laboratory first established FBLN5 as a novel target for TGF-β in fibroblasts and endothelial cells. To better understand the pathophysiology of FBLN5, we carried out microarray analysis to identify fibroblast genes whose expressions were regulated by FBLN5 and TGF-β. In doing so, we identified fibromodulin (Fmod) as a novel target gene of FBLN5, and we validated the differential expression of Fmod and 12 other FBLN5-regulated genes by semi-quantitative real time PCR. Fmod belongs to the small leucine-rich family of proteoglycans, which are important constituents of mammalian extracellular matrices. Interestingly, parental 3T3-L1 fibroblasts displayed high levels of nuclear factor-κB (NF-κB) activity, although those engineered to express Fmod constitutively exhibited significantly reduced NF-κB activity, suggesting that Fmod functions to inhibit NF-κB signaling. By monitoring alterations in the activation of NF-κB and the degradation of its inhibitor, IκBα, we demonstrate for the first time that Fmod contributes to the constitutive degradation of IκBα protein in 3T3-L1 fibroblasts. Mechanistically, we observed Fmod to delay the degradation of IκBα by promoting the following: (i) activation of c-Jun N-terminal kinase; (ii) inhibition of calpain and casein kinase 2 activity; and (iii) induction of fibroblast apoptosis. Taken together, our study identified a novel function for Fmod in directing extracellular signaling, particularly the regulation of NF-κB activity and cell survival.

Bone marrow stromal cells from multiple myeloma patients uniquely induce bortezomib resistant NF-kappaB activity in myeloma cells

Background

Components of the microenvironment such as bone marrow stromal cells (BMSCs) are well known to support multiple myeloma (MM) disease progression and resistance to chemotherapy including the proteasome inhibitor bortezomib. However, functional distinctions between BMSCs in MM patients and those in disease-free marrow are not completely understood. We and other investigators have recently reported that NF-κB activity in primary MM cells is largely resistant to the proteasome inhibitor bortezomib, and that further enhancement of NF-κB by BMSCs is similarly resistant to bortezomib and may mediate resistance to this therapy. The mediating factor(s) of this bortezomib-resistant NF-κB activity is induced by BMSCs is not currently understood.

Results

Here we report that BMSCs specifically derived from MM patients are capable of further activating bortezomib-resistant NF-κB activity in MM cells. This induced activity is mediated by soluble proteinaceous factors secreted by MM BMSCs. Among the multiple factors evaluated, interleukin-8 was secreted by BMSCs from MM patients at significantly higher levels compared to those from non-MM sources, and we found that IL-8 contributes to BMSC-induced NF-κB activity.

Conclusions

BMSCs from MM patients uniquely enhance constitutive NF-κB activity in MM cells via a proteinaceous secreted factor in part in conjunction with IL-8. Since NF-κB is known to potentiate MM cell survival and confer resistance to drugs including bortezomib, further identification of the NF-κB activating factors produced specifically by MM-derived BMSCs may provide a novel biomarker and/or drug target for the treatment of this commonly fatal disease.

MAGUK-controlled ubiquitination of CARMA1 modulates lymphocyte NF-kappaB activity

The adaptor protein CARMA1 is required for antigen receptor-triggered activation of IKK and JNK in lymphocytes. Once activated, the events that subsequently turn off the CARMA1 signalosome are unknown. In this study, we found that antigen receptor-activated CARMA1 underwent lysine 48 (K48) polyubiquitination and proteasome-dependent degradation. The MAGUK region of CARMA1 was an essential player in this event; the SH3 and GUK domains contained the main ubiquitin acceptor sites, and deletion of a Hook domain (an important structure for maintaining inactive MAGUK proteins) between SH3 and GUK was sufficient to induce constitutive ubiquitination of CARMA1. A similar deletion promoted the ubiquitination of PSD-95 and Dlgh1, suggesting that a conserved mechanism may control the turnover of other MAGUK family protein complexes. Functionally, we demonstrated that elimination of MAGUK ubiquitination sites in CARMA1 resulted in elevated basal and inducible NF-kappaB and JNK activation as a result of defective K48 ubiquitination and increased persistence of this ubiquitination-deficient CARMA1 protein in activated lymphocytes. The coordination of degradation with the full activation of the CARMA1 molecule likely provides an intrinsic feedback control mechanism to balance lymphocyte activation upon antigenic stimulation.

