Epigenetic targeting of Waldenström macroglobulinemia cells with BET inhibitors synergizes with BCL2 or histone deacetylase inhibition

Aim: Waldenström macroglobulinemia (WM) is a low-grade B-cell lymphoma characterized by overproduction of monoclonal IgM. To date, there are no therapies that provide a cure for WM patients, and therefore, it is important to explore new therapies. Little is known about the efficiency of epigenetic targeting in WM. Materials & methods: WM cells were treated with BET inhibitors (JQ1 and I-BET-762) and venetoclax, panobinostat or ibrutinib. Results: BET inhibition reduces growth of WM cells, with little effect on survival. This finding was enhanced by combination therapy, with panobinostat (LBH589) showing the highest synergy. Conclusion: Our studies identify BET inhibitors as effective therapy for WM, and these inhibitors can be enhanced in combination with BCL2 or histone deacetylase inhibition.

TLR-TRIF signaling induces GLI3 to modulate inflammation

Chronic inflammation is associated with several disorders and therefore the identification of novel regulators of inflammation is needed. We identified GLI3 as a novel component of the TLR-TRIF signaling. Stimulation of monocytes with LPS increased GLI3 expression in a hedgehog-independent mechanism. We stimulated cells with MPLA, (TLR4 ligand that signals through TRIF) and polyI:C (TLR3 ligand) and found that IRF3 directly binds to the GLI3 promoter and IRF3 increased GLI3 expression. We generated a conditional knockout (cko) mouse where GLI3 was deleted in myeloid cells using LysM-Cre mediated recombination. IFA-elicited macrophages from cko mice stimulated with LPS showed reduced IL-6, CCL2 and TNF-a secretion compared to macrophages from wild-type (wt) littermates. We also performed RNA sequencing of LPS treated or untreated macrophages from GLI3 cko or wt mice. Using a generalized linear model in edgeR, we identified 495 genes with significant interaction effects between genotype and LPS treatment. Ingenuity Pathway Analysis of the interaction genes revealed “Inflammatory Response” and “Immune Cell Trafficking” pathways as most significantly enriched. The 25 significant interaction genes on these pathways included 9 with a positive interaction (Ccl25, Cd226, Cgas, Hmgn5, Il12b, Lrrc8a, Rapgef3, Rnf122, and Tlr8) and 16 with a negative interaction (Acacb, Adipoq, Ccl1, Ccne1, Cx3cl1, Fry, Gstk1, Mertk, Nqo2, Slc6a4, Sort1, Timd4, Tnfrsf18/GITR, Tnfsf13/APRIL, Tnfsf13b/BAFF, and Trem2). Taken together, these results identify a novel role for GLI3 in mediating TLR-TRIF-induced inflammation and identify a novel set of inflammatory genes that are dependent on GLI3 in response to TLR-TRIF signaling.

GLI3: a mediator of genetic diseases, development and cancer

The transcription factor GLI3 is a member of the Hedgehog (Hh/HH) signaling pathway that can exist as a full length (Gli3-FL/GLI3-FL) or repressor (Gli3-R/GLI3-R) form. In response to HH activation, GLI3-FL regulates HH genes by targeting the GLI1 promoter. In the absence of HH signaling, GLI3 is phosphorylated leading to its partial degradation and the generation of GLI3-R which represses HH functions. GLI3 is also involved in tissue development, immune cell development and cancer. The absence of Gli3 in mice impaired brain and lung development and GLI3 mutations in humans are the cause of Greig cephalopolysyndactyly (GCPS) and Pallister Hall syndromes (PHS). In the immune system GLI3 regulates B, T and NK-cells and may be involved in LPS-TLR4 signaling. In addition, GLI3 was found to be upregulated in multiple cancers and was found to positively regulate cancerous behavior such as anchorage-independent growth, angiogenesis, proliferation and migration with the exception in acute myeloid leukemia (AML) and medulloblastoma where GLI plays an anti-cancerous role. Finally, GLI3 is a target of microRNA. Here, we will review the biological significance of GLI3 and discuss gaps in our understanding of this molecule. Video Abstract.

GLI2-Mediated Inflammation in the Tumor Microenvironment

The tumor microenvironment (TME) plays an important role in the development and progression of cancer and has been shown to contribute to resistance to therapy. Inflammation is one of the hallmarks of cancer implicated in disease phenotype. Therefore, understanding the mechanisms that regulate inflammation in cancer and consequently how inflammatory mediators promote cancer progression is important for our understanding of cancer cell biology. The transcription factor GLI2 was initially identified as a member of the Hedgehog (HH) signaling pathway. During the last decade, studies have shown a novel mechanism of GLI2 regulation independent of HH signaling, where GLI2 consequently modulated several cytokine genes in the TME. These studies highlight a novel role for GLI2 as an inflammatory mediatory independent of HH stimulation. This chapter will discuss canonical and noncanonical pathways of GLI2 regulation and some of the downstream cytokine target genes regulated by GLI2.

Targeting MYC activity in double-hit lymphoma with MYC and BCL2 and/or BCL6 rearrangements with epigenetic bromodomain inhibitors

Double/triple-hit lymphomas (DHL/THL) account for 5–10% of diffuse large B cell lymphoma (DLBCL) with rearrangement of MYC and BCL2 and/or BCL6 resulting in MYC overexpression. Despite the poor prognosis of DHL, R-CHOP chemotherapy remains the treatment backbone and new targeted therapy is needed. We performed comprehensive cytogenetic studies/fluorescence in situ hybridization on DLBCL and Burkitt lymphoma cell lines (n = 11) to identify the DHL/THL DLBCL in vitro model. We identified MYC/IG in Raji and Ramos (single hit); MYC/IG-BCL2 (DHL) in DOHH2, OCI-LY1, SUDHL2, and OCI-LY10; MYC/IG-BCL2/BCL6 (THL) in VAL; and no MYC rearrangement in U2932 and HBL1 (WT-MYC). Targeting MYC in the DHL/THL DLBCLs through bromodomain extra-terminal inhibitors (BETi) (JQ1, I-BET, and OTX015) significantly (p < 0.05) reduced proliferation, similar to WT-MYC cells, accompanied by decreased MYC but not BCL2 protein. Moreover, BETi suppressed MYC transcription and decreased BRD4 binding to MYC promoter in DHL cells. CD47 and PD-L1 are immunoregulatory molecules often expressed on tumors and regulated by MYC. High levels of surface CD47 but not surface PD-L1 was observed in DHL/THL, which was reduced by JQ1 treatment. BETi in combination with Pan-HDAC inhibitor had a limited effect on survival of DHL/THL, while combination of BETi and BCL2 inhibitor (ABT-199) had a significant (p < 0.005) inhibitory effect on survival followed by BCL-XL inhibition. Overall, the data suggests that MYC-expressing DLBCLs are probably addicted to the MYC-oncogenic effect regardless of MYC rearrangements. In summary, we identified an in vitro model for DHL/THL DLBCLs and provide evidence for the therapeutic potential of BET inhibitor alone or in combination with BCL2 inhibitor.