RNAi-mediated c-Rel silencing leads to apoptosis of B cell tumor cells and suppresses antigenic immune response in vivo

c-Rel is a member of the Rel/NF-κB transcription factor family and is predominantly expressed in lymphoid and myeloid cells, playing a critical role in lymphocyte proliferation and survival. Persistent activation of the c-Rel signal transduction pathway is associated with allergies, inflammation, autoimmune diseases, and a variety of human malignancies. To explore the potential of targeting c-Rel as a therapeutic agent for these disorders, we designed a small interfering RNA (siRNA) to silence c-Rel expression in vitro and in vivo. C-Rel-siRNA expression via a retroviral vector in a B cell tumor cell line leads to growth arrest and apoptosis of the tumor cells. Silencing c-Rel in primary B cells in vitro compromises their proliferative and survival response to CD40 activation signals, similar to the impaired response of c-Rel knockout B cells. Most important, in vivo silencing of c-Rel results in significant impairment in T cell-mediated immune responses to antigenic stimulation. Our study thus validates the efficacy of c-Rel-siRNA, and suggests the development of siRNA-based therapy, as well as small molecular inhibitors for the treatment of B cell tumors as well as autoimmune diseases.

Altered BAFF-receptor signaling and additional modifier loci contribute to systemic autoimmunity in A/WySnJ mice

Systemic lupus erythematosus pathology reflects autoantibody-mediated damage due to a failure of B-lymphocyte tolerance. We previously reported that B-lymphopenic A/WySnJ mice develop a lupus-like syndrome and linked this syndrome to the B-cell maturation defect-1 (Bcmd-1) mutant allele of the B-cell-activating factor belonging to the TNF family-receptor (Baffr) gene. Here, we further evaluate the genetic basis for autoimmunity in A/WySnJ mice. We produced B6.Bcmd-1 and AW.Baffr(-/-) congenic mice (N5), and compared them with B6.Baffr(-/-) and A/WySnJ mice with respect to B-lymphocyte development. Bcmd-1-expressing mice had more B cells with greater maturity than Baffr(-/-) mice regardless of genetic background, indicating that Bcmd-1 encodes a partially functional BAFF-R. We also compared these mice for lupus phenotypes to determine whether Bcmd-1 is necessary and sufficient for disease, or whether the Baffr(-/-) (-) allele can also cause autoimmunity. The Baffr(-/-) allele did not lead to autoimmunity on either genetic background. In contrast, the Bcmd-1 allele was necessary and sufficient for development of low levels of IgM autoantibodies in B6.Bcmd-1 mice. However, Bcmd-1 plus unidentified A/WySnJ modifier genes were necessary for development of IgG autoantibodies and renal pathology. We propose that in A/WySnJ mice an excess of BAFF per B cell rescues self-reactive B cells through a partially functional BAFF-R in a B-lymphopenic environment.

Bortezomib-resistant nuclear factor-kappaB activity in multiple myeloma cells

Bortezomib (Velcade/PS341), a proteasome inhibitor used in the treatment of multiple myeloma (MM), can inhibit activation of nuclear factor-kappaB (NF-kappaB), a family of transcription factors often deregulated and constitutively activated in primary MM cells. NF-kappaB can be activated via several distinct mechanisms, including the proteasome inhibitor-resistant (PIR) pathway. It remains unknown what fraction of primary MM cells harbor constitutive NF-kappaB activity maintained by proteasome-dependent mechanisms. Here, we report an unexpected finding that constitutive NF-kappaB activity in 10 of 14 primary MM samples analyzed is refractory to inhibition by bortezomib. Moreover, when MM cells were cocultured with MM patient-derived bone marrow stromal cells (BMSC), microenvironment components critical for MM growth and survival, further increases in NF-kappaB activity were observed that were also refractory to bortezomib. Similarly, MM-BMSCs caused PIR NF-kappaB activation in the RPMI8226 MM cell line, leading to increased NF-kappaB-dependent transcription and resistance to bortezomib-induced apoptosis. Our findings show that primary MM cells frequently harbor PIR NF-kappaB activity that is further enhanced by the presence of patient-derived BMSCs. They also suggest that this activity is likely relevant to the drug resistance development in some patients. Further elucidation of the mechanism of PIR NF-kappaB regulation could lead to the identification of novel diagnostic biomarkers and/or therapeutic targets for MM treatment.

Prevalence of bortezomib-resistant constitutive NF-kappaB activity in mantle cell lymphoma

Background

The proteasome inhibitor bortezomib can inhibit activation of the transcription factor NF-κB, a mechanism implicated in its anti-neoplastic effects observed in mantle cell lymphoma (MCL). However, NF-κB can be activated through many distinct mechanisms, including proteasome independent pathways. While MCL cells have been shown to harbor constitutive NF-κB activity, what fraction of this activity in primary MCL samples is sensitive or resistant to inhibition by bortezomib remains unclear.

Results

Proteasome activity in the EBV-negative MCL cell lines Jeko-1 and Rec-1 is inhibited by greater than 80% after exposure to 20 nM bortezomib for 4 hours. This treatment decreased NF-κB activity in Jeko-1 cells, but failed to do so in Rec-1 cells when assessed by electrophoretic mobility shift assay (EMSA). Concurrently, Rec-1 cells were more resistant to the cytotoxic effects of bortezomib than Jeko-1 cells. Consistent with a proteasome inhibitor resistant pathway of activation described in mouse B-lymphoma cells (WEHI231) and a breast carcinoma cell line (MDA-MB-468), the bortezomib-resistant NF-κB activity in Rec-1 cells is inhibited by calcium chelators, calmodulin inhibitors, and perillyl alcohol, a monoterpene capable of blocking L-type calcium channels. Importantly, the combination of perillyl alcohol and bortezomib is synergistic in eliciting Rec-1 cell cytotoxicity. The relevance of these results is illuminated by the additional finding that a considerable fraction of primary MCL samples (8 out of 10) displayed bortezomib-resistant constitutive NF-κB activity.

Conclusion

Our findings show that bortezomib-resistant NF-κB activity is frequently observed in MCL samples and suggest that this activity may be relevant to MCL biology as well as serve as a potential therapeutic target.

Systemic autoimmunity in BAFF-R-mutant A/WySnJ strain mice

Systemic lupus erythematosis is an autoimmune disease of unknown etiology. Lupus pathology is thought to reflect autoantibody-mediated damage due to a failure of B lymphocyte tolerance. Since excessive B cell-activating factor belonging to the TNF family (BAFF) expression correlates with human and murine lupus, and BAFF signals B cell survival through BAFF-R, it is believed that excessive BAFF-R signaling can subvert B cell tolerance and facilitate lupus development. Here we report the unexpected finding that BAFF-R-mutant A/WySnJ mice develop a lupus-like syndrome. These mice carry the B cell maturation defect-1 (Bcmd-1) mutant allele of the Baffr gene. Bcmd-1 causes premature B cell death and profound B cell deficiency. Despite having 90% fewer splenic B cells than normal mice, A/WySnJ mice had an 18-fold increased frequency of splenocytes secreting IgM antibodies to dsDNA, and increased amounts of circulating IgM and IgG to dsDNA by 9 months of age. By age 11 months, most A/WySnJ mice displayed renal pathology characteristic of lupus, including proteinuria as well as periodic acid-Schiff-positive deposits and glomerular capillary bed destruction. Importantly, we genetically linked this autoimmunity to Bcmd-1, since congenic AW.Baffr(+/+) mice carrying a wild-type allele developed none of these phenotypes. Our data provide the first evidence linking altered BAFF-R signaling to the development of B cell-mediated autoimmunity.