Bone marrow stromal cells interaction with titanium; Effects of composition and surface modification

Inflammation and implant loosening are major concerns when using titanium implants for hard tissue engineering applications. Surface modification is one of the promising tools to enhance tissue-material integration in metallic implants. Here, we used anodization technique to modify the surface of commercially pure titanium (CP-Ti) and titanium alloy (Ti-6Al-4V) samples. Our results show that electrolyte composition, anodization time and voltage dictated the formation of well-organized nanotubes. Although electrolyte containing HF in water resulted in nanotube formation on Ti, the presence of NH4F and ethylene glycol was necessary for successful nanotube formation on Ti-6Al-4V. Upon examination of the interaction of bone marrow stromal cells (BMSCs) with the modified samples, we found that Ti-6Al-4V without nanotubes induced cell proliferation and cluster of differentiation 40 ligand (CD40L) expression which facilitates B-cell activation to promote early bone healing. However, the expression of glioma associated protein 2 (GLI2), which regulates CD40L, was reduced in Ti-6Al-4V and the presence of nanotubes further reduced its expression. The inflammatory cytokine interleukin-6 (IL-6) expression was reduced by nanotube presence on Ti. These results suggest that Ti-6Al-4V with nanotubes may be suitable implants because they have no effect on BMSC growth and inflammation.

Targeting IL-6 receptor reduces IgM levels and tumor growth in Waldenström macroglobulinemia

The tumor microenvironment (TME) plays an important role in cancer cell biology and is implicated in resistance to therapy. In Waldenström macroglobulinemia (WM), a subtype of Non-Hodgkin lymphoma, the TME modulates WM biology by secreting cytokines that promote the malignant phenotype. In previous work, we have shown that TME-IL-6 promotes WM cell growth and IgM secretion in WM. Tocilizumab/Actemra is an anti-IL-6R antibody, which can competitively block IL-6 binding to the IL-6R. We investigated the efficacy of Tocilizumab in a preclinical mouse model of WM that considers the role of the TME in disease biology. Hairless SCID mice were subcutaneously implanted with BCWM.1 or RPCI-WM1 and bone marrow stromal cells. Groups of mice were treated with Tocilizumab or control antibody three times/week for 5 weeks and the effect on tumor burden and disease biology were evaluated. Although Tocilizumab had no effect on mice survival, there was a significant reduction in tumor growth rate in mice injected with RPCI-WM1 cells treated with Tocilizumab. In mice injected with BCWM.1 cells, there was a significant reduction in human IgM secretion in mice sera with Tocilizumab treatment. There was no significant change in mice weight suggesting Tocilizumab induced no toxicities to the mice. Taken together, our data found that administration of Tocilizumab to tumor bearing mice, results in a significant reduction in tumor volume and IgM secretion. Therefore, the evaluation of the role of Tocilizumab in WM patients may provide therapeutic efficacy by reducing IgM production and slowing the rate of tumor growth.

Targeting the tumor microenvironment with the monoclonal antibody Tocilizumab, reduces IgM secretion in Waldenström macroglobulinemia

The tumor microenvironment (TME) plays an important role in cancer and has been shown to play a role in resistance to therapy and is therefore important in cancer cell biology. In Waldenström macroglobulinemia (WM), a B cell malignancy characterized by the overproduction of a monoclonal IgM protein, the TME secrets cytokines that promote malignant phenotype. In previous work, we have shown that TME-IL-6 promotes WM cell growth and IgM secretion in WM. Tocilizumab/Actemra is an anti-IL-6R antibody, which can competitively block IL-6 binding to the IL-6R. Here we investigated the efficacy of Tocilizumab in a preclinical mouse model of WM that considers the role of the TME in disease biology. Hairless SCID mice were injected subcutaneously with BCWM.1 or RPCI-WM1 and bone marrow stromal cells (HS-5) at a ratio of 5:1. Groups of mice with treated with Tocilizumab or control antibody three times/week for 5 weeks and the effect on tumor burden and disease biology were evaluated. Although Tocilizumab had no effect on mice survival, there was a reduction in tumor growth rate in mice injected with RPCI-WM1 cells + stromal cells and treated with Tocilizumab (p=0.0394). In mice injected with BCWM.1 + stromal cells, there was a significant reduction in human IgM secretion in mice sera with Tocilizumab treatment (p=0.0099). There was no significant change in mice weight suggesting Tocilizumab induced no toxicities to the mice. Taken together, our data suggests that administration of Tocilizumab to tumor bearing mice, results in a significant reduction in tumor volume and IgM secretion. Therefore, the evaluation of the role of Tocilizumab in WM patients may provide therapeutic efficacy by reducing IgM production and slowing the rate of tumor growth.

Regulation of GLI3 expression by TLR4 signaling

While acute inflammation is an important host response to infections, chronic inflammation has emerged as a mechanism driving many diseases including autoimmune and malignant diseases. Monocytes are a subset of immune cells that secrete inflammatory cytokines in response to infections through toll-like receptor (TLR) signaling. The cross-talk between TLR signaling and other pathways has been shown to be important for downstream effector functions. We identify a novel role for the transcription factor GLI3, a negative regulator of Hedgehog signaling, in mediating TLR4-induced inflammation. Stimulation of monocytes with LPS increases GLI3 mRNA and protein expression. This occurred in a dose- and time-dependent manner. Investigation of the signaling mechanism suggests that LPS induced GLI3 occurs through the adaptor protein TRIF (but not MyD88). Targeting of transcription factors NFkb, AP-1 and IRF3 by pharmaceutical inhibitors suggests that TLR4-mediated GLI3 is regulated by IRF3. Transfection of our monocyte cell lines with shRNA targeting GLI3 suggests a regulatory role of transcription factor GLI3 in mRNA expression of essential cytokines involved in inflammation including IL-6 and CCL2. We generated conditional GLI3 knockout in mice myeloid cells using LysM-cre mediated recombination. IFA-elicited macrophages from mice with conditional GLI3 knockout driven by LysM-cre stimulated with LPS show reduced IL-6 and CCL2 secretion compared to macrophages from wild-type littermates. Taken together, these data suggest that GLI3 plays a role in innate immunity by regulating TLR4-induced inflammation.

Calf melanin immunomodulates RPE cell attachment to extracellular matrix protein

PURPOSE

It is widely accepted that RPE melanin has a protective effect against oxidative damage in RPE cells. It is possible that an additional protective characteristic of melanin is the ability to modulate RPE cell immune response. In this study, in vitro modeling was used to probe the relationship between RPE pigmentation and immune response by monitoring IL-6 expression and secretion in calf melanin pigmented ARPE-19 cells seeded onto glycated extracellular matrix as a stressor.

METHODS

ARPE-19 cells were left unpigmented or were pigmented with either calf melanin or latex beads, and were then seeded onto RPE-derived extracellular matrix (ECM) or tissue culture-treated plates (no ECM). ECMs were modified by glycation. IL-6 expression was measured using qPCR and IL-6 secretion was determined using an ELISA, both at 30 min and 24 h after seeding. MTT assay was used to quantify cell attachment to glycated matrices 30 min after seeding. In unpigmented ARPE-19 cells, rate of cell attachment to substrate was monitored for 60 min after seeding using a hemacytometer to count unattached cells. Additionally, cell viability was evaluated using the Neutral Red assay 24 h after seeding.

RESULTS

A significant increase in IL-6 expression was observed in calf melanin pigmented cells versus latex bead and unpigmented controls (p < 0.0001) 30 min after seeding onto ECM. Twenty-four hours after seeding, a significant decrease in IL-6 expression was observed in calf melanin pigmented cells (p < 0.0001) versus controls, implicating down-regulation of the cytokine. Additionally, calf melanin pigmented cell populations showed significant increase in attachment compared to unpigmented controls on either no ECM or unmodified ECM.

CONCLUSIONS

Pigmentation of RPE cells with calf melanin resulted in significant changes in IL-6 expression regardless of ECM modification, in vitro. These findings suggest that melanin in the RPE may participate in immune response modulation in the retina with particular regard to cell attachment to protein substrates. The results of this study further implicate the role of chemical changes to melanin in regulating inflammation in retinal disease.

Abstract 193: The tumor microenvironment protects against ibrutinib but not rituximab-mediated control of Waldenström macroglobulinemia (WM) in vivo

The tumor microenvironment (TME) plays an important role in the development and progression of cancer. It has also been shown to play a protective role in resistance to therapy. Therefore, understanding the role of the TME is a vital component of our understanding of malignant cell biology. In Waldenström macroglobulinemia (WM), a B cell malignancy characterized by the overproduction of a monoclonal IgM protein, several studies have shown that the TME plays an important role in malignant disease. Therefore, the goal of this study was to investigate the efficacy of combined targeting of the TME with either Ibrutinib or Rituximab therapy in WM in vivo. SCID mice were injected with RPCI-WM1 + HS-5 stromal cells (5:1 ratio) and upon tumor development, mice were treatment with Ibrutinib (αBTK), Actemra (αIL-6), or a combination of Ibrutinib+Actemra or vehicle controls. An additional group of mice were injected with BCWM.1 + HS-5 cells (5:1 ratio) subcutaneously followed by treatment with Rituxmab (αCD20), Actemra (αIL-6) or both Rituximab+Actemra or controls. There was no improvement in survival of mice treated with Ibrutinib or Actemra as single therapy and combined treatment did not improve survival compared to controls. We also found a reduction in tumor growth rate in mice treated with Ibrutinib + Actemra compared with mice treated with Ibrutinib alone. There was no difference in human IgM secretion among different groups when examining serum samples by ELISA. In the cohort of mice treated with Rituximab, we found that the TME did not provide a protective effect on Rituximab therapy as Rituximab significantly enhanced the survival of mice (p&lt;0.0001). Combined treatment with Rituximab and Actemra did not significantly improve survival compared with Rituximab alone. We also found that mice treated with Rituximab alone had a significant reduction in tumor growth rate and combined therapy did not reduce tumor growth rate beyond that of Rituximab alone. Furthermore, we found a significant reduction in human IgM secretion in mice serum in mice treated with Rituximab alone (p=0.005) or combined therapy (p=0.0007) compared with control mice. However, there was no difference between Rituximab alone and combined therapy. There was no significant change in mice weight over the course of the treatment suggesting that none of these therapies had toxic effects. Taken together, our data suggests that the TME provided a protective effect against Ibrutinib, but not Rituximab therapy and inhibition of IL-6, a cytokine known to modulate the TME in WM did not enhance either therapy.

Citation Format: Weiguo Han, Brandon L. Sklavanitis, David A. Jackson, Stephan J. Matissek, Sherine F. Elsawa. The tumor microenvironment protects against ibrutinib but not rituximab-mediated control of Waldenström macroglobulinemia (WM) in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 193.

Gadolinium borate and iron oxide bioconjugates: Nanocomposites of next generation with multifunctional applications

The systematic investigations concerning the bioconjugation of GdBO₃-Fe₃O₄ nanocomposite and their in vitro biocompatibility with cancer cell lines are reported. The nanocomposites were prepared hydrothermally from magnetite (Fe₃O₄), borax or boric acid and a Gd³⁺ salt. Bioconjugation processes were performed with citric acid and fluorescein isothiocyanate-doped silica, followed by the treatment with folic acid. Overall, the procedure involved "bare or PEGylated Fe₃O₄ as the magnetic core" and "vaterite- or triclinic-type of GdBO₃ as the surface borate layer" for comparative evaluation of the results. The successful vectorization of the nanocomposite particles was demonstrated by quantitative and qualitative analytical data. All bioconjugates displayed soft ferromagnetic properties and negative zeta potential values that are appropriate for biological applications. The ¹⁰B and ¹⁵⁷Gd contents were ca. 10¹⁴ atom/μg making them promising agents for BNCT, GdNCT and the combined GdBNCT. The Gd/Fe molar ratios (0.27-0.63) provided the capability for T1- or dual (T1 + T2) magnetic resonance imaging (MRI). In vitro studies were conducted to investigate the efficiency of targeted FA-conjugated versus non-FA conjugated nanoformulations on Mia-Pa-Ca-2, HeLa and A549 cells. Fluorescence microscopy and flow cytometry data unveiled the essential role of the zeta potential competing with folate targeting in the uptake mechanism. The bioconjugated nanoplatforms of GdBO₃-Fe₃O₄ composite, introduced herein, proved to have potential features of next generation agents for magnetically targeted therapy, fluorescence imaging, magnetic resonance imaging/diagnosis and Neutron Capture Therapy.