Inhibition of beta-TrCP function potentiates UVB-induced apoptosis in hTERT-immortalized normal human keratinocytes

Chronic skin exposure to UV radiation manifests in a score of biochemical events, DNA damage and mutations which can potentially cause skin cancer. The ubiquitin proteasome pathway controls the degradation of a majority of regulatory eukaryotic proteins including those which play a key role in tumorigenesis. SCFbetaTrCP E3 ubiquitin ligases mediate ubiquitination and proteasomal degradation of phosphorylated substrates that play a key role in signal transduction. Activation of several signaling pathways involved in tumorigenesis was shown to elevate expression and activity of beta-TrCP1/2. In this study, we established and characterized human neonatal foreskin keratinocytes, rendered immortal by retroviral introduction of human telomerase reverse transcriptase (hTERT). These skin hTERT immortalized normal keratinocytes (STINKs) maintain characteristic traits of keratinocytes, such as expression of keratins, cytoplasmic localization of basonuclin and susceptibility to high concentration of calcium. We analyzed the response of STINKs to UVB radiation and its classical markers, such as p53 and nuclear factor (NF)-kappaB. We also demonstrate that inhibition of beta-TrCP2 function, by induction of dominant negative beta-TrCP2 (beta-TrCP2DeltaN), accentuates UVB induced apoptosis, and this phenomenon is independent of NF-kappaB and p53 pathways.

PIASy mediates NEMO sumoylation and NF-kappaB activation in response to genotoxic stress

Protein modification by SUMO (small ubiquitin-like modifier) is an important regulatory mechanism for multiple cellular processes. SUMO-1 modification of NEMO (NF-kappaB essential modulator), the IkappaB kinase (IKK) regulatory subunit, is critical for activation of NF-kappaB by genotoxic agents. However, the SUMO ligase, and the mechanisms involved in NEMO sumoylation, remain unknown. Here, we demonstrate that although small interfering RNAs (siRNAs) against PIASy (protein inhibitor of activated STATy) inhibit NEMO sumoylation and NF-kappaB activation in response to genotoxic agents, overexpression of PIASy enhances these events. PIASy preferentially stimulates site-selective modification of NEMO by SUMO-1, but not SUMO-2 and SUMO-3, in vitro. PIASy-NEMO interaction is increased by genotoxic stress and occurs in the nucleus in a manner mutually exclusive with IKK interaction. In addition, hydrogen peroxide (H2O2) also increases PIASy-NEMO interaction and NEMO sumoylation, whereas antioxidants prevent these events induced by DNA-damaging agents. Our findings demonstrate that PIASy is the first SUMO ligase for NEMO whose substrate specificity seems to be controlled by IKK interaction, subcellular targeting and oxidative stress conditions.

NF-kappaB activation by combinations of NEMO SUMOylation and ATM activation stresses in the absence of DNA damage

The inactive transcription factor NF-kappaB is localized in the cytoplasm and rapidly responds to a variety of extracellular factors and intracellular stress conditions to initiate multiple cellular responses. While the knowledge regarding NF-kappaB signaling pathways initiated by extracellular ligands is rapidly expanding, the mechanisms of activation by intracellular stress conditions are not well understood. We recently described a critical role for a small ubiquitin-like modifier (SUMO) modification of NF-kappaB essential modulator (NEMO), the regulatory subunit of the IkappaB kinase, in response to certain genotoxic stress conditions. One important unanswered question is whether the role of this modification is limited to the genotoxic agents or some other signaling pathways also employ SUMOylation of NEMO to regulate NF-kappaB activation. Here, we report that a variety of other stress conditions, including oxidative stress, ethanol exposure, heat shock and electric shock, also induce NEMO SUMOylation, thus demonstrating that DNA damage per se is not necessary for this NEMO modification to occur. Moreover, combinations of certain SUMO stress and ATM (ataxia telangiectasia mutated) activation conditions lead to NF-kappaB activation without inducing DNA damage. Our study helps to conceptualize how individual or a combination of different stress conditions may funnel into this previously unappreciated signal transduction mechanism to regulate the activity of the ubiquitous NF-kappaB transcription factor.