Novel Molecular Mechanism of Regulation of CD40 Ligand by the Transcription Factor GLI2

The interaction between tumor cells and their surrounding microenvironment is essential for the growth and persistence of cancer cells. This interaction is mediated, in part, by cytokines. Although the role of cytokines in normal and malignant cell biology is well established, many of the molecular mechanisms regulating their expression remain elusive. In this article, we provide evidence of a novel pathway controlling the transcriptional activation of CD40L in bone marrow-derived stromal cells. Using a PCR-based screening of cytokines known to play a role in the biology of bone marrow malignancies, we identified CD40L as a novel GLI2 target gene in stromal cells. CD40L plays an important role in malignant B cell biology, and we found increased Erk phosphorylation and cell growth in malignant B cells cocultured with CD40L-expressing stromal cells. Further analysis indicated that GLI2 overexpression induced increased CD40L expression, and, conversely, GLI2 knockdown reduced CD40L expression. Using luciferase and chromatin immunoprecipitation assays, we demonstrate that GLI2 directly binds and regulates the activity of the CD40L promoter. We found that the CCR3-PI3K-AKT signaling modulates the GLI2-CD40L axis, and GLI2 is required for CCR3-PI3K-AKT-mediated regulation of the CD40L promoter. Finally, coculture of malignant B cells with cells stably expressing human CD40L results in increased Erk phosphorylation and increased malignant B cell growth, indicating that CD40L in the tumor microenvironment promotes malignant B cell activation. Therefore, our studies identify a novel molecular mechanism of regulation of CD40L by the transcription factor GLI2 in the tumor microenvironment downstream of CCR3 signaling.

rtfA controls development, secondary metabolism, and virulence in Aspergillus fumigatus

Invasive aspergillosis by Aspergillus fumigatus is a leading cause of infection-related mortality in immune-compromised patients. In order to discover potential genetic targets to control A. fumigatus infections we characterized rtfA, a gene encoding a putative RNA polymerase II transcription elongation factor-like protein. Our recent work has shown that the rtfA ortholog in the model fungus Aspergillus nidulans regulates morphogenesis and secondary metabolism. The present study on the opportunistic pathogen A. fumigatus rtfA gene revealed that this gene influences fungal growth and conidiation, as well as production of the secondary metabolites tryptoquivaline F, pseurotin A, fumiquinazoline C, festuclavine, and fumigaclavines A, B and C. Additionally, rtfA influences protease activity levels, the sensitivity to oxidative stress and adhesion capacity, all factors important in pathogenicity. Furthermore, rtfA was shown to be indispensable for normal virulence using Galleria mellonella as well as murine infection model systems.

The transcription factor GLI2 modulates CD40L expression in the tumor microenvironment

The interaction between tumor cells and the tumor microenvironment (TME) is essential for cancer cell growth and survival. Cytokines play an important role in mediating this crosstalk. Although this interaction is clearly established, the molecular mechanisms mediating this remain elusive. In previous work, we have shown that the transcription factor GLI2 modulates the expression and secretion of IL-6 in the TME. In this study, we screened for novel cytokine targets for GLI2 in bone marrow stromal cells and identified CD40L as a novel target of GLI2. GLI2 overexpression in HS-5, L87, L88 and Saka cells increased CD40L expression by real-time PCR. Conversely, GLI2 knockdown resulted in reduced CD40L expression. Similar results were obtained when screening for protein levels by western blotting. Using a mutant of GLI2 that lacks an N-terminal transcriptional repressor domain, we found an increase in CD40L beyond that observed with full-length GLI2. Bioinformatics analysis of a 2000 bp CD40L promoter region identified 2 candidate GLI binding sites in the CD40L promoter region. Using expression, luciferase and chromatin immunoprecipitation assays, we demonstrate that GLI2 binds to CD40L promoter. Furthermore, GLI2 modulates CD40L promoter activity. We were able to rescue the effect of GLI2 knockdown using an RNAi resistant GLI2 cDNA. Finally, we found that signaling through the CCR3-PI3K-AKT mediates GLI2-CD40L. Taken together, our data identify a novel mechanism regulating CD40L in stromal cells in the TME. Because of the importance of CD40L in malignant B cells, understanding the mechanism of its regulation is of great importance for the development of novel therapies aimed at targeting the malignant bone marrow TME.

Modulation of the IL-6 Receptor α Underlies GLI2-Mediated Regulation of Ig Secretion in Waldenström Macroglobulinemia Cells

Ig secretion by terminally differentiated B cells is an important component of the immune response to foreign pathogens. Its overproduction is a defining characteristic of several B cell malignancies, including Waldenström macroglobulinemia (WM), where elevated IgM is associated with significant morbidity and poor prognosis. Therefore, the identification and characterization of the mechanisms controlling Ig secretion are of great importance for the development of future therapeutic approaches for this disease. In this study, we define a novel pathway involving the oncogenic transcription factor GLI2 modulating IgM secretion by WM malignant cells. Pharmacological and genetic inhibition of GLI2 in WM malignant cells resulted in a reduction in IgM secretion. Screening for a mechanism identified the IL-6Rα (gp80) subunit as a downstream target of GLI2 mediating the regulation of IgM secretion. Using a combination of expression, luciferase, and chromatin immunoprecipitation assays we demonstrate that GLI2 binds to the IL-6Rα promoter and regulates its activity as well as the expression of this receptor. Additionally, we were able to rescue the reduction in IgM secretion in the GLI2 knockdown group by overexpressing IL-6Rα, thus defining the functional significance of this receptor in GLI2-mediated regulation of IgM secretion. Interestingly, this occurred independent of Hedgehog signaling, a known regulator of GLI2, as manipulation of Hedgehog had no effect on IgM secretion. Given the poor prognosis associated with elevated IgM in WM patients, components of this new signaling axis could be important therapeutic targets.

The oncogenic transcription factor IRF4 is regulated by a novel CD30/NF-κB positive feedback loop in peripheral T-cell lymphoma

Peripheral T-cell lymphomas (PTCLs) are generally aggressive non-Hodgkin lymphomas with poor overall survival rates following standard therapy. One-third of PTCLs express interferon regulatory factor-4 (IRF4), a tightly regulated transcription factor involved in lymphocyte growth and differentiation. IRF4 drives tumor growth in several lymphoid malignancies and has been proposed as a candidate therapeutic target. Because direct IRF4 inhibitors are not clinically available, we sought to characterize the mechanism by which IRF4 expression is regulated in PTCLs. We demonstrated that IRF4 is constitutively expressed in PTCL cells and drives Myc expression and proliferation. Using an inhibitor screen, we identified nuclear factor κB (NF-κB) as a candidate regulator of IRF4 expression and cell proliferation. We then demonstrated that the NF-κB subunits p52 and RelB were transcriptional activators of IRF4. Further analysis showed that activation of CD30 promotes p52 and RelB activity and subsequent IRF4 expression. Finally, we showed that IRF4 transcriptionally regulates CD30 expression. Taken together, these data demonstrate a novel positive feedback loop involving CD30, NF-κB, and IRF4; further evidence for this mechanism was demonstrated in human PTCL tissue samples. Accordingly, NF-κB inhibitors may represent a clinical means to disrupt this feedback loop in IRF4-positive PTCLs.

The transcription factor GLI1 interacts with SMAD proteins to modulate transforming growth factor β-induced gene expression in a p300/CREB-binding protein-associated factor (PCAF)-dependent manner

The biological role of the transcription factor GLI1 in the regulation of tumor growth is well established; however, the molecular events modulating this phenomenon remain elusive. Here, we demonstrate a novel mechanism underlying the role of GLI1 as an effector of TGFβ signaling in the regulation of gene expression in cancer cells. TGFβ stimulates GLI1 activity in cancer cells and requires its transcriptional activity to induce BCL2 expression. Analysis of the mechanism regulating this interplay identified a new transcriptional complex including GLI1 and the TGFβ-regulated transcription factor, SMAD4. We demonstrate that SMAD4 physically interacts with GLI1 for concerted regulation of gene expression and cellular survival. Activation of the TGFβ pathway induces GLI1-SMAD4 complex binding to the BCL2 promoter whereas disruption of the complex through SMAD4 RNAi depletion impairs GLI1-mediated transcription of BCL2 and cellular survival. Further characterization demonstrated that SMAD2 and the histone acetyltransferase, PCAF, participate in this regulatory mechanism. Both proteins bind to the BCL2 promoter and are required for TGFβ- and GLI1-stimulated gene expression. Moreover, SMAD2/4 RNAi experiments showed that these factors are required for the recruitment of GLI1 to the BCL2 promoter. Finally, we determined whether this novel GLI1 transcriptional pathway could regulate other TGFβ targets. We found that two additional TGFβ-stimulated genes, INTERLEUKIN-7 and CYCLIN D1, are dependent upon the intact GLI1-SMAD-PCAF complex for transcriptional activation. Collectively, these results define a novel epigenetic mechanism that uses the transcription factor GLI1 and its associated complex as a central effector to regulate gene expression in cancer cells.

Activation of the transcription factor GLI1 by WNT signaling underlies the role of SULFATASE 2 as a regulator of tissue regeneration

Tissue regeneration requires the activation of a set of specific growth signaling pathways. The identity of these cascades and their biological roles are known; however, the molecular mechanisms regulating the interplay between these pathways remain poorly understood. Here, we define a new role for SULFATASE 2 (SULF2) in regulating tissue regeneration and define the WNT-GLI1 axis as a novel downstream effector for this sulfatase in a liver model of tissue regeneration. SULF2 is a heparan sulfate 6-O-endosulfatase, which releases growth factors from extracellular storage sites turning active multiple signaling pathways. We demonstrate that SULF2-KO mice display delayed regeneration after partial hepatectomy (PH). Mechanistic analysis of the SULF2-KO phenotype showed a decrease in WNT signaling pathway activity in vivo. In isolated hepatocytes, SULF2 deficiency blocked WNT-induced β-CATENIN nuclear translocation, TCF activation, and proliferation. Furthermore, we identified the transcription factor GLI1 as a novel target of the SULF2-WNT cascade. WNT induces GLI1 expression in a SULF2- and β-CATENIN-dependent manner. GLI1-KO mice phenocopied the SULF2-KO, showing delayed regeneration and decreased hepatocyte proliferation. Moreover, we identified CYCLIN D1, a key mediator of cell growth during tissue regeneration, as a GLI1 transcriptional target. GLI1 binds to the cyclin d1 promoter and regulates its activity and expression. Finally, restoring GLI1 expression in the liver of SULF2-KO mice after PH rescues CYCLIN D1 expression and hepatocyte proliferation to wild-type levels. Thus, together these findings define a novel pathway in which SULF2 regulates tissue regeneration in part via the activation of a novel WNT-GLI1-CYCLIN D1 pathway.

The transcription factor GLI1 mediates TGFβ1 driven EMT in hepatocellular carcinoma via a SNAI1-dependent mechanism

The role of the epithelial-to-mesenchymal transition (EMT) during hepatocellular carcinoma (HCC) progression is well established, however the regulatory mechanisms modulating this phenomenon remain unclear. Here, we demonstrate that transcription factor glioma-associated oncogene 1 (GLI1) modulates EMT through direct up-regulation of SNAI1 and serves as a downstream effector of the transforming growth factor-β1 (TGFβ1) pathway, a well-known regulator of EMT in cancer cells. Overexpression of GLI1 increased proliferation, viability, migration, invasion, and colony formation by HCC cells. Conversely, GLI1 knockdown led to a decrease in all the above-mentioned cancer-associated phenotypes in HCC cells. Further analysis of GLI1 regulated cellular functions showed that this transcription factor is able to induce EMT and identified SNAI1 as a transcriptional target of GLI1 mediating this cellular effect in HCC cells. Moreover, we demonstrated that an intact GLI1-SNAI1 axis is required by TGFβ1 to induce EMT in these cells. Together, these findings define a novel cellular mechanism regulated by GLI1, which controls the growth and EMT phenotype in HCC.