Nuclear factor-kappaB dimer exchange promotes a p21(waf1/cip1) superinduction response in human T leukemic cells

The nuclear factor-kappaB (NF-kappaB)/Rel transcription factors are recognized as critical apoptosis regulators. We reported previously that NF-kappaB contributes to chemoresistance of CEM human T leukemic cells in part through its ability to induce p21(waf1/cip1). Here, we provide evidence that sequential NF-kappaB-activating signals induce heightened NF-kappaB DNA binding and p21(waf1/cip1) induction in CEM and additional T leukemic cell lines. This response arises from exceedingly low basal expression of the p105/p50 NF-kappaB subunit encoded by the NFKB1 gene in these cell lines. An initial NF-kappaB activation event enhances the recruitment of p65 and ELF1 to the NFKB1 promoter, leading to p65- and ELF1-dependent synthesis of p105/p50, which promotes an exchange of NF-kappaB complexes to p50-containing complexes with an increased DNA-binding activity to certain NF-kappaB target elements. Subsequent stimulation of these cells with an anticancer agent, etoposide, results in augmented NF-kappaB-dependent p21(waf1/cip1) induction and increased chemoresistance of the leukemia cells. Thus, we propose that low basal NFKB1 expression coupled with sequential NF-kappaB activation events can promote increased chemoresistance in certain T leukemic cells.

The role of nuclear factor kappa B in human labour

Preterm birth remains the leading cause of perinatal mortality and morbidity, largely as a result of a poor understanding of the precise mechanisms controlling labour onset in humans. Inflammation has long been recognised as a key feature of both preterm and term labour, with an influx of inflammatory cells into the uterus and elevated levels of pro-inflammatory cytokines observed during parturition. Nuclear factor kappa B (NF-κB) is a transcription factor family classically associated with inflammation. Accumulating evidence points to a role for NF-κB in the physiology and pathophysiology of labour. NF-κB activity increases with labour onset and is central to multiple prolabour pathways. Premature or aberrant activation of NF-κB may thus contribute to preterm labour. The current understanding of NF-κB in the context of human labour is discussed here.

Vav proteins regulate peripheral B-cell survival

Mice lacking all 3 Vav proteins fail to produce significant numbers of recirculating follicular or marginal zone B cells. Those B cells that do mature have shortened lifespans. The constitutive nuclear factor-kappaB (NF-κB) activity of resting naive B cells required Vav function and expression of cellular reticuloendotheliosis (c-Rel). Rel-A was reduced in Vav-deficient B cells. Furthermore, expression of the NF-κB-regulated antiapoptotic genes A1 and Bcl-2 was reduced in mature Vav-deficient B cells. Overexpression of Bcl-2 restored the number of mature follicular B cells in the spleens of Vav-deficient mice. When activated by B-cell receptor (BCR) cross-linking, Vav-deficient B cells failed to activate NF-κB. Vav proteins thus regulate an NF-κB-dependent survival signal in naive B cells and are required for NF-κB function after BCR cross-linking.