Novel AKT1-GLI3-VMP1 pathway mediates KRAS oncogene-induced autophagy in cancer cells

Autophagy is an evolutionarily conserved degradation process of cytoplasmic cellular constituents. It has been suggested that autophagy plays a role in tumor promotion and progression downstream oncogenic pathways; however, the molecular mechanisms underlying this phenomenon have not been elucidated. Here, we provide both in vitro and in vivo evidence of a novel signaling pathway whereby the oncogene KRAS induces the expression of VMP1, a molecule needed for the formation of the authophagosome and capable of inducing autophagy, even under nutrient-replete conditions. RNAi experiments demonstrated that KRAS requires VMP1 to induce autophagy. Analysis of the mechanisms identified GLI3, a transcription factor regulated by the Hedgehog pathway, as an effector of KRAS signaling. GLI3 regulates autophagy as well as the expression and promoter activity of VMP1 in a Hedgehog-independent manner. Chromatin immunoprecipitation assays demonstrated that GLI3 binds to the VMP1 promoter and complexes with the histone acetyltransferase p300 to regulate promoter activity. Knockdown of p300 impaired KRAS- and GLI3-induced activation of this promoter. Finally, we identified the PI3K-AKT1 pathway as the signaling pathway mediating the expression and promoter activity of VMP1 upstream of the GLI3-p300 complex. Together, these data provide evidence of a new regulatory mechanism involved in autophagy that integrates this cellular process into the molecular network of events regulating oncogene-induced autophagy.

MicroRNA expression in tumor cells from Waldenstrom's macroglobulinemia reflects both their normal and malignant cell counterparts

MicroRNAs (miRNAs) are involved in the regulation of many cellular processes including hematopoiesis, with the aberrant expression of differentiation-stage specific miRNA associated with lymphomagenesis. miRNA profiling has been essential for understanding the underlying biology of many hematological malignancies; however the miRNA signature of the diverse tumor clone associated with Waldenstrom's macroglobulinemia (WM), consisting of B lymphocytes, plasmacytes and lymphoplasmacytic cells, has not been characterized. We have investigated the expression of over 13 000 known and candidate miRNAs in both CD19(+) and CD138(+) WM tumor cells, as well as in their malignant and non-malignant counterparts. Although neither CD19(+) nor CD138(+) WM cells were defined by a distinct miRNA profile, the combination of all WM cells revealed a unique miRNA transcriptome characterized by the dysregulation of many miRNAs previously identified as crucial for normal B-cell lineage differentiation. Specifically, miRNA-9(*)/152/182 were underexpressed in WM, whereas the expression of miRNA-21/125b/181a/193b/223/363 were notably increased (analysis of variance; P<0.0001). Future studies focusing on the effects of these dysregulated miRNAs will provide further insight into the mechanisms responsible for the pathogenesis of WM.

GLI2 transcription factor mediates cytokine cross-talk in the tumor microenvironment

Tumor cells interact with their surrounding microenvironment to survive and persist within the host. Cytokines play a key role in regulating this crosstalk between malignant cells and surrounding cells in the microenvironment. Although this phenomenon is clearly established, the molecular mechanisms mediating this cellular event remain elusive. Here, using as a model bone marrow stromal cells, we describe a novel signaling mechanism initiated by CCL5 in these cells leading to up-regulation of immunoglobulin secretion by malignant B cells. CCL5 increases IL-6 expression and secretion in bone marrow stromal cells. IL-6 in turn induces Ig secretion by malignant B cells. Analysis of the mechanism reveals that CCL5 signaling induces GLI2 through a PI3K-AKT-IκBα-p65 pathway and requires GLI2 transcriptional activity to modulate IL-6 expression and Ig secretion in vitro and in vivo. Together, these results identify a novel signaling pathway mediating the stromal-cancer cell interactions, leading to increased Ig production by malignant cells.

The oncogenic effect of sulfatase 2 in human hepatocellular carcinoma is mediated in part by glypican 3-dependent Wnt activation

Heparan sulfate proteoglycans (HSPGs) act as coreceptors or storage sites for growth factors and cytokines such as fibroblast growth factor and Wnts. Glypican 3 (GPC3) is the most highly expressed HSPG in hepatocellular carcinoma (HCC). Sulfatase 2 (SULF2), an enzyme with 6-O-desulfatase activity on HSPGs, is up-regulated in 60% of primary HCCs and is associated with a worse prognosis. We have previously shown that the oncogenic effect of SULF2 in HCC may be mediated in part through up-regulation of GPC3. Here we demonstrate that GPC3 stimulates the Wnt/β-catenin pathway and mediates the oncogenic function of SULF2 in HCC. Wnt signaling in vitro and in vivo was assessed in SULF2-negative Hep3B HCC cells transfected with SULF2 and in SULF2-expressing Huh7 cells transfected with short hairpin RNA targeting SULF2. The interaction between GPC3, SULF2, and Wnt3a was assessed by coimmunoprecipitation and flow cytometry. β-catenin-dependent transcriptional activity was assessed with the TOPFLASH (T cell factor reporter plasmid) luciferase assay. In HCC cells, SULF2 increased cell surface GPC3 and Wnt3a expression, stabilized β-catenin, and activated T cell factor transcription factor activity and expression of the Wnt/β-catenin target gene cyclin D1. Opposite effects were observed in SULF2-knockdown models. In vivo, nude mouse xenografts established from SULF2-transfected Hep3B cells showed enhanced GPC3, Wnt3a, and β-catenin levels.

CONCLUSION

Together, these findings identify a novel mechanism mediating the oncogenic function of SULF2 in HCC that includes GPC3-mediated activation of Wnt signaling via the Wnt3a/glycogen synthase kinase 3 beta axis.

Abstract 3917: Molecular mechanisms underlying hedgehog-GLI oncogenic function via interaction with the TGF-beta-SMAD4 axis

Crosstalk between signaling pathways is crucial to the initiation, progression and maintenance of the transformed phenotype. Therefore, characterization of these signaling interactions is fundamental for the understanding of the complex and varied network of events that leads to the development and spread of tumors. The Hedgehog (HH)-GLI pathway, an important carcinogenic cascade, is required for the growth and survival of tumors of diverse origin. Recent reports, mainly from animal models, suggest that key signaling interactions are required by HH-GLI signaling to modulate cancer-associated cellular functions. However, the molecular mechanisms underlying this phenomenon in cancer and non-cancer cells remain elusive. Our preliminary data show a crosstalk between the HH-GLI axis and TGF-beta pathway, a well-characterized tumor suppressor/oncogenic signaling pathway. Luciferase reporter and expression assays in combination with genetic and pharmacological manipulations of the TGFbeta pathway show that this cascade is able to activate GLI transcriptional activity, even in the absence of an active HH signaling. The TGFbeta pathway is required to maintain active GLI transcriptional complexes at GLI target genes. Further analysis of this molecular interaction suggests that TGFbeta pathway-mediated activation of GLI transcription factors requires an intact SMAD4, thus suggesting a potential mechanism mediating this functional interaction. The knowledge derived from this study provides both mechanistic insight into the contribution of this HH-GLI/TGF-beta pathway interaction to carcinogenesis and could serve as a foundation for development of new therapeutic approaches for tumors with active HH-GLI and TGF cascades.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3917.

Primers on molecular pathways - cycling toward pancreatic cancer

Human cells divide and proliferate during the early stages of life to support development, and throughout adult life to support normal cellular turnover. Each dividing cell follows an orderly and tightly regulated series of events known as the cell cycle. This process ensures proper cellular division that maintains DNA and chromosomal integrity and responds appropriately to external signals which communicate the level of demand for new cells. In cancer, genetic mutations leading to the overexpression of proteins which support cell cycle progression, or the downregulation of proteins involved in cell cycle inhibition contributes to the dysregulated cellular division and proliferation of malignant cells. The resulting uninhibited cellular proliferation provides ample opportunity for additional genetic mutations that lead to tumor progression. In the following review, we provide a brief introduction to the cell cycle and a discussion of the mechanism underlying the dysregulation of the cell cycle in human cancer. We pay particular attention to pancreatic adenocarcinoma, an aggressive tumor that has a 5-year survival rate of 3-5%, and is the fourth leading cause of cancer mortality in the US. and IAP.

Cytokines in the microenvironment of Waldenström's macroglobulinemia

Waldenström's macroglobulinemia (WM) is a lymphoplasmacytic lymphoma characterized by the overproduction of a monoclonal IgM protein that accumulates in the serum. Although the pathologic findings in this disease entity are reasonably well defined, the mechanisms that regulate malignant B-cell growth and monoclonal protein synthesis are less well understood. Cytokines are known to regulate many biologic processes in normal lymphocyte development including immunoglobulin production, and the presence of cytokines within the tumor microenvironment of WM is likely to contribute to malignant cell growth and survival as well as immunoglobulin production. Several studies have suggested that cytokines are potentially dysregulated in WM, however the precise role played by cytokines in WM biology is not clearly defined. This report therefore highlights our current understanding of the role of cytokines in the microenvironment of WM and how they affect malignant cell persistence and function in the bone marrow of patients.

CDDO-imidazolide mediated inhibition of malignant cell growth in Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM) is a B-cell malignancy that remains incurable. Synthetic triterpenoids (ST), 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), its methyl ester derivative (CDDO-Me) and imidazolide derivative (CDDO-Im) induce cell death and inhibit growth of various malignancies and hold promise as treatment for cancer patients. We examined the therapeutic potential of these compounds in WM. All three forms of CDDO induced equal toxicity in BCWM.1 cells. In malignant B cells from WM patients, CDDO-Im induced the greatest toxicity. CDDO-Im inhibited proliferation at nanomolar concentrations and arrested the cells in G0/G1. CDDO-Im induced apoptotic cell death that was partially abolished in the presence of caspase inhibitor. CDDO-Im also inhibited survival pathways that have been shown to be important in WM. Overall, our data suggest that ST are likely to provide therapeutic efficacy for WM patients.

T-cell epitope peptide vaccines

T-cell immunotherapy is a promising treatment option for cancer. The identification of tumor antigens that are recognized by the immune system has allowed for the generation of vaccines for various malignancies. Due to the ease of manufacturing and characterizating peptide-based vaccines they have been used to stimulate antitumor T-cells. This article will review the use of peptide-based vaccines for the treatment of cancer by inducing antitumor T-lymphocyte responses.

Generation of tumoricidal PAX3 peptide antigen specific cytotoxic T lymphocytes

The transcription factor PAX3 is expressed during early embryogenesis and in multiple cancer types, including embryonal rhabdomyosarcoma (ERMS), Ewing sarcoma (ES) and malignant melanoma (MEL), suggesting that it could function as a general tumor associated antigen. Major histocompatibility complex (MHC) peptide binding algorithms were used to predict potential epitopes in PAX3 capable of stimulating in vitro naïve HLA-A0201 restricted cytotoxic T-lymphocytes (CTLs). Two peptides, PAX3-282 (QLMAFNHLI) and a modified version of this peptide PAX3-282.9V (QLMAFNHLV), were capable of inducing antigen-specific CTLs. Of these peptides, PAX3-282.9V was the most efficient inducer of primary CTL response. These CTLs were able to lyse HLA-A0201 expressing target cells that were pulsed with peptide, and more importantly, were effective in killing tumor cells that express PAX3, including ERMS, ES and MEL cell lines. These findings provide compelling evidence that peptide PAX3-282 is naturally processed by tumors and is presented in the context of HLA-A0201 in adequate amounts to allow CTL recognition. Also, PAX3-282.9V is an effective immunogenic peptide able to induce CTL recognition of PAX3-containing tumors and may be used as an antitumor peptide vaccine.

Selective activation of TACI by syndecan-2

B-lymphocyte homeostasis and function are regulated by complementary actions of the TNFR family members TACI, BCMA, and BAFF-R, which are expressed by mature B cells. How these receptors are differentially activated is not entirely understood, because the primary ligand BAFF binds to all three. We searched for alternative ligands for TACI using recombinant TACI-Fc fusion protein as a probe and identified syndecan-2 as a new binding partner. TACI binding appears to require heparan sulfate posttranslational modifications of syndecan-2, because free heparin or pretreatment with heparitinase blocked the interaction. Syndecan-2 bound TACI but bound neither BAFF-R nor BCMA. Transfected cells expressing syndecan-2 activated signaling through TACI, as indicated by an NFAT-specific reporter. Syndecan-1 and syndecan-4 were also able to induce TACI signaling in a similar manner. This is the first identification of ligands that selectively activate TACI without simultaneously triggering BCMA or BAFF-R. This finding may help explain the alternative outcomes of signaling from this family of receptors in B cells.