Perillyl Alcohol Inhibits a Calcium-Dependent Constitutive Nuclear Factor-κB Pathway

The cell death induced by the monoterpene anticancer agent perillyl alcohol correlates to the increased expression of certain proapoptotic genes known to influence cell survival. Whereas sequence-specific DNA-binding factors dictate the expression patterns of genes through transcriptional regulation, those transcriptional factors influencing constitutive cell survival with perillyl alcohol treatment are not well studied. Here, we investigated whether the monoterpenes can regulate the activity of nuclear factor-kappaB (NF-kappaB), a calcium-dependent transcription factor necessary for survival in the WEHI-231 B-lymphoma cells. Unique among the monoterpenes, perillyl alcohol short-term treatment induced a persistent decrease of calcium levels, whereas other various monoterpenes caused transient reductions in calcium levels. Perillyl alcohol treatment also rapidly elicited reductions of NF-kappaB DNA-binding activity and target gene induction, which was associated with an increase in apoptosis in these B-lymphoma cells. This apoptosis was directly due to NF-kappaB because its prior activation abolished the cell killing effects of perillyl alcohol treatment. Our findings suggest that perillyl alcohol can inhibit NF-kappaB function to modulate gene expression patterns and cell survival of certain B-lymphoma cells. The effects of perillyl alcohol were not limited to these B-lymphoma cells but were also observed in MDA-MB 468 cells, an estrogen receptor-negative breast cancer cell line. These results identify a calcium-dependent NF-kappaB pathway as a molecular target of perillyl alcohol activity in different cancer cell types.

Evidence for a phosphorylation-independent role for Ser 32 and 36 in proteasome inhibitor-resistant (PIR) IkappaBalpha degradation in B cells

Constitutive NF-kappaB activity has emerged as an important cell survival regulator. Canonical inducible NF-kappaB activation involves IkappaB kinase (IKK)-dependent dual phosphorylation of Ser 32 and 36 of IkappaBalpha to cause its beta-TrCP-dependent ubiquitylation and proteasomal degradation. We recently reported that constitutive NF-kappaB (p50/c-Rel) activity in WEHI231 B cells is maintained through proteasome inhibitor-resistant (PIR) IkappaBalpha degradation in a manner that requires Ser 32 and 36, without the requirement of a direct interaction with beta-TrCP. Here we specifically examined whether dual phosphorylation of Ser 32 and 36 was required for PIR degradation. Through mutagenesis studies, we found that dual replacement of Ser 32 and 36 with Glu permitted beta-TrCP and proteasome-dependent, but not PIR, degradation. Moreover, single replacement of either Ser residue with Leu permitted PIR degradation in WEHI231 B cells. These results indicate that PIR degradation occurs in the absence of dual phosphorylation, thereby explaining the beta-TrCP-independent nature of the PIR pathway. Additionally, we found evidence that PIR IkappaBalpha degradation controls constitutive NF-kappaB activation in certain multiple myeloma cells. These results suggest that B lineage cells can differentiate between PIR and canonical IkappaBalpha degradation through the absence or presence of dually phosphorylated IkappaBalpha.

Inhibition of IκBα Nuclear Export as an Approach to Abrogate Nuclear Factor-κB–Dependent Cancer Cell Survival

Deregulation of the transcription factor nuclear factor-κB (NF-κB) leading to its constitutive activation is frequently observed in human cancer. Because altered NF-κB activities often promote the survival of malignant cells, its inhibition is regarded as a promising anticancer strategy. Because activation of the latent cytoplasmic NF-κB complex can be induced by a wide variety of different stimuli, its deregulation may occur by an equally large number of distinct mechanisms. This diversity raises a conundrum in conceptualizing general approaches to attenuate NF-κB activity in cancer. Here, we provide evidence that inhibition of IκBα nuclear export is a viable target to generally abrogate constitutive NF-κB activity in different cancer cell types. We show that inhibition of IκBα nuclear export has an important course of events in cancer cells harboring constitutive NF-κB activity—an initial increase in the pool of stable nuclear NF-κB/IκBα complexes that leads to a reduction of constitutive NF-κB activity and subsequent induction of apoptosis. Importantly, similar effects on multiple different cancer cell types indicate that inhibition of nuclear export of IκBα leads to broad inhibition of constitutive NF-κB activation regardless of various deregulated, upstream events involved.