B-lymphocyte stimulator (BLyS) stimulates immunoglobulin production and malignant B-cell growth in Waldenstrom macroglobulinemia

Waldenström macroglobulinemia (WM) is a serious and frequently fatal B-cell malignancy associated with an elevated monoclonal IgM protein in the serum. Many of the mechanisms leading to this disease are not yet known. B-lymphocyte stimulator (BLyS) is a TNF family member that is critical for maintenance of normal B-cell development and homeostasis. BLyS is overexpressed in a variety of B-cell malignancies and has been shown to inhibit apoptosis in malignant B cells. It also regulates immunoglobulin secretion by normal B cells. To determine the relevance of BLyS in WM, we examined the role of BLyS in WM patient samples. Malignant B cells were found to bind soluble BLyS and variably express the receptors BAFF-R, TACI, and BCMA. We also found expression of BLyS in bone marrow specimens by immunohistochemistry and elevated serum BLyS levels in patients with WM. BLyS, alone or in combination with cytokines that induce immunoglobulin production, was found to increase IgM secretion by malignant B cells. Furthermore, BLyS was found to increase the viability and proliferation of malignant B cells from WM patients. Due to the role of BLyS in WM, strategies to inhibit BLyS may potentially have therapeutic efficacy in these patients.

Recognition of six-transmembrane epithelial antigen of the prostate-expressing tumor cells by peptide antigen-induced cytotoxic T lymphocytes

The identification of novel markers and therapeutic targets in advanced cancer is critical for improving diagnosis and therapy. Six-transmembrane epithelial antigen of the prostate (STEAP) is expressed predominantly in human prostate tissue and in other common malignancies including prostate, bladder, colon, and ovarian carcinomas, and in Ewing's sarcoma, suggesting that it could function as an almost universal tumor antigen. We have used MHC peptide binding algorithms to predict potential STEAP sequences capable of stimulating in vitro naïve HLA-A2-restricted CTLs. Four of six peptides predicted by these algorithms were able to induce antigen-specific CTLs that killed peptide-pulsed HLA-A2 target cells. Two of these peptides, STEAP-292 (MIAVFLPIV) and a modification of this peptide STEAP-292.2L (MLAVFLPIV), were the most efficient in the induction of primary CTL responses. More importantly, these CTLs were able to respond to tumor cells that express HLA-A2 and STEAP (colon, bladder, prostate, Ewing's sarcoma, and melanoma). Our results provide strong evidence that STEAP-292 is naturally processed by many tumor types and is presented in the context of HLA-A2 in sufficient amounts to allow recognition by CTLs. Also because STEAP-292.2L is a more immunogenic peptide able to induce CTL recognition of these STEAP-containing tumors and may have potential as an antitumor peptide vaccine.

Murine γ-Herpesvirus-68-Induced IL-12 Contributes to the Control of Latent Viral Burden, but Also Contributes to Viral-Mediated Leukocytosis

Early IFN-alpha/beta production, followed by the development of a viral-specific CTL response, are critical factors in limiting the level of murine gamma-herpesvirus-68 (gammaHV-68) infection. Development of a long-lived CTL response requires T cell help, and these CTLs most likely function to limit the extent of infection following reactivation. The importance of IL-12 in the development and/or activity of Th1 cells and CTLs is well documented, and we investigated the kinetics and magnitude of gammaHV-68-induced IL-12 production. Following intranasal infection, IL-12 and IL-23 mRNA expression was up-regulated in lung and spleen and lung, respectively, followed by increased levels of IL-12p40 in lung homogenates and sera. Exposure of cultured macrophages or dendritic cells to gammaHV-68 induced secretion of IL-12, suggesting that these cells might be responsible for IL-12 production in vivo. gammaHV-68 infection of mice made genetically deficient in IL-12p40 expression (IL-12p40(-/-)) resulted in a leukocytosis and splenomegaly that was significantly less than that observed in syngeneic C57BL/6 mice. IL-12p40(-/-) mice showed increased levels of infectious virus in the lung, but only at day 9 postinfection. Increased levels of latent virus in the spleen at day 15 postinfection were also observed in IL-12p40(-/-) mice when compared with syngeneic C57BL/6 mice. An overall reduction in gammaHV-68-induced IFN-gamma production was observed in IL-12p40(-/-) mice, suggesting that most of the viral-induced IFN-gamma in C57BL/6 mice was IL-12 dependent. Taken together, these results suggest that gammaHV-68-induced IL-12 contributes to the pathophysiology of viral infection while also functioning to limit viral burden.

Reduced CTL response and increased viral burden in substance P receptor-deficient mice infected with murine gamma-herpesvirus 68

One component of the protective host response against mucosal pathogens includes the local production and increased expression of certain neuropeptides and their receptors. The present study further demonstrates this fact by investigating the contribution that substance P receptor expression makes toward immunity against a gamma-herpesvirus infection. Following intragastric inoculation with murine gamma-herpesvirus 68 (gamma HV-68), expression of substance P and its receptor was increased in mucosal and peripheral lymphoid organs in wild-type strains of mice. These results suggested that this receptor/ligand pair might be an important component of the host response against this viral infection. Such a hypothesis was supported by the demonstration that mice, genetically deficient in substance P receptor expression, showed an increased viral burden when compared with syngeneic C57BL/6 mice. Furthermore, substance P receptor-deficient mice showed a reduced CTL response against gamma HV-68, suggesting a mechanism to explain this increased viral burden. Such limitations in the Ag-specific CTL response in substance P receptor-deficient mice could result from lowered expression of IL-12 during viral infection. Consistent with this hypothesis, increases in mRNA encoding IL-12 and secretion of this cytokine into sera of infected, wild-type animals were markedly reduced in substance P receptor-deficient mice. These studies demonstrate that genetic elimination of substance P receptors in mice results in an increased gamma-herpesvirus burden and an altered host response.